Showing papers in "Marine Ecology Progress Series in 2006"

Regulation of microbial populations by coral surface mucus and mucus-associated bacteria

Abstract: Caribbean populations of the elkhorn coral Acropora palmata have declined due to envi- ronmental stress, bleaching, and disease. Potential sources of coral mortality include invasive microbes that become trapped in the surface mucus and thrive under conditions of increased coral stress. In this study, mucus from healthy A. palmata inhibited growth of potentially invasive microbes by up to 10-fold. Among cultured bacteria from the mucus of A. palmata, 20% displayed antibiotic activity against one or more tester strains, including the pathogen implicated in white pox disease. A novel mucus- mediated selection for coral symbionts revealed a discrete subset of bacteria and selected for isolates that produce antibiotics. This result suggests that coral mucus plays a role in the structuring of beneficial coral-associated microbial communities and implies a microbial contribution to the antibacterial activity described for coral mucus. Interestingly, antibiotic activity was lost when mucus was collected during a summer bleaching event. Isolates from apparently healthy A. palmata tissue during this event lacked antibiotic-producing bacteria and were dominated by members of the genus Vibrio, including species implicated in temperature-dependent bleaching of corals worldwide. This indicates an environmental shift from beneficial bacteria, and variability in the protective qualities of coral mucus, which may lead to an overgrowth of opportunistic microbes when temperatures increase. Finally, coral mucus inhibited antibiotic activity and pigment production in a poten- tially invasive bacterium, illustrating that coral mucus may inactivate mechanisms used for bacterial niche establishment.

Lipid storage in marine zooplankton

Abstract: Zooplankton storage lipids play an important role during reproduction, food scarcity, ontogeny and diapause, as shown by studies in various oceanic regions. While triacylglycerols, the primary storage lipid of terrestrial animals, are found in almost all zooplankton species, wax esters are the dominant storage lipid in many deep-living and polar zooplankton taxa. Phospholipids and diacylglycerol ethers are the unique storage lipids used by polar euphausiids and pteropods, respec- tively. In zooplankton with large stores of wax esters, triacylglycerols are more rapidly turned over and used for short-term energy needs, while wax esters serve as long-term energy deposits. Zooplankton groups found in polar, westerlies, upwelling and coastal biomes are characterized by accumulation of large lipid stores. In contrast, zooplankton from the trades/tropical biomes is mainly composed of omnivorous species with only small lipid reserves. Diapausing copepods, which enter deep water after feeding on phytoplankton during spring/summer blooms or at the end of upwelling periods, are characterized by large oil sacs filled with wax esters. The thermal expansion and com- pressibility of wax esters may allow diapausing copepods and other deep-water zooplankton to be neutrally buoyant in cold deep waters, and they can thus avoid spending energy to remain at these depths. Lipid droplets are often noted in zooplankton ovaries, and a portion of these droplets can be transferred to developing oocytes. In addition to lipid droplets, zooplankton eggs have yolks with lipovitellin, a lipoprotein with approximately equal amounts of protein and lipid. The lipovitellin lipid is predominantly phosphatidylcholine, so during reproduction females must convert a portion of their storage lipid into this phospholipid. Developing embryos use their lipovitellin and lipid droplets for energy and materials until feeding begins. The various functions storage lipids serve during the dif- ferent life history stages of zooplankton are very complex and still not fully understood and hence offer a multitude of fascinating research perspectives.

Global analysis of response and recovery of benthic biota to fishing

Abstract: Towed bottom-fishing gears are thought to constitute one of the largest global anthropogenic sources of disturbance to the seabed and its biota. The current drive towards an ecosystem approach in fish- eries management requires a consideration of the im- plications of habitat deterioration and an understand- ing of the potential for restoration. We undertook a meta-analysis of 101 different fishing impact manipu- lations. The direct effects of different types of fishing gear were strongly habitat-specific. The most severe impact occurred in biogenic habitats in response to scallop-dredging. Analysis of the response of differ- ent feeding guilds to disturbance from fishing re- vealed that both deposit- and suspension-feeders were consistently vulnerable to scallop dredging across gravel, sand and mud habitats, while the re- sponse of these groups to beam-trawling was highly dependent upon habitat type. The biota of soft-sedi- ment habitats, in particular muddy sands, were sur- prisingly vulnerable, with predicted recovery times measured in years. Slow-growing large-biomass biota such as sponges and soft corals took much longer to recover (up to 8 yr) than biota with shorter life-spans such as polychaetes (<1 yr). The results give a possi- ble basis for predicting the outcome of the use of dif- ferent fishing gears in a variety of habitats with poten- tial utility in a management context.

Variation in demersal fish species richness in the oceans surrounding New Zealand: an analysis using boosted regression trees

Abstract: We analysed relationships between demersal fish species richness, environment and trawl characteristics using an extensive collection of trawl data from the oceans around New Zealand. Analyses were carried out using both generalised additive models and boosted regression trees (sometimes referred to as 'stochastic gradient boosting'). Depth was the single most important envi- ronmental predictor of variation in species richness, with highest richness occurring at depths of 900 to 1000 m, and with a broad plateau of moderately high richness between 400 and 1100 m. Richness was higher both in waters with high surface concentrations of chlorophyll a and in zones of mixing of water bodies of contrasting origins. Local variation in temperature was also important, with lower richness occurring in waters that were cooler than expected given their depth. Variables describing trawl length, trawl speed, and cod-end mesh size made a substantial contribution to analysis out- comes, even though functions fitted for trawl distance and cod-end mesh size were constrained to reflect the known performance of trawl gear. Species richness declined with increasing cod-end mesh size and increasing trawl speed, but increased with increasing trawl distance, reaching a plateau once trawl distances exceed about 3 nautical miles. Boosted regression trees provided a powerful analysis tool, giving substantially superior predictive performance to generalized additive models, despite the fitting of interaction terms in the latter.

Global bathymetric patterns of standing stock and body size in the deep-sea benthos

Abstract: We present the first global-scale analy- sis of standing stock (abundance and biomass) for 4 major size classes of deep-sea biota: bacteria, meta- zoan meiofauna, macrofauna and megafauna. The community standing stock decreases with depth; this is a universal phenomenon that involves a com- plex transition in the relative importance of the different size groups. Bacterial abundance and biomass show no decline with depth. All 3 animal size groups experience significant exponential de- creases in both abundance and biomass. The abun- dance of larger animals is significantly lower and decreases more rapidly than for smaller groups. The resulting drop in average body size with depth con- firms Thiel's size-structure hypothesis on very large spatial scales. In terms of their proportion of total community biomass, smaller size classes replace larger size classes. The upper continental slope is dominated by macrofaunal biomass, and the abyss by bacterial and meiofaunal biomass. The dramatic decrease in total community standing stock and the ascendancy of smaller organisms with depth has important implications for deep-sea biodiversity. The bathyal zone (200 to 4000 m) affords more eco- logical and evolutionary opportunity in the form of energy availability for larger organisms, and conse- quently supports higher macrofaunal and mega- faunal species diversity than the abyss (> 4000 m).

Inhibition of coral recruitment by macroalgae and cyanobacteria

Abstract: Coral recruitment is a key process in the maintenance and recovery of coral reef eco- systems. While intense competition between coral and algae is often assumed on reefs that have undergone phase shifts from coral to algal dominance, data examining the competitive interactions involved, particularly during the larval and immediate post-settlement stage, are scarce. Using a series of field and outdoor seawater table experiments, we tested the hypothesis that common species of macroalgae and cyanobacteria inhibit coral recruitment. We examined the effects of Lyngbya spp., Dictyota spp., Lobophora variegata (J. V. Lamouroux) Womersley, and Chondrophycus poiteaui (J. V. Lamouroux) Nam (formerly Laurencia poiteaui) on the recruitment success of Porites astreoides lar- vae. All species but C. poiteaui caused either recruitment inhibition or avoidance behavior in P. astreoides larvae, while L. confervoides and D. menstrualis significantly increased mortality rates of P. astreoides recruits. We also tested the effect of some of these macrophytes on larvae of the gorgon- ian octocoral Briareum asbestinum. Exposure to Lyngbya majuscula reduced survival and recruit- ment in the octocoral larvae. Our results provide evidence that algae and cyanobacteria use tactics beyond space occupation to inhibit coral recruitment. On reefs experiencing phase shifts or tempo- rary algal blooms, the restocking of adult coral populations may be slowed due to recruitment inhibi- tion, thereby perpetuating reduced coral cover and limiting coral community recovery.

Techniques for cetacean-habitat modeling

Abstract: Cetacean-habitat modeling, although still in the early stages of development, represents a potentially powerful tool for predicting cetacean distributions and understanding the ecological processes determining these distributions. Marine ecosystems vary temporally on diel to decadal scales and spatially on scales from several meters to 1000s of kilometers. Many cetacean species are wide- ranging and respond to this variability by changes in distribution patterns. Cetacean-habitat models have already been used to incorporate this variability into management applications, including im- provement of abundance estimates, development of marine protected areas, and understanding cetacean-fisheries interactions. We present a review of the development of cetacean-habitat models, organized according to the primary steps involved in the modeling process. Topics covered include purposes for which cetacean-habitat models are developed, scale issues in marine ecosystems, cetacean and habitat data collection, descriptive and statistical modeling techniques, model selection, and model evaluation. To date, descriptive statistical techniques have been used to explore cetacean-habitat relationships for selected species in specific areas; the numbers of species and geographic areas exam- ined using computationally intensive statistic modeling techniques are considerably less, and the de- velopment of models to test specific hypotheses about the ecological processes determining cetacean distributions has just begun. Future directions in cetacean-habitat modeling span a wide range of possibilities, from development of basic modeling techniques to addressing important ecological questions.

Biodiversity and the functioning of seagrass ecosystems

Abstract: Biodiversity at multiple levels — genotypes within species, species within functional groups, habitats within a landscape — enhances productivity, resource use, and stability of seagrass ecosystems. Several themes emerge from a review of the mostly indirect evidence and the few exper- iments that explicitly manipulated diversity in seagrass systems. First, because many seagrass com- munities are dominated by 1 or a few plant species, genetic and phenotypic diversity within such foundation species has important influences on ecosystem productivity and stability. Second, in sea- grass beds and many other aquatic systems, consumer control is strong, extinction is biased toward large body size and high trophic levels, and thus human impacts are often mediated by interactions of changing 'vertical diversity' (food chain length) with changing 'horizontal diversity' (heterogene- ity within trophic levels). Third, the openness of marine systems means that ecosystem structure and processes often depend on interactions among habitats within a landscape (landscape diversity). There is clear evidence from seagrass systems that advection of resources and active movement of consumers among adjacent habitats influence nutrient fluxes, trophic transfer, fishery production, and species diversity. Future investigations of biodiversity effects on processes within seagrass and other aquatic ecosystems would benefit from broadening the concept of biodiversity to encompass the hierarchy of genetic through landscape diversity, focusing on links between diversity and trophic interactions, and on links between regional diversity, local diversity, and ecosystem processes. Maintaining biodiversity and biocomplexity of seagrass and other coastal ecosystems has important conservation and management implications.

Wind turbine underwater noise and marine mammals: implications of current knowledge and data needs

Abstract: The demand for renewable energy has led to construction of offshore wind farms with high-power turbines, and many more wind farms are being planned for the shallow waters of the world's marine habitats. The growth of offshore wind farms has raised concerns about their impact on the marine environment. Marine mammals use sound for foraging, orientation and communication and are therefore possibly susceptible to negative effects of man-made noise generated from con- structing and operating large offshore wind turbines. This paper reviews the existing literature and assesses zones of impact from different noise-generating activities in conjunction with wind farms on 4 representative shallow-water species of marine mammals. Construction involves many types of activities that can generate high sound pressure levels, and pile-driving seems to be the noisiest of all. Both the literature and modeling show that pile-driving and other activities that generate intense impulses during construction are likely to disrupt the behavior of marine mammals at ranges of many kilometers, and that these activities have the potential to induce hearing impairment at close range. The reported noise levels from operating wind turbines are low, and are unlikely to impair hearing in marine mammals. The impact zones for marine mammals from operating wind turbines depend on the low-frequency hearing-abilities of the species in question, on sound-propagation conditions, and on the presence of other noise sources such as shipping. The noise impact on marine mammals is more severe during the construction of wind farms than during their operation.

Marine nurseries and effective juvenile habitats: concepts and applications

Abstract: Much recent attention has been focused on juvenile fish and invertebrate habitat use, particularly defining and identifying marine nurseries. The most significant advancement in this area has been the development of a standardized framework for assessing the relative importance of juvenile habitats and classifying the most productive as nurseries. Within this framework, a marine nursery is defined as a juvenile habitat for a particular species that contributes a greater than average number of individuals to the adult population on a per-unit-area basis, as compared to other habitats used by juveniles. While the nursery definition and framework provides a powerful approach to identifying habitats for conservation and restoration efforts, it can omit habitats that have a small per-unit-area contribution to adult populations, but may be essential for sustaining adult populations. Here we build on the nursery concept by developing a framework for evaluating juvenile habitats based on their overall contribution to adult populations, and introduce the concept of Effective Juvenile Habitat (EJH) to refer to habitats that make a greater than average overall contribution to adult populations.

Chronic bottom trawling alters the functional composition of benthic invertebrate communities on a sea-basin scale

Abstract: Bottom trawling causes widespread physical disturbance of sediments in seas and oceans and affects benthic communities by removing target and non-target species and altering habitats. One aspiration of the ecosystem approach to management is to conserve function as well as biodiversity, but trawling impacts on benthic community function need to be understood before they can be managed. Here we present the large scale and long term impact of chronic trawling on the functional composition of benthic invertebrate communities using a comprehensive set of functional traits. The effects of chronic trawling disturbance on the functional composition of faunal benthic invertebrate communities, as sampled with a small beam trawl, were investigated at 6 to 13 sites in each of 4 contrasting regions of the North Sea. Each site was subject to known levels of trawling disturbance. Information on the life history and ecological function traits of the taxa sampled was translated into fuzzy coding and used to analyse the relationship between life history and functional roles within the ecosystem. Multivariate analyses were used to examine changes in the distribution of traits over gradients of trawling intensity. Changes in the functional structure of the community due to the effects of long-term trawling were identified in 3 of the 4 areas sampled. Filter-feeding, attached and larger animals were relatively more abundant in lightly trawled areas, while areas with higher levels of trawling were characterised by a higher relative biomass of mobile animals and infaunal and scavenging invertebrates. Univariate analysis of selected traits confirmed the patterns observed in multivariate analysis. These results demonstrate that chronic bottom trawling can lead to large scale shifts in the functional composition of benthic communities, with likely effects on the functioning of coastal ecosystems.

Water, not food, contributes the majority of strontium and barium deposited in the otoliths of a marine fish

Abstract: We quantified the relative contributions of water and food to strontium (Sr) and barium (Ba) deposited in otoliths of juvenile mummichogs Fundulus heteroclitus. Fish were reared in sea- water spiked with 86 Sr and 137 Ba significantly beyond natural values to obtain distinct isotopic signatures for water and food. Element abundances (Sr:Ca and Ba:Ca) and isotope ratios ( 88 Sr: 86 Sr and 138 Ba: 137 Ba) were quantified in water samples using solution-based inductively coupled plasma- mass spectrometry (ICP-MS), and 88 Sr: 86 Sr and 138 Ba: 137 Ba ratios in otoliths were quantified using laser ablation ICP-MS. The relative contributions of water and food sources to otolith aragonite were assessed using a simple linear isotope mixing model. Water sources contributed 83% of Sr and 98% of Ba in otoliths formed in spiked seawater. Our results indicate that water chemistry is the dominant factor controlling the uptake of Sr and Ba in the otoliths of marine fishes. Thus, chemical signatures recorded in the otoliths of marine fishes should reflect the ambient water composition of these ele- ments at the time of deposition.

Phenotypic plasticity of habitat use by three temperate eel species, Anguilla anguilla, A. japonica and A. rostrata

Abstract: Habitat use patterns of 3 species of temperate eels, Anguilla anguilla, A. japonica and A. rostrata, were investigated using otolith strontium:calcium ratio life history transects. Published and unpublished data from 6 sites (Canada, United States, Sweden, France, Taiwan and Japan) sam- pled across the geographical range of each eel species were compiled. Sr:Ca patterns indicated that the 3 species displayed similar patterns of habitat use. In all sites, patterns of habitat use consisted of either residency in one habitat (fresh, brackish, or marine) or movements between habitats. One movement pattern consisted of either a single change or 2 changes of habitat from fresh to brackish waters, or from brackish water to freshwater. Seasonal movements between fresh and brackish waters were observed for all 3 species. When only a single habitat switch event was detected, it occurred between 3 and 5 yr of age. Occurrence of eels with no freshwater experience was demon- strated, but such eels accounted for a smaller proportion of the overall sample than eels with some (even brief) freshwater experience. Contrary to the common convention that these are obligate catadromous species, we must now consider them as facultative catadromous, with far more flexibil- ity in habitat use. The most variable parameter among study sites was the relative proportion, rather than the diversity, of lifetime spent in the various habitat use patterns. Eels found at higher latitudes exhibited a greater probability of remaining in the lower reaches of watersheds in brackish water. Diversity of habitat use appears to be a common strategy of temperate eel species, and, as a life his- tory tactic, is under environmental control.

Role of Elevated Organic Carbon Levels and Microbial Activity in Coral Mortality

Abstract: Coral reefs are suffering a long-term global decline, yet the causes remain contentious. The role of poor water quality in this decline is particularly unclear, with most previous studies providing only weak correlations between elevated nutrient levels and coral mortality. Here we experimentally show that routinely measured components of water quality (nitrate, phosphate, ammonia) do not cause substantial coral mortality. In contrast, dissolved organic carbon (DOC), which is rarely measured on reefs, does. Elevated DOC levels also accelerate the growth rate of microbes living in the corals’ surface mucopolysaccharide layer by an order of magnitude, suggesting that mortality occurs due to a disruption of the balance between the coral and its associated microbiota. We propose a model by which elevated DOC levels cause Caribbean reefs to shift further from coral to macroalgal dominance. Increasing DOC levels on coral reefs should be recognized as a threat and routinely monitored.

Selective foraging by fish-eating killer whales Orcinus orca in British Columbia

Abstract: As the apex non-human marine predator, the killer whale Orcinus orca feeds on a wide diversity of marine fauna. Different ecotypic forms of the species, which often exist in sympatry, may have distinct foraging specialisations. One form found in coastal waters of the temperate NE Pacific Ocean, known as the 'resident' ecotype, feeds predominantly on salmonid prey. An earlier study that used opportunistic collection of prey remains from kill sites as an indicator of predation rates suggested that resident killer whales may forage selectively for chinook salmon Oncorhynchus tshawytscha, the largest but one of the least abundant Pacific salmon species. Potential biases in the prey fragment sampling technique, however, made the validity of this finding uncertain. We under- took field studies of foraging behaviour of resident killer whales to resolve this uncertainty and to examine potential variation in prey selection by season, geographical area, group membership and prey availability. Foraging by resident killer whales was found to frequently involve sharing by 2 or more whales. Prey fragments left at kill sites resulted mostly from handling and breaking up of prey for sharing, and all species and sizes of salmonids were shared. Resident killer whale groups in all parts of the study area foraged selectively for chinook salmon, probably because of the species' large size, high lipid content, and year-round availability in the whales' range. Chum salmon Oncorhynchus keta, the second largest salmonid, were also taken when available, but smaller sock- eye O. nerka and pink O. gorbuscha salmon were not significant prey despite far greater seasonal abundance. Strong selectivity for chinook salmon by resident killer whales probably has a significant influence on foraging tactics and seasonal movements, and also may have important implications for the conservation and management of both predator and prey.

Stable isotopes indicate sex-specific and long-term individual foraging specialisation in diving seabirds

Abstract: An important aspect of foraging ecology is the extent to which different individuals or genders within a population exploit food resources in a different manner. For diving seabirds, much of this information relates either to short-term dietary data or indirect measures such as time budgets. Moreover, dietary specialisation can be difficult to detect due to biases associated with conventional sampling techniques. We used stable isotope ratios in blood and feathers to infer trophic and habitat specialisations among 4 diving seabird taxa — the gentoo penguin Pygoscelis papua, the macaroni penguin Eudyptes chrysolophus, the South Georgian shag Phalacrocorax (atriceps) georgianus and the Kerguelen shag P. (atriceps) verrucosus. This allowed us to investigate foraging specialisation and assess whether social dominance or differences in foraging preferences explained the observed patterns. In all taxa where sexes were known we found that males foraged at a higher trophic level (δ 15 N values) than females, although this was not significant in macaroni penguins. We believe that this is linked to a dual foraging strategy among female macaroni penguins. For South Georgian shags, we found that sex-related dietary differences persisted for long periods (inferred from stable isotope analyses of feathers and blood). We suggest that the trophic differences are driven by differ- ences in physiological performance, with males tending to dive deeper than females because of their larger size, and hence able to access higher trophic level prey items. Moreover, male and female shags tend to forage at different times of day; therefore, social dominance by males is unlikely to be driving the observed differences. We also recorded highly significant relationships between stable isotope signatures in blood (representing the breeding season diet) and those in feathers (mostly rep- resenting the previous non-breeding season diet) in both the South Georgian and Kerguelen shags. This strongly suggests that these 2 taxa include individuals with distinct foraging specialisation (and most probably foraging locations) that are maintained over long periods.

Most corals may not change their symbionts

Abstract: Many corals (stony corals and octo- corals) rely on their symbiotic algae (zooxanthellae) for survival. Under stress, zooxanthellae are ex- pelled, resulting in coral bleaching. The hypothesis that corals may survive climate change by ex- changing algal types is shown here to be potentially applicable only to a minority of corals. Data on 442 coral species from 43 studies reveal that only a few coral species may be able to change their symbionts. The ability to change symbionts seems to be linked to whether a coral species can host multiple zooxanthella clades, either at different depths on the same reef, on different reefs or at different geographic locations, or concurrently within the same colony. The combined data set shows that only 23% of coral species host multiple zoo- xanthella clades. Most coral species (77%) exhibit fidelity to a narrow subset of a single zooxanthella clade, some even to specific algal genotypes within a clade. These specific algal genotypes in coral species hosting a single algal clade do not change over time. Furthermore, no algal change occurs when a coral colony is either transplanted to differ- ent environments, or subjected to stressors such as disease or increased temperatures. For the majority of corals, therefore, algal switching does not appear to occur. These coral species will survive only if the existing host-symbiont combination withstands the changing conditions. If climate warming con- tinues, coral reefs may undergo a change in bio- diversity such that only a subset of symbiotic corals may persist.

Mapping world-wide distributions of marine mammal species using a relative environmental suitability (RES) model

Abstract: The lack of comprehensive sighting data sets precludes the application of standard habi- tat suitability modeling approaches to predict distributions of the majority of marine mammal species on very large scales. As an alternative, we developed an ecological niche model to map global distrib- utions of 115 cetacean and pinniped species living in the marine environment using more readily available expert knowledge about habitat usage. We started by assigning each species to broad-scale niche categories with respect to depth, sea-surface temperature, and ice edge association based on synopses of published information. Within a global information system framework and a global grid of 0.5° latitude/longitude cell dimensions, we then generated an index of the relative environmental suit- ability (RES) of each cell for a given species by relating known habitat usage to local environmental conditions. RES predictions closely matched published maximum ranges for most species, thus repre- senting useful, more objective alternatives to existing sketched distributional outlines. In addition, raster-based predictions provided detailed information about heterogeneous patterns of potentially suitable habitat for species throughout their range. We tested RES model outputs for 11 species (north- ern fur seal, harbor porpoise, sperm whale, killer whale, hourglass dolphin, fin whale, humpback whale, blue whale, Antarctic minke, and dwarf minke whales) from a broad taxonomic and geo- graphic range, using data from dedicated surveys. Observed encounter rates and species-specific pre- dicted environmental suitability were significantly and positively correlated for all but 1 species. In comparison, encounter rates were correlated with <1% of 1000 simulated random data sets for all but 2 species. Mapping of large-scale marine mammal distributions using this environmental envelope model is helpful for evaluating current assumptions and knowledge about species' occurrences, espe- cially for data-poor species. Moreover, RES modeling can help to focus research efforts on smaller geographic scales and usefully supplement other, statistical, habitat suitability models.

Impacts of offshore wind farm construction on harbour porpoises: acoustic monitoring of echolocation activity using porpoise detectors (T-PODs)

Abstract: Offshore wind farming is a new emerging technology in the field of renewable energies. This study investigates the potential impact of the construction of one of the first major, offshore wind farms (>100 MW) on harbour porpoises Phocoena phocoena by means of acoustic porpoise detectors (T-PODs) monitoring porpoise echolocation activity. The monitoring program was established as a modified BACI (before, after, control, impact) design, with 6 monitoring stations equally distributed between the impact area and a nearby reference area. Mean waiting times, defined as the period between 2 consecutive encounters of echolocation activity, increased from 6 h in the baseline period to 3 d in the wind farm area during the construction. This increase was 6 times larger than changes observed in the reference area. One specific construction activity, involving the ramming and vibration of steel sheet piles into the seabed, was associated with an additional significant increase in waiting time of 4 to 41 h, in both the construction and reference areas. Assuming that echolocation activity is related to harbour porpoise density, the analysis shows that their habitat-use changed substantially, with the porpoises leaving the construction area of the offshore wind farm. Acoustic monitoring from fixed positions provides data with a high temporal resolution, but low spatial reso- lution, which can be analysed at a variety of scales, and can be applied to harbour porpoises and other echolocating cetaceans.

Chemical defence against bacteria in the red alga Asparagopsis armata: linking structure with function

Abstract: Although numerous algal products have antimicrobial activity, limited knowledge of metabolite localisation and presentation in algae has meant that ecological roles of algal natural products are not well understood. In this study, extracts of Asparagopsis armata had antibacterial activity against marine (Vibrio spp.) and biomedical (Escherichia coli, Pseudomonas aeruginosa and Staphylococcus spp.) strains. The major natural products in both life-history stages of A. armata (as determined by gas chromatography-mass spectrometry analysis (GC-MS)) were bromoform (0.58 to 4.3% of dry weight (DW)) and dibromoacetic acid (DBA) (0.02 to 2.6% DW), and each compound was active against these same bacteria. To resolve whether this antibiotic activity was ecologically rele- vant, we examined the localisation of metabolites in the specialised cells of A. armata and observed a delivery mechanism for the release of metabolites to the surface. Bromoform and DBA were sub- sequently quantified in the surrounding medium of laboratory cultures, establishing their release from the alga. In a novel ecological test of algal natural products, halogenated metabolites in A. armata were manipulated by omitting bromine from an artificial seawater medium. Significantly higher densities of epiphytic bacteria occurred on algae that no longer produced halogenated metabolites. Both bromoform and DBA were more active against bacteria isolated from algae lacking brominated metabolites than algae producing normal amounts of these compounds. Taken together, these results indicate that halogenated metabolites of A. armata may be important in reducing epiphytic bacterial densities.

Going against the flow: retention, range limits and invasions in advective environments

Abstract: Increasing globalization has spread invasive marine organisms, but it is not well under- stood why some species invade more readily than others. It is also poorly understood how species' range limits are set generally, let alone how anthropogenic climate change may disrupt existing species boundaries. We find a quantitative relationship that determines if a coastal species with a benthic adult stage and planktonic larvae can be retained within its range and invade in the direc- tion opposite that of the mean current experienced by the larvae (i.e. upstream). The derivation of the retention criterion extends prior riparian results to the coastal ocean by formulating the criterion as a function of observable oceanic parameters, focusing on species with obligate benthic adults and planktonic larvae, and quantifying the effects of iteroparity and longevity. By placing the solutions in a coastal context, the retention criterion isolates the role of 3 interacting factors that counteract down- stream drift and set or advance the upstream edge of an oceanic species' distribution. First, spawning over several seasons or years enhances retention by increasing the variation in the currents encoun- tered by the larvae. Second, for a given population growth rate, species with a shorter pelagic period are better retained and more able to spread upstream. And third, prodigious larval production improves retention. Long distance downstream dispersal may thus be a byproduct of the many propagules often necessary to ensure local recruitment and persistence of a population in an advective environment.

Whale distribution in relation to prey abundance and oceanographic processes in shelf waters of the Western Antarctic Peninsula

Abstract: The Western Antarctic Peninsula (WAP) is a biologically rich area supporting large standing stocks of krill and top predators (including whales, seals and seabirds). Physical forcing greatly affects productivity, recruitment, survival and distribution of krill in this area. In turn, such interactions are likely to affect the distribution of baleen whales. The Southern Ocean GLOBEC research program aims to explore the relationships and interactions between the environment, krill and predators around Marguerite Bay (WAP) in autumn 2001 and 2002. Bathymetric and environmental variables including acoustic backscattering as an indicator of prey abundance were used to model whale distribution patterns. We used an iterative approach employing (1) classification and regression tree (CART) models to identify oceanographic and ecological variables contributing to variability in humpback Megaptera novaeangliae and minke Balaenoptera acutorstrata whale distribution, and (2) generalized additive models (GAMs) to elucidate functional ecological relationships between these variables and whale distribution. The CART models indicated that the cetacean distribution was tightly coupled with zooplankton acoustic volume backscatter in the upper (25 to 100 m), and middle (100 to 300 m) portions of the water column. Whale distribution was also related to distance from the ice edge and bathymetric slope. The GAMs indicated a persistent, strong, positive relationship between increasing zooplankton volume and whale relative abundance. Furthermore, there was a lower limit for averaged acoustic volume backscatter of zooplankton below which the relationship between whales and prey was not significant. The GAMs also supported an annual relationship between whale distribution, distance from the ice edge and bathymetric slope, suggesting that these are important features for aggregating prey. Our results demonstrate that during the 2 yr study, whales were consistently and predictably associated with the distribution of zooplankton. Thus, humpback and minke whales may be able to locate physical features and oceanographic processes that enhance prey aggregation.

Species diversity, invasion success, and ecosystem functioning: disentangling the influence of resource competition, facilitation, and extrinsic factors

Abstract: Experimental manipulations and observational surveys often produce conflicting con- clusions regarding the effects of native species diversity on community susceptibility to invasion. Both provide useful pieces of information, but typically each asks fundamentally different questions. Surveys tell us that locations with species-rich native communities are characterized by conditions that promote exotic species richness, whereas experiments tell us that, within a location, the loss of resident species increases the likelihood of the establishment of new species. In the present study, we apply observational data to a study of the consequences of species loss for invasion in order to assess the generality across scales and the relative importance of experimental results. We begin by using long-term recruitment data to explore how small-scale mechanisms of biotic resistance could operate on a landscape scale. We find that individual species have complementary seasonal recruitment pat- terns such that more diverse communities might be able to more consistently fill space that opens throughout the season, leading to reduced invasion success. However, field surveys of native and invader richness show that the slope of the relationship between native and invader diversity changes with the availability of resources (space) and the presence of habitat-forming foundation species. In these systems, biotic resistance appears to be important only when resources are scarce and foundation species are rare. Thus, we conclude that biotic resistance, as identified in experi- ments, is a consistent effect of diversity that can be explained mechanistically at even a landscape scale, but that it plays a dominant role only when total diversity is constrained by resource limitation. This situation is common in experimentally constructed communities, but may be less so in nature.

Unusual population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae) in East Asian waters

Abstract: A population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizo- stomeae) occurred in the Sea of Japan in 2002 and 2003, causing severe damage to fisheries. There was a further population explosion in 2004, but on a much smaller scale. In both years, young medusae began to appear in the Tsushima and Korea Strait in July and August, followed by a north- ward expatriation in the Tsushima Current to the northern Sea of Japan. We obtained scyphistomae of this species by artificial fertilization, and reared them to the young medusa stage in the laboratory. Asexual reproduction of scyphistomae occurred by means of podocyst formation. A thermal increase from 13 to 23°C induced strobilation, followed by liberation of 3 to 7 ephyrae from a strobila. The ephyrae developed to metephyrae having a complex canal system and characteristically possessing long reddish purple filiform appendages. By 40 d post-liberation, the metephyrae had grown to medusae in which the central mouth had closed and been replaced by numerous mouthlets on both oral wings and scapulets. The results from both laboratory-rearing experiments and field investiga- tions were combined to construct the seasonal life cycle and geographical distribution of N. nomurai in eastern Asian waters. Possible causes for the mass occurrence of N. nomurai, which has tended to be more frequent in the last decade, are discussed.

Nursery function of tropical back-reef systems

Abstract: Similar to nearshore systems in temperate latitudes, the nursery paradigm for tropical back-reef systems is that they provide a habitat for juveniles of species that subsequently make onto- genetic shifts to adult populations on coral reefs (we refer to this as the nursery function of back-reef systems). Nevertheless, we lack a full understanding of the importance of the nursery function of back-reef systems to the maintenance of coral reef fishes and invertebrate populations; the few stud- ies that have examined the nursery function of multiple habitats indicate that the relationship between juvenile production in back-reef habitats and their subsequent contribution to adult popu- lations on reefs remain poorly understood. In this synopsis we (1) synthesize current knowledge of life history, ecological and habitat influences on juvenile distribution patterns and nursery function within back-reef systems; (2) outline a research strategy for assessing the nursery function of various habitat types in back-reef systems; and (3) discuss management recommendations, particularly in regard to how improved knowledge of the nursery function of back-reef systems can be used in fish- eries and ecosystem management, including habitat conservation and restoration decisions. The research strategy builds on research recommendations for assessing the nursery function of temper- ate habitats and includes 4 levels of research: (1) building conceptual models to guide research and management; (2) identifying juvenile habitat use patterns; (3) measuring connectivity of juvenile and adult populations between habitats; and (4) examining ecological processes that may influence pat- terns assessed in Level 2 and Level 3 research. Research and modeling output from Levels 1 to 4 will provide an improved ecological understanding of the degree and importance of interconnections between coral reef and adjacent back-reef systems, and will provide information to managers that will facilitate wise decisions pertaining to habitat conservation, habitat restoration, and ecosystem- based management, and the maintenance of sustainable fisheries.

Vertical and horizontal migrations by the jumbo squid Dosidicus gigas revealed by electronic tagging

Abstract: Dosidicus gigas is a large and powerful oceanic squid that is economically valuable and eco- logically important in the eastern Pacific Ocean. We employed electronic tagging methods to provide the first long-term monitoring of the natural behaviors of D. gigas in its mesopelagic habitat. Seven pop-up satellite tags logged depth and temperature for a total of 842 h, and a conventional archival tag yielded 780 h of continuous time-series data. Horizontal movements of nearly 100 km over 3 d were observed, and these were temporally associated with an established trans- Gulf migration. Squid consistently spent most daylight hours at depths >250 m, the approximate upper boundary of a midwater hypoxic zone termed the oxy- gen minimum layer (OML). A diel migration brought squid to near-surface waters at dusk, but a highly vari- able amount of diving back into the OML occurred throughout the night. Rhythmic vertical movements within the OML often occurred, and sojourns of up to 6 h in this hypoxic zone below 300 m were observed. Laboratory experiments revealed a high resting rate of oxygen consumption under normal conditions, but this rate decreased drastically under hypoxic conditions such as would be associated with the OML in nature. These findings suggest that D. gigas has physiological adaptations that permit constant foraging in both oxygenated near-surface waters and within the OML.

Satellite-monitored movements of humpback whales Megaptera novaeangliae in the Southwest Atlantic Ocean

Abstract: Southern Hemisphere humpback whales Megaptera novaeangliae migrate from wintering grounds in tropical latitudes to feeding areas in the Antarctic Ocean. It has been hypo- thesized that the population wintering off eastern South America migrates to feeding grounds near the Antarctic Peninsula (ca. 65° S, 60° W) and/or South Georgia (54° 20' S, 36° 40' W), but direct evi- dence to support this has never been presented. Between 19 and 28 October 2003, 11 humpback whales (7 females and 4 males) were instrumented with satellite transmitters off Brazil (ca. 18° 30' S, 39° 30' W) to investigate their movements and migratory destinations. Mean tracking time for the whales was 39.6 d (range = 5 to 205 d) and mean distance travelled was 1673 km per whale (range = 60 to 7258 km). Movements on the wintering ground showed marked individual variation. Departure dates from the Brazilian coast ranged from late October to late December. Whales migrated south through oceanic waters at an average heading of 170° and travelled a relatively direct, linear path from wintering to feeding grounds. Two whales were tracked to feeding grounds in offshore areas near South Georgia and in the South Sandwich Islands (58° S, 26° W) after a 40 to 60 d long migration. Historical catches and current sighting information support these migratory routes and destinations. This study is the first to describe the movements of humpback whales in the western South Atlantic Ocean.

Benthic community response to ice algae and phytoplankton in Ny Ålesund, Svalbard

Abstract: We assessed the digestibility and utilization of ice algae and phytoplankton by the shallow, subtidal ben- thos in Ny Alesund (Kongsfjord) on Svalbard (79° N, 12° E) using chlorophyll a (chl a), essential fatty acids (EFAs) and stable isotopes as tracers of food consumption and assimi- lation Intact benthic communities in sediment cores and individuals of dominant benthic taxa were given ice algae, phytoplankton, 13 C-enriched ice algae or a no food addi- tion control for 19 to 32 d Ice algae and phytoplankton had significantly different isotopic signatures and relative con- centrations of fatty acids In the food addition cores, sedi- ment concentrations of chl a and the EFA C20:5(n-3) were elevated by 80 and 93%, respectively, compared to the control after 12 h, but decreased to background levels by 19 d, suggesting that both ice algae and phytoplankton were rapidly consumed Whole core respiration rates in the ice algae treatments were 14 times greater than in the other treatments within 12 h of food addition In the ice algae treatment, both suspension and deposit feeding taxa from 3 different phyla (Mollusca, Annelida and Sipuncula) exhibited significant enrichment in δ13 C values compared to the control Deposit feeders (15% uptake), however, ex- hibited significantly greater uptake of the 13 C-enriched ice algae tracer than suspension feeders (3% uptake) Our study demonstrates that ice algae are readily consumed and assimilated by the Arctic benthos, and may be prefer- entially selected by some benthic species (ie deposit feed- ers) due to their elevated EFA content, thus serving as an important component of the Arctic benthic food web

Mangroves as fish habitat: 50 Years of field studies

Abstract: Mangroves dominate undisturbed nat- ural shorelines of many sub-tropical and tropical regions, yet their utilization by fishes is poorly understood. To provide the first comprehensive list of empirical field studies for comparative and ref- erence purposes, we assembled and quantified aspects of 111 mangrove-fish surveys published between 1955 and 2005. Differences in the location, purpose, methodology, data gathered, and analyses performed among studies have resulted in a frag- mented literature making cross-study comparisons difficult, at best. Although the number of published studies has increased over time, a geographical bias in the literature has persisted towards studies performed in the USA and Australia, and against studies performed in Southeast Asia and West Africa. The typical survey design has examined <10 fixed locations on a monthly or bimonthly basis for a period of less than 2 yr. Water temperature and salinity measurements have been the most reported habitat variables; others, such as structural and landscape measures, continue to be rare. Moreover, the focus to date has been on identifying assemblage-level patterns of fish use, with very few studies providing species-specific estimates of abundance, growth, mortality, and secondary pro- duction. Unless future studies strive towards ob- taining such estimates, gauging the importance of mangroves as fish habitat and their broader contri- bution to ecosystem diversity and production will remain elusive.

Radiocarbon-based ages and growth rates of Hawaiian deep-sea corals

Abstract: The radial growth rates and ages of three different groups of Hawaiian deep-sea 'corals' were determined using radiocarbon measurements. Specimens of Corallium secundum, Gerardia sp., and Leiopathes glaberrima, were collected from 450 {+-} 40 m at the Makapuu deep-sea coral bed using a submersible (PISCES V). Specimens of Antipathes dichotoma were collected at 50 m off Lahaina, Maui. The primary source of carbon to the calcitic C. secundum skeleton is in situ dissolved inorganic carbon (DIC). Using bomb {sup 14}C time markers we calculate radial growth rates of {approx} 170 {micro}m y{sup -1} and ages of 68-75 years on specimens as tall as 28 cm of C. secundum. Gerardia sp., A. dichotoma, and L. glaberrima have proteinaceous skeletons and labile particulate organic carbon (POC) is their primary source of architectural carbon. Using {sup 14}C we calculate a radial growth rate of 15 {micro}m y{sup -1} and an age of 807 {+-} 30 years for a live collected Gerardia sp., showing that these organisms are extremely long lived. Inner and outer {sup 14}C measurements on four sub-fossil Gerardia spp. samples produce similar growth rate estimates (range 14-45 {micro}m y{sup -1}) and ages (range 450-2742 years) as observed for the live collected sample. Similarly, with a growth rate of < 10 {micro}m y{sup -1} and an age of {approx}2377 years, L. glaberrima at the Makapuu coral bed, is also extremely long lived. In contrast, the shallow-collected A. dichotoma samples yield growth rates ranging from 130 to 1,140 {micro}m y{sup -1}. These results show that Hawaiian deep-sea corals grow more slowly and are older than previously thought.