Showing papers on "Benthic zone published in 1992"

Couplings of watersheds and coastal waters: sources and consequences of nutrient enrichment in Waquoit Bay, Massachusetts

Abstract: Human activities on coastal watersheds provide the major sources of nutrients entering shallow coastal ecosystems. Nutrient loadings from watersheds are the most widespread factor that alters structure and function of receiving aquatic ecosystems. To investigate this coupling of land to marine systems, we are studying a series of subwatersheds of Waquoit Bay that differ in degree of urbanization and hence are exposed to widely different nutrient loading rates. The subwatersheds differ in the number of septic tanks and the relative acreage of forests. In the area of our study, groundwater is the major mechanism that transports nutrients to coastal waters. Although there is some attenuation of nutrient concentrations within the aquifer or at the sediment-water interface, in urbanized areas there are significant increases in the nutrient content of groundwater arriving at the shore’s edge. The groundwater seeps or flows through the sediment-water boundary, and sufficient groundwater-borne nutrients (nitrogen in particular) traverse the sediment-water boundary to cause significant changes in the aquatic ecosystem. These loading-dependent alterations include increased nutrients in water, greater primary production by phytoplankton, and increased macroaglal biomass and growth (mediated by a suite of physiological responses to abundance of nutrients). The increased macroalgal biomass dominates the bay ecosystem through second- or third-order effects such as alterations of nutrient status of water columns and increasing frequency of anoxic events. The increases in seaweeds have decreased the areas covered by eelgrass habitats. The change in habitat type, plus the increased frequency of anoxic events, change the composition of the benthic fauna. The data make evident the importance of bottom-up control in shallow coastal food webs. The coupling of land to sea by groundwater-borne nutrient transport is mediated by a complex series of steps; the cascade of processes make it unlikely to find a one-to-one relation between land use and conditions in the aquatic ecosystem. Study of the process and synthesis by appropriate models may provide a way to deal with the complexities of the coupling.

Trophic interactions and direct physical effects control phytoplankton biomass and production in an estuary

Abstract: The recent invasion of San Francisco Bay by the suspension-feeding clam Putamocorbula amurensis has provided an opportunity to document the ecological consequences of a major biological disturbance. Previous work over the last two decades has shown that phytoplankton biomass in the upper estuary is low (2-3 mg Chl a m-3) during seasonal periods of high river flow and short residence time, and it is usually high (peak > 30 mg Chl a m-3) during the summer-autumn seasons of low river flow and long residence time. However since P. amurensis became widespread and abundant in 1987, the summer phytoplankton biomass maximum has disappeared, presumably because of increased grazing pressure by this newly introduced species. For the period 1977-l 990, mean estimated primary production was only 39 g C mm2 yr-’ during years when bivalve suspension feeders were abundant (>2,000 mm2), compared to 106 g C m-2 yr-’ when bivalves were absent or present in low numbers. These observations support the hypothesis that seasonal and interannual fluctuations in estuarine phytoplankton biomass and primary production can be regulated jointly by direct physical effects (e.g. river-driven transport) and trophic interactions (episodes of enhanced grazing pressure by immigrant populations of benthic suspension feeders).

Ecology of sea ice biota 2. Global significance.

Abstract: The sea ice does not only determine the ecology of ice biota, but it also influences the pelagic systems under the ice cover and at ice edges. In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined. In ice-covered seas, high algal concentrations (blooms) occur in association with several types of conditions. Blooms often lead to high sedimentation of intact cells and faecal pellets. In addition to ice-related blooms, there is progressive accumulation of organic matter in Arctic multi-year ice, whose fate may potentially be similar to that of blooms. A fraction of the carbon fixed by microalgae that grow in sea ice or in relation to it is exported out of the production zone. This includes particulate material sinking out of the euphotic zone, and also material passed on to the food web. Pathways through which ice algal production does reach various components of the pelagic and benthic food webs, and through them such top predators as marine mammals and birds, are discussed. Concerning global climate change and biogeochemical fluxes of carbon, not all export pathways from the euphotic zone result in the sequestration of carbon for periods of hundreds of years or more. This is because various processes, that take place in both the ice and the water column, contribute to mineralize organic carbon into CO2 before it becomes sequestered. Processes that favour the production and accumulation of biogenic carbon as well as its export to deep waters and sequestration are discussed, together with those that influence mineralization in the upper ice-covered ocean.

An equilibrium model of organic chemical accumulation in aquatic food webs with sediment interaction

Abstract: A five-compartment steady-state food-web model is constructed that includes a benthic invertebrate compartment Four exposure routes are considered in the description of accumulation by benthic animals ingestion of particulate contaminants associated with (a) sediment organic carbon and (b) overlying phytoplankton and ventilation of free dissolved contaminant in (c) interstitial and (d) overlying water Normalization of organism lipid-based chemical concentration to sediment organic carbon (the biota sediment factor, BSF) or to overlying water concentration (the bioaccumulation factor, BAF) indicates the significance of the sediment/overlying water partition coefficient for systems that have a benthic component The impact of the benthic component on a forage fish is related directly to this partitioning Application of the model to an amphipod-scul pin web for Lake Ontario indicates (a) amphipod water exposure is a combination of interstitial and overlying water concentrations, (b) amphipod feeding appears to be a combination of overlying phy toplankton and sediment organic carbon, (c) amphipod and sculpin chemical assimilation efficiency appears to be a complicated function of octanol-water partition coefficient, (d) observed BAF for amphipod and sculpin is about one order of magnitude higher than log Kow in the range 5 5 to 7 0 and is calculated to be due almost entirely to food-web transfer from the sediment, as opposed to uptake from the water route

Sediment Toxicity Assessment

Abstract: (Section Headings): Assessing Sediment Quality. Sediment Variability. Sediment Collection and Processing: Factors Affecting Realism. Ecosystem Assessment Using Estuarine and Marine Benthic Community Structure. Evaluation of Sediment Contaminant Toxicity: The Use of Freshwater Community Structure. The Emergence of Functional Attributes as EndPoints in Ecotoxicology. The Significance of In-Place Contaminated Marine Sediments on the Water Column: Processes and Effects. Plankton, macrophyte, Fish, and Amphibian Toxicity Testing of Freshwater Sediments. Assessment of Sediment Toxicity to Marine Benthos. Freshwater Benthic Toxicity Tests. Biomarkers in Hazard Assessments of Contaminated Sediments. Models, Muddles and Mud: Predicting Bioaccumulation of Sediment-Associated Pollutants. Sediment Bioaccumulation Testing with Fish. Integrative Assessments in Aquatic Ecosystems. Management Framework for Contaminated Sediments. Puget Sound Case Study. The Effects of Contaminated Sediments in the Elizabeth River. Index.

Ecology and Palaeoecology of Benthic Foraminifera.

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Habitat Heterogeneity and The Functional Signifiance of Fish in River Food Webs

Abstract: had little effect on algae or invertebrates associated with gravel. Gravel-dwelling heptageniid mayflies were behaviorally inhibited from using tops of stones in fish enclosures, and stone surfaces had more chironomid tubes in fish enclosures than in fish exclosures. However, no effects on epilithic algae or densities of invertebrates comparable to those of biota on boulder-bedrock substrates were detected. These spatially varying predator effects in a river parallel results from marine benthic systems, where strong effects of large predators documented for rocky intertidal habitats and unvegetated soft bottoms are not conspicuous in seagrass beds.

The role of benthic foraminifera in deep-sea food webs and carbon cycling

Abstract: Benthic foraminifers are a major element in deep-sea sediment and hard-substrate communities, sometimes accounting for 50% or more of eukaryotic biomass. They feed at a low trophic level, consuming mainly planktonic and other detritus and bacteria. Some species have metabolic adaptations enabling them to respond quickly to pulsed detrital inputs with rapid rates of reproduction and growth. These foraminifers probably assist microorganisms in the breakdown of fresh detrital material, while others are deposit feeders which convert more refractory organic substances into biomass. DOM uptake may be important, although no data exist as yet to substantiate this. Foraminifers are consumed by a wide variety of organisms, including selective and non-selective deposit feeders and specialised predators, and probably represent an important link between lower and higher levels of deep-sea food webs. A variety of non-trophic interactions between metazoans and foraminifers, for example, the provision of physical substrates, may facilitate access to enhanced food supplies. Thus, foraminifera playa largely unquantified but potentially significant role in deep-sea carbon cycling

Carbon fluxes and burial rates over the continental slope and rise off central California with implications for the global carbon cycle

Abstract: In situ microelectrode, box-core pore water gradient, and in situ benthic chamber estimates of organic carbon degradation and CaCO3 dissolution are combined with organic-C and carbonate-C accumulation rates to approximate the total carbon flux to the seafloor along two transects of the continental slope and rise off central California. Microelectrode profiles of dissolved O2 demonstrate that sediments at 13 sites, ranging in water depth from 580 to 4080 m, become anoxic below the uppermost 0.4–3 cm of the sediment column. If a current-swept area of nondeposition on the upper slope is excluded, we find total organic-C and carbonate-C fluxes to the seafloor vary from 40 to 100 μmol C cm−2yr−1 and from 32 to 91 μmol C cm−2yr−1, respectively. From the distribution of these fluxes there is no indication that total fluxes or remineralization rates of organic or carbonate carbon are influenced markedly by conditions in the oxygen minimum zone. Instead, the upper continental rise with its system of submarine valleys and fans stands out as the most important locus for carbon deposition and remineralization. When benthic fluxes and burial rates are extrapolated over the whole slope and rise of the region, aerobic respiration is the major mechanism of organic matter oxidation, and organic-C and carbonate-C recycling are on average 87% and 98% efficient, respectively. These results suggest that modern sediments on the outer regions of continental margins are important sources of CO2 that is injected directly into ocean deep water. However, if benthic carbon fluxes on the central California margin are typical of margins globally, this injection rate is less than 0.7 Gt C yr−1, which does not indicate a significant anthropogenic enhancement of carbon export to continental slopes and rises.

The Southern Ocean Benthic Fauna and Climate Change: A Historical Perspective

Abstract: Environmental change is the norm and it is likely that, particularly on the geological timescale, the temperature regime experienced by marine organisms has never been stable. These temperature changes vary in timescale from daily, through seasonal variations, to long-term environmental change over tens of millions of years. Whereas physiological work can give information on how individual organisms may react phenotypically to short-term change, the way benthic communities react to long-term change can only be studied from the fossil record. The present benthic marine fauna of the Southern Ocean is rich and diverse, consisting of a mixture of taxa with differing evolutionary histories and biogeographical affinities, suggesting that at no time in the Cenozoic did continental ice sheets extend sufficiently to eradicate all shallow-water faunas around Antarctica at the same time. Nevertheless, certain features do suggest the operation of vicariant processes, and climatic cycles affecting distributional ranges and ice-sheet extension may both have enhanced speciation processes. The overall cooling of southern high-latitude seas since the mid-Eocene has been neither smooth nor steady. Intermittent periods of global warming and the influence of Milankovitch cyclicity is likely to have led to regular pulses of migration in and out of Antarctica. The resultant diversity pump may explain in part the high species richness of some marine taxa in the Southern Ocean. It is difficult to suggest how the existing fauna will react to present global warming. Although it is certain the fauna will change, as all faunas have done throughout evolutionary time, we cannot predict with confidence how it will do so.

Hypoxia-induced structural changes in the diet of bottom-feeding fish and Crustacea

Abstract: Interactive effects of three alternating normoxia-hypoxia cycles on benthic prey exploitation by mobile fish (spot, Leiostomus xanthurus; and hogchoker, Trinectes maculatus) and a burrowing crustacean (Squilla empusa) were investigated in the York River, Chesapeake Bay, Virginia, USA, in 1989. Predators collected in four depth strata (A: 5 to 10 m; B: 10 to 14 m; C: 14 to 20 m; D:>20 m) variously affected by hypoxia were separated into size classes (three for spot and two each for hogchoker and mantis shrimp) to examine potential ontogenetic influences in prey selection. The most severe effects of hypoxia on the benthos occurred in the two deepest strata (C and D) and decreased in shallower strata (B>A), with Stratum A never affected by low oxygen. Predators investigated exhibited dietary evidence of optimal prey exploitation during or immediately after hypoxic events. In most instances gut contents contained significantly larger, deeper-burrowing prey during periods of low oxygen than during alternating peroids of normal oxygen levels. Spot consumed a greater biomass (45 to 73%) of polychaetes than other prey, with crustaceans initially also constituting a main dietary component but decreasing in importance later in the study period. The deep-burrowing anemone, Edwardsia elegans, was an important prey species for spot, particularly in the lower depth strata affected by hypoxia. Prey consumed by 10-to 15-cm-long spot increased significantly in size during some hypoxic events, suggesting a sublethal effect of hypoxia on large benthic species. Polychaetes (primarily Glycera americana, Notomastis latericeus and Loimia medusa) were dominant dietary components in hogchoker, making up between 85 and 98% of the diet. Bivalve siphons became important prey for hogchoker in the three deepest strata and were only consumed after the August hypoxia. Stomach contents of mantis shrimp were difficult to identify in most instances due to the near complete mastication of consumed prey. Crustaceans were important prey initially but became less conspicuous in the diet subsequent to the July hypoxia event, when hydroids became more dominant. Overall, predator species exhibited optimal exploitation of moribund or slowly recovering benthos affected by hypoxia. The sublethal effects of hypoxia through increased availability of benthos to resident predators can have important consequences for energy flow in areas such as the York River which experience periodic low-oxygen cycles.

Ecology and evolution of sympatric sticklebacks (Gasterosteus): evidence for a species-pair in Paxton Lake, Texada Island, British Columbia

Abstract: Two forms of Gasterosteus coexist in Paxton Lake on Texada Island, British Columbia. One form (benthic) is predominantly a littoral, benthic forager, whereas the other form (limnetic) is an open-wa...

Factors regulating periphytic algal biomass

Abstract: To assess the principal factors regulating periphytic algal communities, I conducted a field study along a productivity gradient of Swedish and Antarctic lakes ranging from extremely low productivity meltwater to highly productive lakes. Because the Antarctic lakes lack fish, as well as molluscs anId insect larvae, the data set provides considerable variation in food web composition, offering a rare opportunity to evaluate the importance of these factors in determining the biomass of periphytic algae. Among the possible factors investigated, water temperature, substrate characteristics, and food web composition seem to be of minor importance. Instead, there was a curvlinear relationship between the biomass of sediment-associated periphytic algae and lake productivity, suggesting a shift from nutrient limitation to light limitation caused by phytoplankton. A temporal study in the littoral zone of one of the lakes included in the spatial study showed that the temporal variation in periphyton biomass within the lake was low compared to the variation between lakes. Th,e temporal study also strengthened suggestions from the spatial study by pointing to nutrient availability as a major factor determining periphytic algal biomass. In phycological as well as in ecological literature, studies on periphytic (attached) algae are far more rare than studies on phytoplankton. In spite of that periphytic algae attain high biomass (Moss 1968; Hansson 1988a) and may contribute up to 80% of the primary production (Persson et al. 1977). Furthermore, periphytic algae are a major food resource for benthic invertebrates (Lamberti et al. 1989) and may retain part of the newly mineralized nutrients at the sediment surface, thereby having a competitive: impact on phytoplankton (Carlton and Wetzel 1988; Hansson 1989, 1990). Hence, the fact that periphytic algae are rare guests in the scientific literature is obviously not due to insignificance in the ecosystem. Instead, the reason is probably that the attached ialgal assemblage is far more difficult to work: with than the phytoplankton. Sampling i,s laborious and complicated and determination of primary production on natural substrata is difficult. Many methodological problems remain unsolved (Sundbgck 1983). Acknowledgments This study was supported with grants from the Crafoord Foundation and the Magnus Bergwall Foundation. Logistic support during fieldwork in Antarctica was provided by the Swedish Antarctic Research Program (SWEDARP). The Abisko Scientific Research Station provided logistic support during field studies in subarctic Sweden. Kathleen McTigue checked the English. Despite the apparent technical problems, it is important to improve the knowledge of periphytic algal dynamics because this life form constitutes an important link in lake ecosystems. My aim was to assess which factors are important -for periphytic algal growth in different types of lakes. My basic hypothesis is that the relative importance of each factor varies temporally within a lake and spatially among lakes. This hypothesis was tested in field survey studies by measuring the temporal and spatial variation in periphyton biomass and in some potentially regulating factors. The temporal study was performed in a southern Swedish lake over 13 months; the spatial study included 18 Antarctic and 16 Swedish lakes that varied in productivity from extremely low to very high. Variation in the biomass of periphytic algae may be caused by several factors, including substratum composition, temperature, grazing, light, and nutrient supply. The importance of these factors in determining periphyton biomass is still unknown, mainly because studies usually focus on one, or a few, of the factors. Several studies have demonstrated that perip hytic algae are co mpetitively depressed by phytoplankton (shading) in eutrophic lakes (Stevenson et al. 1985; Hansson 1988,a), suggesting a negative relation between periphytic algal biomass and productivity of lakes. Moreover, sediment-dwelling algae are known to take

Paleocene to Eocene benthic foraminiferal isotopes and assemblages: Implications for deepwater circulation

Abstract: Early Paleogene warm climates may have been linked to different modes and sources of deepwater formation. Warm polar temperatures of the Paleocene and Eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters. The possibility of increasing ocean heat transport through the production of warm saline deep waters (WSDW) in the Tethyan region has generated considerable interest. In addition, General Circulation Model results indicate that deepwater source regions may be highly sensitive to changing basin configurations. To decipher deepwater changes, we examined detailed benthic foraminiferal faunal and isotopic records of the late Paleocene through the early Eocene (∼60 to 50 Ma) from two critical regions: the North Atlantic (Bay of Biscay Site 401) and the Pacific (Shatsky Rise Site 577). These records are compared with published data from the Southern Ocean (Maud Rise Site 690, Islas Orcadas Rise Site 702). During the late Paleocene, similar benthic foraminiferal δ18O values were recorded at all four sites. This indicates uniform deepwater temperatures, consistent with a single source of deep water. The highest δ13C values were recorded in the Southern Ocean and were 0.5‰ more positive than those of the Pacific. We infer that the Southern Ocean was proximal to a source of nutrient-depleted deep water during the late Paleocene. Upper Paleocene Reflector Ab was cut on the western Bermuda Rise by cyclonically circulating bottom water, also suggesting a vigorous source of bottom water in the Southern Ocean. A dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest Paleocene in the Southern Ocean. This is a short-term (<100 kyr), globally synchronous event which also is apparent in both the Atlantic and Pacific records as a carbon isotopic excursion of approximately 1‰. Faunal analyses from the North Atlantic and Pacific sites indicate that the largest benthic foraminiferal faunal turnover of the Cenozoic was synchronous with the isotopic excursion, lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation. We speculate that the Southern Ocean deepwater source was reduced or eliminated at the time of the excursion. During the early Eocene, Southern Ocean δ13C values remained enriched relative to the North Atlantic and Pacific. However, the Southern Ocean was also enriched in δ18O relative to these basins. We interpret that these patterns indicate that although the Southern Ocean was proximal to a source of cool, nutrient-depleted water, the intermediate to upper deep water sites of the North Atlantic and Pacific were ventilated by a different source that probably originated in low latitudes, i.e., WSDW.

Indicator Bacterial Survival in Stream Sediments

Abstract: The impact of grazing cattle (Bostauras) on water quality has been the subject of considerable interest as water quality standards become more restrictive. Benthic sediments have been found to harbor signaficantly higher concentrations of enteric bacteria than the overlying water. In this study, the survival of fecal coliform and fecal streptococci organisms was demonstrated to be significantly longer in sediment laden waters than in those without sediment and further the survival was longer in the sediment-laden waters than in a supernatant from that same sediment suspended in water.

Primary production dynamics in seagrass beds of Mississippi Sound: the contributions of seagrass epiphytic algae, sand microflora, and phytoplankton

Abstract: Primary production rates of 4 autotrophic components in Halodule wrightii Aschers. beds off Horn Island in Mississippi Sound (USA) were measured over an annual cycle. Hourly production rates varied from as little as 0.9 mg C m-' for H, wrightii leaves in winter to as high as 1143 mg C m-' for eplphytic algae during summer. Stepwise multiple regression showed that only 15 % of the variation in hourly epiphytic algal production could be related to a single environmental variable (i.e. light energy). Variations in hourly production rates for the other productivity components were best explained by light energy, water temperature, tidal range and blade density; R2 for these regressions was 0.66 and 0.80 for phytoplankton and seagrass blades respectively. The epiphytic algal assemblage on H. wrightii leaves was dominated by the red alga Acrochaetium flexuosum Vickers and 12 taxa of araphid, monoraphid and biraphid diatoms. Phytoplankton over the beds were virtually all centric diatoms, whereas the microflora associated with the sandy sediments in which H. wrightii was rooted was dominated by small pennate diatoms. Annual production rates (g C were estimated as follows: epiphytic algae (905), phytoplankton (468), sand microflora (339) and Halodule wriyhtij (256). System production was dominated by the microalgae, with the contribution of H. rvrightji blades being only 13 % of the total. Epiphytic algae were the single most important productivity con~ponent, being responsible for 46 and 60 % of total system and benthic production respectively. The high standing crops and production rates of the epiphytic and benthic microalgae are of interest in that recent studies have indicated these algae can be the principal source of organic matter in seagrass food webs.

Aquatic insects as bioindicators of trace element contamination in cobble-bottom rivers and streams

Abstract: Trace element bioaccumulation was studied in immature benthic insects from two contaminated river systems to develop these animals as bioindicators. In one river, Cu, Cd, Pb, and Zn were analysed i...

Arctic biogeography: The paradox of the marine benthic fauna and flora.

Abstract: The marine benthic fauna and flora that inhabit the shallow arctic sublittoral zone comprise a relatively young marine assemblage characterized by species of either Pacific or Atlantic affinity and notably few endemics. The young character of nearshore arctic communities, as well as their biogeographical composition, is largely a product of the Pleistocene glaciation. However, analysis of more recent collections and comparison between the origins of the benthic fauna and flora present some interesting paradoxes to biogeographers. One enigma is the low frequency of algal species with Pacific affinities in the Arctic, especially in the Chukchi, Beaufort and East Siberian Seas of the Eastern Arctic, which receive direct inputs of northward-flowing Pacific waters. In contrast, animal species with Pacific affinities are found throughout the nearshore regions of the Arctic, reaching their highest frequency in the marginal seas between the New Siberian Islands and the Canadian Archipelago. Organization of published and unpublished data, additional field collections, and the use of cladistics and molecular DNA techniques by systematists are a high priority for future research in reconstructing the evolution of the arctic biotic assemblage.

Effects of disturbance on benthic functional structure and production in mountain streams

Abstract: To assess the role of macrofauna consumers in organic matter dynamics of headwater streams, we applied seasonal insecticide treatments to a southern Appalachian Mountain stream and compared benthic community structure between this and two other streams. Production was estimated in the two major habitats: mixed cobble-gravel-sand substrate and bedrock outcrop. Using the proportional availability of the habitats in each stream, production over the entire stream was measured. Annual habitat-weighted production in the untreated streams during the two study years ranged from 8.9 to 14.0 g AFDM m -2 yr -1 , 81 to 86% of which was attributed to insects. Habitat-weighted production was distributed rather evenly among the collector-gatherer (32-41%), shredder (23-31%), and predator (28-33%) functional groups. Collector-filterer and scraper groups accounted for less than 9% of total habitat-weighted production in all three streams. Insecticide applications resulted in dramatic changes in the macr...

Benthic foraminiferal distribution and biomass related to pore-water oxygen content: central California continental slope and rise

Abstract: Benthic foraminiferal distributions and biomass were investigated with respect to bottom-water and pore-water dissolved oxygen concentrations and sedimentary organic carbon content at nine stations (624–3728 m) along two transects perpendicular to the central California coast. These stations were selected to intersect the oxygen minimum zone (OMZ) as it impinges on the seafloor. Foraminiferal numerical densities were determined at selected depths within the uppermost 9 cm of box cores, using either an adenosine triphosphate (ATP) assay or a Rose Bengal vital staining technique. Foraminiferal abundances from surficial sediments, as determined by the staining technique, varied considerably and were negatively correlated to bottom-water oxygen concentration. Maximal numerical densities occurred at a depth of 998 m, which is within the OMZ; values ranged from 0 to 11.8 individuals cm−3 (determined by the ATP method) in surficial sediments. Six of nine cores exhibited subsurface maxima in foraminiferal abundance, and seven of the cores had subsurface foraminiferal biomass maxima. Results indicate that certain species are infaunal while others only live in the surface sediment interval, an important observation for paleoceanographic studies utilizing stable isotopic analyses of deep-sea benthic foraminifera.