Subsurface Deposit Feeders Research Articles

Structural and functional aspects of the benthic communities in the deep Angola Basin

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 260:43-53 (2003) - doi:10.3354/meps260043 Structural and functional aspects of the benthic communities in the deep Angola Basin Ingrid Kröncke1,*, Michael Türkay2 1Senckenberg Institute, Department for Marine Research, Südstrand 40-44, 26382 Wilhelmshaven, Germany 2Senckenberg Institute, Department for Aquatic Zoology, Senckenberganlage 25, 60325 Frankfurt am Main, Germany *Email: ingrid.kroencke@senckenberg.de ABSTRACT: During the RV ŒMeteor¹ expedition ŒDIVA I¹ the macro- and megafaunal communities were studied in 6 areas of the deep Angola Basin in July 2000. Water depths varied between 5162 and 5497 m. The macrofauna was dominated by polychaetes, peracarids and bivalves; the megafauna by ophiurids, bivalves and actiniarians. Abundance and biomass of macro- and megafauna were similar to other non-oligotrophic deep sea areas >4000 m. Predatory polychaetes, peracarids and facultative surface deposit feeders or predatory sipunculids occurred in similar ratios in all areas. Facultative subsurface deposit-feeding or predatory nematodes and oligochaetes increased towards the northern Areas 4 to 6. The percentage of surface-deposit and interface-feeding organisms such as polychaetes and ophiurids, which dominated in Areas 2 and 3, decreased towards the north. For megafauna, the ratio of organisms feeding as suspension feeder or predator as well as surface-deposit feeder increased from south to north. In the northern Areas 4 to 6, high numbers of bivalves occurred, which feed as surface or subsurface deposit feeders. TOC and chlorophyll a contents in sediment, as well as macro- and megafaunal abundance and biomass, were lower in the southern Areas 1 to 3 than in the northern Areas 4 to 6. These differences seem to be connected to the different water masses north and south of the Angola-Benguela Front, which cross the transect of our 6 study sites. In the north, the Angola Basin is a highly productive region fed by the South Equatorial Counter Current and water masses from the Zaire (Congo) River, whereas in the south, the cold Benguela Oceanic Current is less productive. The structure and function of the benthic fauna in connection with sediment data give evidence for differences in food supply north and south of the front. KEY WORDS: Angola Basin · Deep sea · Macrofauna · Megafauna · TOC · Chlorophyll a · Food availability · Benguela Oceanic Current Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 260. Online publication date: September 30, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

The distribution of benthic infauna of a Texas salt marsh in relation to the marsh edge

Coastal salt marshes in the northern Gulf of Mexico are often highly fragmented, with a large amount of marsh edge, the interface between the vegetated marsh surface and shallow open water. Nekton predators, including many juvenile fishery species, aggregate near this marsh edge, and benthic infaunal populations are a primary source of prey for many of these predators. We examined the fine-scale (1–10 m) distributions of benthic infauna in relation to the edge of a Texas, USA salt marsh. Every six weeks for nearly a year, we sampled marsh sediments at five locations: on nonvegetated bottom 1 m from the marsh edge and on the vegetated marsh surface at 1, 3, 5, and 10 m from the edge. Surface-dwelling annelid worms and peracarid crustaceans were most abundant in low-elevation sediments near the marsh edge for most sampling periods. Because the marsh slope varied within the study area, we could distinguish between correlative relationships with elevation and distance from the marsh edge. Distributions of common surface-dwelling species were often unrelated to elevation but almost always negatively related to distance from the marsh edge. Abundances of near-surface direct deposit feeders and omnivores were related to both distance from edge and elevation. In contrast to surface dwellers, densities of abundant subsurface deposit feeders (mainly oligochaetes) were frequently greatest in sediments located away from the marsh edge. Surface and near-surface dwelling infauna are an important prey resource for nekton, including many juvenile fishery species that concentrate near the marsh edge. Populations of these infaunal prey fluctuated seasonally, with the greatest densities occurring during winter and early spring when predator abundances are generally low. Infaunal densities decreased dramatically near the marsh edge from the late spring through early fall, and this decrease coincides with historically high seasonal densities of nekton predators. Our data suggest that there is a strong trophic link between infauna and nekton near the marsh edge and that this relationship contributes to the high fishery productivity derived from Gulf Coast marshes.

Long-term changes in a Mediterranean benthic community: Relationships between the polychaete assemblages and hydrological variations of the Rhône River

Long-term changes in a macrobenthic, muddy community of the French Mediterranean coast, near the mouth of the Rhone River, were studied using 14 samples collected between 1963 and 1996 at 70-m depth. No drastic change in the community was observed over this time period. A factor correspondence analysis (FCA) performed with the most frequent polychaete species revealed that 3 sample groups were related to trends in the Rhone River discharge. Between 1965 and 1976, the effects of dumping events close to the study site acted in synergy with river drought leading to a drop in the abundance of the most common species of the community (e.g.,Sternaspis scutata). Floods were observed to be the main factor structuring the polychaete assemblages. These floods were subsequently followed, over a period of several years, by peaks of opportunistic species (Heteromastus filiformis, Prionospio cirrifera) and, with a time lag of 1 or 2 yr, by peaks ofS. scutata. Autumn and early winter floods were mainly the result of heavy rainfalls on the Mediterranean part of the drainage basin. They transported large amounts of mineral and particulate organic matter that increased the surface and subsurface deposit feeders assemblages. Late winter and spring floods originated from the north of the basin. They proportionally brought more dissolved material and were followed by developments of suspension and surface deposit feeders. Eutrophication of the area due to increased nitrate concentrations in the river is suggested to be responsible for the abundance, since the 1980s, of small-sized deposit feeders. There is a good parallel between the cumulative mean deviations of the river discharge and the quantity of soles caught in the area with a time lag of 4 yr between these two curves. These results may be of value to the management of the regional resources.

Comparing rate and depth of feeding in benthic deposit-feeders: a test on two amphipods, Monoporeia affinis (Lindström) and Pontoporeia femorata Kröyer

Feeding depth is a critical aspect of habitat use by deposit-feeders. There is evidence of two partly separated food webs in infaunal benthos, where one relies directly on newly sedimented fresh phytodetritus, available mostly at the sediment surface, while the other primarily uses older organic matter in the sediment. We have developed a procedure for objective experimental identification of these two feeding types without relying on assumptions based on morphology. The rate and depth of feeding in the two deposit-feeding amphipods Monoporeia affinis and Pontoporeia femorata were studied in two laboratory experiments using 14C-labelled diatoms ( Skeletonema costatum) as food. Experiments were performed in spring and summer, with diatoms added on top and mixed down into the sediment in the spring experiment, and either on top or mixed into the sediment in the summer experiment. Treatments included the two species both in sympatry and allopatry, and at field-relevant densities between 1000 and 2600 individuals m −2. An overall greater 14C-assimilation was found for M. affinis, confirming that M. affinis has a higher ingestion rate and metabolism than P. femorata. In the spring experiment, M. affinis had similar 14C-assimilation both in treatments with labelled algae in the sediment and with labelled algae on the sediment surface, while P. femorata had ∼4× greater assimilation when the algae were mixed into the sediment. The summer experiment showed the same pattern for P. femorata, but M. affinis had ∼3× greater assimilation from algae spread on the sediment surface. No significant differences were found between densities or between sympatric and allopatric treatments indicating that competition between the two species had little effect under the conditions of the experiments. We conclude that the two species differ in feeding depth, with M. affinis more of a surface deposit-feeder and P. femorata almost exclusively a subsurface deposit-feeder, suggesting that they use partly different food resources. Depending on their local abundance, the two amphipods will affect mineralisation and bioturbation rates differently.

Fate of phytodetritus in marine sediments: functional importance of macrofaunal community

A 54 d incubation of intact sediment box-cores from 2 different macrofaunal sediment com- munities from the Swedish west coast was performed under controlled laboratory conditions in April to June 1999. One community was dominated by passive suspension feeders the other by subsurface de- posit feeders. The box-cores were seeded with 14 C-labelled detritus of the diatom Skeletonema costa- tum in order to mimic a post-spring-bloom situation. In addition to the labelled diatom phytodetritus, the box-cosms initially contained chlorophyll a with concentrations between 1 and 1.5 µg ml -1 in the top cm of the sediment. The experiment thus provided an opportunity to estimate degradation rates of the nat- urally occurring chlorophyll with a natural benthic fauna present over a ca. 2 mo period. Using a dia- genetic model to describe the vertical distribution of chlorophyll a (chl a), and using the same, previously published, degradation rate constant in both communities (0.03 d -1 ), gave mixing coefficients (DB, cm 2 d -1 ) that were on average >2 times higher in the community (L18) dominated by deposit feeders than in the suspension-feeding community (S3): 2.5 ± SD 1.7 and 0.86 ± SD 0.50, respectively. This indicates a higher mixing rate at L18. This difference in mixing between the 2 communities was supported by changes in vertical distribution of 14 C-labelled phytodetritus over the 54 d period. The mixing coefficients ( DBs) were positively correlated with biomass of subsurface deposit feeders but not with total biomass. Background chl a was higher at L18 than at S3. A quantitative comparison of the total chl a inventories at the start and end of the experiment suggested a low overall degradation rate (no significant overall change) in the chl a, far from the reaction rate constant of 0.03 d -1 often used in the literature. Similarly, the total 14 C activity in the cosms did not change significantly over the study period, suggesting a small loss of 14 CO2 from the cosms relative to the 14 C-pool size. The labelled algal matter distributions showed clear mixing over the 2 months in both communities with a higher mixing rate in the deposit-feeding community than the suspension-feeding community. Mixing also occurred deeper in the deposit-feed- ing community. Uptake of labelled matter by macrofauna was similar in the 2 communities, but differed markedly between species and trophic groups. At the end of the incubation, surface deposit feeders had an order of magnitude higher weight-specific 14 C activity than suspension feeders and subsurface de- posit feeders. The proportion of macrofaunal uptake of total 14 C activity in the cosms was small, on the order of 5%. The results support the idea that community species composition is important for the fate of sedimented phytodetritus and that macrofaunal influence on degradation of sedimentary chlorophyll is small at this time of the year. The initial fate of the bloom material was burial in the sediment rather than consumption by heterotrophs. The findings are thus in accordance with the hypothesis that a part of the spring phytoplankton bloom may be buried for a while in the sediment before being remineralised.

The influence of deposit-feeding on chlorophyll-<I>a</I> degradation in coastal marine sediments

To determine how macrofaunal activity affects rates and mechanisms of Chlorophyll- a (Chl-a) decomposition, we measured Chl- a concentrations during laboratory incubations of surface sediment with varying abundances of a subsurface deposit-feeder, Yoldia limatula. Decomposition patterns of Chl-a in sediment cores with and without a layer of algal-enriched sediment added to the surface were compared. Decomposition rate constants, kd, were calculated from the loss of reactive Chl- a and further quantie ed using a nonsteady state, depth-dependent, reaction-diffusion model. Values of kd decreased approximately exponentially with depth and were directly proportional to the number of Yoldia present.Yoldiaincreased the kd of both natural sedimentary Chl- a and algal enriched Chl- a in the upper 2 cm by up to 5.7 3 . Surface sediment porosity, penetration depths of a conservative tracer of diffusion (Br 2 ), and oxidized metabolic substrates (e.g. Fe(III)) all increased signie cantly in the presence of Yoldia. Macrofaunal bioturbation increased the importance of suboxic degradation pathways. These experiments demonstrated that organic compounds from a single source can have a continuum of degradation rate constants as a function of biogenically determined environmental conditions (Chl- a kd , 0.0043‐ 0.20 d 2 1 ). In particular, Chl- a can have a continuum of kd values related to redox conditions, transport, and macrofauna abundance as a function of depth.

Trophic structure of macrobenthos in the Gulf of St. Lawrence and on the Scotian Shelf

The Gulf of St. Lawrence and Scotian Shelf provide a diversity of oceanographic conditions in a continental margin setting. Climate is markedly seasonal, and bathymetry and hydrodynamic conditions cover a broad range, significantly influencing the patterns of organic matter sedimentation and, potentially, benthic community dynamics. Samples for analysis of benthic macrofauna and sediment microorganisms were collected at six stations in the Gulf of St. Lawrence (GSL) and the Scotian Shelf during winter and summer cruises, as part of the Canadian Joint Global Ocean Flux Study. Multivariate analyses indicate significant site-related trends in trophic guilds, benthic assemblages, and microbial activity, some of which are related to geomorphological characteristics (bathymetry, topography, and substratum). Macrofaunal trophic guild data show that the stations with relatively deep settling basins (Cabot Strait and Emerald Basin), dominated by surface deposit feeders, were distinct from stations with sloping bottoms (Anticosti Gyre and Anticosti Channel), where subsurface deposit feeders dominated or surface and subsurface deposit feeders were equally abundant. Deposit feeders (surface and subsurface trophic groups) made up >60% of the benthic communities, except at the Scotian slope station where they represented 44% of the total benthic abundances. Based on the data collected in both the water column and the sediment at three deep stations in the GSL, we hypothesize that the proportion of surface and subsurface deposit feeders, and thus the nature of bioturbation activity, is related to the magnitude and pattern of organic matter supply from the euphotic zone.

Effects of dissolved oxygen and fresh organic matter on the bioturbation potential of macrofauna in sublittoral sediments off Central Chile during the 1997/1998 El Niño

A study off Concepcion, central Chile, during the 1997/1998 El Nino (EN) revealed that the concentration of dissolved oxygen and the organic content and quality of the sediment control the vertical distribution of macrofauna in the sediment and bioturbation potential. The study area, char- acterized by organic-rich, silty sediments, lies within the most intense upwelling center off the coast of Chile, and is subject to the seasonal influx of hypoxic subsurface waters. Five stations (28 to 120 m depth) were sampled seasonally. The vertical distribution and integrated biomass and abundance of macrofauna (>0.5 mm) were determined, as well as the dissolved oxygen content of the bottom water (BWDO) and sediment parameters such as total organic carbon (TOC), the C/N ratio, sulphide content, chl a content, and the thickness of the oxidized zone. Chl a proved to be a good indicator of fresh (high- quality) organic matter. Major components contributing to variation in the macrofauna feeding guilds, bioturbation categories, and their vertical position in the sediment were: (1) the relative bioturbation potential (contribution of bioturbating taxa to the assemblage) and (2) the vertical distribution and ratio of surface-to subsurface deposit-feeders. Higher levels of BWDO and a lower quality of organic matter at the sediment surface tended to provide better conditions for potentially strong bioturbators, while lower BWDO levels and higher-quality organic matter were accompanied by the dominance of tube-dwelling, surface-defecating (and hence weakly bioturbating) species. Higher TOC levels and lower-quality organic matter at the surface resulted in deeper vertical distributions of animals and a higher relative abundance of subsurface deposit-feeders. During the study period, BWDO levels in- creased, while the total organic carbon and the quality of organic matter decreased. These conditions encouraged the vertical penetration of macrofauna into the sediment column and the relatively larger contribution of stronger bioturbators to the assemblage. The most drastic changes in faunal lifestyles and vertical distribution during the 1997/1998 EN were observed within the Bay of Concepcion, an area usually characterized by sulphidic sediments under the conditions of severe seasonal hypoxia or anoxia obtaining during 'normal' (i.e. non-EN) years; and in the deepest shelf site, which usually experiences permanent hypoxia because of the influence of the 'oxygen minimum zone'.

Spatial changes in sublittoral soft-bottom polychaete assemblages due to river inputs and sewage discharges

Spatial changes in species composition and structure of sublittoral soft-bottom polychaete assemblages along a transect parallel to the shoreline off the Barcelonès and Maresme regions on the Spanish Catalan coast (NW Mediterranean sea) are described. The transect (20 m mean depth) covers 30 km through an area affected by both water sewage discharges and river outflow. These effluents generate a spatial gradient of both silt and organic enrichment, according to the prevailing southerly currents in the zone. South of the effluents, eutrophized sediments supported a macrofaunal assemblage which was typical of polluted bottoms, characterized by the massive presence of Capitella capitata and Malacoceros fuliginosus, high abundance and biomass, low values of species richness, and a simplified trophic structure dominated by surface and subsurface-deposit feeders. North of the effluents, both the mud and organic matter content in sediment decreased drastically and the polychaete assemblages described were progressively less affected with distance. Thus, a clear change in species composition, as well as low values of abundance and biomass, increases in species richness, and a more complex trophic structure on the polychaete assemblages was observed north rather than south of the effluents.

Macrozoobenthic community structure in two Portuguese estuaries: Relationship with organic enrichment and nutrient gradients

The aim of this work consists in the study of the structural and functional aspects of the macrozoobenthic communities and their relationships with the organic enrichment and nutrient gradients in water and sediment. The study was carried out in two coastal ecosystems under strong anthropogenic pressure: the Sado estuary and the Aveiro Lagoon. Samples were collected at four stations between October 1994 and April 1995. The results obtained allowed us to state that spatial variability, both horizontal and vertical, was higher than the temporal variability. This was due to local hydrodynamism, organic load and granulometric structure of the sediment. Comparing the community structure at the different stations, it was possible to observe the existence of disturbance cases not directly related to organic enrichment gradients. The interpretation of the functional role of the macrozoobenthic communities at the water-sediment interface was based on the trophodynamic group classification. This approach allowed us to state that the sensitivity of different groups to organic enrichment, confirming the role of burrower subsurface-deposit feeders as opportunists associated with organic enrichment and, on the other hand, the influence of certain trophodynamic groups in the nutrient transfer processes, particularly the association between tube-builder omnivores and burrower carnivore and nitrate content in interstitial water.

The deep-sea macrobenthos on the continental slope of the northwestern Mediterranean Sea: a quantitative approach

As part of the ECOMARGE operation (J.G.O.F.S. France), macrobenthic assemblages in the Toulon Canyon were described and quantified on the basis of sampling carried out between 250 and 2000 m depth on the Mediterranean continental slope. Results show that Mediterranean bathyal assemblages are made up mainly of continental shelf eurybathic species. The qualitative and quantitative composition of populations varies with depth on the slope and also varies with station position at equivalent depth, whether on the flanks or in the canyon channel. Various analyses have provided evidence on the factors responsible for this population distribution pattern. No single factor emerges as predominant, but rather a group of factors, which are related to the nature and origin of sediments and more particularly their grain size distribution, geochemical composition and mode of transportation and sedimentation (benthic nepheloid or originating from the water column), act in conjunction to determine the pattern. Comparison with ocean continental slopes shows that in the Mediterranean Sea the absence of tidal current modifies the trophic structure of the macrobenthic assemblages, which are characterized by a dominance of surface and subsurface deposit feeders as compared to a dominance of suspension feeders and carnivores in the upper and median part of the slope in the ocean. Surface dumping of dredge spoil at the canyon head and channelling of waste induces an increase of organic matter and pollutant concentrations in sediment from the upper part of the canyon channel but does not give rise to any marked population degradation.

Composition, abundance and stratification of soft-bottom macrobenthos from selected areas of the Ross Sea shelf (Antarctica)

Composition, abundance and stratification of soft-bottom macrobenthos were studied at three selected sites on the Ross Sea shelf (Antarctica) with different geomorphology and sedimentation regimes. Sites A (southwest Ross Sea, 810 m depth) and B (Joides basin, 580 m depth) were characterized by biogenic mud and clay sediments, whereas site C (Mawson bank, 450 m depth) featured sandy sediments mixed with a conspicuous biogenic component characterized by shells and tests of calcareous invertebrates (mainly barnacles of the genus Bathylasma). The macrofauna of sites A and B was mainly composed of infaunal polychaetes and bivalves. The assemblages comprised both surface and sub-surface deposit feeders, including some conveyor-belt polychaetes (Maldanidae and Capitellidae) that are responsible for high sediment mixing and bioturbation. The macrobenthos of site C was dominated by crustaceans, polychaetes and echinoderms (ophiuroids), and mainly by filter feeders and epifaunal or interstitial forms. Abundances were higher (up to 1040 ind. m−2) at site B than at sites A and C (430 and 516 ind. m−2, respectively). At sites A and B the benthos was mainly concentrated in the upper 5 cm of the sediment, and abundances declined sharply in the deeper sediment layers. These results indicate a high degree of consistency between sediment features and benthic community structure, which are both strongly related to local hydrography and bottom dynamics. Sites A and B represent areas where the organic input to the seafloor by vertical sedimentation from the upper water column is high. Site C, however, is characterized by high sediment instability and food particles advecting mainly horizontally. The community is more physically controlled by unpredictable, and probably frequent, disturbance events (e.g., bottom turbid currents, sediment reworking and displacement). Individuals were relatively small, indicating that probably they are not able to grow up to the adult size and reproduce. The community may be represented by “pseudopopulations” depending on the settlement of larvae invading from neighbouring areas.

The meiofauna:macrofauna ratio across the continental slope of the Goban Spur (north-east Atlantic)

Meio- and macrofauna density and biomass were estimated at the OMEX-transect across the continental slope of the Goban Spur at water depths ranging from 208 to 4460 m in the north-east Atlantic. A linear increase in the ratio between meio- and macrofauna densities with increasing water depth was found. At the continental shelf meiofauna densities were ∼50 times higher than macrofauna densities, whereas in the abyss meiofauna densities were more than 1000 times higher. This change in ratio was due to a significant decrease in macrofauna densities with increasing water depth, whereas the meiofauna densities stayed more or less at the same level. The ratio in biomass between meio- and macrofauna showed a dip at ∼1000 m. At this depth macrofauna biomass was ∼55 times higher than meiofauna biomass, whereas at ∼4500 m macrofauna biomass was only about three times higher. Macrofauna biomass was high at ∼1000 m, due to the high mean individual weight of the macrofauna, whereas meiofauna biomass and mean individual weight were low at this depth.Meiofauna consisted of ∼90% nematodes. Within the macrofaunal fraction (>0.5 mm) a linear increase in the ratio between nematodes and macrofauna sensu stricto with depth was found. At the deepest station ∼20% of the macrofaunal fraction were nematodes, at the shallowest station only ∼2%. Thus, large nematodes became relatively more important with increasing water depth. Within the macrofauna a decrease in the abundance of filter- and surface deposit-feeders relative to the subsurface deposit-feeders with increasing water depth was observed, which may be related to a change in food input. As no decrease in mean individual weight with increasing water depth within either group could be observed, the change in meio:macrofauna ratios along the OMEX-transect merely reflects a change in taxonomic (functional) composition, rather than a change in size.

Assessment of Sedimentary Cu Availability: A Comparison of Biomimetic and AVS Approaches

Sedimentary Cu bioavailability during deposit feeding is determined by both the digestive physiology of the organisms and the geochemistry of the sediments. We assessed the contribution of these two factors by using a biomimetic approach involving extraction of Cu with digestive fluids of two deposit feeders and one suspension feeder and a geochemical approach measuring Cu associated with acid-volatile sulfide (AVS) in sediments. Cu bioavailability determined by the biomimetic method varied among species with varying digestive physiology but all showed a marked increase when SEMCu-AVS ≥ 0, corroborating the premise underlying the AVS method in determining sedimentary Cu bioavailability. The existence of a positive SEMCu-AVS threshold (0.4−1.5 μmol/g-sediment) suggests the existence of additional Cu-binding phases or mixed Cu(I)−Cu(II) sulfides in sediments. In addition, Cu bioavailable to digestive fluids was much less than that measured as SEMCu-AVS, indicating that the AVS method overestimates Cu bioavailability to digestive fluid of deposit feeders. Incubation of digestive fluids with two Cu-bound model phases, goethite and sulfide, corroborated the relative unavailability of sulfide-bound Cu. Subsurface deposit feeders feeding on anoxic sediments may be exposed to less Cu than their surface-feeding counterparts in Cu-contaminated environments.

Mesocosm investigation into the effects of bioturbation on the diversity and structure of a subtidal macrobenthic community

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 189:181-193 (1999) - doi:10.3354/meps189181 Mesocosm investigation into the effects of bioturbation on the diversity and structure of a subtidal macrobenthic community Stephen Widdicombe1,2,*, Melanie C. Austen1 1Centre For Coastal & Marine Sciences, Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PL1 2PY, United Kingdom 2Plymouth Environmental Research Centre, (Department of Biological Sciences), University of Plymouth, Drake Circus, Plymouth PL4 8AA, United Kingdom *E-mail: s.widdicombe@pml.ac.uk ABSTRACT: Benthic mesocosm experiments have highlighted the importance of bioturbation in maintaining levels of diversity and setting community structure in subtidal macrobenthic assemblages. In the mesocosm facility of the Norwegian Institute for Water Research (NIVA) at Solbergstrand, Norway, partitioned boxes of sediment were subjected to continuous disturbance through bioturbation for a period of 20 wk. The effect of type and intensity of bioturbation on the macro-infauna was examined by exposing different partitioned areas to different bioturbating species at different densities. The 3 test macrofauna species used were the bivalves Nuculoma tenuis (subsurface deposit feeder) and Abra alba (surface deposit/suspension feeder) at 3 different densities, and the heart urchin Brissopsis lyrifera (subsurface burrowing deposit feeder) at a single density. The presence of N. tenuis at low densities resulted in significantly higher levels of α and β diversity than were observed in the undisturbed or highly disturbed treatments. Previous experiments have shown that B. lyrifera also elicits a response in the associated fauna consistent with the 'intermediate disturbance hypothesis'. Such a response was not observed in the A. alba treatments. Multivariate data analysis demonstrated that the response of the associated fauna was influenced by the identity of the organism causing the disturbance. It was also evident that different elements of the community responded differently to bioturbation. This paper makes comparisons between the responses of macrofauna and meiofauna to bioturbation. Our experimental results suggest that the identity, density and distribution of large bioturbating organisms are important factors in the structuring of infaunal communities and in setting and maintaining levels of diversity in apparently homogeneous areas. KEY WORDS: Diversity · Disturbance · Bioturbation · Macrofauna · Meiofauna · Nuculoma tenuis · Abra alba · Brissopsis lyrifera Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 189. Publication date: November 26, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Effects of a deposit-feeding invertebrate on the entrapment of Zostera marina L. seeds

Eelgrass, Zostera marina, relies upon seed dispersal for colonization of new habitats. The seeds are not readily transported in suspension; however, they have low erosion thresholds and are subject to horizontal transport as bedload at relatively low bottom shear stress. Field germination patterns suggest that seeds rarely travel far from the point of release and quickly become buried in the sediment, even in habitats where boundary-layer flows exceed those necessary to erode seeds. In many sedimentary habitats it is likely that the activities of benthic and demersal organisms will affect the horizontal movement and burial of seeds, thus providing an explanation for the patterns of seedling establishment in previously reported experiments. We investigated the effects of a common animal in estuarine sediments on the entrapment of Z. marina seeds. In a series of flume experiments we manipulated the densities of the subsurface deposit-feeding polychaete Clymenella torquata (Low: 96 worms m −2; Medium: 192 worms m −2; High: 288 worms m −2) and related trapping of seeds to worm density and bioturbation rates. The results suggest that modifications to the sediment surface (i.e. topographic relief) resulting from feeding and defecation activities of subsurface deposit feeders can act to trap seeds. Seeds were trapped in the medium and high density worm treatments in greater numbers than in the low density and no worm treatments. Our findings indicate that benthic invertebrates, through their modification of sediments may affect the horizontal (bedload) and, hence, vertical (burial) transport of Z. marina seeds.

Modelling the Deposition and Biological Effects of Organic Carbon from Marine Sewage Discharges

The impacts of particulate organic carbon on marine benthic ecosystems have been modelled mathematically. The principal model (BenOss-Biological Effects and Organic Solids Sedimentation) links various modules: particle tracking; a resuspension module which accounts for both deposition and resuspension of carbon at the sea bed; a chemical module which removes organic carbon according to its degradability using the G-model; and a biological module which predicts benthic community structure on the basis of carbon availability. The model predicts the benthic effects of reducing carbon input.Observations of benthic community structure are related to predictions of carbon deposition arising from a discharge. Predictions of carbon deposition are correlated with changes in total species abundance, abundance of subsurface deposit-feeders and suspension-feeders.

Effects of biological disturbance on diversity and structure of meiobenthic nematode communities

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 174:233-246 (1998) - doi:10.3354/meps174233 Effects of biological disturbance on diversity and structure of meiobenthic nematode communities Melanie C. Austen*, Stephen Widdicombe, Nicoletta Villano-Pitacco Centre for Coastal and Marine Sciences, Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PL1 3DH, United Kingdom *E-mail: m.austen@pml.ac.uk ABSTRACT: Benthic mesocosm experiments have shown that subtidal macrofauna species with contrasting feeding behaviour and mobility can alter the structure of natural subtidal meiobenthic nematode assemblages. Test macrofauna species were the bivalves Nuculoma tenuis (subsurface-deposit feeder) and Abra alba (surface-deposit/suspension feeder) at 3 different densities and the heart urchin Brissopsis lyrifera (subsurface burrowing deposit feeder) at a single density. α and β nematode diversity were affected by disturbance of different intensities in the bivalve treatments in a way that is consistent with the intermediate disturbance hypothesis regardless of type of disturbance. These measures of community structure did not differentiate between contrasting types of disturbance. Multivariate community analysis indicated that the species response in the assemblage was more sensitive to the type of disturbance than the intensity of disturbance. Differential responses of the nematode species did not reflect their depth distribution in natural field sediment and the likely depth at which the test macrofauna species were active. Nor was the response simply a predator-prey interaction with certain species targeted by the predator; the interactions appear to be more complex. Our experimental results suggest that patches of sediment which are dominated by high abundances or biomass of one or a few species, a situation which is encountered in the field, are important in maintaining regional diversity. These patches will create a heterogeneous mosaic of communities with different diversities and different species compositions. KEY WORDS: Meiofauna · Nematode · Diversity · Community structure · Predation · Disturbance · Abra alba · Nuculoma tenuis · Brissopsis lyrifera Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 174. Publication date: November 26, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Trophic function in estuaries: response of macrobenthos to natural and contaminant gradients

Trophic ecology of macrobenthic communities in estuaries of the northern Gulf of Mexico was used to infer community function, determine effects of contaminants on macrobenthos, and provide insight into community responses following disturbance. The taxa that numerically dominated the region included few large, deep-burrowing suspension feeders that typify estuaries elsewhere. This pattern is indicative of disturbance, and results in dominance by trophic groups that live near the sediment–water interface (early benthic-community succession). Trophic structure was significantly related to several sediment contaminants (especially metals, polynuclear aromatic hydrocarbons, DDT), and three environmental gradients (salinity, depth, and sediment silt–clay content). Generally, trophic diversity increased and proportion of subsurface-deposit feeders (SSDF) decreased with salinity, meaning that a more even distribution of trophic structure was found at high-salinity stations. The trophic shift toward dominance by shallow, subsurface-deposit feeders in contaminated habitats may have dire implications for fisheries. Several important commercial and recreational fisheries of the region depend on fish that feed primarily at the sediment surface. Higher proportion of subsurface-deposit feeders, coupled with low macrobenthic density in contaminated sediments, may imply that limited energy is transferred to higher trophic levels.

底層の貧酸素化が内湾浅海底生生物群集の変化に及ぼす影響

Changes in the benthic community structure, relating to a decline in bottom dissolved oxygen concentration in the shallow muddy bottom of Mikawa Bay, were observed throughout a 50 days period during the early summer of 1996. Water mass movements related to tides and winds were largely responsible for changes in the bottom oxygen concentration. During the observation period, the dissolved oxygen deficiency tended to progress as the water temperature increased, which probably caused an increase in decomposition of organic matter on the bottom. An increase in the apparent dissolved oxygen consumption rate was mainly due to decomposition of newly deposited organic matter from water column rather than that of existing bottom sediment. Biomass of bacteria increased during the early stage of the dissolved oxygen deficiency, but decreased in the later stage, resulting in an increase of undecomoposed detritus in the sediment. Benthic chlorophyll fluctuated mainly with changes in sunlight intensity, but decreased when severe dissolved oxygen deficiency conditions prevailed. Differeces in the ability to tolerate the oxygen deficiency amongst meio-and macro-benthos species were observed. Almost all benthos species, however, decreased during the severe oxygen deficiency period, except for subsurface deposit feeders.