High Benthic Biomass Research Articles

A morphogenetic characterisation of a potentially dominant African marine species in Europe

Studying the early stages of the introduction of non-indigenous species (NIS) is crucial as it allows immediate management actions aimed at preventing NIS spread at a time when these actions are more likely to be effective. Recent species introductions present unique opportunities to study key aspects of the invasion process. However, comprehensive information on how and when NIS are first introduced remains rare. We assessed the characteristics of the introduction of a member of the widespread Pyura stolonifera species group (Chordata, Tunicata) in Europe. These ascidians are important bioengineer species that can attain amongst the highest benthic biomass per surface area ever reported. We collected introduced individuals on the coast of the northwestern Iberian Peninsula, an area with high shipping traffic and one of the world’s most important mussel farming regions. The specimens were analysed using taxonomic and genetic tools. Both field surveys and taxonomic analysis showed that one of the African members of the species group, Pyura herdmani, has recently been introduced to Europe and, although it does not yet form the large aggregates found in the native range, it is already well-established. Genetic data revealed that only the northwest African lineage of P. herdmani has been introduced to Europe. Considering the low dispersal capabilities of the early life-history stages of P. herdmani, the introduction of this species into Europe can only be explained via human mediated transport of NIS. In order to prevent any detrimental effects on both native biota and/or economically-important anthropogenic activities, regular monitoring of recent NIS introductions is urgently required.

Community structure and association network of prokaryotic community in surface sediments from the Bering-Chukchi shelf and adjacent sea areas.

The Bering-Chukchi shelf is one of the world's most productive areas and characterized by high benthic biomass. Sedimentary microbial communities play a crucial role in the remineralization of organic matter and associated biogeochemical cycles, reflecting both short-term changes in the environment and more consistent long-term environmental characteristics in a given habitat. In order to get a better understanding of the community structure of sediment-associated prokaryotes, surface sediments were collected from 26 stations in the Bering-Chukchi shelf and adjacent northern deep seas in this study. Prokaryote community structures were analyzed by metabarcoding of the 16S rRNA gene, and potential interactions among prokaryotic groups were analyzed by co-occurrence networks. Relationships between the prokaryote community and environmental factors were assessed. Gammaproteobacteria, Alphaproteobacteria, and Flavobacteriia were the dominant bacterial classes, contributing 35.0, 18.9, and 17.3% of the bacterial reads, respectively. The phototrophic cyanobacteria accounted for 2.7% of the DNA reads and occurred more abundantly in the Bering-Chukchi shelf. Prokaryotic community assemblages were different in the northern deep seas compared to the Bering-Chukchi shelf, represented by the lowered diversity and the increased abundant operational Taxonomic Units (OTU), suggesting that the abundant taxa may play more important roles in the northern deep seas. Correlation analysis showed that latitude, water depth, and nutrients were important factors affecting the prokaryote community structure. Abundant OTUs were distributed widely in the study area. The complex association networks indicated a stable microbial community structure in the study area. The high positive interactions (81.8-97.7%) in this study suggested that symbiotic and/or cooperative relationships accounted for a dominant proportion of the microbial networks. However, the dominant taxa were generally located at the edge of the co-occurrence networks rather than in the major modules. Most of the keystone OTUs were intermediately abundant OTUs with relative reads between 0.01 and 1%, suggesting that taxa with moderate biomass might have considerable impacts on the structure and function of the microbial community. This study enriched the understanding of prokaryotic community in surface sediments from the Bering-Chukchi shelf and adjacent sea areas.

Differences in the carbon flows in the benthic food webs of abyssal hill and plain habitats

AbstractInputs of detritus from the surface ocean are an important driver of community dynamics in the deep sea. The assessment of the flow of carbon through the benthic food web gives insight into how the community is sustained, and its resilience to fluctuations in food supply. We used a linear inverse model to compare the carbon flow through the food webs on an abyssal hill and the nearby plain at the Porcupine Abyssal Plain sustained observatory (4850 m water depth; northeast Atlantic), to examine the partitioning of detrital input in these substantially different megafaunal communities. We found minimal variation in carbon flows at the plain over two years, but differences in the detrital inputs and in the processing of that carbon input between the hill and plain habitats. Suspension feeding dominated metazoan carbon processing on the hill, removing nearly all labile detritus input to the system. By contrast, half of all labile detritus was deposited and available for deposit feeders on the abyssal plain. This suggests that the biomass on the hill is dependent on a more variable carbon supply than the plain. The presence of millions of abyssal hills globally suggests that the high benthic biomass and respiration, and reduced deposition of detritus may be pervasive, albeit with varying intensity.

Linkages between sea-ice coverage, pelagic–benthic coupling, and the distribution of spectacled eiders: Observations in March 2008, 2009 and 2010, northern Bering Sea

Icebreaker-based sampling in the northern Bering Sea south of St. Lawrence Island in March of 2008, 2009, and 2010 has provided new data on overall ecosystem function early in the annual productive cycle. While water-column chlorophyll concentrations (<25mgm−2 integrated over the whole water column) are two orders of magnitude lower than observed during the spring bloom in May, sea-ice algal inventories of chlorophyll are high (up to 1g m−3 in the bottom 2-cm of sea-ice). Vertical fluxes of chlorophyll as measured in sediment traps were between 0.3 and 3.7mgm−2d−1 and were consistent with the recent deposition (days’ to weeks’ time scale) of chlorophyll to the surface sediments (0–25mgm−2 present at 0–1cm). Sediment oxygen respiration rates were lower than previous measurements that followed the spring bloom, but were highest in areas of known high benthic biomass. Early spring release of sedimentary ammonium occurs, particularly southeast of St. Lawrence Island, leading to bottom-water ammonium concentrations of >5µM. These data, together with other physical, biological, and nutrient data, are presented here in conjunction with observed sea-ice dynamics and the distribution of an apex predator, the Spectacled Eider (Somateria fischeri). Sea-ice dynamics in addition to benthic food availability, as determined by sedimentation processes, play a role in the distribution of spectacled eiders, which cannot always access the greatest biomass of their preferred bivalve prey. Overall, the data and observations indicate that the northern Bering Sea is biologically active in late winter, but with strong atmospheric and hydrographic controls. These controls pre-determine nutrient and chlorophyll distributions, water-column mixing, as well as pelagic–benthic coupling.

Standing stocks and body size of deep-sea macrofauna: Predicting the baseline of 2010 Deepwater Horizon oil spill in the northern Gulf of Mexico

A composite database encompassing 6 benthic surveys from years 1983 to 2003 was constructed to evaluate the distribution of macrofaunal biomass in the deep Gulf of Mexico (GoM) prior to the Deepwater Horizon oil spill. Predictive models based on optimal scaling of ocean color data and high resolution bathymetry were employed to map the benthic biomass in the vicinity of spill site because no previous sampling had been conducted at that exact location. The predicted biomass declines with water and mixed layer depth and is an increasing function of surface primary production and temporal variation of sea surface temperature. The decline of animal size with depth, however, was a function of a shift of dominant abundance from large to small taxa. At a local scale, high benthic biomass in the N GoM was associated with the enhanced productivity by the nutrient-laden Mississippi River outflows, offshore transport of the river plumes, and upwelling along the northern edge of the Loop Current. The apparent biomass enhancement at the Mississippi and De Soto Canyon and deep sediment fan was presumably related to lateral down-slope advection of organic carbon from the surrounding continental margin. Except for the Campeche Bank, the meager biomass of the Mexican margin may reflect the characteristic low-productivity Caribbean water that enters the GoM through Yucatan Strait. Benthic biomass in the N GoM was not statistically different between comprehensive surveys in the years 1983–1985 and 2000–2002. The stock assessment and biomass predictions from 669 cores at 170 locations throughout the deep GoM provide an important baseline of the sediment-dwelling fauna that may be subjected to immediate or long-term impacts from the oil spill or from climate change.

The relationship between sea ice break-up, water mass variation, chlorophyll biomass, and sedimentation in the northern Bering Sea

The northern Bering Sea shelf is dominated by soft-bottom infauna and ecologically significant epifauna that are matched by few other marine ecosystems in biomass. The likely basis for this high benthic biomass is the intense spring bloom, but few studies have followed the direct sedimentation of organic material during the bloom peak in May. Satellite imagery, water column chlorophyll concentrations and surface sediment chlorophyll inventories were used to document the dynamics of sedimentation to the sea floor in both 2006 and 2007, as well as to compare to existing data from the spring bloom in 1994. An atmospherically-derived radionuclide, 7Be, that is deposited in surface sediments as ice cover retreats was used to supplement these observations, as were studies of light penetration and nutrient depletion in the water column as the bloom progressed. Chlorophyll biomass as sea ice melted differed significantly among the three years studied (1994, 2006, 2007). The lowest chlorophyll biomass was observed in 2006, after strong northerly and easterly winds had distributed relatively low nutrient water from near the Alaskan coast westward across the shelf prior to ice retreat. By contrast, in 1994 and 2007, northerly winds had less northeasterly vectors prior to sea ice retreat, which reduced the westward extent of low-nutrient waters across the shelf. Additional possible impacts on chlorophyll biomass include the timing of sea-ice retreat in 1994 and 2007, which occurred several weeks earlier than in 2006 in waters with the highest nutrient content. Late winter brine formation and associated water column mixing may also have impacts on productivity that have not been previously recognized. These observations suggest that interconnected complexities will prevent straightforward predictions of the influence of earlier ice retreat in the northern Bering Sea upon water column productivity and any resulting benthic ecosystem re-structuring as seasonal sea ice retreats in the northern Bering Sea.

Walrus areas of use in the Chukchi Sea during sparse sea ice cover

The Pacific walrus Odobenus rosmarus divergens feeds on benthic invertebrates on the con- tinental shelf of the Chukchi and Bering Seas and rests on sea ice between foraging trips. With climate warming, ice-free periods in the Chukchi Sea have increased and are projected to increase further in fre- quency and duration. We radio-tracked walruses to estimate areas of walrus foraging and occupancy in the Chukchi Sea from June to November of 2008 to 2011, years when sea ice was sparse over the conti- nental shelf in comparison to historical records. The earlier and more extensive sea ice retreat in June to September, and delayed freeze-up of sea ice in Octo- ber to November, created conditions for walruses to arrive earlier and stay later in the Chukchi Sea than in the past. The lack of sea ice over the continental shelf from September to October caused walruses to forage in nearshore areas instead of offshore areas as in the past. Walruses did not frequent the deep waters of the Arctic Basin when sea ice retreated off the shelf. Walruses foraged in most areas they occu- pied, and areas of concentrated foraging generally corresponded to regions of high benthic biomass, such as in the northeastern (Hanna Shoal) and south- western Chukchi Sea. A notable exception was the occurrence of concentrated foraging in a nearshore area of northwestern Alaska that is apparently de - pauperate in walrus prey. With increasing sea ice loss, it is likely that walruses will increase their use of coastal haul-outs and nearshore foraging areas, with consequences to the population that are yet to be understood.

A model study of the regulation of blue mussels by nutrient loadings and water column stability in a shallow estuary, the Limfjorden

Danish estuaries are characterised by being shallow, eutrophic and with high benthic biomass dominated by suspension feeders. However, the standing stock of benthic fauna is often higher than would be expected from the relation to residence time of sea water or to annual primary production found in other estuaries. The present study investigated how the biomass of benthic suspension feeders was regulated by food supply produced due to eutrophication and supplied to the benthos by vertical mixing. This was tested using a 1D water column model calibrated and validated against monitoring data from a 5 years period in the Limfjorden. The model described vertical hydrodynamics and -pelagic biogeochemistry, sediment dynamics and was coupled to a Dynamic Energy Budget model for blue mussels. The modelled biomass of blue mussels showed a dome-shaped relationship to water column stability that was most pronounced combined with high nutrient loadings. At strong stratification, there was little coupling between the upper productive layer and mussels causing food limitation. In addition, hypoxia induced mass mortality of mussels during summer at high nutrient loadings. Under well-mixed conditions, mussels were capable of depleting phytoplankton in the whole water column and food limitation occurred resulting in a lower annual mussel biomass. The optimal conditions for growth of benthic suspension feeders in the long term would therefore be periods of stratification that are long enough to allow the phytoplankton to bloom at the surface layer and short enough to prevent benthic suspension feeders from starving or suffer from hypoxia.

Can bottom trawling disturbance increase food production for a commercial fish species?

Fishery closures and marine protected areas are increasingly being used as tools to achieve sustainable fisheries. The “plaice box”, a gear restriction area in the North Sea that was established to reduce the bycatch of undersized plaice ( Pleuronectes platessa ), is considered ineffective because there has been a shift in the distribution of juvenile plaice to the waters that remained open to bottom trawlers. Here we examine the hypothesis that bottom trawling benefits the small benthic invertebrates that form the food source for plaice and that the plaice box had a negative impact on food production for plaice. A size-based model of benthic communities indicates that the production of prey was low without trawling and maximal in areas that are trawled once to twice a year. Therefore, bottom disturbance may improve the feeding conditions for species that feed on small invertebrates. As plaice aggregate at the locations with the highest benthic biomass, this may explain the observed redistribution to areas outside the plaice box. We conclude that the plaice box may not have been the most appropriate measure to protect plaice from discarding and that the species’ ecology should be considered when choosing the most appropriate management measure to achieve an objective.

Effects of heavy metal contamination on the macrobenthic fauna in estuaries: The case of the Seine estuary

Heavy metal contamination levels are generally higher in estuaries than in the open sea. Some estuaries, the Seine estuary for example, have particularly high pollution levels of metals, yet continue to support a very high benthic biomass and remain quite productive. Measurements of sediment contamination are highly variable due to diverse chemical analysis methods, sediments origin and sources of contaminants found in the estuaries. Salinity appears to be the principal factor controlling contaminant distribution in the sediment and the overlying and/or interstitial waters; it also affects the bioavailability of contaminants in estuarine sediments. Of course, the response to contaminants varies greatly among species and assemblages. Trace metals explain only a small part of the variation in benthic community structure. Some species, such as the shrimp Crangon crangon, appears vulnerable to metal pollution, while other species, such as Scrobicularia plana, are able to tolerate quite high levels of cadmium in their tissue. This paper demonstrates the wide variability of benthic responses to contamination, which is probably due to the high spatio-temporal heterogeneity of the estuary. To reduce the problems due the heterogeneity and variability observed to date in the available results, it will be necessary to encourage integrated estuarine studies, in which sedimentologists, chemists, and biologists work together on the same campaigns at the same sites.

Multi-decadal synthesis of benthic–pelagic coupling in the western arctic: Role of cross-shelf advective processes

Abstract Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m−2) and chlorophyll (>150 mg m−2) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll,

Recent research on Arctic benthos: common notions need to be revised

Increased public awareness of the global significance of polar regions and opening of the Russian Arctic to foreign researchers have led to a pronounced intensification of benthic research in Arctic seas. The wealth of information gathered in these efforts has markedly enhanced our knowledge on the Arctic benthos. While some scientific concepts have been corroborated by the novel findings (e.g., low endemism and high faunistic affinity to northern Atlantic assemblages), other common notions need to be revised, particularly with regard to the often-cited differences between Arctic seas and the Southern Ocean. It has been demonstrated that benthos assemblages vary broadly in diversity between Arctic regions and that, hence, the idea of a consistently poor Arctic benthos—being in stark contrast to the rich Antarctic bottom fauna—is an undue overgeneralization. In terms of biogeographic diversity, both Arctic and Antarctic waters seem to be characterized by intermediate species richness. Levels of disturbance—a major ecological agent known to heavily affect benthic diversity and community structure—have been assumed to be relatively high in the Arctic but exceptionally low in the Southern Ocean. The discovery of the great role of iceberg scouring in Antarctic shelf ecosystems, which has largely been overlooked in the past, calls for a reconsideration of this notion. The novel data clearly demonstrate that there are marked differences in geographical and environmental setting, impact of fluvial run-off, pelagic production regime, strength of pelago–benthic coupling and, hence, food supply to the benthos among the various Arctic seas, impeding the large-scale generalization of local and regional findings. Field evidence points to the great significance of meso-scale features in hydrography and ice cover (marginal ice zones, polynyas, and gyres) as ‘hot spots’ of tight pelago–benthic coupling and, hence, high benthic biomass. In contrast, the importance of terrigenic organic matter discharged to the Arctic seas through fluvial run-off as an additional food source for the benthos is still under debate. Studies on the partitioning of energy flow through benthic communities strongly suggest that megafauna has to be adequately considered in overall benthic energy budgets and models of carbon cycling, particularly in Arctic shelf systems dominated by abundant echinoderm populations. Much progress has been made in the scientific exploration of the deep ice-covered Arctic Ocean. There is now evidence that it is one order of magnitude more productive than previously thought. Therefore, the significance of shelf–basin interactions, i.e., the importance of excess organic carbon exported from productive shelves to the deep ocean, is still debated and, hence, a major topic of on-going research. Another high-priority theme of current/future projects are the ecological consequences of the rapid warming in the Arctic. Higher water temperatures, increased fluvial run-off and reduced ice cover will give rise to severe ecosystem changes, propagating through all trophic levels. It is hypothesized that there would be a shift in the relative importance of marine biota in the overall carbon and energy flux, ultimately resulting in a switch from a ‘sea-ice algae–benthos’ to a ‘phytoplankton–zooplankton’ dominance.

Habitat selection by ice-associated pinnipeds near St. Lawrence Island, Alaska in March 2001

Aerial surveys of ice-associated pinnipeds were conducted south of St. Lawrence Island in March 2001. The observed distributions of bearded seals (Erignathus barbatus), ribbon seals (Phoca fasciata), ringed seals (P. hispida), spotted seals (P. largha), and walruses (Odobenus rosmarus) were compared to the distributions of ice habitat types and benthic communities. Randomization tests were used to investigate habitat selection for each species. Both ringed seals and walruses preferred large ice floes (>48 m in diameter) that were common in the interior ice pack. Spotted seals favored smaller ice floes (<20 m in diameter) common near the ice edge, and bearded seals avoided large floes and preferred transitional habitat between small and large floes. Ringed seals also seemed to prefer areas with greater than 90% sea ice coverage, and bearded seals preferred 70–90% sea ice coverage while avoiding areas with greater than 90% coverage. All species, except spotted seals, were seen most frequently in a region of high benthic biomass, and randomization tests suggested that bearded seals actively selected that region.

Effects of clam species dominance on nutrient and energy acquisition by spectacled eiders in the Bering Sea

The spectacled eider Somateria fischeri, a 'threatened' species, winters in pack ice of the Bering Sea. In dives of 40 to 70 m for benthic invertebrates, the high energy costs of foraging are offset by high benthic biomass. However, there is evidence that the dominant clam prey has changed from Macoma calcarea to Nuculana radiata, perhaps adversely affecting the foraging energetics of the eiders. We studied effects of differences in nutrient and energy content, crushing resistance of shells, digestibility, gut retention time, areal density, shell length, and depth in the sediments on the relative foraging value of M. calcarea versus N. radiata. To avoid using a 'threatened' species for experiments, we used common eiders Somateria mollissima for digestion studies and white-winged scoters Melanitta fusca (the same size as spectacled eiders) for foraging studies. For the prey size range comprising 93% of the eiders' diet (18 to 30 mm), M. calcarea including shells was lower in ash, and higher in nitrogen, lipid, and energy, than N. radiata. Digestibility was 76% for M. calcarea ver- sus 67% for N. radiata, but gut retention time did not differ. In a tensometer, crushing resistance was much higher for N. radiata than M. calcarea for shells 18 to 24 mm long, but did not differ for 24 to 30 mm because shells of N. radiata were often severely abraded. For scoters foraging on freshly thawed Macoma balthica buried in sand in an aquarium 1.8 m deep, intake (no. s -1 ) decreased by 31% when burial depth in the sediments was increased from 4 to 7 cm; most N. radiata are <4 cm deep, and most M. balthica eaten by eiders are probably 7 to 10 cm deep. Considering energy con- tent, digestibility, and intake rates at these burial depths for 1200 clams m -2 , energy assimilated was 14 to 19% higher for N. radiata than M. calcarea of the same length classes. However, larger M. cal- carea yielded 58% higher intake of assimilable energy than smaller N. radiata. These patterns emphasize that relative foraging value depends strongly on size (age) structures of different prey populations, which vary with recruitment, growth, and mortality in different seasons and years. Our results show that impacts of long-term benthic change on eiders depend not only on shifts in total clam abundance, but also on species differences in digestibility, size structure, and size-dependent nutrient content and burial depth.

Seasonal variation in sedimentation of organic materials in the St. Lawrence Island polynya region, Bering Sea

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 226:13-26 (2002) - doi:10.3354/meps226013 Seasonal variation in sedimentation of organic materials in the St. Lawrence Island polynya region, Bering Sea Lee W. Cooper1,*, Jacqueline M. Grebmeier1, Inguar L. Larsen2, Victor G. Egorov3, Chris Theodorakis4, Holly P. Kelly1, James R. Lovvorn5 1Department of Ecology and Evolutionary Biology, 569 Dabney Hall, University of Tennessee, Knoxville, Tennessee 37996, USA 2Teledyne Brown Engineering, 108 Quality Lane, Knoxville, Tennessee 37931, USA 3Institute of Energy Problems of Chemical Physics (Branch), 142432 Chernogolovka (Moscow Region), Russia 4Institute of Environmental and Human Health, Texas Tech University, PO Box 41163, Lubbock, Texas 74049-1163, USA 5Department of Zoology, University of Wyoming, Laramie, Wyoming 82071, USA *E-mail: lcooper1@utk.edu ABSTRACT: A polynya that forms each winter south of St. Lawrence Island in the Bering Sea is located near very high standing stocks of macrobenthic invertebrates on this Arctic continental shelf. Sampling during or just after the ice melt in 1990, 1993, and 1994 revealed water-column, sediment particle and chemical distributions that were consistent with a high flux of organic materials to the sediments during the ice retreat. In contrast, lower phytoplankton biomass observed in late summer and fall of 1993, 1998, and 1999 was associated with seasonal declines in sedimentation indicators such as chlorophyll a in the water column and deposited on the surface sediments, lower occurrences of an atmospherically derived radionuclide beryllium-7 (7Be) in surface sediments, and lower sediment oxygen demand. Moreover, observations under late-winter conditions in April 1999 did not support a direct, continuous linkage between water-column production when the winter polynya is active and the very high benthic biomass and productivity observed on this shallow (30 to 60 m) shelf. For example, deposition of recent water-column production to the sediments in April was significantly lower than that during and just after the ice retreat in May and June. This lower rate of deposition in April was inferred from proxy indicators including photosynthetically-competent chlorophyll extractable from surface sediments, the presence of 7Be in surface sediments, and sediment oxygen demand. Despite high nutrient concentrations, water-column chlorophyll a concentrations were also uniformly lower (0.5 to 2 mg m-3) in April than in May and June. Measurements of the underwater light and ultraviolet radiation field and analysis of DNA damage to dosimeters indicated that the low chlorophyll a biomass is probably not influenced by UV radiation in late winter and early spring. The stable carbon isotope composition of organic carbon in surface sediments suggests that open-water production in the polynya, relative to the adjacent production of sea-ice algae, is not large enough to influence the isotopic composition of organic materials in surface sediments near the polynya. KEY WORDS: Bering Sea · Polynya · Benthic-pelagic coupling · Beryllium-7 · Ultraviolet radiation · Carbon isotopes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 226. Online publication date: January 31, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Episodic particulate fluxes at southern temperate mid-latitudes (42–45°S) in the Subtropical Front region, east of New Zealand

Sediment traps were deployed for almost 1 yr at two sites near 178°40′E in 1996–1997 on Chatham Rise (New Zealand). These sites were either side of the Subtropical Front (STF), which is a biologically productive zone, characterised by moderate atmospheric CO 2 uptake. At each site, PARFLUX sediment traps (Mk 7G–21) were deployed at 300 and 1000 m in 1500 m water depth. At 42°42′S, north of the STF, approximately 80% of the integrated total mass, POC and biogenic silica flux at 300 m occurred in a 7-day pulse in austral mid-spring (1064, 141 and 6 mg m −2 d −1, respectively, in early October). This pulse was recorded a week later in the 1000 m trap, indicating a particle sinking rate of 100 m d −1. In contrast, at 44°37′S, south of the STF, the main flux of total mass and biogenic silica occurred 3 weeks later in late spring (289 and 3 mg m −2 d −1, respectively, in early November). Organic carbon, nitrogen and phosphorus fluxes were persistently high over spring at the southern site, although total POC flux integrated over 3 months was only 60 mg m −2 d −1. Thus, up to 2–3 times more material was exported north of the STF, compared with fluxes measured <200 km away to the south. As an integrated proportion of the annual total mass flux, however, more organic carbon was exported south of the STF (17% cf. 5–14%). Furthermore, organic material exported in spring from southern waters was labile and protein-rich (C : N — 8–16, C : P — 200–450, N : P — 13–36), compared to the more refractory, diatom-dominated material sinking out north of the STF in spring (C : N 9–22, C : P 50–230, N : P 5–19). These observations are consistent with anomalously high benthic biomass and diversity observed on south Chatham Rise. Resuspension and differential particle settling are probable causes for depth increases in particulate flux. Estimated particle source areas may be up to 120 km away due to high levels of mesoscale activity and mean flow in the STF region.

Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. Ill Benthic food supply and carbon cycling

Benthic carbon c y c h g in the northern Bering and Chukchi Seas was hypothesized to be regulated by variable primary production regimes in the overlying water: the highly productive (-250 to 300 g C m-2 yr-l) Bering Shelf-Anadyr Water (BSAW) and the less productive (-50 g C m-2 yr-l) Alaska Coastal Water (ACW). Sediment oxygen uptake was correlated with water column parameters and surface sediment C/N ratios characteristic of each water type. Total sediment oxygen uptake rates decreased from a mean 19.2 mm01 O2 m-2 d-' in BSAW to a mean 8.7 mm01 O2 m-' d-' in ACW. Mean benthic aerobic respiration rates significantly varied interannually in BSAW, although they were consistently 2 to 3 times greater in BSAW than in ACW within any one year, indicating that interannual variability in water column primary production may have a direct influence on the availability of organic carbon to the benthos. The explanation for higher respiration rates in the benthos beneath BSAW negates an expected reduction due to colder temperatures. A reduction in organic matter to the benthos in ACW apparently limits benthic metabolism even at higher temperatures. Macrofaunal respiration and bioturbation in high benthic biomass regions were important components in benthic carbon cycling.

Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. I. Food supply source and benthic bio-mass

The shelf waters of the northern Bering and Chukchi Seas are ice-covered for 7 mo of the year, but despite thls harsh environment, they are characterized by high benthic biomass. Coupling between water column primary production and the benthos was investigated in summers 1984 to 1986 by measurements of sediment characteristics in relation to those of the water column. Low surface sediment C/N ratios (5.8 to 7.6) suggested a higher quality, nitrogen-rich marine carbon supply to the benthos in the highly productive (ca 250 to 300 g C m-' yr-') Bering Shelf-Anadyr Water (BSAW) compared to lower quality, higher C/N ratios (7 7 to 14 0) in sediment under the less productive (ca 50 g C m-' yr-l) Alaska Coastal Water (ACW). Stable carbon isotope ratios suggested a manne origin for organic matter in BSAW compared to a mixture of manne and terrestrial input in ACW. Mean benthic biomass was significantly different between water locations, with mean benthic biomass decreasing from 20.2 g C m-* under BSAW to 6.3 g C m-2 under ACW Summer benthic biomass remained seasonally constant for the 3 yr. Benthic communities underlying BSAW received a high quality marine food supply on a regular basis interannually, while those in ACW received an interannually variable amount of temgenous organic matter in addition to marine organic matter. We conclude that the quality and quantity of organic carbon deposited to the benthos directly influence benthic biomass.

Abyssal benthos of the central Indian Ocean

Quantitative studies of the abyssal benthos (3600 to 5300 m) of the central Indian Ocean show a rich fauna and high standing crops. Density of 3 meiofaunal and 12 macrofaunal taxa are large (2175 to 15233; x = 6441 m −2) Polychaetes (41.6%), peracarid crustaceans (31.7%), ophiuroids (12.2%), echiuroid-bryozoa (9.7%), molluscs (4.8%), and agglutinating rhizopod protozoans form the macrofauna. Meiofaunal taxa are nematodes (69.4%), harpacticoid copepods (26.6%), and ostracods (4%). Meiofauna abundances are positively correlated with distance from shore, whereas the distribution and abundance of macrofauna are independent of variations in depth and distance from the shore. Ratio of macro to meiofauna in the total population is 1 to 31. The benthic standing crop is uniformly high (0.54 to 13.73 g m −2; x = 2.70 g m −2) and many times larger than previously reported for comparable depths in other oceans and from the same region. Biomass values are significantly related to distance from shore and the type of substratum. Contribution of macro and meiofauna to the total standing crop was in the ratio of 31 to 1. High benthic biomass and rich fauna are consequences of high organic production in the euphotic zone. The correlation between biomass of the total oxidizable organic matter in the water column and the benthic standing crop is statistically significant ( r = −0.64) at the P < 0.05 level. Rich fauna and high standing crop were associated with the occurrence of polymetallic nodules.