Showing papers in "Marine Ecology Progress Series in 1995"
TL;DR: In this paper, a simple expression enables prediction of the effect of photosynthetic and calcifying systems on air-sea CO2 exchange at all spatial scales (from organism to ecosystem).
Abstract: A simple expression enables prediction of the effect of photosynthetic and calcifying systems on air-sea CO2 exchange at all spatial scales (from organism to ecosystem) Input data are: gross primary production (Pg), respiration (R), net calcification (G) and the ratio of CO2 released to CaC03 precipitated (ψ); the output is the amount of dissolved inorganic carbon (Fco2) which needs to be exchanged with the atmosphere to balance biologically mediated changes in the concentration of dissolved inorganic carbon In an open sea water system: Fco2 = -Pg + R + ψG Coral reef data were used in the model to illustrate the relative influence of organic and inorganic carbon metabolism on ocean-atmosphere CO2 cycling A coral reef comprised of calcareous and non-calcareous organisms can be shown to act as a sink for atmospheric CO2 when excess (= net) production is high and CaC03 precipitation is low These characteristics are not typical of actively developing reef systems which typically exhibit a nearly balanced organic carbon metabolism (Pg/R = 1) and relatively high rates of calcification In these circumstances, reef communities can be expected to cause CO2 evasion to the atmosphere This prediction is confirmed by the only existing measurement of air-sea CO2 flux in a coral reef system
783 citations
631 citations
TL;DR: In this article, the authors showed that coral respiration in light was calculated as the difference between the measured gross and net photosynthesis, and was found to be >6 times higher at a saturating irradiance of 350 pEm m 2 s 1 than the dark respiration measured under identical hydrodynamic conditions (flow rate of 5 to 6 cm ssl).
Abstract: During experimental light-dark cycles, O9 in the tissue of the colonial scleractinian corals Favia sp. and Acropora sp reached >250 % of air saturation after a few minutes in light. Immediately after darkenmg, 0; was depleted rapidly, and within 5 mm the 0; concentration at the tissue surface reached <2 % of air saturation. The pH of the tissue changed within 10 min from about 8.5 in the light to 7.3 m the dark. Oxygen and pH profiles revealed a diffusive boundary layer of flow-dependent thickness, which limited coral respiration in the dark. The light field at the tissue surface (measured as scalar irradiance, Eo) differed strongly with respect to light intensity and spectral composition from the incident collimated light (measured as downwelling irradiance, Ed) Scalar irradiance reached up to 180 % of Ed at the coral tissue surface for wavelengths subject to less absorption by the coral tissue (600 to 650 run and >680 nm). The scalar irradiance spectra exhibited bands of chlorophyll a (chl a ) (675 run), chl c (630 to 640 nm) and pendinin (540 nm) absorption and a broad absorption band due to chlorophyl l~ and carotenoids between 400 and 550 nm. The shape of both action spectra and photosynthesis vs irradiance (Pvs I) curves depended on the choice of the light intensity parameter. Calculations of miha1 slopes and onset of light saturation, Ik, showed that P vs Eo curves exhibit a lower initial slope and a higher 4 than corresponding Pvs Ed curves. Coral respiration in light was calculated as the difference between the measured gross and net photosynthesis, and was found to be >6 times higher at a saturating irradiance of 350 pEm m 2 s 1 than the dark respiration measured under identical hydrodynamic conditions (flow rate of 5 to 6 cm ssl).
517 citations
456 citations
TL;DR: There was no relationship between sponge color and deterrency, suggesting that sponges are not aposematic and that color variation is the result of other factors, and the invalidity of previous assessments of chemical defense based on toxicity was confirmed.
Abstract: Laboratory feeding assays employing the common Canbbean wrasse Thalassoma bifasciatum were undertaken to determine the palatability of food pellets containing natural concentrations of crude organic extracts of 71 species of Caribbean demosponges from reef, mangrove, and grassbed habitats. The majority of sponge species (69%) yielded deterrent extracts, but there was considerable interand intraspecific vanability in deterrency. Most of the sponges of the aspiculate orders Verongida and Dictyoceratida yielded highly deterrent extracts, as did all the species in the orders Homosclerophorida and Axinellida. Palatable extracts were common among species in the orders Hadromerida, Poecilosclerida and Haplosclerida. Intraspecific variability was evident, suggesting that, for some species, some individuals (or portions thereof) may be chemically undefended. Reef sponges generally yielded more deterrent extracts than sponges from mangrove or grassbed habitats, but 4 of the 10 most common sponges on reefs yielded palatable extracts (Callyspongia vaginalis, Mycale laevis, Niphates erecta, Iotrochota birotulata), including those most commonly eaten by sponge-eating reef fish. The presence of symbiotic zoanthid cnidarians of the genus Parazoanthus in the tissues of otherwise palatable sponges had little effect on the deterrency of tissue extracts, indicating that these commensal polyps do not confer a chemical defense by association There was no relationship between sponge color and deterrency, suggesting that sponges are not aposematic and that color variation is the result of other factors. There was also no relationship between the toxicity of sponge extracts (as determined in previous studies) and deterrency, confirming the invalidity of previous assessments of chemical defense based on toxicity. Although chemical antipredatory defenses are important strategies for most Caribbean sponges, some common species appear to rely on other tactics.
392 citations
TL;DR: Stable-isotope analysis may be well suited to establ~shing the importance of polynyas as sites of high primary productivity and tight benthic-pelagic coupling relative to regions of more permanent ice cover and compared with other Arctic and temperate marine food webs.
Abstract: We used stable carbon (l3C/I2C) and nitrogen ( f S ~ / ' \" ) isotope analysis to investigate linkages between sources of primary production and the pelagic and benthic components of the Northeast Water (NEW) Polynya off northeastern Greenland. Ice algae was enriched in 13C (mean 6I3C = -18.6 vs -27.9%) and I5N [mean 6 1 5 ~ = 8.3 vs 4.9%0) over particulate organic matter [POM) suggesting that the relative importance of these sources might be traced isotopically. Most grazing crustaceans and filter-feeding bivalves had 6I3C and 6 1 5 ~ values in the range of -21 to -23% and 7 to 9x0, respectively, indicating a direct pathway from POM. Close benthic-pelagic coupling was also confirmed for other benthic organisms examined with the exception of the predatory or deposit feeding echinoderms Ophioctin, Ophiacantha and Pontaster. Compared with other Arctic and temperate marine food webs, stable-carbon isotope values for the NEW Polynya were depleted in I3C. A S1'N trophic model that incorporated taxon-specific isotopic fractionation factors indicated that the NEW Polynya consisted of 4.5 to 5 trophic levels. Stable-isotope analysis Inay be well suited to establ~shing the importance of polynyas as sites of high primary productivity and tight benthic-pelagic coupling relative to regions of more permanent ice cover.
390 citations
TL;DR: It is suggested that the higher concentrations of DOCL in eutrophic as opposed to oligotrophic systems may be explained by a higher 'theoretical community half-saturation constant' (K,) in eUTrophic systems.
Abstract: The utilization of dissolved organic carbon (DOC) by bacteria in grazer-free cultures can be used to measure the concentration of labile DOC (DOCL). A database of 126 measurements was used to test whether or not the concentration of DOCL is positively related to total DOC. A positive and significant correlation between DOCL and DOC was found for the entire database as well as for lakes, rivers and seawater. An average response of about 0.17 pm01 DOCL pmol-' DOC could be calculated and 60% of the variance was explained by DOC. The DOCL concentration averaged 14, 19, and 19% of the total DOC pool in lakes, rlvers and seawater, respectively; however, the median value of 25% for rivers was about twice the values for lakes and seawater The high relative amount of DOCL in half the rivers was explained by anthropogenic influence. The control of DOCL concentrations was analyzed according to models of bacterial and substrate interactions applying Michaelis-Menten-Monod kinetics. It is suggested that the higher concentrations of DOCL in eutrophic as opposed to oligotrophic systems may be explained by a higher 'theoretical community half-saturation constant' (K,) in eutrophic systems. The consequence of a higher K, will be a higher steady-state concentration of labile substrate, as was found. Other possible explanations were analyzed, but rejected as major causes for the crosssystem difference.
322 citations
TL;DR: Damage to blood cell lysosomes was investigated in vitro in mussels Mytilus galloprovincialis collected from a series of sites in the Lagoon of Venice, Italy, and correlated with total tissue burdens for a range of contaminants.
Abstract: Damage to blood cell lysosomes was investigated in vitro in mussels Mytilus galloprovincialis collected from a series of sites in the Lagoon of Venice, Italy, and correlated with total tissue burdens for a range of contaminants. Retention of the cationic probe neutral red within the lysosomal compartment over time was used as a measure of damage to the lysosomal membrane. Multi-stepwise regression analysis was used to explore the relationship between altered cellular physiology and total body burdens of contaminants. Organochlorines (DDT, HCH and Aroclor 1254), mercury and cobalt were the principle factors involved in evoking pathological responses.
319 citations
TL;DR: In this paper, the utility of analyses of abundance data at taxonomic levels higher than species, in the interpretation of results from manne surveys, is examined using nematode and macrofauna data from a sublittoral dredgings disposal site and from an intertidal site known to be influenced by heavy metal pollution.
Abstract: The utility of analyses of abundance data at taxonomic levels higher than species, in the interpretation of results from manne surveys, is examined using nematode and macrofauna data from a sublittoral dredgings disposal site and from an intertidal site known to be influenced by heavy metal pollution. A more objective approach than has hitherto been the case in comparisons of multivariate patterns from data at different taxonomic levels is taken, and the concept of a 'second-stage' multidimensional scaling (MDS), in which rank correlat~ons between pairs of similarity matrices themselves become the elements of a second s~milarity matrix, an ordination of which gives a summary of the conclusions, is introduced. It is shown that analyses of both the sublittoral and intertidal estuarine nematode communities are robust to aggregation to the level of genus, but further aggregation alters the perceived pattern of impact. Aggregation of macrofauna abundances to families has only a small effect on analyses of the sublittoral community, and none on analyses of the less d~ver se intertidal macrofauna. Aggregating macrofauna data to phyla has some effect on consequent analyses in both situations. Whichever component of the benthos is examined, and at whatever taxonomic level the analyses are carried out, interpretable results are possible, especially if the pattern of commun~ty change is marked, as in both surveys examined in this study.
318 citations
TL;DR: It is concluded that P limitation provokes elevated PER m exponentially growing phytoplankton which is not utilized efficiently by the natural bacterial consortia which would allow the PER to coagulate and eventually form mucilage.
Abstract: Batch cultures of Chaetoceros affinis grown under nitrogen- (N:P = 5) and phosphorus- (N:P = 100) limited conditions exhibited 30 and 100% higher rates of photosynthetic extracellular release (PER), respectively, than C affims grown under balanced nutrient conditions (N.P = 16). Inoculations of natural bacterial assemblages to PER derived from phytoplankton grown under these different nutrient regimes exhibited highest potential bacterial growth yields (- 46 %) on PER derived from balanced growth. Analysis of the dissolved monomeric (MCHO) and polymeric (PCHO) carbo- hydrate pool and of the dissolved free amino acid (DFAA) fraction of the PER indicated significantly higher specific release rates of these components for phytoplankton grown under P limitation Based on the fluctuation of the MCHO, PCHO and DFAA pool in the batch cultures and on bacterial extra- cellular enzymatic activity (EEA) and bacterial growth yield we have evidence that under P-limited conditions bacteria are not taking up the available carbon efficiently. Bacteria growing on PER derived from N-lmted conditions exhibited high bacterial a- and p-glucosidase activity, while under P limta- tion low EEA was detectable. Extrapolating our results to the severely P-limited summer conditions of the Northern Adriatic Sea, we might conclude that P limitation provokes elevated PER m exponentially growing phytoplankton which is not utilized efficiently by the natural bacterial consortia. This would allow the PER to coagulate and eventually form mucilage.
317 citations
TL;DR: Turbulence has the largest effect on prey encounters for predators with low motility and long reactlon distances, and the potentially negatlve effects of turbulence on copepod feedlng currents, prey perception and capture success are explored.
Abstract: ABSTFUCT Turbulence may enhance contact rates between planktonic predators and their prey We formulate slmple and general models of prey encounter rates, taklng into account the behaviours and motility patterns of both prey and predator as well as turbulent fluld motlon Uslng these models we determine the levels of turbulence (as clmipation rate) at which ambient fluid motlon is lmportant in enhancing prey encounter rates for vanous types of predators (e g ambush and cruise predators, suspension feeders) Generally, turbulence has the largest effect on prey encounters for predators with low motility and long reactlon distances Also, turbulence is most important for meso-sized (mm to cm) predators and insignificant for smaller and larger predators The effect of turbulence on copepods is specifically examined For copepods that establish feeding currents, turbulence is of minor importance, for ambush feeding copepods, such as Acartldae and many cyclopoids, turbulence has a dominant influence on prey encounter rates The effect on cruising predators is intermediate Application of the models to situations examined experimentally demonstrates a hlgh predictive performance Finally we explore and model the potentially negatlve effects of turbulence on copepod feedlng currents, prey perception and capture success At typical and even high turbulent lntenslties none of these IS slgnificantly affected
TL;DR: Activity was the net result of the inhibitory effect by benthic microalgae and the stimulatory effect of the benthlc infauna, and it was concluded that the stlmulatory effect of bioturbatlng infauna is of mlnor importance to the annual denltnf~cation budget.
Abstract: Measurements of seasonal vanation In oxygen fluxes nutiient fluxes and denltrif~catlon were obtalned in an estuarine sedlment lnhablted by benthlc microalgae and bloturbating infauna Oxygen dynamics in the upper sediment strata were found to be controlled by the ln~croalgae and there was a net flux of O2 out of the sediment during spring and autumn Hlgh assimllatlon by the microalgae reduced the efflux of NH,and PO, ' from the sediment to the water column dunng daytime Denltrification based on NO-, from the water column (D,,] only occurred in wlnter and spnng, when NO, was present in the water column and act~vity was proportional to the water column NO, concentratlon The rate of D,, was reduced during day t~me when the upper oxic zone of the sediment increased due to 0, production by benthic m~croalgae Coupled nitrif~catlon-denltrlfication (D,) In the sedlment was stimulated by the O2 production durlng win te~ and spnng at which times NO? and NH,' were present in the wciter column In hlgh concentrations In contrast, d u r ~ n g summer when the concentration of NO; and NH,In the water column was low, benthic microalgae Inhibited D, by competing with nltr~fying bacterla for NH,' D,, accounted for 80'Yi of the total denltrificatlon during winter, while on an annual basis. D, and D, edch accounted for 50% of the total denitnficatlon activity Benthic ~ n f a u n a , such as Corophlurn spp Hydrob~a spp , and N e r e ~ s pp , occurred in densities of up to several thousand ind in from May to October Oxygen consumption, D,, and D, were llneaily correlated with the dens~ ty of the amphlpod Coroph~um spp , all the processes studied belng stimulated by the pumping of 02and NO3 -nch water through the burrows in the upper 2 to 6 cm of the sediment Dunng summer, the D, activity was, therefore, the net result of the inhibitory effect by benthic microalgae and the stimulatory effect of the benthlc infauna However, as the concentration of lnorganlc nitrogen in the overlying water and the sediment nitrification potent~al are both low in shallow coastal waters during summer, when b e n t h ~ c infauna dens~ ty is high we conclude that the stlmulatory effect of bioturbatlng infauna on both D, and D, IS of mlnor importance to the annual denltnf~cation budget
TL;DR: The role of algal size as a controlling factor for nltrogen uptake kinetics was examined by comparing published values of N uptake rate and half-saturation constants in micro and macroalgae.
Abstract: The role of algal size as a controlling factor for nltrogen uptake kinetics is examined by comparing published values of N uptake rate and half-saturation constants in microand macroalgae. The uptake kinetics differ substantially among algae very different in size. Microalgae take up nitrogen much faster per unit of biomass than macroalgae at both high and low substrate concentrations, and microalgae have significantly higher affinity for nitrogen than macroalgae. These typical differences in the uptake kinetics among small and large algae are commonly attributed to size-specific differences in the relative surface area (SA:V). Regression analysis demonstrates that size-specific variations in the kinetic parameters can be attributed to changes in relative surface area over an extensive range of algal sizes, covering both microand macroalgae. These results agree with previously described relationships between maximum uptake rate of nutrients (nitrogen and phosphorus) and SA:V within narrow size-ranges (either phytoplankton or macroalgae), and emphasize the existence of a general coupling between physiological and morpholog~cal properties in algae.
TL;DR: In this paper, it is argued that the microbial food web during summer stratification has a net accumulation of dissolved organic carbon (DOG) and DOP, which would make downwards transport of DOC with winter deep water formation a potentially effective mechanism in C sequestration from the atmosphere.
Abstract: In light of evidence suggesting that both phytoplankton and bacteria in the Mediterranean Sea are limited by the availability of phosphorus rather than of nitrogen, and that most of the P in the photic zone during summer stratification exists as dissolved organic compounds (DOP), we address the question of how these observations may interact with the 'biological pump' transporting carbon to deep waters. From theoretical considerations, the C storage via sinking particles should function better in a P- than in an N-limited system. It is argued, however, that the microbial food web during summer stratification has a net accumulation of dissolved organic carbon (DOG) and DOP. The limited data available suggest a high DOC:DOP value which would make downwards transport of DOC with winter deep water formation a potentially effective mechanism in C sequestration from the atmosphere. Part of the DOC accumulating in the photic zone appears to be readily biodegradable. This is in conflict with a simple model of phytoplankton-bacterial competition for phosphate since phytoplankton, as an inferior competitor, would be expected to be reduced in biomass until autochthonous production of organic C falls to a level where bacteria become C-limited. The conflict is resolved by including microzooplankton grazing as a controlling factor of bacterial biomass.
TL;DR: The species composition of seagrass meadows can be altered by intensive grazing, which favours rapidly growing, early pioneer species, such as Halophila ovalis, at the expense of slower growing but dominant species such as Zostera capricorni.
Abstract: In Moreton Bay, Australia, dugongs (Dugong dugon) often graze in large herds at the same location for weeks to months. Such grazing reduced seagrass shoot density by 65 to 95 %, aboveground biomass by 73 to 96% and belowground biomass by 31 to 71 % at 3 sites ranging in size from 2 to 75 ha. Following even the most intense and sustained grazing, the space between surviving tufts of seagrass remains small (
TL;DR: The virusto-bacteria ratio was significantly higher in freshwater than marine environments, and there were significantly more bacteria per unit chlorophyll in the authors' freshwater samples, suggesting that this difference is related to the increased dependence of freshwater bacteria on allochthonous material relative to marine systems, as well as the increased relative importance of photosynthetic cyanobacteria in lakes.
Abstract: In order to investigate the factors controlling viral abundance, 22 lakes In Quebec were surveyed. We measured viral and bacterial abundance, bacterial production, chlorophyll a, total phosphorus and DOC (dissolved organic carbon) concentrations. Regression models built with these data were compared to models based on literature data, which to date have been collected largely from marine sites Positive empirical relationships were found between viral abundance and (1) chlorophyll a concentrations, (2) bacterial abundances, (3) bacterial production, and (4 ) total phosphorus concentration. There was little to no trend in the virus-to-bacteria ratio with increasing trophy. Analysis of covariance revealed significant differences between relations in marine and freshwater systems. The virusto-bacteria ratio was significantly higher in freshwater (mode = 22.5) than marine environments (mode = 2.51, and there were significantly more bacteria per unit chlorophyll in our freshwater samples. We suggest that this difference is related to the increased dependence of freshwater bacteria on allochthonous material relative to marine systems, as well as the increased relative importance of photosynthetic cyanobacteria in lakes.
TL;DR: In this article, multivariate statistical analyses of data on environmental variables and benthic fauna from 14 oil and gas fields obtained from 24 surveys collected between 1985 and 1993 are presented.
Abstract: Multivariate statistical analyses of data on environmental variables and benthic fauna from 14 oil and gas fields obtained from 24 surveys collected between 1985 and 1993 are presented. At all fields oil-based drilling mud was used. The purpose of this study was to investigate contamination gradients, assess effects on benthic fauna both spatially and temporally and to evaluate measures such as diversity indices, indicator species and multivariate analysls techniques in assessment of pollution. Results from analyses of baseline surveys of environmental variables and fauna were charactensed by a lack of distinct gradients in station placement, having a typical shot-gun pattern in PCA-, DCAand MDS-ordination analyses. Likewise there was no consistency in which environmental variables correlated with the fauna. Contamination was assessed using all the physical and chemical data in classification and PCA-ordination analyses Clear patterns were found using 4 categories, conveniently termed initial, moderate, severe and gross. The categories were usually apparent as rings radiating from the platform. Initial contamination of the outermost areas at most fields was shown as elevated levels of barium and total hydrocarbons (THC) and sometimes also by elevated levels of zinc, copper, cadmium and lead. Three fields were studied in particular and showed contaminated areas of over 100 km2 (Valhall), over 15 km2 (Gyda) and over 10 km2 (Veslefrikk). After a period of 6 to 9 yr contamination had spread, so that nearly all of the outermost stations 2 to 6 km away from the platforms showed evidence of contamination. Thus, the existing sampling design is no longer suitable for assessment of the area contaminated. Effects on the fauna showed, as with contamination, 4 categories. Analyses hnking fauna and environmental variables indicated that the effects were mainly related to THC, barium and strontium, but also to metals like zinc, copper, cadmium and lead, which are all discharged in drill-cuttings. Effects on the fauna closely followed the patterns of contamination with only a few stations at each field that were contaminated not showing effects. Thus the areas showing effects were only slightly less than the areas contaminated. Subsequent to cessation of discharges biodegradation of oil and reduced concentrations of THC were observed. Yet there was an extension of areas where the fauna was affected several years after cessation of dnll-cutting discharges This may indicate that barite and related compounds associated with the discharges also have an environmental impact. However, preliminary results from fields using only water-based mud clearly indicate a reduction in environmental contamination and biological Impact, compared to effects reported here, for oil-based drill-cuttings. Diversity indices appl~ed to the data did not show the extent of effects and such Indices alone should not be used to interpret changes. The consistent patterns that the multlvariate techniques were able to detect showed that these methods were far superior. Analyses of the initial effects on the fauna showed that there were no consistent patterns in changes in species composition over fields or time, and thus the search for 'universal' sensitive indicator species does not seem to be rewarding. Yet under gross effects of pollution there were consistent patterns with the same species dominating. Finally, the initial effects of pollution included severe reductions in organisms that are key components of the benthic communities and also food for bottom-living fish, and are thus ecologically important. The new fauna which establishes in the contanunated sedirnents close to platforms, often with high abundance, will probably be less valuable as a food source for fish populations since it is of small size and lives sub-surface.
TL;DR: Grazing and sedimentation, as well as call lysis, are structuring mechanisms for algal bloom dynamics, which illustrates the importance of phytoplankton cell lysis in providing energy for the microbial loop.
Abstract: The influence of grazing, sedimentation and phytoplankton cell lysis on the dynamics of a coastal pelagic ecosystem in the Southern Bight of the North Sea was studied during spring/summer 1992. Diatoms in the > 8 pm size fraction dominated during early spring, due to size-differential control by microzooplankton. This diatom spring bloom became silicate depleted and declined by sedimentation. A Phaeocystis bloom developed in early summer. Phytoplankton cell lysis was the major loss factor for Phaeocystjs, accounting for 75% of the decline of the bloom. Bacterial production was positively correlated with phytoplankton cell lysis, and bacterial carbon demand could be supplied by cell lysis. This illustrates the importance of phytoplankton cell lysis in providing energy for the microbial loop. A new method (nicotine addit~on technique) was used to estimate mesozooplankton grazing on microzooplankton. h4esozooplankton appeared to prefer microzooplankton as a food source, though there occasionally was substantial grazing on phytoplankton. We conclude that grazing and sedimentation, as well as call lysis, are structuring mechanisms for algal bloom dynamics.
TL;DR: Observations suggest that some species actively migrate to a microenvironment with a particular oxygen concentration, rather than maintaining a stable position with respect to the sediment-water interface, which is consistent with vertical migratory response of benthic forammifera.
Abstract: This experimental study investigated the vertical migratory response of benthic
forammifera in sediments that were initially oxygenated, to variations in dissolved-oxygen concentrations
ranging from well-oxygenated to dysaerobic conditions. Two box cores, with a carpet of polychaete
tubes extending above the sediment-seawater interface, were recovered from 71 m water depth
in Oslofjord, southern Norway. The seawater oxygen concentration of one box core was decreased
every 4 wk, to a minimum value of <0.2 ml 0; 1'. Aerated seawater circulation was maintained in
the other (control) box core. In a time course, 2 subcores were taken from each mesocosm every 4 wk
and sectioned in 0 5 cm mtervals to depths of 2.0 cm, and 1.0 cm intervals from 2.0 to 4.0 cm. The
portion of the polychaete tubes extending into the overlymg water was collected and treated as an
additional sample. Live foramimferal distributions were examined in the > 63 pm fraction of each interval
shallower than 2 cm using both an ATP assay and a rose Bengal staining method, while only rose
Bengal was used to assess distributions from 2 to 4 cm. Results indicate that larger numbers of live and
stained forammifera are found on the polychaete tubes and in the superficial 0.5 cm of sediment after
exposure to dysaerobic conditions compared to original and control abundances. After re-oxygenation
for 4 mo, the foraminifera re-migrated into the sediments, exhibiting distributions similar to those of
the control mesocosm. These observations suggest that some species actively migrate to a microenvironment
with a particular oxygen concentration, rather than maintaining a stable position with
respect to the sediment-water interface.
TL;DR: It is confirmed that the sponge die-off was widespread and its occurrence coincided with areas that had been exposed to the cyanobacteria bloom, and this cascade of disturbances has dramatically altered the community structure of affected hard bottom areas and demonstrates the coupled dynamics of this shallow marine ecosystem.
Abstract: Florida Bay, the shallow lagoon separating mainland Florida and the Florida Keys, USA, is experiencing an unprecedented series of ecological disturbances. In 1991, following reports of other ecosystem perturbations, we observed widespread and persistent blooms of cyanobacteria that coincided with the decimation of sponge communities over hundreds of square kilometers. Juvenile Caribbean spiny lobsters Panulirus argus, among other animals, rely on sponges for shelter; the impact of sponge loss on the abundance of lobsters and their use of shelter, in particular, has been dramatic. The loss of sponges on 27 experimental sites in hard bottom habitat in central Florida Bay resulted in the redistribution of juvenile lobsters among the remaining shelters, an influx of lobsters into sites where artificial shelters were present, and a decline in lobster abundances on sites without artificial shelters. Diver surveys of sponge damage at additional sites in central Florida Bay confirmed that the sponge die-off was widespread and its occurrence coincided with areas that had been exposed to the cyanobacteria bloom. This cascade of disturbances has dramatically altered the community structure of affected hard bottom areas and demonstrates the coupled dynamics of this shallow marine ecosystem.
TL;DR: The main demographic implications of these findings are that mortality is independent of body mass per se, that sac spawners suffer higher overall mortality rates than broadcast spawners and nauplii suffer higher mortality than copepodids.
Abstract: We compiled information from the literature on female and egg sizes and maximum egg production, growth and developmental rates in marine planktonic copepods. While specific growth and developmental rates are ~nvariant with body mass, weight-specific fecundity scales w ~ t h female body mass-026 in both broadcast-spawning and egg-carrying copepods. Egg sizes increase with female size and, consequently, egg production rates (no. of eggs p-' d-') are constant with size. Developmental rates were similar among egg-carrying and broadcast-spawning copepods, but the latter grow faster by 30 to 50% and have we~ght-specific fecundities that are 2.5 times and egg production rates that are 7.5 times those of the former. Nauplii develop faster (by a factor of 2) but grow slower (by 20 to 40%) than copepodites in both spawning types. The main demographic implications of these findings are (1) that mortality is independent of body mass per se, ( 2 ) that sac spawners suffer higher overall mortality rates than broadcast spawners and (3) nauplii suffer higher mortality than copepodids.
TL;DR: The results support the hypothesis of Stevenson (1978, Microb Ecol 4:127-133) that very small bacteria are mainly dormant (inactive) while bigger bacteria are more likely to be active and suggest that phagotrophic protists will preferentially crop the active portion of the bacterial community if they select their prey according to size.
Abstract: By directly measuring the size distribution of active (cells that took up and reduced the redox dye CTC, 5-cyano-2,3-ditolyl tetrazolium chloride) and inactive cells in a natural coastal bacterial community, we tested the hypothesis that the likelihood of a bacterium being active in marine plankton is a function of its size. The average size of an inactive bacterium was 0.055 pm3 while the average size of an active bacterium was 0.12 pm3. This average size was constant even after 3 d of incubation in dialysis bags placed in situ, which increased the percentage of active bacteria in the community from 6 to ca 43 %. The probability of a bacterium being active was a linear function of its size, from ca 5% for cells o f 0.01 l.1n13 to 100% for cells of the largest sizes. These results (1) support the hypothesis of Stevenson (1978, Microb Ecol 4:127-133) that very small bacteria are mainly dormant (inactive) while bigger bacteria are more likely to be active; (2) reconcile 2 apparently opposing observations, (a) commonly found higher specific activities in the larger size classes of bacterioplankton and (b) allometry regularities by which smaller unicellular organisms tend to have higher specific growth rates than larger organisms of similar metabolic mode; and (3) suggest that phagotrophic protists will preferentially crop the active portion of the bacterial community if they select their prey according to size.
TL;DR: In this paper, the authors investigated the survival of animals caught by a 4 m beam trawl, in order to identify those species most sensitive to capture, such as starfish, hermit crabs and molluscs.
Abstract: The passage of a beam trawl across the seabed leads to the direct mortality, or indirect mortality through subsequent predation, of some benthic species. In addition, animals retained in, or those that pass through, the cod end may also die as a result of the fishing process. The extent of this additional mortality needs to be quantified to calculate total mortality of non-target species associated with this type of fishery. Hence, we investigated the survival of animals caught by a 4 m beam trawl, in order to identify those species most sensitive to capture. Starfishes, hermit crabs and molluscs were highly resistent to the effects of capture (>60% survived in all cases). Fishes (except dogfish), sea urchins and swimming crabs suffered higher mortality after capture. Generally, the majority of the animals that passed through the meshes of the cod end survived. Experimental investigation of the cause of damage to certain species concluded that the chaln matrix fitted to the gear was largely responsible for the injuries sustained. The types of injuries and then extent were species-specific, and were related to the fragility and physical characteristics of each species. Our experiments revealed that whlle some species are highly sensitive to capture, others are capable of surviving the effects of capture
TL;DR: In this article, a total of 53 species of juvenile fish were caught over a two-year study period in two mangrove lines estuaries in Moreton Bay in NSW.
Abstract: A total of 53 species of juvenile fish were caught over a two yr study period in two mangrove lines estuaries in Moreton Bay. Comparing juvenile fish communities among mangrove forests, seagrass beds and mudflats identified significant differences in species richness and abundances of juveniles. Mangrove sites within Moreton Bay play a more important role and have greater potential as nursery habitats than do adjacent habitats. -from Authors
TL;DR: The findings suggest that prey selection in A. tonsa may be partly governed by turbulence in the ocean, and that ambush-mode feeding is much more dependent on turbulence than suspensionmode feeding.
Abstract: The copepod Acartia tonsa exhibits 2 different feeding modes: when feeding on small phytoplankton cells it sets up a feeding current and acts as a suspension feeder; when feeding on motile prey it acts as an ambush feeder. We examined experimentally the effects of small-scale turbulence on feeding rates in these 2 modes. The different feeding behaviours were triggered by offering the copepods diatoms Thalassiosira weissfloqii and ciliates Strombidium sulcatum, respectively. Turbulence at 5 different intensities (energy dissipation rate, E, between 4 X I O ~ and 3.7 X 10' cm2 s ~ ) was generated by an oscillating grid. In ambush feeding mode, low (realistic) intensities of turbulence (E = 1 0 ' ~ to 1 0 ~ cm2 s ~ ) enhanced clearance rates by up to a factor of 4 above those observed in calm water Higher intensities of turbulence ( E = 10-' to 10' cm2 s ~ ) resulted in a depression of clearance rates, although the rates were still significantly higher than those observed in calm water. The depression of clearance rates at high turbulence intensities was due partly to a decline in capture success, but mainly to a decrease in reactive distance, because turbulence interferes with prey perception by disturbing the hydrodynamical signal generated by motile prey. The negative effects were evident only at turbulence intensities exceeding those normally encountered by A tonsa in its natural habitat. In suspension feeding mode, low intensities of ambient turbulence (E = I O ~ to 10-2 cm2 s-" had negligible effects on clearance rates, while at higher turbulence intensities (E = 10-I to 10' cm2 s ~ ) we observed a negatlve effect (depression of clearance rate). The negative effects become evident when ambient turbulent fluid shear approaches the maximum shear rate of the copepod's feeding current, and we hypothesize that at these intensities the feeding current is eroded. Again the negative effects were observed only at turbulence intensities higher than those typically experienced by A. tonsa in the sea. The differential response to turbulence of the 2 feeding behaviours, including the negative effects, were accurately predicted by encounter rate and feeding behaviour models proposed by korboe & Saiz (1995; Mar Ecol Prog Ser 122:135-145). Because feeding behaviour is specific to the prey (phytoplankton vs mot~le prey), and because ambush-mode feeding is much more dependent on turbulence than suspensionmode feeding, our findings suggest that prey selection in A. tonsa may be partly governed by turbulence in the ocean. This may explain why rnicrozooplankton at times dominates the diet of A. tonsa and other copepods, even though it is numerically scarce relative to phytoplankton in the environment.
TL;DR: The series of successional biological changes shifted by the death and denudation of corals shifts the ecological balance between constructive and destructive forces on a coral reef in favor of the latter.
Abstract: Carbonate skeletons of hermatypic corals harbor diverse populations of microboring organisms. The assemblages of euendohthic (boring) algae and cyanobactena inhabiting the corallum of hve corals are different from those that colonize dead and denuded coral skeletons. The species composition of endoliths in live corals is a result of a selection in favor of ohgophotic, positively phototropic, fast-growing taxa which can cope with the accretion rates of coral skeleton. Following the death and denudation of corals, the bioerosion of their skeletons changed profoundly with respect to (1) species composition of dominant endolithic microorganisms, (2) their boring patterns and (3) the direction of microbormg activity. Skeletons of live colonies of Pontes lobata were bored from the inside outward by the siphonalean chlorophyte Ostreobim quekettii. Dead and denuded parts of coral skeleton were colonized at the surface and bored inward by a succession of euendoliths, starting with colonization of the short-lived opportunistic pioneer endolith Phaeophila dendroides (Chlorophyta), followed by Mastigocoleus t es ta rm and Plectonema terebrans (cyanobacteria), to establish within 2 yr a stable 0. queketto-dominated endolith community. The sequence of colonization and successional changes was determined usmg experimentally exposed carbonate substrates. During the life of the coral, the endoliths are protected from grazers. Their bioerosive activity keeps pace with the rate of coral accretion but avoids the skeletal surface adjacent to the coral tissue. The green bands formed by endohths within the skeleton of live corals bear relevance to sclerochronological interpretations. Their formation reflects either variation m coral growth rates or algal seasonality, but most likely a combination of both. Endoliths in dead coral skeletons are exposed to grazing by mollusks, echinoderms and scarid fish, which significantly increases overall bioerosion rates. In the absence of intensive grazing, dead parts of coral skeleton are overgrown by epilithic algal turf. The series of successional biological changes tnggered by the death and denudation of corals shifts the ecological balance between constructive and destructive forces on a coral reef in favor of the latter.
TL;DR: In this article, the authors monitored the settlement of crabs (primarily Cancer spp.) and sea urchins Strongylocentrotus spp. in conjunction with physical variables associated with coastal circulation to investigate how physical conditions influence recruitment along the coast.
Abstract: During spring and summer 1993, we monitored settlement of crabs (primarily Cancer spp.) and sea urchins Strongylocentrotus spp. in conjunction with physical variables associated with coastal circulation to investigate how physical conditions influence the spatial distribution of recruitment along the coast. Observations were made along a 100 km stretch of the northern California coast (USA), from the Gulf of the Farallones north to Point Arena. Temperature, salinity and wind stress data indicated fluctuations in upwelling and provided evidence for the alongshore, northward flow of warm, low salinity water during upwelling relaxation events which typically lasted several days. On a weekly time scale, crab settlement was positively correlated with temperature, and negatively correlated with salinity, indicating that settlement occurred during relaxation events. Correlations were higher north of Point Reyes, where high settlement occurred only during relaxation, than south of Point Reyes, where settlement occurred both during relaxation events and to a lesser degree during upwelling. Overall crab settlement was higher south of Point Reyes. On a daily time scale, crab settlement north of Point Reyes was associated with the sharp increase in temperature observed as the relaxation current reached that point on the coast. This association suggested that crabs were transported northward alongshore In the thermal front which propagated northward during each relaxation event. This alongshore transport mechanism may be responsible for the predictable pattern of settlement variability within this system: with continuous, event-modulated settlement south of Point Reyes and episodic, event-dependent settlement to the north. Similar physical/biological interactions may occur at other points along this coast and along the midlatitude boundaries of other oceans.