Food web flows through a sub-arctic deep-sea benthic community

The benthic food web of the deep Faroe–Shetland Channel (FSC) was modelled by using the linear inverse modelling methodology. The reconstruction of carbon pathways by inverse analysis was based on benthic oxygen uptake rates, biomass data and transfer of labile carbon through the food web as revealed by a pulse-chase experiment. Carbon deposition was estimated at 2.2 mmol C m⁻² d⁻¹. Approximately 69% of the deposited carbon was respired by the benthic community with bacteria being responsible for 70% of the total respiration. The major fraction of the labile detritus flux was recycled within the microbial loop leaving merely 2% of the deposited labile phytodetritus available for metazoan consumption. Bacteria assimilated carbon at high efficiency (0.55) but only 24% of bacterial production was grazed by metazoans; the remaining returned to the dissolved organic matter pool due to viral lysis. Refractory detritus was the basal food resource for nematodes covering ∼99% of their carbon requirements. On the contrary, macrofauna seemed to obtain the major part of their metabolic needs from bacteria (49% of macrofaunal consumption). Labile detritus transfer was well-constrained, based on the data from the pulse-chase experiment, but appeared to be of limited importance to the diet of the examined benthic organisms (<1% and 5% of carbon requirements of nematodes and macrofauna respectively). Predation on nematodes was generally low with the exception of sub-surface deposit-feeding polychaetes that obtained 35% of their energy requirements from nematode ingestion. Carnivorous polychaetes also covered 35% of their carbon demand through predation although the preferred prey, in this case, was other macrofaunal animals rather than nematodes. Bacteria and detritus contributed 53% and 12% to the total carbon ingestion of carnivorous polychaetes suggesting a high degree of omnivory among higher consumers in the FSC benthic food web. Overall, this study provided a unique insight into the functioning of a deep-sea benthic community and demonstrated how conventional data can be exploited further when combined with state-of-the-art modelling approaches.     

崂山湾潮间带食物网结构的碳稳定同位素初步研究

通过对1993年8月和1994年2和5月在崂山湾潮间带采集的底栖生物碳稳定同位素组成(δ13C值)的分析,发现该区底栖动物的主要食物来源以δ13C值大致可划分为4类:水体中的颗粒有机质(POM)、底栖硅藻、大型底栖藻类和底泥中的有机物质(SOM).研究结果表明,底栖动物的碳稳定同位素组成与其所摄食的食物的碳稳定同位素组成有密切的关系,因此,底栖动物的碳稳定同位素组成可以用于研究其食物来源.碳稳定同位素数据证实,双壳类等滤食性动物的食物来源主要是POM;甲壳动物的δ13C值的范围较大,证明其食物来源的多样性;底栖硅藻是多数腹足类食物来源的相当重要组成部分.用碳稳定同位素示踪剂对该区底栖-水体耦合作用的初步研究表明,水体中的POM是底栖动物的重要食物来源,但底泥中有机质和底栖硅藻也是许多底栖动物食物来源的相当重要的组成部分.     

A preliminary study on benthos food web structure of tidal zone in the Laoshan Bay by using stable carbon isotopes

By analyses of carbon isotopic composition(δ¹³C values) of the benthos collected in the Laoshan Bay in August 1993 and February and May 1994, it is found that the main food sources of the benthos can be divided into four groups in terms of carbon isotope composition: Particulate Organic Matter (POM),benthic diatoms, benthic macroalgae and the organic matter in sediments.The results show that the carbon isotopic composition of the benthic animals has a close relation with that of the food they take in.The carbon isotopic compositions of benthos may be useful in elucidating their food sources.The carbon isotopic data have confirmed that POM is the main food source of the benthic filter feeders such as bivalves; crustaceans have a wide range of δ¹³C values, showing their food source has diversity; benthic diatoms are an important fraction of the food for most of gastropods.A preliminary investigation of the benthic-pelagic coupling in that region using the stable carbon isotopic tracers has confirmed the importance of POM as a food source for benthos in this region,but the organic matter in sediments and benthic diatoms are also relatively important for a lot of benthic animals.The benthic-pelagic coupling in the Laoshan Bay temperate ecosystem is not so tight as that in ecosystems at higher latitudes such as north-eastern water polynya.     

Biological Responses to Seasonally Varying Fluxes of Organic Matter to the Ocean Floor: A Review

Deep-sea benthic ecosystems are sustained largely by organic matter settling from the euphotic zone. These fluxes usually have a more or less well-defined seasonal component, often with two peaks, one in spring/early summer, the other later in the year. Long time-series datasets suggest that inter-annual variability in the intensity, timing and composition of flux maxima is normal. The settling material may form a deposit of “phytodetritus” on the deep-seafloor. These deposits, which are most common in temperate and high latitude regions, particularly the North Atlantic, evoke a response by the benthic biota. Much of our knowledge of these responses comes from a few time-series programmes, which suggest that the nature of the response varies in different oceanographic settings. In particular, there are contrasts between seasonal processes in oligotrophic, central oceanic areas and those along eutrophic continental margins. In the former, it is mainly “small organisms” (bacteria and protozoans) that respond to pulsed inputs. Initial responses are biochemical (e.g. secretion of bacterial exoenzymes) and any biomass increases are time lagged. Increased metabolic activity of small organisms probably leads to seasonal fluctuations in sediment community oxygen consumption, reported mainly in the North Pacific. Metazoan meiofauna are generally less responsive than protozoans (foraminifera), although seasonal increases in abundance and body size have been reported. Measurable population responses by macrofauna and megafauna are less common and confined largely to continental margins. In addition, seasonally synchronised reproduction and larval settlement occur in some larger animals, again mainly in continental margin settings. Although seasonal benthic responses to pulsed food inputs are apparently widespread on the ocean floor, they are not ubiquitous. Most deep-sea species are not seasonal breeders and there are probably large areas, particularly at abyssal depths, where biological process rates are fairly uniform over time. As with other aspects of deep-sea ecology, temporal processes cannot be encapsulated by a single paradigm. Further long time-series studies are needed to understand better the nature and extent of seasonality in deep-sea benthic ecosystems. This revised version was published online in August 2006 with corrections to the Cover Date.     

基于碳、氮稳定同位素的雅浦海沟底栖生物食物来源和营养级初探

为了分析雅浦海沟中底栖生物群落的食物来源和营养级,本研究分析了雅浦海沟真光层中浮游植物和浮游动物、海底沉积物和巨型底栖生物（海绵、海参、海蛇尾、海星、海葵和钩虾）中的碳、氮稳定同位素组成。研究发现雅浦海沟真光层中的浮游植物和浮游动物δ13C值[（-22.8±0.4）‰和（-21.8±0.8）‰]和δ15N值[（5.4±0.4）‰和（6.8±0.2）‰]与巨型底栖生物的δ13C值（-20.1‰~-16.8‰）和δ15N值（11.9‰~17.9‰）的差异超过了一个营养级,表明作为底栖生物的初始食物来源的浮游植物和浮游动物在向下输送的过程中经历了食物链传递和细菌的降解。巨型底栖生物的δ15N和δ13C值之间无显著的相关性,此外不同物种之间营养级也存在明显差异,表现为海绵的营养级相对较高（3.4~4.7）,海参（3.3~3.6）、海蛇尾（3.4~3.5）和海星（3.2~3.7）的营养级较为接近,钩虾（2.9~3.3）和海葵（3.1）的营养级则相对略低,反映了底栖生物不同物种之间食物来源的多样化。     

Diets of eight fish species from the upper slope off the Wairarapa coast,North Island,New Zealand,with notes on the diets of others

The diets of eight demersal fish species from the upper continental slope (c. 24CM‐50 m) were determined from samples taken during late January and early February 2004, off the Wairarapa coast, North Island, New Zealand. Diets were from a combination of benthopelagic and benthic sources, with most species exhibiting ontogenetic shifts in diet, in that larger‐bodied food (fish and/or natant decapod prawns) was more important in the diets of larger fish. Javelinfish (Lepidorhynchus denticulatus), silver roughy (Hoplostethus mediterraneus), and capro dory (Capromimus abbreviatus) had predominantly benthopelagic diets, whereas the diets of sea perch (Helicolenus percoides), Bollons’ rattail (Caelorinchus bollonsi), two‐banded rattail (C. biclinozonalis), and silverside (Argentina elongata) were predominantly benthic, with the crab Carcinoplax victoriensis an important food item. The diet of Oliver's rattail (C. oliverianus) was a mix of benthopelagic and benthic organisms. Generally, levels of dietary overlap between the eight species were low. Overall, the diets of these fish probably reflect regional and seasonal levels of food availability. Notes on food observed in the stomachs of a further 18 species, for which there were fewer than 10 stomach samples per species are also provided.     

Vertical Distribution of Meiobenthos in Bathyal Sediments of the Eastern Mediterranean Sea: Relationship with Labile Organic Matter and Bacterial Biomasses

Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments.     

Bacterioplankton and bacteriobenthos of the Amur estuary and the adjacent areas in the Summer of 2006

This work presents the results of the study of the plankton and benthic microbiocenoses of the Amur estuary. It is shown that the distribution of the total abundance and indicator groups of the bacteriobenthos are characterized by stronger heterogeneity compared with the bacterioplankton and that it depends on the Amur river drainage and the bottom type. The river drainage helps by increasing the overall bacterioplankton abundance in the near-mouth part of the estuary. Microorganisms utilizing low concentrations of OM play a major role in the processes of the OM utilization in the water and bottom sediments. Saprophytic bacteria play a significant role in the OM utilization only in the water at certain sampling sites in the Tatarskiy Strait and Sakhalin Bay and in the bottom sediments taken in the mouth part of the estuary. Some parts of the estuary subject to organic contamination are found according to the microbiological characteristics. It is shown that the fluctuation of the salinity leads to a change of the share of bacteria with different food demands in the microbial community.     

Water Flow, Trophic Depletion, and Benthic Macrofauna Impoverishment in a Submarine Cave from the Western Mediterranean

Abstract. Biotic zonation and severe impoverishment of benthic macrofauna are two of the most conspicuous features of submarine caves. The prevailing explanation assumes trophic depletion caused by reduction of water flow. However, no isolation of water was found in the studied Catalan submarine cave, even in the wall microlayer. Fluorescein diffusion was so fast that it was detectable everywhere in the cave already only a few minutes after the injection. The rate of dissolution of plaster spheres was even greater in the cave than in a nearby tunnel – without benthic macrofauna impoverishment – showing a considerable water flow. The oxygen concentration of water in dialysis bags placed at varying distances from the cave walls showed that no wall microlayer gradients were present.
Biochemical gradients did not indicate any decrease in food supply. Although photosynthetic pigment concentration generally decreased inside the cave, and although the gradients were not linear but formed different patterns throughout the cave, the BOD₅, the POM, the C:N ratio, the [³H]-thymidine incorporation rate, and the ETS activity were higher in the inner part of the cave. There was an accumulation of detritic material and bacteria in the inner parts that constitute a plausible food supply for benthic macrofauna.
If neither water motion nor food supply can be invoked, research into the causes of zonation and disappearence of benthic macrofauna is proposed to be carried out on biotic interactions and behavioural processes.     

Regional decoupling between NW Atlantic barnacle recruit and adult density is related to changes in pelagic food supply and benthic disturbance

We investigated the regional variation in barnacle (Semibalanus balanoides) recruit and adult abundance on the NW Atlantic coast. At the end of the recruitment season (June–July), we sampled wave-exposed rocky intertidal sites in two regions on the open Atlantic coast (Maine, AM, and Nova Scotia, AN) and in two regions on the Gulf of St. Lawrence coast (Northumberland Strait, GN, and Cape Breton Island, GC). Recruit density was highest in the southernmost region (AM), followed by GN and, then, by AN and GC. Regional values of nearshore primary productivity (satellite data of chlorophyll-a concentration, a surrogate for phytoplankton abundance) were highest for AM and GN, suggesting that food supply (barnacles are filter feeders) is an important factor determining regional recruitment patterns. Adult barnacle density was regionally decoupled from recruit density. Adults occurred in very low abundances on the Gulf of St. Lawrence coast (GN and GC) and were relatively abundant on the Atlantic coast (AM and AN), although always in much lower abundances than recruits. The low adult densities on the Gulf of St. Lawrence coast seem to result mainly from intense ice scour, as this coast freezes extensively every winter, as opposed to the ice-free Atlantic coast. Ice scour thus appears to override regional recruitment differences in determining adult density. Therefore, our data suggest that both pelagic food supply and benthic disturbance contribute to setting regional patterns in barnacle population structure on the NW Atlantic coast.     

Meiofaunal abundances and faunal similarity on the continental rise off the coast of California

Metazoan meiofauna (e.g., nematodes, benthic copepods) play important roles in deep-sea sediment communities, but information as basic as standing stocks is not known for much of the world ocean. We therefore sampled six stations: one near the 2700-m isobath and one near the 3700-m isobath off northern, central, and southern California. We counted benthic copepods, both Desmoscolecidae and nondesmoscolecid nematodes, kinorhynchs, nauplii, and ostracods from multiple-corer samples. Nematodes from our 2700-m and 3700-m stations, and ostracods and nauplii from our 3700-m stations, were unusually abundant compared to those from other stations from comparable depths in the Pacific.Off California, the abundances of benthic copepods, kinorhynchs, and nondesmoscolecids at the 2700-m stations were significantly greater than those at the 3700-m stations. Abundance of benthic copepods was correlated with the percentage of medium sand in the sediment, so sediment texture could be important to them. That of kinorhynchs was correlated with the concentration of chloroplastic-pigment equivalents and percentage nitrogen, so consumable material from the euphotic zone could be important to them. In contrast to the usual pattern of decreasing abundance with depth, Desmoscolecidae abundance in the central region was greater at the 3700-m than at the 2700-m station.The three regions differed significantly in both kinorhynch and ostracod abundances, independently of depth. In the food-poor deep sea, animals are expected to be more abundant where food is plentiful. Unexpectedly, ostracod abundance was negatively correlated with all food variables. A possible explanation is that the natural enemies of ostracods are abundant where food is abundant.Multivariate faunal similarity at 2700 m differed significantly from that at 3700 m, independently of regions. Benthic copepods were most responsible for the difference. Regions also differed in multivariate faunal similarity independently of depth. In general, faunal similarity is expected to decrease as separation distance increases, but unexpectedly, the northern- and southern-region faunas were more similar to each other than to the central-region fauna. Kinorhynchs were most responsible for this pattern.     

Floating mucus aggregates derived from benthic microorganisms on rocky intertidal reefs: Potential as food sources for benthic animals

Mucus films, flocs or foams consisting of fine sand, algae and detritus frequently occur in the surface waters of rocky intertidal reef flats during incoming tide. These masses are referred to as mucus aggregates. We examined the developmental process of mucus aggregates and their abundance, distribution, migration and trophic composition. The trophic composition of mucus aggregates was then compared to those of sediments to evaluate their potential nutritional value for benthic animals. The organic matter content, chlorophyll a concentration, microalgal density and bacteria-derived fatty acid contents of mucus aggregates were higher than those observed in sediment, suggesting that mucus aggregates contain not only high levels of organic matter but also dense concentrations of microalgae and bacteria; therefore, mucus aggregates may serve as a qualitatively more energetic food source for benthic fauna compared to sediments. Benthic diatoms were the most abundant organisms in mucus aggregates. Large numbers of diatoms were trapped in fine mineral particles and mucilage-like strings, suggesting that a portion of the mucus is secreted by these benthic microalgae.Mucus aggregate accounted for only 0.01-3.9% of the daily feeding requirements of the dominant detritivore, Ophiocoma scolopendrina (Echinodermata: Ophiuroidea) over the entire sampling area. In contrast, for the species population on the back reef, where mucus aggregates ultimately accumulate, mucus aggregates provided from 0.4 to 113.3% of food for this species. These results suggest that mucus aggregate availability varies spatiotemporally and that they do not always provide adequate food sources for O. scolopendrina populations.     

NotesBenthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata , Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower continental slope- trough b     

Carbon flows in the benthic food web at the deep-sea observatory HAUSGARTEN (Fram Strait)

The HAUSGARTEN observatory is located in the eastern Fram Strait (Arctic Ocean) and used as long-term monitoring site to follow changes in the Arctic benthic ecosystem. Linear inverse modelling was applied to decipher carbon flows among the compartments of the benthic food web at the central HAUSGARTEN station (2500 m) based on an empirical data set consisting of data on biomass, prokaryote production, total carbon deposition and community respiration. The model resolved 99 carbon flows among 4 abiotic and 10 biotic compartments, ranging from prokaryotes up to megafauna. Total carbon input was 3.78±0.31 mmol C m⁻² d⁻¹, which is a comparatively small fraction of total primary production in the area. The community respiration of 3.26±0.20 mmol C m⁻² d⁻¹ is dominated by prokaryotes (93%) and has lower contributions from surface-deposit feeding macro- (1.7%) and suspension feeding megafauna (1.9%), whereas contributions from nematode and other macro- and megabenthic compartments were limited to <1%. The high prokaryotic contribution to carbon processing suggests that functioning of the benthic food web at the central HAUSGARTEN station is comparable to abyssal plain sediments that are characterised by strong energy limitation. Faunal diet compositions suggest that labile detritus is important for deposit-feeding nematodes (24% of their diet) and surface-deposit feeding macrofauna (∼44%), but that semi-labile detritus is more important in the diets of deposit-feeding macro- and megafauna. Dependency indices on these food sources were also calculated as these integrate direct (i.e. direct grazing and predator–prey interactions) and indirect (i.e. longer loops in the food web) pathways in the food web. Projected sea-ice retreats for the Arctic Ocean typically anticipate a decrease in the labile detritus flux to the already food-limited benthic food web. The dependency indices indicate that faunal compartments depend similarly on labile and semi-labile detritus, which suggests that the benthic biota may be more sensitive to changes in labile detritus inputs than when assessed from diet composition alone. Species-specific responses to different types of labile detritus inputs, e.g. pelagic algae versus sympagic algae, however, are presently unknown and are needed to assess the vulnerability of individual components of the benthic food web.     

Benthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out.The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth.Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough.From continental shelf edge to the bottom of Okinawa Trough,benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages:(1) Continental shelf break assemblage,dominated by Cibicides pseudoungerianus,corresponds to subsurface water mass of the Kuroshio Current;(2) upper continental slope assemblage,dominated by Cassidulina carinata,Globocassidulina subglobosa,corresponds to intermediate water mass of the Kuroshio Current;(3) intermediate continental slope assemblage,dominated by Uvigerina hispida,corresponds to the Okinawa Trough deep water mass above the carbonate lysocline.     

不同海产动物和烟台海域不同海区的紫贻贝（Mytilus edulis）对重金属（Cr）富集的研究

产于烟台的５种海产经济动物对Ｃｒ的富集存在明显差异。底栖的滤食性贝类（紫贻贝Ｍ．ｅｄｕｌｉｓ、栉孔扇贝Ｃｈｌａｍｙｓｆａｒｒｅｒｉ、菲律宾蛤仔Ｒｕｄｉｔａｐｅｓｐｈｉｌｉｐｐｉｎｅｎｓｉｓ）的富集量远远超过自游泳的种类（中华马鲛Ｓｃｏｍｂｅｒｏｍｏｒｕｓｓｉｎｅｎｓｉｓ，长额七腕虾Ｈｅｐｔａｃａｒｐｕｓｐａｎｄａｌｏｉｄｅｓ）。紫贻贝为理想的海洋重金属Ｃｒ污染的指示动物．烟台海域各海区紫贻贝体内Ｃｒ含量最高，向边远海区逐渐降低。５种海产动物体内Ｃｒ的含量均在食品允许范围之内。     

Ecosystem dynamics of the Pacific-influenced Northern Bering and Chukchi Seas in the Amerasian Arctic

The shallow continental shelves and slope of the Amerasian Arctic are strongly influenced by nutrient-rich Pacific waters advected over the shelves from the northern Bering Sea into the Arctic Ocean. These high-latitude shelf systems are highly productive both as the ice melts and during the open-water period. The duration and extent of seasonal sea ice, seawater temperature and water mass structure are critical controls on water column production, organic carbon cycling and pelagic–benthic coupling. Short food chains and shallow depths are characteristic of high productivity areas in this region, so changes in lower trophic levels can impact higher trophic organisms rapidly, including pelagic- and benthic-feeding marine mammals and seabirds. Subsistence harvesting of many of these animals is locally important for human consumption. The vulnerability of the ecosystem to environmental change is thought to be high, particularly as sea ice extent declines and seawater warms. In this review, we focus on ecosystem dynamics in the northern Bering and Chukchi Seas, with a more limited discussion of the adjoining Pacific-influenced eastern section of the East Siberian Sea and the western section of the Beaufort Sea. Both primary and secondary production are enhanced in specific regions that we discuss here, with the northern Bering and Chukchi Seas sustaining some of the highest water column production and benthic faunal soft-bottom biomass in the world ocean. In addition, these organic carbon-rich Pacific waters are periodically advected into low productivity regions of the nearshore northern Bering, Chukchi and Beaufort Seas off Alaska and sometimes into the East Siberian Sea, all of which have lower productivity on an annual basis. Thus, these near shore areas are intimately tied to nutrients and advected particulate organic carbon from the Pacific influenced Bering Shelf-Anadyr water. Given the short food chains and dependence of many apex predators on sea ice, recent reductions in sea ice in the Pacific-influenced sector of the Arctic have the potential to cause an ecosystem reorganization that may alter this benthic-oriented system to one more dominated by pelagic processes.     

Antarctic shallow water benthos in an area of recent rapid glacier retreat

The West Antarctic Peninsula is one of the fastest warming regions on Earth. Faster glacier retreat and related calving events lead to more frequent iceberg scouring, fresh water input and higher sediment loads, which in turn affect shallow water benthic marine assemblages in coastal regions. In addition, ice retreat creates new benthic substrates for colonization. We investigated three size classes of benthic biota (microbenthos, meiofauna and macrofauna) at three sites in Potter Cove (King George Island, West Antarctic Peninsula) situated at similar water depths but experiencing different disturbance regimes related to glacier retreat. Our results revealed the presence of a patchy distribution of highly divergent benthic assemblages within a relatively small area (about 1 km²). In areas with frequent ice scouring and higher sediment accumulation rates, an assemblage mainly dominated by macrobenthic scavengers (such as the polychaete Barrukia cristata), vagile organisms and younger individuals of sessile species (such as the bivalve Yoldia eightsi) was found. Macrofauna were low in abundance and very patchily distributed in recently ice‐free areas close to the glacier, whereas the pioneer nematode genus Microlaimus reached a higher relative abundance in these newly exposed sites. The most diverse and abundant macrofaunal assemblage was found in areas most remote from recent glacier influence. By contrast, the meiofauna showed relatively low densities in these areas. The three benthic size classes appeared to respond in different ways to disturbances likely related to ice retreat, suggesting that the capacity to adapt and colonize habitats is dependent on both body size and specific life traits. We predict that, under continued deglaciation, more diverse, but less patchy, benthic assemblages will become established in areas out of reach of glacier‐related disturbance.     

Increased benthic grazing: An alternative explanation for low phytoplankton biomass in northern San Francisco Bay during the 1976–1977 drought

Among the consequences of extremely low river flow into northern San Francisco Bay during a two-year drought were (1) a gradual increase in salinity, (2) an unusual decline in chlorophyll a concentration, and (3) the upstream migration of estuarine benthic invertebrates to the normally brackish area of the bay. Total abundance in the benthos at a shallow monitoring site increased from a normal 2000 to greater than 20 000 individuals m^?2 during the summer of 1977, presumably in response to the increased salinity. Estimated filtration rates derived from equations in the literature for one of the species, the suspended-feeding bivalve Mya arenaria ranged from 1 to 4 m³ m^?2 day^?1 during 1977 depending on abundance and mean size on sampling dates. Because water depth at this site is less than 2 m, Mya could have filtered all of the particles (including diatoms) from the water column on the order of once per day. Several other immigrant species undoubtedly contributed to the removal of particles from the near-bottom water as well. Increased benthic grazing, therefore, could have accounted for the anomalously low phytoplankton biomass observed during the drought. These results suggest that during periods of prolonged low river flow and increased salinity benthic food webs could become more important than planktonic food webs in the upper part of the estuary.     

Food sources of benthic animals on intertidal and subtidal bottoms in inner Ariake Sound,southern Japan,determined by stable isotopes

To evaluate the relative importance of possible food sources, including riverine particulate organic matter, reeds, benthic microalgae, seaweeds, cultured laver (Porphyra) and coastal phytoplankton, for commercial bivalves and co-occurring benthic animals, 73 macrofaunal species were collected from intertidal and subtidal soft bottoms in the inner part of Ariake Sound, Kyushu, southern Japan, and their isotopic compositions were analyzed. The results revealed that (1) both intertidal and subtidal food webs were constituted of 3 trophic levels, (2) suspension-feeding bivalves utilize a mixture of benthic microalgae and coastal phytoplankton, and omnivores and carnivores incorporate benthic microalgae and phytoplankton through their intermediate prey, and (3) 3 bivalves (Scapharca kagoshimensis, Modiolus metcalfei and Atrina lischkeana) inhabiting both intertidal and subtidal bottoms showed similar seasonal fluctuations, suggesting no difference in the diet composition among the species and between the 2 habitats. We conclude that a large biomass of benthic microalgae which was approximately equal to that of phytoplankton and the strong tidal currents that would resuspend benthic microalgae and transport them to subtidal bottom areas account for the benthic microalgal and phytoplankton based trophic structure in the inner part of Ariake Sound.