Abundance Of Infauna Research Articles

Macrobenthic community responses to long-term environmental change in an east Australian sub-tropical estuary

Long-term temporal and spatial differences in benthic community structure in Port Curtis (a semi-enclosed estuary in Queensland, Australia) were examined from quantitative grab samples. A total of 2660 grabs were collected from 30 fixed sites over the 6-year study period, and 35 421 individuals and 409 species identified. Few species were highly abundant and nearly 90% were apparently undescribed. Species abundance data revealed strong ecological gradients that were principally driven by depth and sediment grain size. Depth related differences in benthos were most pronounced between the subtidal and intertidal zones, and total abundance and richness were both significantly lower in the intertidal. Total abundance and richness were also found to be significantly lower in sediments that were either extremely coarse or extremely fine. Over the 6-year period of this study, mean species richness and abundance progressively declined 72% and subsequently recovered by 68%. Similar temporal trends were displayed by all common dietary groups (filter feeders, deposit feeders, scavengers and predators), and it appears that drivers underpinning observed changes have a consistent influence at most trophic levels. Explanations for long-term trends in abundance and richness were determined through correlation analyses with key environmental variables. Both species richness and abundance were highly correlated (positively) with turbidity measurements observed 4 months previously. This finding suggests that high levels of turbidity promote recruitment and growth of benthic organisms in Port Curtis. Strong correlations between regional rainfall, freshwater inflow, nutrient and chlorophyll a concentrations, further support the hypothesis that recent changes in benthic productivity (as defined by total infaunal abundance) within the estuary are principally the result of long-term climatic cycles including El Niño events.

Influence of wave exposure on South African mussel beds and their associated infaunal communities

This study investigates effects of wave exposure on beds of the mussel Mytilus galloprovincialis and the infaunal communities associated with them. Nine sites of varying wave exposure were sampled near Groenrivier, on the west coast of South Africa. Wave exposure was measured using a Palumbi device, and exposure ranged from 7.17×103 to 18.49×103 N m−2. Percentage mussel cover at each site was measured using 50×50 cm quadrats, and three 10×10 cm samples were removed from the mussel beds in the mid-intertidal zones of each site for examination of infauna. Percentage mussel cover, mean mussel length, mussel biomass and mussel bed depth all peaked at intermediate exposures, declining towards both the most sheltered and most exposed sites. Infaunal species diversity and richness both showed the reverse trend, peaking at the most sheltered and most exposed sites, and declining at intermediate exposures. Neither infaunal abundance, nor biomass, was significantly correlated to wave exposure, although abundance was highest at sheltered sites and biomass greatest at the most exposed site, which was dominated by limpets and large robust polychaetes.

The epibenthic megafaunal and benthic infaunal invertebrates of Port Foster, Deception Island (South Shetland Islands, Antarctica)

Abstract Otter trawl and grab samples (0.3 mm sieve) collected in Port Foster, Deception Island, from March 1999 to November 2000 as part of the ERUPT Antarctic ecosystem study were used to assess the status of the epibenthic megafaunal and benthic infaunal communities, which were heavily impacted by the volcanic eruptions of 1967–1970. Additional otter trawls were collected in coastal waters off Livingston and King George Islands to compare the epibenthic megafauna community of Port Foster with that of open coastal Antarctic environments. The epibenthic and infaunal communities of mid-bay Port Foster have significantly recovered since 1967 when mid-bay dredge and grab samples yielded a total of four individuals in two dredge hauls and an infaunal abundance of 40 individuals m −2 . Port Foster trawls from this study yielded an average of 26.2 taxa for the five sampling dates, with a cumulative total of 68 taxa. The epibenthic community at Port Foster was primarily composed of deposit feeding taxa with the ophiuroid, Ophionotus victoriae the dominant organism. Livingston and King George trawls yielded a total of 99 and 135 taxa, respectively, with a dominant suspension-feeding community of sponges and tunicates supporting a more diverse rich epibenthic fauna. Benthic infaunal abundance and biomass averaged 85,566.3 individuals m −2 and 121.951 g m −2 . Foraminifera, nematodes, and polychaetes were the most abundant infauna in Port Foster sediments representing 59.05%, 17.48% and 16.38% of total abundance, respectively. Bivalve mollusks and polychaetes were the major contributors to the biomass, with 48.375% and 45.294% of total wet weight, respectively. Abundant populations of microbiota (foraminiferans) and meiofauna (nematodes) suggest that, as in other benthic habitats, these small but numerous organisms play a key role in carbon utilization and the food web. Sediment type and food resources are major factors controlling the benthic community structures of Port Foster and Livingston and King George Islands. The accumulation of sediments in Port Foster from wind and melt-runoff associated with past volcanic activity limits the suspension feeding community and is a possible source of metals contamination. Warming of the Antarctic polar environment will likely increase sedimentation at Port Foster and open coastal areas as glaciers melt and land surfaces are exposed to wind and rain.

Assessing Marine Ecosystem Health: The long-term effects of fishing on functional biodiversity in North Sea benthos

Assessments based on the taxonomic composition and relative abundance of taxa provide valuable information about the effects of anthropogenic activities on benthic systems. However, international agreements also require active conservation of ecosystem functioning as well as biological assemblages. We must therefore learn more about how ecosystems function and why changes occur within them in order to fully understand the implications of human activities. Biological traits analysis allows systems to be described in terms of the characteristics of member taxa, describing functional diversity whilst retaining information on taxa distributions. This study used biological traits analysis to investigate the long-term effects of fishing on benthic infaunal communities. Infaunal abundance was recorded over three decades at two stations, one within and one outside a fishing ground in the central western North Sea. Each taxon present was categorised for the degree to which it exhibited certain biological traits. The distribution of these traits within a sample produced a picture of functional diversity. Multivariate analyses were used to compare trait composition at the stations over time, thus depicting how community functioning responded to physical disturbance. The assemblages at the two stations were functionally distinct at the onset of the study; with differences in size, feeding type and reproductive method. The functional structure changed over time at the station within the fishing ground as the level of exploitation varied. Large animals, predators, scavengers and those eating invertebrates or carrion dominated years of light effort in the fishing ground but were less represented when effort increased. No such changes occurred at the station outside the fishing ground. Fishing seems to have some effect on benthic functional biodiversity and this effect is most obvious when moving from low to moderate levels. The differences between stations at the start of the timeseries may reflect variations in the physical environment or may result from effects of fishing that predate the timeseries.

Spatial patterns in sedimentary macrofaunal communities on the south coast of Newfoundland in relation to surface oceanography and sediment characteristics

This is the first comprehensive study of the community structure and spatial distribution of macrofauna in deep, muddy sediments of Placentia Bay, Newfoundland, and the adjacent shelf. The study examines the influence of water column (e.g. chlorophyll a [chl a], temperature and salinity) and sediment characteristics (e.g. grain size, carbon and nitrogen content) on infaunal patterns. Box-core samples were collected at 10 sites in June and July of 1998 from the head of the bay to the edge of the continental shelf. Multivariate analyses of community composition and environmental variation indicated inshore and offshore groupings. Inshore communities had lower species richness, diversity and densities. Fauna living deeper in the sediment were also more abundant in offshore areas. The inshore region was characterised by greater mixed-layer temperatures, higher surface chl a and large amounts of relatively fresh organic carbon (low C/N ratios) in sediments. Within the inshore sites, high levels of organic carbon influenced macrofaunal assemblages that were similar to those characteristic of organic-rich areas. Surface chl a concentration was positively correlated with sedimentary organic carbon, which was the most important predictor of infaunal abundance. At broad scales, surface chl a and sedimentary organic carbon were negatively related to infaunal abundance. Moreover, this pattern was confounded by particularly low densities at 3 inshore sites where organic levels were very high, and elevated densities at 1 productive offshore site. Low densities at these 3 inshore sites may be a result of sulphide production in sediments, or of poor food quality. Broad-scale patterns (inshore vs offshore) of community composition and abundance in Placentia Bay are largely influenced by surface oceanography through production export.

Top-down versus bottom-up limitation in benthic infaunal communities: Direct and indirect effects

Top-down effects of predators and bottom-up effects related to resource availability can be important in determining community structure and function through both direct and indirect processes. Their relative influence may vary among habitats. We examined the effects of nutrient enhancement and predation in southeastern North Carolina to determine relative effects on benthic macrofaunal communities. Short-term nutrient additions and predator exclusions were conducted in two estuaries to examine main and interactive effects on benthic microalgae and infauna. This ex- perimental approach was complemented by comparisons of microalgal biomass, infaunal abundance and composition, predator abundance and predator exclusion among four estuarine systems that varied in background nutrient levels. In the short-term experiments, nutrient enhancement induced increased microalgal biomass but had limited effects on abundances or sizes of infauna. Predator exclusion increased the density of sedentary and near-surface dwelling fauna, but we did not observe interactions between predation and responses to nutrient additions, as might be predicted from a simple cascade model. General patterns of abundance were explained to a larger extent by interannual and among- estuary patterns. These results indicate a lack of simple trophic cascade responses for this community over a short time scale and little evidence for local interactive effects. The lack of interactive effects may reflect the opportunistic nature of the dominant infaunal species and potentially different time and spatial scales for the effects of predation and resource controls.

Polychaete indicator species as a source of natural halogenated organic compounds in marine sediments

Studies of pollutant impact on the marine environment assume that organic contaminants are anthropogenic in origin. However, many common polychaete worms and sediments contain readily detectable concentrations of brominated natural products that are often analogues of chlorinated anthropogenic contaminants. Both polychaetes and sediments are used extensively in environmental toxicology and monitoring, and the extent to which natural halometabolites may confound these studies is unknown. To characterize further the relationship among infauna, indicator species, and sedimentary halogenated organics, we examined sediments and infauna from a pristine habitat and animals maintained under laboratory culture for haloorganics using gas chromatography/mass spectrometry. Natural haloorganics are a consistent feature of pristine marine soft-bottom habitats, and their spatial and temporal variation correlates with the abundance of infauna that produce these metabolites. Abundant organohalogens are also present in the widespread polychaete indicator species Capitella sp. I and Streblospio benedicti but absent from the marine invertebrate toxicology model Neanthes arenaceodentata. Studies from the individual to the community level within the fields of ecology, toxicology, and environmental chemistry could be readily confounded by failing to consider these novel animal and habitat characteristics.

RELATIONSHIPS BETWEEN ACUTE SEDIMENT TOXICITY IN LABORATORY TESTS AND ABUNDANCE AND DIVERSITY OF BENTHIC INFAUNA IN MARINE SEDIMENTS: A REVIEW

Autesedimenttoxicity testshave become important in regulatory, monitoring, and scientificprograms, partly because it has been assumed that they are indicative of ecological damage to benthic infaunal resources. Data from tests of sediment toxicity and measures of benthic community structure were examined from > 1,400 saltwater samples to determine the relationships between acute toxicity and changes in the abundance and diversity of infauna resources. Data were compiled from studies conducted along portions of the Atlantic, Gulf of Mexico, and Pacific coasts of the United States. There was considerable variability among the data sets in the relationships between laboratory results and benthic measures. However, in 92% of the samples classified as toxic, at least one measure of benthic diversity or abundance was <50% of the average reference value. In 67% of these samples, at least one measure of benthic infauna abundance or diversity was <10% of average reference conditions. No amphipods were found in 39% of samples that were classified as toxic, whereas amphipods were absent from 28% of the nontoxic samples. In many survey areas, the abundance of crustaceans (notably the amphipods) decreased in the infauna as amphipod survival decreased in the laboratory tests. There appeared to be a break point in the data indicating that, generally, amphipod abundance in the field was lowest when survival in the laboratory tests dropped below 50% of controls. Based on the weight of evidence from all the data analyses, we conclude that ecologically relevant losses in the abundance and diversity of the benthic infauna frequently corresponded with reduced amphipod survival in the laboratory tests.

Relationships between acute sediment toxicity in laboratory tests and abundance and diversity of benthic infauna in marine sediments: A review

Acute sediment toxicity tests have become important in regulatory, monitoring, and scientific programs, partly because it has been assumed that they are indicative of ecological damage to benthic infaunal resources. Data from tests of sediment toxicity and measures of benthic community structure were examined from > 1,400 saltwater samples to determine the relationships between acute toxicity and changes in the abundance and diversity of infauna resources. Data were compiled from studies conducted along portions of the Atlantic, Gulf of Mexico, and Pacific coasts of the United States. There was considerable variability among the data sets in the relationships between laboratory results and benthic measures. However, in 92% of the samples classified as toxic, at least one measure of benthic diversity or abundance was < 50% of the average reference value. In 67% of these samples, at least one measure of benthic infauna abundance or diversity was < 10% of average reference conditions. No amphipods were found in 39% of samples that were classified as toxic, whereas amphipods were absent from 28% of the nontoxic samples. In many survey areas, the abundance of crustaceans (notably the amphipods) decreased in the infauna as amphipod survival decreased in the laboratory tests. There appeared to be a break point in the data indicating that, generally, amphipod abundance in the field was lowest when survival in the laboratory tests dropped below 50% of controls. Based on the weight of evidence from all the data analyses, we conclude that ecologically relevant losses in the abundance and diversity of the benthic infauna frequently corresponded with reduced amphipod survival in the laboratory tests.

Small-scale patterns of nekton use among marsh and adjacent shallow nonvegetated areas of the Galveston Bay Estuary, Texas (USA)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 193:217-239 (2000) - doi:10.3354/meps193217 Small-scale patterns of nekton use among marsh and adjacent shallow nonvegetated areas of the Galveston Bay Estuary, Texas (USA) Lawrence P. Rozas*, Roger J. Zimmerman NOAA/National Marine Fisheries Service, Southeast Fisheries Science Center, 4700 Avenue U, Galveston, Texas 77551-5997, USA *E-mail: lawrence.rozas@noaa.gov ABSTRACT: We quantified and compared nekton and infaunal densities among vegetated (edge Spartina alterniflora, inner Spartina alterniflora, Scirpus maritimus, Juncus roemerianus, and Spartina patens marsh) and shallow nonvegetated (marsh pond, marsh channel, cove, and shallow bay) areas of upper Galveston Bay and East Bay, Texas. In 2 seasons (spring and fall) of high nekton abundance, and over 2 yr, we collected 267 quantitative samples (upper Galveston Bay, 1993 = 127 and East Bay, 1994 = 140) using a 1 m2 drop sampler. The vegetated marsh surface consistently contained more species (i.e. higher species richness) and total numbers of decapod crustaceans than nonvegetated areas. In contrast, fish species richness and densities of total fishes on the marsh and in nonvegetated areas were not significantly different in most comparisons. Most numerically dominant species of nekton seemed to exhibit at least some degree of habitat selection. Within vegetation, 2 factors, elevation and proximity to open water, were most important in influencing the distribution of nekton. Low marsh edge dominated by Spartina alterniflora or Scirpus maritimus was apparently selected by most species that used the marsh surface including brown shrimp Farfantepenaeus aztecus, blue crab Callinectes sapidus, and daggerblade grass shrimp Palaemonetes pugio. White shrimp Litopenaeus setiferus and striped mullet Mugil cephalus also were concentrated in low edge marsh; although in one comparison, densities of these 2 species in edge and inner S. alterniflora were not significantly different. In contrast, gulf killifish Fundulus grandis and sheepshead minnow Cyprinodon variegatus were most abundant on inner S. alterniflora or S. patens marsh. Other fishes (gulf menhaden Brevoortia patronus, spot Leiostomus xanthurus, bay anchovy Anchoa mitchilli, blackcheek tonguefish Symphurus plagiusa, and Atlantic croaker Micropogonias undulatus) had higher densities over nonvegetated bottoms than on the marsh surface. Specific habitat types that these pelagic species seemed to favor were marsh channels (gulf menhaden, bay anchovy), marsh ponds (spot), and coves (Atlantic croaker, blackcheek tonguefish). Overall, marsh-surface and adjacent nonvegetated habitat types contained much higher densities of most nekton than the shallow bay. Infaunal densities were estimated from sediment cores, and taxa (mainly annelids, crustaceans, molluscs, and insects) were most abundant in nonvegetated areas contiguous with marsh in the spring. Factors that influenced infaunal abundance are complex and may include predation, flooding patterns, elevation, and distance to edge. Our study has important implications for designing marsh-creation projects. Based on our results, we recommend creating a variety of marsh and contiguous shallow-water areas to enhance nekton biodiversity. To maximize fishery habitat, priority should be given to constructing low marsh edge by creating large areas of low marsh interspersed with a dense network of shallow channels and interconnected ponds. KEY WORDS: Fishery species · Gulf of Mexico · Habitat comparisons · Habitat selection · Nursery areas · Penaeid shrimps · Tidal marsh · Restoration Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 193. Publication date: February 28, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Protocols for Sample Design and Implementation—Collecting Ephemeral Data During Emergency Response for Natural Resource Damage Assessments

ABSTRACT During the emergency phase of an oil or hazardous material spill, natural resource managers and trustees must quickly develop and implement study plans to collect ephemeral data on the extent and degree of contamination and the potential biological injury resulting from the spill. Manuals and guidelines have been developed by various groups, yet these documents have proven to be too difficult to use during the chaotic, early days of a spill emergency. To provide better guidance, a series of brief (two-page) protocol summaries have been prepared for the types of sampling activities likely to be conducted during the emergency phase of spill, supporting both response and natural resource damage assessment (NRDA) objectives. Protocols have been prepared for collection of samples of the source oil(s), water samples, intertidal sediments, subtidal sediments, and shellfish tissues for chemical and histopathological analysis. Protocols are also being prepared for procedures to measure salt marsh injury, visual estimates of abundance and percent cover in quadrats, and quantitative measurements of infaunal abundance.

Interactive Effects of Nutrient Additions and Predation on Infaunal Communities

Nutrient additions represent an important anthropogenic stress on coastal ecosystems. At moderate levels, increased nutrients may lead to increased primary production and, possibly, to increased biomass of consumers although complex trophic interactions may modify or mask these effects. We examined the influence of nutrient additions and interactive effects of trophic interactions (predation) on benthic infaunal composition and abundances through small-scale field experiments in 2 estuaries that differed in ambient nutrient conditions. A blocked experimental design was used that allowed an assessment of direct nutrient effects in the presence and absence of predation by epibenthic predators as well as an assessment of the independent effects of predation. Benthic microalgal, production increased with experimental nutrient additions and was greater when infaunal abundances were lower, but there were no significant interactions between these factors. Increased abundances of one infaunal taxa,Laeonereis culveri, as well as the grazer feeding guild were observed with nutrient additions and a number of taxa exhibited higher abundances with predator exclusion. In contrast to results from freshwater systems there were no significant interactive effects between nutrient additions and predator exclusion as was predicted. The infaunal responses observed here emphasize the importance of both bottom-up (nutrient addition and primary producer driven) and top-down (predation) controls in structuring benthic communities. These processes may work at different spatial and temporal scales, and affect different taxa, making observation of potential interactive effects difficult.

The Effect of Migratory Shorebirds on the Benthic Species of Three Southwestern Atlantic Argentinean Estuaries

We experimentally evaluate the effect of migratory shorebirds on the benthic fauna of three southwestern Atlantic Argentinean stop-over and wintering sites: Bahia Samborombon (35°30′–36°22′S, 57°23′W), Mar Chiquita coastal lagoon (37°40′S, 57°26′W), and Bahia Blanca (38°48′–39°25′S, 50°–62°25′W). The experiments consisted of exclusion ceilings and controls (both 1 m2), with 10 replicates each and aligned at the same tidal level. During December 1994–May 1995 these experiments were done, twice in Bahia Samborombon, twice at two sites (Sotelo and Celpa) 4 km apart in Mar Chiquita coastal lagoon, and three times in Bahia Blanca. Three polychaete species (Laeonereis acuta, Nephtys fluviatilis, andHeteromastus similis) were found in similar densities in both areas of the Mar Chiquita lagoon.L. acuta andN. fluviatilis were affected in Sotelo, but there was no treatment effect in Celpa. In Sotelo the most abundant shorebirds were Hudsonian godwit (Limosa haemastica), American golden plover (Pluvialis dominica), and White-rumped sandpiper (Calidris fuscicollis), and in Celpa the most abundant shorebirds were White-rumped sandpiper, two-banded plower (Charadrius falklandicus), and lesser yellowlegs (Tringa flavipes). The largest polychaete densities were in the upper sediment layer (0–6 cm), which was also the most affected layer. Three polychaete species were found in Bahia Samborombon (L. acuta, H. similis, andNeanthes succinea), but onlyH. similis showed a treatment effect. The most abundant shorebirds in Samborombon were white-rumped sandpiper and two-banded plover. No effect was detected in Bahia Blanca, where the most abundant shorebirds were white-rumped sandpiper and American golden plover. In all cases, the species affected by shorebirds were the most abundant species. From the two sites of Mar Chiquita, there was a treatment effect only in Sotelo, which was also the area with higher shorebirds counts. However, much lower densities observed in Samborombon (similar to the unaffected area of Mar Chiquita) also produced a significant decrease in infaunal abundance. These evidences also suggest that just selection of study sites may produce different views of the interaction between shorebirds and benthic species.

Infaunal predation regulates benthic recruitment: an experimental study of the influence of the predator Nephtys hombergii (Savigny) on recruits of Nereis diversicolor (O.F. Müller)

Field and laboratory experiments were carried out to examine predatory activity effects of the infaunal polychaete Nephtys hombergii on the recruitment of Nereis diversicolor. Using N. diversicolor juveniles as prey, we tested the effects of (1) the temperature variations on predatory activity and (2) the predator density ( d=114 and 342 ind. m −2) on prey mortality, on their growth and their escape behaviour. In the field, N. diversicolor alone ( d=13750 ind. m −2), and N. hombergii ( d=114 and 342 ind. m −2) and N. diversicolor juveniles together were enclosed in 15-cm dia. PVC cylinders during 12 weeks, from 7 March to 30 May 1995, in a mudflat of the Rance Estuary. In the presence of the predator, the biomass of N. diversicolor juveniles declined 8–12× more than in control cylinders, whereas their individual weight was increased. Although it had little effect on the biomass of prey, predator density regulated the consumption by N. hombergii. Predation activity was minimal, but effective, at a temperature of 7°C, increased between 9 and 11°C, and became constant above 11°C. In the laboratory, gradual or sudden temperature variations had little effect on predatory activity of N. hombergii, presumably because they were already physiologically active. Reduction in the abundance of infauna may be due to prey emigration as well as predation: beyond their mortality, N. hombergii induced, proportional to its density, the emigration of juveniles. The experimental results suggest that infaunal predation, by regulating recruit densities, should be considered in addition to the interactions between adults as a strong force structuring soft-bottom communities.

The effect of biogenic irrigation intensity and solute exchange on diagenetic reaction rates in marine sediments

The activities of infaunal macrobenthos strongly influence the pathways, rates, and extent of organic matter remineralization and associated reactions in marine sediments. Solute transport during irrigation is a particularly important process that stimulates microbial activity and net remineralization, both within and adjacent to the bioturbated zone. Part of the stimulation proximal to the bioturbated zone is due to redox oscillation and oxidant supply during transport, but part of both the near and far-field effects are a result of other factors. Experiments designed to simulate different degrees of diffusive exchange, and thus infaunal abundances or activity, demonstrate a regular and strong dependence of anaerobic remineralization on diffusive transport. For example, net production of NH 4 + , HPO 4 = , I - , and Mn ++ increases as the effective distance between burrows becomes ≤2 cm (burrow abundance ≥800 m -2 ) in otherwise identical anoxic sediment. Corresponding changes in sedimentary bacterial numbers, exoenzyme activity, per cell growth rate (RNA), and solid phase properties (N, C/N, P) indicate that the increases in net rates are due in part to an absolute increase in total production. Transport-reaction models and experimental results demonstrate that relative decreases in the uptake of solutes into biomass, abiogenic precipitation reactions, and increased removal of inhibiting metabolites all occur simultaneously, enhancing both total and net remineralization. The phenonomenological first-order rate constant for organic matter decomposition is therefore a function not only of the reductant and oxidant pool properties, but also the environmental transport regime. Solid phase reaction products can differ substantially as a function of diffusive openness. For example, both organic P and the organic Plinorganic P ratio increase in more diffusively-open (irrigated) compared to diffusively-closed, anoxic sediment. The sensitivity of solute concentrations, microbial activity and diagenetic reaction balances to diffusive transport regime, indicates that macrofauna can functionally manipulate these properties through relatively small changes in burrow spacing patterns and individual burrow geometries.

Sediment community structure around a whale skeleton in the deep Northeast Pacific: Macrofaunal, microbial and bioturbation effects

Chemoautotrophic communities on lipid-rich whale skeletons are known from a total of 16 modern and fossil sites in the deep Pacific Ocean. While the attached fauna of modern whale bones has been studied, the impact of whale falls on surrounding sediment assemblages remains largely unevaluated. Using the research submersible Alvin, we sampled the sediment community at distances of 0, 0.5, 1, 2, 4, and ∼100 m from the lipid-rich skeleton of a 21 m balaenopterid on the 1240 m seafloor in Santa Catalina Basin. When sampled in 1988 and 1991, the skeleton had been on the seafloor for >4 yr and supported a large attached chemoautotrophic assemblage. Sedimentary organic content, microbial biomass and bacterial abundance were not significantly different near the skeleton than in background sediments, and pore-water sulfide concentrations were only modestly elevated (to ⩽20 μM) adjacent to the bones. The species composition of infaunal macrobenthos near the skeleton was similar to that in background sediments, providing little evidence of a specialized enrichment and/or sulfophilic assemblage. Nonetheless, macrofaunal abundance within 0.5 m of the skeleton was reduced by >40%, due to a decline in the paraonid polychaete Levinsenia oculata. The reduction in L. oculata (the community dominant) caused a sharp increase in rarefaction diversity near the skeleton. Bioturbation intensities, evaluated from 234Th profiles, were also dramatically reduced in sediments near the skeleton, as were rates of extracellular lipase activity. We postulate that reduced infaunal abundance and bioturbation near the skeleton resulted from the interference effects of vesicomyid clam-shell debris, and that the low bioturbation rates in turn limited extracellular lipase activity. We conclude that whale skeletons, and the remains of their associated chemoautotrophic assemblages, may physically impact nearby sediment communities for years after the organic and sulfide enrichment effects of whale falls have dissipated, yielding changes in infaunal diversity and bioturbation.

Meroplankton abundance in the Northeast Water Polynya: Insights from oceanographic parameters and benthic abundance patterns

Abstract We investigated meroplankton (planktonic larvae of benthic organisms) abundance and distribution in the Northeast Water (NEW) Polynya, located on the northeast coast of Greenland, from July 15 to August 15, 1992. Meroplankton was present at all sites visited (0.03–84.83 individuals per m 3 ); at one station meroplankton comprised 8.28% of total zooplankton. Total meroplankton abundance was correlated with total zooplankton abundance and total benthic infaunal abundance but was not correlated with either microscopic carbon concentration or primary productivity. Examination of distribution data for barnacle nauplii and adults indicated that both adults and larvae were concentrated at the same locations. Patterns of distribution were also examined for stelleroid plutei, polychaete larvae and trochophores. There were distinct geographic patterns in total and class-specific meroplankton distributions, with maximal abundances occurring over the Belgica Bank and in the eastern regions of the Westwind Trough and minimal abundances in the Belgica Trough. The apparent control of meroplankton distribution by the hydrography of the region, coupled with the correlation between meroplankton, zooplankton and adult infaunal abundance, reinforces the hypothesis that hydrography plays a major role in controlling the distribution of biota in the NEW polynya (Ambrose and Renaud, 1995; Ashjian et al., 1995, 1997-this volume; Smith et al., 1995; Piepenburg et al., 1997-this volume).

Infaunal community changes as a result of commercial clam cultivation and harvesting

Manila clams, Tapes philippinarum (Adams and Reeve) are cultivated beneath plastic netting, to protect them from excessive predation, and harvested after approximately two years. Both the on-growing and harvesting process have the potential to alter benthic communities. In order to study these effects, we surveyed a clam lay and uncultivated areas at a site of commercial clam cultivation in south-east England. Surveys were undertaken at the end of the growing stage, immediately after harvesting by suction dredge and seven months later. Infaunal abundance was greatest within a net covered clam lay than in proximate and distant control areas, but the total number of species encountered was similar in all areas (20–22). These differences were not attributable to variation in sediment structure or environmental variables between the areas sampled. Tube-building polychaetes, such as Lanice conchilega and Euclymene lumbricoides, were particularly abundant within the cultivated area as was the errant polychaete, Syllis gracilis. Harvesting by suction dredge altered sediment composition by removing the larger sand fractions down to the underlying clay substratum, consequently there was a large reduction in the density of all individuals and the total number of species. Seven months later, no significant difference was found between the infaunal community in the harvested clam lay or either of the control areas and sedimentation had nearly restored the sediment structure. These observations indicate that the practice of clam cultivation does not have long-term effects on the environment or benthic community at this site.

Effects of macrobenthic burrows on infaunal communities in tropical tidal flats

The effects of burrows on the infaunal community In a tropical t~da l flat were studied on the northeast coast of Australia. A comparative survey of infauna In burrows versus adjacent sediment was carr~ed out for the burrows of 3 crustaceans (Scopimera inflata, Uca spp.. Callianassa austrahensis) and a brachiopod (Llngula anatjna). More (1.5 to 2 . 5 ~ ) infauna occurred within burrows than in adjacent sediments Densities of meiobenthic nematodes, copepods and Platyhelminthes were significantly higher wlthin the burrows of Uca spp., C. australiensis and L. anatina. In the latter 2 cases multivariate analyses showed distinct communities in burrows and adjacent sediment, although this was not consistent over time for the brachiopod burrows. No differences in community composition were detected in the cases of Uca spp. and S. inflata. In a field experiment. C. austral~ensis was excluded from 7 sites, and infaunal abundances and species compositions were followed for 1 yr and compared with control sites. From the very beginning, me~ofaunal densities were significantly lower in the exclusion sites, mainly due to reduced densities of nematodes and copepods. The effect of the shrimp exclus~on on macrofauna was less pronounced, but after 1 yr total numbers of macrofauna were significantly lower in the exclusions, due to the distribution of amphipods. The results showed that promotive interactions play an important role in structuring tropical tldal flat communities.

Spatial and temporal patterns of the infaunal community near a major ocean outfall in Southern California

Effects of waste water discharge from a major ocean outfall in Southern California to the benthic infaunal community were examined during a 5-year monitoring programme. Natural features, primarily water depth, accounted for 82% of the variability in the infaunal community, while discharge-related effects represented less than 8% of the variability. The area immediately adjacent to the diffuser had the strongest outfall effects. Infaunal abundance showed a pattern of enhancement centred at the outfall. Diversity was also high, indicating that the area was not characterized by a degraded community.