Multiple trophic resources for a chemoautotrophic community at a cold water brine seep at the base of the Florida Escarpment

The biological community that surrounds the hypersaline cold water brine seeps at the base of the Florida Escarpment is dominated by two macrofaunal species: an undescribed bivalve of the family Mytilidac and a vestimentiferan worm, Escarpia laminata. These animals are apparently supported by the chemoautotrophic fixation of carbon via bacterial endosymbionts. Water column and sediment data indicate that high levels of both sulfide and methane are present in surface sediments around the animals but absent from overlying waters. Stable isotopic analyses of pore water indicate that there are two sources of sulfide: the first is geothermal sulfide carried in groundwater leaching from the base of the escarpment, and the second is microbial sulfide produced in situ. The vestimentiferan E. laminata, and the mytilid bivalve (seep mussel) live contiguously but rely on different substrates for chemoautotrophy. Enzyme assays, patterns of elemental sulfur storage and stable isotopic analyses indicate that E. laminata relies on sulfide oxidation and the seep mussel on methane oxidation for growth.     

Sediment characteristics and colonization of soft-bottom benthos: a field manipulation experiment

A field manipulation experiment was carried out to test the effects of sediment characteristics (particle size and organic content) on colonization of soft-bottom benthos. Defaunated mud and sand in experimental trays were exposed at sub-tidal levels of two sites with sandy and muddy sea bottom, and retrieved monthly for examination of benthic composition. Seventy-eight out of the 107 species recorded, and 50% of the dominant species identified in the present study, were common in both the sand and mud trays. Classification analysis revealed higher faunal similarity of benthic composition in both sediment types within each of the two study sites. Results of three-way ANOVA (Sediment, Site and Time) showed that sediment effect was only significant for colonization of bivalves and gastropods, but not for polychaetes, amphipods, total species and individual numbers, or overall benthic diversity and evenness. This suggested that many of the benthic species can colonize both sediment types, and that factors other than sediment particle size and organic content may play a significant role in determining colonization of these species. The faunal composition of the same sediment type between sites was found to be different, indicating that the availability and abundance of benthic larvae/adults may be more important than sediment characteristics in determining benthic settlement. An increase in faunal similarity between mud and sand was observed over the study period, implying that the importance of sediment characteristics to benthic colonization decreased with exposure time. Received: 29 November 1996 / Accepted: 16 January 1997     

Community structure of the benthos in Scottish sea-lochs. II. Spatial pattern

Spatial pattern in the distribution of the macrobenthos was studied from series of van Veen grab samples taken in a systematic pattern in Lochs Etive and Creran, W. Scotland. Each series was collected in a circular pattern at 7 stations. Plots of the variances of the numerical occurrences of the species in the samples against their means revealed greater deviation from the random expectation in the case of the 2 muddy sand stations than for the soft-mud stations, with only 1 exception. Two tests of goodness-of-fit to the Poisson distribution were also applied. The degree of concordance between the 3 measures of non-randomness applied was measured. The best correlation was found between values of the ratio of variance: mean and the test statistic D of the Kolmogorov-Smirnov goodness-of-fit test. It was not possible to discuss the biological basis for the pattern measured, except for a few species shown to be markedly aggregated. No clear trend emerged from attempts to detect differences in pattern with various ecological groupings of the macrobenthos. However, from the use of the test values as sample statistics illustrative of overall community pattern, it was possible to conclude that the fauna of the shallow, usually current-swept areas of muddy sand in the sea-lochs investigated was more aggregated than that on the, usually deeper, soft-mud sediments in quieter water.     

Community structure of the benthos in Scottish Sea-lochs. IV. Multivariate spatial pattern

Most studies of spatial patterns of invertebrates in soft sediments have concentrated on populations of individual species. Those that examined patterns in communities have tended to employ categorical analytical techniques. Using macrofaunal abundance data from van Veen grab samples collected 20 to 100 m apart in known spatial arrangements from Scottish sea-lochs, the relationships between patterns in macrobenthic species composition and distances between samples were explored using matrix correlations in a non-parametric framework. Using a simple definition of spatial structure, i.e. that intersample distances are monotonically correlated with intersample species-similarity, spatial structure at each of seven stations was assessed using non-parametric Mantel tests based on rank-correlations. Changes in community structure were positively correlated with distance at all sites in Loch Etive, on both current-swept muddy sands and soft deep muds. Different components of the macrobenthos contributed to spatial pattern at each site. Simple spatial structure was also detectable at a muddy-sand site in Loch Creran, but neither on soft mud, nor at the soft mud site in the Firth of Lorne. The concept of rank-correlograms was introduced. These were used to examine the extent and form of spatial structure in different components of the macrobenthos at each site. Relationships between similarity and distance were neither simple nor consistent. Results were compared to previous studies which used the same data, and it was concluded that studies carried out at a particular scale, or on a particular component of the benthos, are unlikely to be successful in predicting spatial relationships at other scales or for other components of the benthos. Correlational rather than categorical analyses are recommended for exploratory studies of spatial relationships in the benthos. Analyses of the spatial structure at these seven sea-loch sites suggests that by ensuring that samples are at least 40 m apart an investigator is unlikely to underestimate variability or otherwise invalidate statistical analyses based on the use of the samples as replicates. Spacing samples up to 100 m apart may increase variability estimates, further reducing the chance of concluding that a difference exists when one does not. Received: 4 May 1999 / Accepted: 8 March 2000     

Community structure of the benthos in Scottish sea-lochs. III. Further studies on patchiness

Large-scale patchiness in the distribution of the benthic fauna was investigated in Loch Etive (Scottish west coast) by two series of van Veen grab hauls. Each series was taken along a traverse across the width of the loch, with sampling points about 100 m apart. One sample series was taken on sandy mud and the other, at a greater depth, on soft mud. Two approaches in data processing were applied: (1) The variance: mean ratio and the Morisita I tests for significant aggregation were applied to the species abundances in the sample series; (2) 3 measures of sample homogeneity, each involving the calculation of an index of faunal similarity, were applied to the separate samples. The results, however, could not show significant differences between the two series of samples. These findings were compared to results obtained from (a) a previous study, where differences in patchiness between areas were shown for a smaller scale of sampling design in Loch Etive and neighbouring areas, and to which the I method is also applied here; and (b) the results of applying the variance: mean ratio and I tests to data published by Holme (1953). The present results indicate greater aggregation at the present scale of sampling than for the previous, smaller scale of sampling, or for the comparable scale of Holme's sampling. The degree of concordance shown by the values of I for the circular-design sampling to the values of the 3 measures of patchiness applied previously, and to the means of the species abundances, was measured by Spearman's rank correlation coefficient. The results clearly demonstrated the I values, unlike the others measured, to be almost completely independent of the mean. It was concluded that, for comparing the pattern from benthic samples using standard-size bottom samplers, where the mean may vary widely between each set of samples, the I method is probably most useful.     

Effects of an unusual natural temperature increase on a baltic soft-bottom community

The effects of a sudden, extraordinary temperature rise upon a soft-bottom community in the northern Baltic Sea were studied continuously for more than a month, during the summer of 1968. The mean bundance of the total macrofauna on the muddy bottom amounted to ca 6×10³ individuals · m^-2, on the sandy bottom to 2×10⁴ individuals· m^-2. The meiofauna, only sampled in the mud, averaged 1×10⁶ individuals · m^-2, with nematodes, oligochaetes and ostracods as dominating groups. During this period, the redoxpotential-discontinuity (RPD)-layer successively moved upwards in the muddy bottom, being relatively stable in the sand. The mud surface showed a succession of microbial communities. The initially oxidized, yellow surface film, with patches of diatoms and red Spirula, changed to a more grayish layer, with purple areas here interpreted as Chromatium and white spots of Beggiatoa. The latter dominated during the last part of the period, covering vast areas of the bottom like a gigantic cobweb. The endofauna was forced upwards by the emerging RPD-layer, the more sensitive components dying off, facultative anaerobes and nematodes flourishing. The described temperature increase of about 10 C° simulates the effects of a 3000 MW nuclear plant.     

Parasitism as a determinant of community structure on intertidal flats

The burrowing and movement ability of the New Zealand cockle Austrovenus stutchburyi is reduced when infected by echinostome trematodes. Previous experimental evidence from a single site suggests that this parasite-induced behavioural change of a key bivalve can affect the structure of the surrounding benthic community. By using multiple regression analyses on data collected from 17 intertidal flats, we here show that cockle parasitism is associated with macrozoobenthic community structure on a larger spatial scale. Regressions were performed for animal abundance, biomass, species diversity and species richness separately, entering cockle parasitism (infection intensity), presence/absence of ghost shrimps (Callianassa filholi), cockle density, primary producer abundance and organic content, particle size, sorting coefficient and gravel content of the substrate as predictors. Next to ghost shrimps, cockle parasitism was the best predictor of animal abundance by affecting (mainly positively) 8 of the 49 most widespread species significantly. Cockle parasitism was also associated with the biomass of anthozoans (positively), nemerteans (negatively) and bivalves (positively), whereas overall animal biomass was positively related to the sorting coefficient of the substrate. Species diversity was positively associated with cockle parasitism and gravel content of the substrate. Species richness was significantly associated with cockle parasitism (positively), ghost shrimps (negatively) and abundance of primary producers (positively) in combination. The impact of cockle parasitism on benthic community structure is believed governed directly or indirectly by (1) reduced sediment disturbance, (2) increased surface structural complexity and (3) availability of larval trematodes as an additional food source.     

Diversity of soft-bottom benthos in a tropical estuary: Gulf of Nicoya,Costa Rica

The community structure of soft-bottom infauna is described for the Gulf of Nicoya, Costa Rica, Central America, with special reference to the relationship between diversity and a tropical estuary. Of the 205 species of invertebrates collected in July, 1980, polychaetes comprised 58.6% by number of species and 68.1% by number of individuals. Density ranged from zero to 8 744 m^-2 with a mean of 1 269 m^-2 per station, and biomass ranged from zero to 10.986 g m^-2 with a mean of 2.010 g m^-2. Numerical analysis indicated considerable faunal homogeneity, characterized by polychaetes. Five major polychaete feeding guilds were recognized. From measures of diversity we concluded that the soft-bottom community of the Gulf of Nicoya was not rich for a tropical estuary. Physical processes (riverine runoff and frontal systems) mainly influenced community structure and function in the lower Gulf whereas biological processes (predation) seemed to prevail in the upper Gulf.Southern California Ocean Studies Consortium Contribution No. 23     

The vertical structure of a pelagic community in the tropical ocean

The vertical structure of the ecosystem in the euphotic zone of the western Equatorial Pacific has been studied. The studies were based on a continuous sounding of the bioluminescence field, with simultaneous, vertically aimed sampling made with the aid of a 5l water bottle and plankton nets. The bioluminescence field has a two-maxima structure with a more pronounced and permanent lower maximum found in the oligotrophic regions as deep as 60 to 100 m. In the narrow (10 m) layer of maximum bioluminescence, the concentration of zooplankton, as well as the concentration, activity and production of bacteria and phytoplankton, are several times higher than those in immediately adjacent waters at greater or lesser depth. At the same time, the concentration of nutrient salts in that layer diminishes sharply and approaches zero in the overlying water. Analysis of the data obtained shows that the production processes above the lower maximum layer are dependent not only on the turbulent influx of nutrient salts from the underlying layers, but also on the horizontal supply from the zone of upwelling. A pelagic community, in its different time aspects from the moment of water ascending until its sinking in the convergence zone, is suggested as a common system for modelling.     

Resident mysids: community structure,abundance and small-scale distributions in a coral reef lagoon

Seasonal and diel variations in community structure and abundance of coral-reef lagoon mysids were examined at Davies Reef in the central region of the Great Barrier Reef (GBR) between June 1980 and May 1981. Twenty-five mysid species belonging to three subfamilies of the family Mysidae were captured during the study, with six new records for the GBR. The epibenthic mysid community differed from that in the overlying water, was faunistically uniform, but formed characteristic seasonal and diel groupings. The dominant epibenthic species were Erythrops sp., Anisomysis pelewensis, Doxomysis littoralis, A. laticauda, Prionomysis stenolepis, A. lamellicauda, and A. australis, five of which formed schools. Total mysid abundances ranged between 110 and 790 m^-3 with peak abundance in October. Schooling species occurred at local densities of up to 500 000 m^-3. Mysids were absent from shallow and midwater depths during the day, but were distributed throughout all depths at night with peak abundances in mid-water and deep layers. The dominant species in the water column at night were Pseudanchialina inermis, A. laticauda and Gastrosaccus indicus, in descending order of abundance. Lagoonal mysids contribute little to the food of sessile reef planktivores, as all but three species remain concentrated near or on the lagoon floor both day and night. The contribution of resident lagoon mysids to reef trophodynamics is probably through remineralization of lagoon detritus. Given the vast reef areas comprised of sandy lagoons, the large populations and relatively large size of lagoon mysids, this trophodynamic role may be of considerable importance.A.I.M.S. Contribution No. 477     

Effect of canopy removal on a rocky shore community metabolism and structure

The effects of the permanent removal of the canopy-forming alga Fucus serratus was studied in terms of both functioning and diversity on a mid–low rocky shore ecosystem in the south-west English Channel (48°N 43.686′, 3°W 59.282′). Ecosystem functioning was examined as net or gross primary productivity (NPP or GPP) and respiration (Resp) measured through CO₂ fluxes. Diversity was examined as number and composition of species. Measurements were performed in situ, during emersion times, without altering target assemblages. The experiment was designed with two treatments [control (C) or canopy removed (CR)] and five replicates, and was conducted over an 18-month period (from February 2006 to August 2007) to integrate the seasonal variability. The mean GPP and Resp were severely reduced in CR treatment compared to control throughout the survey. The mean NPP was not affected at first, due to the development of opportunistic green algae, but was drastically reduced after 9 months of experiment. The canopy removal affected neither the number of species nor their distribution among trophic groups, and the algal community was only slightly affected. The abundance and biomass of mobile invertebrates, however, were greatly reduced in the absence of canopy. This indicates an important effect of the dominant alga on the higher trophic levels of the community. At this tidal level, the canopy did not seem to affect the community by dampening the environmental stress but by providing food, habitat or both.     

Habitat biodiversity as a determinant of fish community structure on coral reefs

Increased habitat diversity is often predicted to promote the diversity of animal communities because a greater variety of habitats increases the opportunities for species to specialize on different resources and coexist. Although positive correlations between the diversities of habitat and associated animals are often observed, the underlying mechanisms are only now starting to emerge, and none have been tested specifically in the marine environment. Scleractinian corals constitute the primary habitat-forming organisms on coral reefs and, as such, play an important role in structuring associated reef fish communities. Using the same field experimental design in two geographic localities differing in regional fish species composition, we tested the effects of coral species richness and composition on the diversity, abundance, and structure of the local fish community. Richness of coral species overall had a positive effect on fish species richness but had no effect on total fish abundance or evenness. At both localities, certain individual coral species supported similar levels of fish diversity and abundance as the high coral richness treatments, suggesting that particular coral species are disproportionately important in promoting high local fish diversity. Furthermore, in both localities, different microhabitats (coral species) supported very different fish communities, indicating that most reef fish species distinguish habitat at the level of coral species. Fish communities colonizing treatments of higher coral species richness represented a combination of those inhabiting the constituent coral species. These findings suggest that mechanisms underlying habitat-animal interaction in the terrestrial environment also apply to marine systems and highlight the importance of coral diversity to local fish diversity. The loss of particular key coral species is likely to have a disproportionate impact on the biodiversity of associated fish communities.     

Stability and structure of a fish community on a coral patch reef in Hawaii

Two complete collections of the fishes residing on an isolated coral patch reef ( 1500 m²) at Oahu, Hawaii, were made 11 years apart. Of the 112 species of fishes in both collections combined, only 40% were in common, but these made up more than 85% of the wet biomass in each collection. The two assemblages of fishes were similar in trophic structure and standing crop. Many coral reef fish communities are dominated by carnivorous forms. In the present study, planktivorous fishes were the most important trophic group in the community; this was related to abundant zooplankton resources. Following the second collection in 1977, recolonization by fishes was followed for 1 year. Recolonization proceeded rapidly and was primarily by juvenile fishes well beyond larval metamorphosis. Within 6 months of the second collection, the trophic structure had been re-established. The MacArthur-Wilson model of insular colonization described the recolonization process and predicted an equilibrium situation in less than 2 years. The recolonization data suggested that chance factors may explain the colonization process on a small scale, but a relatively deterministic pattern emerged when considering the entire reef. Thus, at the community level the fishes are a persistent and predictable entity.     

Chemical and colloidal analyses of natural seep water collected from the exploratory studies facility inside Yucca Mountain,Nevada, USA

Yucca Mountain is being considered as a geological repository for the USA’s spent nuclear fuel and high-level nuclear waste. Numerous groundwater seeps appeared during March 2005 within the exploratory studies facility (ESF), a tunnel excavated in the mountain. Because of the relevance to radionuclide transport and unsaturated zone-modeling studies, we analyzed the seep samples for major anions and cations, rare earth elements, and colloids. Major ion species and elemental concentrations in seep samples reflect interaction of the water with the volcanic rock and secondary calcites. Elemental fractograms from flow-injection field-flow fractionation ICP–MS scans detected Br, Ca, Cl, Cu, Fe, I, Mg, Si, Sr, W, and U at void fractions, suggesting they may be present in the form of dissolved anions. Colloids approximately 10 nm in hydrodynamic diameter, possibly calcite, were also present in the seepage samples. Geochemical calculations indicate, however, these may be an artifact (not present in the groundwater) which arose because of loss of CO₂ during sample collection and storage.     

The influence of water stability on the vertical structure of a phytoplankton community

The vertical distribution of the phytoplankton community in association with water column stability was examined for 1 year in an inshore area of the Southern Aegean Sea. An analysis of variance model (split-plot design) was applied to evaluate the variations in the vertical profile of diatoms, flagellates and coccolithophores. When either weak stratification or mixing conditions prevailed, diatoms in general were uniformly distributed throughout the water column while flagellates and coccolithophores appeared occasionally stratified. During the strong stratification period, all taxa demonstrated significant variations in abundance between depths in most cases. However, none of these taxa was confined to a single depth stratum during either the water mixing or the stratification period, but were all present at all depths during all seasons. The results demonstrate clearly that the parameter taxon is an important component in ecological observations on the vertical distribution of phytoplankton.     

Population structure of the Spanish sardine Sardinella aurita: natural morphological variation in a genetically homogeneous population

The importance of larval dispersal in determining the distribution and abundance of benthic marine organisms is well recognized; however, the contribution of post-larval dispersal has not been measured. I compared the dispersal of swimming larvae with that of rafting colonies in a population of compound ascidians, Botrylloides sp., living attached to leaves of the eelgrass Zostera marina in Tomales Bay, California, USA in 1990–1992. Colonies rafting on broken eelgrass traveled over 200 times farther and had comparable recruitment success relative to swimming larvae. The recruitment of rafting colonies into new habitats was facilitated by the ability of thesecolonial animals to grow asexually onto surrounding substrata. Rafting colonies brooded larvae that were subsequently relased after the colony settled into a new habitat. These results suggest that colonization of new habitats can occur by post-larvae as well as larvae, and that long-range dispersal by species with short-lived larvae may occur by post-larval rafting.     

Intraspecific variation in a predator affects community structure and cascading trophic interactions

Intraspecific phenotypic variation in ecologically important traits is widespread and important for evolutionary processes, but its effects on community and ecosystem processes are poorly understood. We use life history differences among populations of alewives, Alosa pseudoharengus, to test the effects of intraspecific phenotypic variation in a predator on pelagic zooplankton community structure and the strength of cascading trophic interactions. We focus on the effects of differences in (1) the duration of residence in fresh water (either seasonal or year-round) and (2) differences in foraging morphology, both of which may strongly influence interactions between alewives and their prey. We measured zooplankton community structure, algal biomass, and spring total phosphorus in lakes that contained landlocked, anadromous, or no alewives. Both the duration of residence and the intraspecific variation in foraging morphology strongly influenced zooplankton community structure. Lakes with landlocked alewives had small-bodied zooplankton year-round, and lakes with no alewives had large-bodied zooplankton year-round. In contrast, zooplankton communities in lakes with anadromous alewives cycled between large-bodied zooplankton in the winter and spring and small-bodied zooplankton in the summer. In summer, differences in feeding morphology of alewives caused zooplankton biomass to be lower and body size to be smaller in lakes with anadromous alewives than in lakes with landlocked alewives. Furthermore, intraspecific variation altered the strength of the trophic cascade caused by alewives. Our results demonstrate that intraspecific phenotypic variation of predators can regulate community structure and ecosystem processes by modifying the form and strength of complex trophic interactions.     

Increased primary production shifts the structure and composition of a terrestrial arthropod community

Numerous studies have examined relationships between primary production and biodiversity at higher trophic levels. However, altered production in plant communities is often tightly linked with concomitant shifts in diversity and composition, and most studies have not disentangled the direct effects of production on consumers. Furthermore, when studies do examine the effects of plant production on animals in terrestrial systems, they are primarily confined to a subset of taxonomic or functional groups instead of investigating the responses of the entire community. Using natural monocultures of the salt marsh cordgrass Spartina alterniflora, we were able to examine the impacts of increased plant production, independent of changes in plant composition and/or diversity, on the trophic structure, composition, and diversity of the entire arthropod community. If arthropod species richness increased with greater plant production, we predicted that it would be driven by: (1) an increase in the number of rare species, and/or (2) an increase in arthropod abundance. Our results largely supported our predictions: species richness of herbivores, detritivores, predators, and parasitoids increased monotonically with increasing levels of plant production, and the diversity of rare species also increased with plant production. However, rare species that accounted for this difference were predators, parasitoids, and detritivores, not herbivores. Herbivore species richness could be simply explained by the relationship between abundance and diversity. Using nonmetric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM), we also found significant changes in arthropod species composition with increasing levels of production. Our findings have important implications in the intertidal salt marsh, where human activities have increased nitrogen runoff into the marsh, and demonstrate that such nitrogen inputs cascade to affect community structure, diversity, and abundance in higher trophic levels.