Showing papers in "Marine Biology in 2001"

The culturable microbial community of the Great Barrier Reef sponge Rhopaloeides odorabile is dominated by an α-Proteobacterium

Abstract: The microbial community cultured from the marine sponge Rhopaloeides odorabile Thompson et al. is dominated by a single bacterium, designated strain NW001. Sequence analysis of 1212 bp of the16S rRNA gene of strain NW001 indicates that it is a member of the α-subgroup of the class Proteobacteria. The association between this bacterium and its host sponge was observed in healthy R. odorabile collected from six different reefs in the Great Barrier Reef representing a geographic distance of 460 km, and in four collections in different seasons in 1997–1998 at Davies Reef (18°49.6′S; 147°34.49′E). The proportion of colonies of strain NW001 in samples from R. odorabile, expressed as a percentage of the total heterotrophic bacterial colony count, showed no significant spatial (range: 81–98%) or temporal differences (range: 81–99%), although colony counts of strain NW001 varied by up to two orders of magnitude between reef sites and sampling periods. The location of strain NW001 within the sponge mesohyl was visualized by in situ hybridization, using fluorescently labeled probes based on the 16S rRNA gene sequence of this strain. Cells of strain NW001 surround the choanocyte chambers, suggesting that these bacteria may play a role in nutrient uptake by the sponge. The absence of strain NW001 from corresponding seawater samples indicates that it has a specific, intimate relationship with R. odorabile and is not being utilized as a food source. A unique cyanobacterium related to the genera Leptolyngbya and Plectonema was also isolated from R. odorabile and characterized by 16S rRNA gene sequencing.

High genetic diversity and relative specificity among Symbiodinium-like endosymbiotic dinoflagellates in soritid foraminiferans

Abstract: Soritids are large calcareous foraminiferans abundant in Indo-Pacific coral reefs. Soritids are known to host endosymbionts morphologically and genetically similar to Symbiodinium-like dinoflagellates commonly found in corals and other marine invertebrates. In order to examine the phylogenetic relationships between symbionts present in foraminiferal and coelenterate hosts, we used DNA sequencing and PCR-based RFLP methods to analyse 157 foraminiferal and 110 coral DNA samples from 12 localities in Guam (Micronesia) collected in July 1999 and December 1999. Ribosomal DNA sequences were obtained for 14 foraminiferal and 12 coral samples. Sequence analyses allowed identification of six different Symbiodinium phylotypes among soritids and two phylotypes among examined coelenterates. A single phylotype, previously described as lineage C, was common in foraminiferans and corals. The PCR-based RFLP analysis of 157 foraminiferal and 110 coral samples shows that lineage C dominates coral symbiont communities, accounting for 78% in both sampling periods. On the other hand, our data show that lineages C and Fr6 dominated foraminiferal symbiont communities in July 1999 versus a clear predominance of lineages C and Fr3 in November 1999. The other three phylotypes present in soritids (Fr1, Fr4, Fr5) were uncommon and seem to occur seasonally. The phylogenetic analysis of the present data indicates relative specificity of soritid symbionts compared to other Symbiodinium-like dinoflagellates, but the causes of this specificity are not yet understood.

Population development of the invader ctenophore Mnemiopsis leidyi, in the Black Sea and in other seas of the Mediterranean basin.

Abstract: In the last two decades of the twentieth century, the ctenophore Mnemiopsis leidyi (A. Agassiz) has invaded the Black, Azov, Marmara and Aegean Seas, and, recently, the Caspian Sea. Here, we compare its spatial and temporal distribution, seasonal dynamics and the time and duration of reproduction. We also discuss factors that control its abundance throughout its invasive range and its effect on ecosystems. Observations are based on the long-term field data collected by three research institutes. An analysis of the effects of temperature, salinity, prey (zoo- and ichthyoplankton) availability and predation (by ctenophores of the genus Beroe) on M. leidyi population size, and the effects of M. leidyi on zoo- and ichthyoplankton, and on fish populations in the Black and Azov Seas is also provided. With the Black Sea current, M. leidyi spreads to the upper layers of the Sea of Marmara, where it now occurs around the year. At regular intervals, the Black Sea current also takes it to the northern Aegean Sea. In contrast, it has to re-invade the Sea of Azov every spring or summer, dying out during winter when the temperature drops below 4°C. The warm summer and mild winter temperatures, relatively low salinity and abundance of prey in the Black Sea are close to optimal for M. leidyi, while they are suboptimal in the northern Aegean Sea, where salinity and temperature are often too high. In the Black Sea the absence of gelatinous and other predators led to an enormous ctenophore abundance for a decade, but with the appearance of Beroe ovata in 1999, M. leidyi abundance greatly decreased. Analysis of seasonal dynamics of M. leidyi in the Black Sea and in other seas of the Mediterranean basin indicates similarities in the timing of maximum abundance and biomass, in spite of some differences in the initiation and duration of reproduction. A peak biomass and density occurred in 1989 in the Black and Azov Seas and in 1990 in the other seas. The M. leidyi invasion negatively affected the ecosystems of the Black Sea and the Sea of Azov. The zooplankton, ichthyoplankton and zooplanktivorous fish stocks all underwent profound changes. Similar effects, but less pronounced, were recorded in the Sea of Marmara. Effects on Mediterranean food chains have, so far, remained insignificant. Salinity is probably supraoptimal here, and several predators prevent M. leidyi from reaching outbreak levels.

Annual population development and production by Calanus finmarchicus, C. glacialis and C. hyperboreus in Disko Bay, western Greenland

Abstract: The populations of the copepod species Calanus finmarchicus, C. glacialis and C. hyperboreus were investigated in Disko Bay during a 14-month period in 1996-1997. The three species were predominant in the copepod community. The biomass reached a maximum at the beginning of June (127 mg C m -3 ). From the end of July until the end of April the following year, the biomass was <1-6 mg C m -3 . All three species showed seasonal ontogenetic migration. The spring ascent for all three species was just prior to or in association with the break-up of sea ice and the development of the spring bloom, whereas descent occurred over a larger time span during summer. The main overwintering stages were CV for C. finmarchicus, CIV and CV for C. glacialis and C. hyperboreus. Peak abundance of juvenile copepodites, representing the new generation, was in August for C. finmarchicus, in July for C. glacialis and in May/June for C. hyperboreus, From the timing of reproduction and the population development, the life cycles were deduced to be 1 year for C. finmarchicus and at least 2 years for C. glacialis and C. hyperboreus. Secondary production and potential grazing impact of the Calanus community were estimated by two methods based on specific egg-production rates and temperature-dependent production. The Calanus community was not able to control the primary producers during the spring bloom but probably did during post-bloom. The estimates also indicated that grazing on ciliates and heterotrophic dinoflagellates contributes as an essential food source in the post-bloom period.

Movements and activity of male and female dogfish in a tidal sea lough: alternative behavioural strategies and apparent sexual segregation

Abstract: Movements and habitat selection of male and female dogfish, Scyliorhinus canicula, in a tidal sea lough in south-west Ireland were determined over two temporal scales. Continuous acoustic tracking of four individuals (two males, two females) for 6 days was used to monitor fine-scale changes in behaviour patterns and extent of home ranges. Mark-recapture by number-tagging dogfish captured at sampling stations during August-September in consecutive years was used to reveal long-term philopatric behaviour. Transmitter-tagged male dogfish showed very similar behavioural patterns of low activity during the day in deep water (12–24 m depth) followed by more rapid movements into shallow areas (<4 m) at dusk to feed, before returning to the core space in deep water at dawn. Home ranges occupied by males overlapped almost entirely and were centred in an area where tidal currents form gyres and large crab prey are found. Female S. canicula exhibited a different behavioural strategy. They refuged in caves in shallow water (0.5–1.5 m) during the day and during the 6-day tracking period were nocturnally active two or three times, primarily in deep water. Activity areas of females did not overlap with those of males. Acoustic telemetry, netting, underwater surveys and tag returns revealed males and females were apparently segregated by sex in the lough. Mark-recapture data showed males and females were recaptured from the locations where they were originally caught between 359 and 371 days earlier suggesting at least seasonal segregation in consecutive years. Because female dogfish store sperm enabling temporal separation of the energetically demanding act of copulation with the process of egg-laying, we suggest that this apparent spatial segregation by sex could be driven by the need for females to conserve energy by limiting multiple matings during a time when mating coincides with a peak in egg production and laying.

The biology of larvae from the reef coral Porites astreoides , and their response to temperature disturbances

Abstract: Pelagic larvae play a fundamental role in the life history of virtually all scleractinian corals, yet much of their biology remains unexplored. One aspect of coral larvae – their response to temperature perturbations – has potentially important consequences for understanding the effects of global warming and El Nino–Southern Oscillation events on coral recruitment. The present study tests the effects of temperature perturbations on coral larvae using Porites astreoides larvae as a model system. In June 1999, larvae were collected from 18 m depth on Conch Reef, Florida, and incubated at ambient (28°C), depressed (26°C), and elevated (33°C) temperatures in outdoor tanks shaded from direct sunlight. Treatments were repeated with new larvae every 24 h, and treatment effects quantified as larval motility, mortality, metamorphosis and metabolism. Elevated temperature significantly increased mortality and metamorphosis, and a similar trend was observed at the reduced temperature, although this was not significant. Neither elevated nor reduced temperatures affected larval motility. Gross photosynthesis (P) was significantly depressed by elevated and reduced temperatures, and respiration (R) varied proportionately with temperature (Q 10≈2), although this effect was not statistically significant. At the highest temperature the P/R ratio declined to <1, indicating that thermal stress reduces the potential for autotrophy. Together, these results suggest that elevated temperatures affect coral larvae by depressing photosynthesis and creating an energy shortage, which ultimately could reduce recruitment (by increasing mortality), shorten larval longevity and favor premature metamorphosis. An unexpected finding was that larvae differed physiologically among release dates. Although preliminary, this suggests that larval fitness in Porites spp. may vary depending on the day of release, a phenomenon that could have significant ramifications with respect to the population structure of adults.

The relationship between swimming ability and habitat use in wrasses (Labridae)

Abstract: Habitat use is described for a local assemblage of wrasses (family Labridae) at the among-habitat and microhabitat scales of two fringing reef sites at Lizard Island, northern Great Barrier Reef. Visual censuses were used to determine the distribution and abundance of species in five reef habitat zones, and their relative positions within the water column over the reef flat. Based on previous theoretical and empirical analysis of labrid locomotion, mean pectoral fin aspect-ratio residuals were used as an estimate of swimming performance to examine the relationship between swimming ability and habitat use. Among-habitat distributions of inferred swimming ability displayed a distinct dichotomy between shallow and deep reef habitat zones, suggesting a relationship with wave energy. High wave energy (shallow) habitats were characterised by labrids with high (above 0.2) pectoral fin aspect-ratio residuals (fish that use lift-based swimming and achieve high sustained swimming speeds). Although low (below –0.2) aspect-ratio residual species were only in abundance in low wave energy (deeper) habitats, they were also present in low numbers (<7 individuals/100 m2) on the high wave energy reef flat. Water-column use within the reef flat indicated that these low aspect-ratio residual species display a restricted use of the water column and may use substratum complexity and boundary layer effects as a refuge from high levels of water movement. Overall, locomotor morphology was a good predictor of among-habitat and microhabitat use for wrasses at this location. We propose that locomotor performance may be a general force in shaping habitat use by wrasses over these two spatial scales. Some deviations from these general patterns are discussed with regard to the role of behaviour as a mediating factor between morphology and ecology.

Spatial and temporal pattern in seagrass community composition and productivity in south Florida

Abstract: We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites, delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as a benchmark against which future change in the system can be quantified.

Spatial pattern and the habitat structure of a Mediterranean rocky reef fish local assemblage

Abstract: Spatial pattern of the fish assemblage inhabiting a littoral rocky reef was examined in relation with its habitat, by means of spatial (correlograms, Mantel tests) and regression (GLM, RDA) analysis techniques. Several biological variables showed an aggregated spatial pattern, although with different patch sizes −180 m for total abundance and ∼400 to 500 m for species richness. Habitat complexity, as measured by rugosity, number of medium-sized boulders and verticality, and Posidonia cover showed a small-scale spatial pattern (with a patch size of ∼120 to 200 m), while the alternation of rock (covered or not by Posidonia) and sand, and also wind exposure, showed a larger scale aggregation (400–500 m). Regarding the relationship among biological and environmental variables on a small spatial scale (101 m), the 17 more frequent species showed significant, and usually linear relationships, with descriptors either of complexity, heterogeneity, or both, while habitat structure accounts for a important portion (12–40%, depending on the analysis) of the observed variability in fish assemblage structure. Therefore, spatial structure of biological data would be determined, to some extent, by that of habitat. Habitat heterogeneity of rocky substrate seems to promote species richness in the studied area, so that each bottom type (patches of sand, clumps of Posidonia) embedded in the rocky matrix would provide specific resources for more or less specialized species. For its part, habitat complexity favors at the same time a higher number of species and higher abundances. Habitat structure is thus likely to drive a large part of spatial variability in the distribution and abundance of Mediterranean rocky reef fishes, especially when abundance is assessed on small spatial scales. We argue that knowledge about this “natural” variability can help to separate the influence of habitat from other sources of variation, such as the effect of protection from fisheries.

Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters

Abstract: Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day−1) and microzooplankton grazing (range: 0.00–2.10 day−1) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations also varied widely (0.19–13.65 μg l−1). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l−1. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska, and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries in the transfer of primary production to higher trophic levels in these coastal marine food webs.

Latitudinal variability in symbiont specificity within the widespread scleractinian coral Plesiastrea versipora

Abstract: We examined the genetic diversity of symbiotic dinoflagellates (Symbiodinium sp) in the widespread hermatypic coral Plesiastrea versipora from tropical/subtropical (north-eastern Australia) and temperate waters (south-eastern Australia) using restriction fragment length polymorphisms of partial 18S ribosomal DNA (rDNA), together with sequence analysis of partial 28S rDNA This study revealed that P versipora associates with at least two distinct genotypes of symbiotic dinoflagellates and that the presence of these genotypes varies with latitude P versipora colonies from subtropical and tropical waters contained symbionts belonging to Symbiodinium clade C, while P versipora colonies at high-latitude sites contained clade B Variability within the two groups of symbionts (clades H and C) was minimal, suggesting possible host fidelity The geographically distinct varieties of symbionts within the tissue of this hermatypic coral are likely to be associated with algal physiological differences, which in turn may relate to changing selective pressures as a function of latitude along the eastern Australian seaboard

Tolerance to high temperatures and potential impact of sea warming on reef fishes of Gorgona Island (tropical eastern Pacific)

Abstract: Knowledge of upper thermal-tolerance limits of marine organisms in the tropical eastern Pacific (TEP) is important because of the influence of phenomena such as El Nino and global warming, which increase sea temperature. Laboratory experiments were conducted to determine the critical thermal maximum (CTM) of reef fishes from the TEP. In 15 reef fishes of Gorgona Island (TEP) the CTM was between 34.7°C and 40.8°C. None of these CTMs was exceeded by sea temperature in the TEP during any of the strongest El Nino events in this century (32°C during El Nino 1982–1983 and 1997–1998), which indicates that all species studied here may tolerate El Nino maximum temperatures. In addition, the CTM of the least-tolerant species was 8°C above the current mean sea temperature in a wide range of latitudes in the TEP. This suggests that fishes live far from their upper thermal tolerance limits and that the current global-warming trend is still unlikely to be dangerous for these species. If sea temperature continues to increase at the current rate, in about a century sea temperature could exceed the thermal tolerance of some reef fishes and threaten them with extinction. Such risk, however, might occur sooner if the sea temperature during El Nino also increased in step with the global warming, but also because other processes involved in maintaining population, such as reproduction, can be affected at lower temperatures. The possible ability of reef fishes to adapt to increases in sea temperature is discussed.

Light regime in an Arctic fjord: a study related to stratospheric ozone depletion as a basis for determination of UV effects on algal growth.

Abstract: Solar radiation as a primary abiotic factor affecting productivity of seaweeds was monitored in the Arctic Kongsfjord on Spitsbergen from 1996 to 1998. The radiation was measured in air and underwater, with special emphasis on the UV-B (ultraviolet B, 280–320 nm) radiation, which may increase under conditions of stratospheric ozone depletion. The recorded irradiances were related to ozone concentrations measured concurrently in the atmosphere above the Kongsfjord with a balloon-carried ozone probe and by TOMS satellite. For comparison, an ozone index (a spectroradiometrically determined irradiance of a wavelength dependent on ozone concentration, standardized to a non-affected wavelength) was used to indicate the total ozone concentration present in the atmosphere. Weather conditions and, hence, solar irradiance measured at ground level were seldom stable throughout the study. UV-B irradiation was clearly dependent on the actual ozone concentration in the atmosphere with a maximal fluence rate of downward irradiance of 0.27 W m−2 on the ground and a maximal daily fluence (radiation exposure) of 23.3 kJ m−2. To characterize the water body, the light transmittance, temperature and salinity were monitored at two different locations: (1) at a sheltered shallow-water bay and (2) at a wave-exposed, deep-water location within the Kongsfjord. During the clearest water conditions in spring, the vertical attenuation coefficient (Kd) for photosynthetically active radiation (PAR) was 0.12 m−1 and for UV-B 0.34 m−1. In spring, coinciding with low temperatures and clear water conditions, the harmful UV radiation penetrated deeply into the water column and the threshold irradiance negatively affecting primary plant productivity was still found at about 5–6 m depth. The water body in spring was characterized as a Jerlov coastal water type 1. With increasing temperature in summer, snow layers and glacier ice melted, resulting in a high discharge of turbid fresh water into the fjord. This caused a stratification in the optical features, the salinity and temperature of the water body. During melt-water input, a turbid freshwater layer was formed above the more dense sea water. Under these conditions, light attenuation was stronger than defined for a Jerlov coastal water type 9. Solar radiation was strongly attenuated in the first few metres of the water column. Consequently, organisms in deeper water are protected against harmful UV-B radiation. In the surface water, turbidity decreased when rising tide caused an advection of clearer oceanic water. In the course of the summer season, salinity continuously decreased and water temperature increased particularly in shallow water regions. The impact of global climate change on the radiation conditions under water and its effects on primary production of seaweeds are discussed, since organisms in the eulittoral and upper sublittoral zones are affected by UV radiation throughout the polar day. In clearer water conditions during spring, this may also apply to organisms inhabiting greater depths.

Planktonic larval duration and settlement marks on the otoliths of Mediterranean littoral fishes

Abstract: The planktonic larval duration (PLD) was estimated for 42 species of littoral fishes from the north-western Mediterranean Sea. Daily increments and settlement marks on the otoliths (sagittae or lapilli) of new settlers and post-settlers were used to determine the larval stage duration. We also used PLD in the new settlers of some species to confirm the accuracy of the settlement marks in post-settlers. The duration of the planktonic larval stage ranges from 9 days in Symphodus ocellatus to 55 days in Xyrichtis novacula and 71 days in Lipophrys trigloides. Species in the same family did not display any clear tendency toward having similar PLDs. On the other hand, larval duration tended to be similar within a genus, with the exception of Lipophrys. Among conspecifics, the time spent in the plankton usually varied only by 2–7 days, except in Aidablennius sphynx, Lipophrys trigloides, Coris julis and Thalassoma pavo. No clear patterns were discernible in genera, with some species that settled in winter and other species that settled in summer, although we observed a certain tendency of individuals of closely related species (e.g. family Sparidae) to have a shorter larval duration in the warmer part of the year than in the colder part of the year. Settlement marks have been observed on the otoliths of all the species studied, and the PLDs in new settlers are an appropriate means of validating settlement marks. A rapid decrease in increment width over settlement (type Ia) is the most common type of mark (66.7% of the total species studied).

A comparison of catches of fishes and invertebrates by two light trap designs, in tropical NW Australia

Abstract: Light traps were deployed in two sampling programs. In the first, small and large traps were released to drift with the current at stations along a cross-shelf transect on the NW Shelf off the coast of Western Australia. In the second program, pairs of small and large traps were deployed on moorings 150 m off the coastline. The composition and size-frequency distributions of catches of fishes in small and large traps were similar for both modes of deployment. In drifting traps, nearly 78% of this catch was composed of reef fishes, and these were collected in significantly greater numbers by the small design than by large traps (9.51 vs. 5.84 individuals h–1, respectively). Nine taxa (amphipods, mysids, crab megalopae, copepods, cumaceans, isopods, caridean shrimps, polychaetes and the euphausiid, Pseudeuphausia latifrons) accounted for 99% of the total catch of invertebrates by drifting traps. Of these, catches of amphipods, copepods, cumaceans and P. latifrons were greater in large traps than in small traps (3,134 vs. 1,687 h–1, 1,018 vs. 214 h–1, 551 vs. 165 h–1 and 74 vs. 9 individuals h–1, respectively). In contrast, crab megalopae were more abundant in catches by small traps than by large traps (3,134 vs. 1,687 individuals h–1, respectively). The catch rate of fishes in moored traps was higher than in drifting traps (105 vs. 20 fishes h–1) and was dominated by baitfishes (86% of total catch). Reef fishes were also captured in greater numbers by small traps than by the large design (10.17 vs. 4.4 individuals h–1) in this mode of deployment. Despite these differences in catch rates, multivariate analysis showed that cross-shelf patterns in catches of fishes and invertebrates were mapped equally well by both trap designs. Variation in the efficiency of trap designs thus appears to be small when compared to changes in the composition and abundance of zooplankton assemblages that occur at scales of tens of kilometers.

Lipid metabolism of the Antarctic krill Euphausia superba and its ecological implications

Abstract: Various developmental stages (early larvae to adults) of Euphausia superba have been collected in different seasons in the Weddell Sea, the Lazarev Sea and off the Antarctic Peninsula to investigate the role of lipids and fatty acids in the life cycle of the Antarctic krill. The total-lipid data for E. superba exhibited seasonal variations, with low lipid levels in late winter/early spring and the highest levels in autumn. Seasonal changes were most pronounced in the immature and adult specimens, increasing from about 10% lipid of dry mass to more than 40%. The fatty-acid compositions of the younger stages were dominated by 20:5(n-3), 22:6(n-3) and 16:0. These are typical phospholipid fatty acids, which are major biomembrane constituents. The phospholipid composition was similar in the older stages. With increasing storage of triacylglycerols in the lipid-rich immature and adult stages, the fatty acids 14:0, 16:0 and 18:1(n-9) prevailed, comprising about 70% of total triacylglycerol fatty acids. The trophic-marker fatty acids 16:1(n-7) and 18:4(n-3), indicating phytoplankton ingestion, were less abundant. They reflected, however, the dependence of the larvae on phytoplankton as well as the seasonal changes in algal composition. The generally close linear relationships between fatty acids and lipid suggest that the fatty-acid compositions of the collected specimens were largely independent of the respective developmental stage, season and region. The linear fit indicates that triacylglycerol accumulation started at a level of about 5% of total lipid. Considering the various overwintering scenarios under discussion, the life cycle and reproductive strategies of krill are discussed in the context of the lipid metabolism and fatty-acid composition of E. superba. Lipid production is effective enough to accumulate large energy reserves for the dark season, but E. superba does not exhibit the sophisticated biosynthetic pathways known from other Antarctic euphausiids and copepods. Although important, lipid utilisation appears to be just one of several strategies of E. superba to thrive under the extreme Antarctic conditions, and this pronounced versatility may explain the success of this species in the Southern Ocean.

Satellite telemetry tracking of swordfish, Xiphias gladius, off the eastern United States

Abstract: Swordfish (Xiphias gladius) were tagged with satellite "pop-off" tags that release from the fish after a preprogrammed time, float to the sea surface, and transmit present position and archived temperature data. Swordfish were tagged on the "Charleston Bump," a topographic feature on the Blake Plateau east of South Carolina and Georgia. This feature is an important swordfishing ground and may be a spawning and nursery area. Swordfish were tagged in spring of 2000 to determine movements in relation to the Charleston Bump, and tags were programmed to pop off the fish at 30 days (n=10 tags), 60 days (n=10), and 90 days (n=9). Although four swordfish were found in the vicinity of the Charleston Bump up to 90 days after tagging, most moved considerable distances to the east and northeast and were subsequently located in association with offshore seamounts, submarine canyons of the Middle Atlantic Bight, and with thermal fronts of the northern wall of the Gulf Stream. The longest minimum (i.e., straight-line) distance tracked was 2,497 km, and maximum speed inferred from tracking was 34 km/day. Seawater temperature data archived by the tags reflected diel vertical migrations in swordfish.

Contribution of mangrove detritus to juvenile prawn nutrition: a dual stable isotope study in a Malaysian mangrove forest

Abstract: Dual stable C and N ratio analyses of primary producers and prawns have clarified the important role of mangrove detritus as the primary food source of juvenile prawns inhabiting the upper estuaries of the Matang mangrove swamp in Malaysia. The contribution of mangrove carbon to prawn tissues, as high as 84%, decreased in the offshore direction, as the contribution by phytoplankton became progressively more important. Prawns located 2 km outside the mangrove swamp still exhibited a dependency of 15–25% on mangrove carbon, but farther offshore (7–10 km) in shallow waters, the prawn's food was basically phytoplankton, with some contribution from benthic microalgae. Comparative stable C and N isotope ratios of tissue and gut contents indicate that prawns basically assimilated what they consumed.

The hunting strategy of white sharks (Carcharodon carcharias) near a seal colony

Abstract: The degree to which white sharks, Carcharodon carcharias, are social while hunting is unclear. Our aim was to describe the behavior and interactions among white sharks hunting seals near a seal colony. We attached ultrasonic beacons to five adult white sharks, 4.5–5.2 m long, and recorded their movements and behavior toward each other over a 15-day period in October 1997 at Ano Nuevo Island, California. This site is home to colonies of four species of seals and sea lions. Two additional sharks, females 5.5 and 4.7 m in length, were later tracked intensively during periods of 12 and 3 days during October 1998 and November 1999, respectively. We recorded stomach temperature (indicative of feeding on warm-bodied seals) and swimming depths from the 5.5-m female, swimming speed and depth from the 4.7-m female. We monitored the movements and behavior of these sharks using an array of sonobuoys moored near the island; the receptive field measured 1 km2. Our principal findings were: (1) the sharks spent a mean time of 39.5% of each day patrolling within the receptive field; (2) no shark ever moved far out of it; (3) the sharks spent an equal amount of time and activity in the receptive field at all times of the day, daytime, twilight, and nighttime; (4) movements with respect to the island rookery were most often back and forth parallel to the shoreline, (5) tracks of three sharks, tagged at the same time and place, overlapped more often than those of the other two sharks; and (6) some sharks patrolled certain areas in the field preferentially, but there was no conclusive evidence that they defended these areas as territories. Feeding appeared to be infrequent: only two likely feeding bouts occurred during a cumulative 78-day/shark period that individuals were monitored at Ano Nuevo Island. The behavior and movements of the sharks were consistent with a hunting strategy, in which individuals search for prey independently but, at the same time, remain close enough to each other to “sense” and exploit a kill by any one of them by joining in on the kill to feed.

Molecular genetic evidence for probable reticulate speciation in the coral genus Madracis from a Caribbean fringing reef slope

Abstract: For many corals, the existence of morphologically distinct yet sympatric populations/species implies reproductive isolation. Conversely, the presence of many intermediate and overlapping morphologies combined with synchronous, mass spawning suggests incomplete reproductive isolation. In Madracis (Scleractinia: Astrocoeniina: Pocilloporidae), high levels of morphological plasticity among the five most commonly recognized species (M. mirabilis, M. senaria, M. decactis, M. formosa and M. pharensis) on Caribbean reefs led us to question species boundaries. Phylogenetic relationships were investigated at the intra-individual, inter-individual and inter-specific levels using the ITS1-5.8S-ITS2 region (ca. 613 bp) of the ribosomal DNA cistron. Inter-specific divergence was ca. 6%, while intra-individual and intra-specific divergences ranged from 0% to 4.9% and 3.3% to 3.5%, respectively. M. senaria and M. mirabilis formed monophyletic groups. M. formosa, M. decactis and M. pharensis formed a paraphyletic complex. High levels of intra-individual and intra-specific ITS polymorphism in the decactis-formosa-pharensis cluster may be the result of very recent speciation within the clade (i.e. maintenance of ancestral polymorphism and incomplete lineage sorting), or the result of repeated introgressive hybridization among the three taxa. Polymorphism parsimony of 89 sites, including nine that showed additivity, revealed a phylogenetic topology more consistent with inter-taxal hybridization. Results are discussed in terms of weak reproductive barriers, and phylogenetic fission and fusion under Veron's model of reticulate speciation in corals. Ecological studies involving Madracis should consider M. decactis, M. formosa and M. pharensis as a complex.

Life on glass houses: sponge stalk communities in the deep sea

Abstract: Photographs of the deep-sea floor often show organisms attached to biogenic structures that protrude from the soft bottom. In particular, the stalks of glass sponges (hexactinellids) provide hard substrata and act as habitat islands for deep-sea fauna. The primary objectives of this study were to determine the abundance of glass sponge “stalks” at an abyssal station in the NE Pacific, to identify the fauna associated with stalks, and to compare the distribution patterns of epifaunal taxa both horizontally and vertically. Densities of stalks and large epifauna were estimated from analysis of ∼9 km of photographic transects taken in 1994–1995 at station M (34°45′N; 123°00′W; 4,100 m depth) off California, USA. At least 87% of the stalks were the spicule columns of live or dead hexactinellids in the genus Hyalonema (Gray, 1832). Stalks appeared to be distributed randomly across the sea floor (density: 0.13 stalks m−2). A colonial zoanthid, Epizoanthus stellaris (Hertwig, 1888), inhabited 20% of the stalks and was the most commonly observed epifaunal organism, followed by other suspension feeders that generally were situated at the top of the structures. Thirty-five stalk communities were collected in tube cores in 1994–1995 using the submersible “Alvin”. A total of 139 taxa was associated with these hard-substratum habitats (another five species were observed only in photographs). Although taxon richness was high, the species diversity of these communities was relatively low due to the dominance in percentage abundance of a foraminiferan, Cibicides lobatulus (Walker and Jakob, 1798), and a serpulid polychaete, Bathyvermilia sp. (Zibrowius, 1973). The relationship between number of taxa and surface area of the stalks yielded a slope (z-value) typical of islands with a low rate of immigration. Three-dimensional complexity created by branching epifauna on the stalks provided more surface area and a variety of cryptic microhabitats. Vertical zonation on the stalks appeared to be controlled by biological interactions among species, with solitary fauna and certain functional groups of colonial organisms restricted by sheet-like colonial organisms that appeared to be dominant space competitors.

Mycosporine-like amino acids prevent UVB-induced abnormalities during early development of the green sea urchin Strongylocentrotus droebachiensis

Abstract: Experiments were performed to determine how ultraviolet radiation (UVR) in the environmentally relevant range affects development of the sea urchin Strongylocentrotus droebachiensis (Muller) and whether mycosporine-like amino acids (MAAs), present in the early life stages, reduce UV-induced damage. Eggs, embryos, and larvae contained five MAAs having absorption maxima ranging from 320 to 334 nm. Eggs contained principally shinorine and porphyra-334, which absorb maximally at 334 nm and half-maximally at 312 and 348 nm, spanning much of the environmental range of biologically effective UVR. Concentrations of MAAs remained constant in unirradiated embryos through the gastrula stage, but decreased significantly in two-armed pluteus larvae. Daily exposure to combined photosynthetically active radiation (PAR, 400–700 nm) and UVR did not affect the concentration of MAAs in these embryos up to the two-armed pluteus stage. Prism larvae of sea urchins and the sand dollar Echinarachnius parma (Lamarck) did not accumulate shinorine from the surrounding seawater. Daily exposure of embryos to UVA (320–400 nm) and UVB (295–320 nm) radiation in the presence of PAR induced delays and abnormalities during development, and removing UVB eliminated this effect. Abnormalities in embryos included thickening of the blastoderm wall, filling of the blastocoel by abnormal cells, exogastrulation, and formation of abnormal spicules. The percentage of embryos that developed normally was lower in batches of embryos exposed to PAR + UVA + UVB, except in embryos from urchins maintained on MAA-rich diets. In all cases, the percentage of PAR + UVA + UVB-exposed embryos that developed normally was positively related to the concentration of MAAs in eggs from which the embryos developed. Thus, the MAAs found in S. droebachiensis embryos protect them against UVB-induced abnormalities during their development to at least the four-armed pluteus larval stage.

Elevated levels of nitrogen and phosphorus reduce fertilisation success of gametes from scleractinian reef corals

Abstract: Spawned gametes were collected from colonies of Acropora longicyathus at One Tree Island and Goniastrea aspera at Magnetic Island, Great Barrier Reef, Australia, for use in fertilisation trials. Mean fertilisation rates were significantly reduced compared with controls (P<0.003), when gametes from the branching coral A. longicyathus were exposed to elevated ammonium concentrations at 1 µM and above in one cross (60–64% reduction), and at 100 µM in another cross (16% reduction). Mean fertilisation success of A. longicyathus gametes was also significantly reduced compared with controls in both crosses (P=0.000) at concentrations of 1 µM phosphate and above (35–75% reduction), and at 1 µM ammonium plus 1 µM phosphate and all higher concentrations (68–74% reduction). Similarly, the mean percentage of regular embryos that were developing normally was significantly reduced in most nutrient treatments compared with controls (P=0.000). Fertilisation trials using gametes from the brain coral G. aspera resulted in a significantly lower percentage of regular embryos (P=0.001) and a significantly higher percentage of deformed embryos (P=0.001) developing after exposure to elevated nutrient treatments compared with controls. Mean fertilisation rates for this species were only significantly reduced (P=0.034) in the 50 µM ammonium plus phosphate treatment in one cross (8% reduction), compared with the control. Therefore, ammonium and phosphate enrichment significantly impairs fertilisation success and embryo development in scleractinian reef corals.

Temperature-induced ontogenetic plasticity in sea bass (Dicentrarchus labrax)

Abstract: We studied the ontogeny of Dicentrarchuslabrax comparatively under constant rearing temperatures of 13, 15 and 20°C At hatching, yolk-sac larval morphometry differed significantly between the temperatures and especially between the two extremes, while at the end of the yolk-sac larval stage, it mainly differed between the two lower temperature regimes and that of 20°C Compared with the two lower temperature conditions, at 20°C D labrax presented a significant ontogenetic acceleration which was morphologically expressed either as a significantly smaller total length (TL) at feeding onset, notochord flexion and fin differentiation, or as shifts of the allometric inflection points of 8 out of the 15 morphometric characters studied Additionally, temperature significantly affected the allometry coefficients, with a decreasing growth intensity as the temperature difference decreased The rate of TL growth increased under elevated temperature conditions throughout the entire ontogenetic period, except during the early larval period (feeding onset to metamorphosis onset), at which time D labrax presented equal growth rates at 15°C and 20°C The results are discussed with respect to the ontogeny of the functional morphology and the meanings of temperature-induced ontogenetic plasticity for the survival of fish larvae

Reproductive toxicity of metals in calanoid copepods

Abstract: This study investigated the effect of exposure route on metal accumulation, tissue distribution, and toxicity in the marine copepods Acartia hudsonica and A tonsa Sublethal toxicity was measured as decreases in egg production, hatching rate, ovarian development and protein (yolk) content of the egg When algal food, exposed to Hg at 1 nM or Cd at 5 nM resulting in cells containing 34 and 64 nmol metal g–1 dry weight, respectively, was ingested over a 4-h period by copepods, the total copepod body burden increased nine-fold for Hg and two-fold for Cd over background concentrations, and egg production decreased by 50% Sublethal concentrations of metals were >2 orders of magnitude lower than LC50 concentrations Hatching rate, ovarian development and egg protein content all decreased following trophic exposure to metals, implying that the process of yolk accumulation (vitellogenesis) was affected Exposure to dissolved Cd had no effect, but dissolved Hg at concentrations as low as 025 nM did affect egg production Different toxic effects following different exposure routes were related to different metal distributions in the copepods: exposure to dissolved metal resulted in metal deposition in the exoskeleton, whereas exposure to dietary metal resulted in metal deposition in internal tissues These findings indicate that enrichment of metal concentrations in internal tissues, which occurs primarily after exposure to dietary metal, affects vitellogenesis The reproduction rate decreases by about 75% at metal concentrations only moderately higher than levels in coastal waters Toxicity tests involving aquatic animals need to consider effects following uptake by different pathways, including the trophic transfer of metals

The ichthyofaunal composition of the Elbe Estuary: an analysis in space and time

Abstract: A stow net (90 m2 opening) was used, at regular intervals between July 1989 and June 1993, to collect fish over ca. 4 h on both the flood and ebb tides at five sites distributed at regularly spaced distances throughout the Elbe Estuary. Overall, 53.4% of the species were marine, and some of these were abundant, e.g.Clupea harengus, Pleuronectes flesus, Pomatoschistus minutus, Merlangius merlangus and Sprattus sprattus. However, in terms of number of individuals, such species contributed only 9.1%, compared with 90.0% by anadromous species, which was predominantly due to exceptionally high catches of Osmerus eperlanus. The ichthyofaunal compositions on the flood and ebb tides were similar, even downstream where salinities change markedly during each tidal cycle. Although this is probably due in part to groups of fish being swept first upstream on the flood tide and then back downstream on the ebb tide, several species clearly tended to occupy particular regions of the estuary. Each year the species composition changed sequentially from the most downstream site (max. salinity=ca. 31.4‰) to the most upstream site (max. salinity=ca. 1.5‰), mainly as a result of a sequential decline in the number and abundance of marine species and a progressive increase in the contributions of both anadromous and freshwater species. However, the marine species diagnostic of differences in the compositions among regions varied between years. Thus, for example, the diagnostic species for the downstream sites were C. harengus and M. merlangus in 1990/1991 and S. sprattus in 1992/1993, reflecting differences in the recruitment strengths of these marine species in the two years. The ichthyofaunal composition exhibited pronounced annual cyclical changes in each region and thus occurred irrespective of whether or not the salinity in a region underwent pronounced changes during the year. This cyclicity was attributable to intra-annual variations in the times of recruitment of certain marine species, particularly in the downstream region, and to seasonal migrations of diadromous species into each region, as well as to the movements of freshwater species into the upstream region in winter and early spring.

Latitudinal variation in the reproductive biology of the commensal crab Pinnaxodes chilensis (Decapoda: Pinnotheridae) along the Chilean coast

Abstract: The pinnotherid crab Pinnaxodes chilensis is a common commensal of the edible sea urchin Loxechinus albus along the Chilean coast. Several aspects of the reproductive biology of P. chilensis were examined between April and June 1999, along temperature and salinity gradients, at three sampling sites along the Chilean coast (23°45′S–39°24′S). Results demonstrated significant differences in egg number, egg volume, dry egg weight, and reproductive output of ovigerous females, between the studied populations of northern and central-southern Chile. Egg volume, egg dry weight, and reproductive output of females decreased from high to low latitudes, while egg number increased from high to low latitudes, exhibiting a clear trade-off with egg volume. It has been shown that changes in environmental conditions (e.g. temperature, salinity) along a latitudinal gradient, can generate clines in reproductive characteristics in both free-living and parasitic species.

Coexistence Of Nine Anemonefish Species: Differential Host And Habitat Utilization, Size And Recruitment

Abstract: The region of Madang, Papua New Guinea, has the highest reported species diversity of both anemonefishes (nine species) and their host anemones (ten species). To determine which factors may allow so many anemonefish species to coexist at this location, we studied their patterns of distribution, abundance, and recruitment. Population surveys at three replicate reef sites within four zones situated at varying distances from the mainland (nearshore, mid-lagoon, outer barrier, and offshore) indicated that each species of host anemone and anemonefish lived within a particular range of zones. Each species of anemonefish lived primarily with one species of host. Anemonefish species that lived with the same host species usually had different distribution patterns among zones (e.g., Amphiprion percula occupied Heteractis magnifica in nearshore zones, while A. perideraion occupied H. magnifica in offshore zones). Monitoring of natural populations showed that there were few changes (losses or recruitment) in the number or species of fishes associated with each individual anemone over periods ranging from 3 to 9 months. Recruitment was monitored on anemones with and without residents (resident fishes were removed) within each of three zones (nearshore, mid-lagoon, outer barrier). Significantly more anemonefishes recruited to anemones without resident fishes than to anemones with resident fishes. Each anemonefish species recruited to particular host species and zones. The distribution and abundance of the recruits of each fish species among zones were positively correlated with the distribution and abundance of resident fishes in the benthic habitat. This suggests that the spatial patterns of recruitment among zones strongly determined the distribution and abundance patterns of the benthic populations, and they were not the result of post-recruitment mortality or movement. Coexistence of the nine anemonefish species on the limited anemone resource was considered possible because of niche differentiation (i.e., differences in host and habitat utilization among zones), and the ability of two small species (i.e., Amphiprion sandaracinos and A. leucokranos) to cohabit individual anemones with other anemonefish species.

Associations between the abundance of piscivorous fishes and their prey on coral reefs: implications for prey-fish mortality

Abstract: Few studies have examined predator-prey relationships in diverse communities such as those found on coral reefs. Here we examined patterns of spatial and temporal association between the local abundance of predator and prey fishes at Lizard Island on the Great Barrier Reef, Australia. We predicted that the nature of this association would have implications for patterns of prey-fish mortality. Strong positive relationships between prey and piscivore abundance were found throughout the study. Greater densities of predators and of prey were found on patch-reef habitats, compared with contiguous reef-slope habitats. Declines in prey-fish abundance on patch reefs were density-dependent and correlated with the densities of predators. The relative roles of recruitment and piscivore movement in determining patterns of predator and prey abundance were assessed from surveys of recruit densities and an intensive programme of tagging two species of rock-cod, Cephalopholis cyanostigma and C. boenak (Serranidae), over 2 years. Patterns of recruitment explained little of the variation in the abundance and distribution of piscivorous fish. If movement explains large-scale patterns of distribution, this was not evident from the tagging study. The two rock-cod species were highly sedentary, with individuals on patch reefs seldom moving among reefs. Individuals on reef slopes were also highly site-attached, although they moved greater distances than those on patch reefs. Although the mechanisms responsible remain to be determined, this study demonstrated strong associations between the abundance of piscivorous fish and their prey on coral reefs. This relationship appeared to be an important factor in producing density-dependent declines in the abundance of prey.

Depth and muscle temperature of Pacific bluefin tuna examined with acoustic and pop-up satellite archival tags

Abstract: Six Pacific bluefin tuna were tracked with ultrasonic telemetry and two with pop-up satellite archival tags (PSATs) in the eastern Pacific Ocean in 1997, 1998, and 1999. Both pressure and temperature ultrasonic transmitters were used to examine the behavior of the 2- to 4-year-old bluefin tuna. The bluefin spent over 80% of their time in the top 40 m of the water column and made occasional dives into deeper, cooler water. The mean slow-oxidative muscle temperatures of three fish instrumented with pressure and temperature transmitters were 22.0–26.1 °C in water temperatures that averaged 15.7–17.5 °C. The thermal excesses in slow-oxidative muscle averaged 6.2–8.6 °C. Variation in the temperature of the slow-oxidative muscle in the bluefin was not correlated with water temperature or swimming speeds. For comparison with the acoustic tracking data we examined the depth and ambient temperature of two Pacific bluefin tagged with pop-up satellite archival tags for 24 and 52 days. The PSAT data sets show depth and temperature distributions of the bluefin tuna similar to the acoustic data set. Swimming speeds calculated from horizontal distances with the acoustic data indicate the fish mean speeds were 1.1–1.4 fork lengths/s (FL s−1). These Pacific bluefin spent the majority of their time in the top parts of the water column in the eastern Pacific Ocean in a pattern similar to that observed for yellowfin tuna.