Abundance Of Benthic Organisms Research Articles

Water quality assessment in an irrigation pond based on adult caddisfly (Insecta: Trichoptera) assemblages

Caddisfly fauna are abundant benthic organisms in freshwater ecosystems and are considered effective bioindicators of water quality. A study of caddisfly biodiversity and its application for use as an indicator species to assess water quality in aquatic environments was conducted in an irrigation pond at the Kasetsart University, Kamphaeng Saen Campus, Nakhon Pathom Province, Thailand. The specimens were sampled monthly from January to December 2020 by portable light traps. A total of 2,771 adult male caddisflies, representing 7 families, 14 genera, and 30 species, were determined over a period of one year. The four most common species (Setodes gangaya, Cheumatopsyche lucida, Paduniella sampati, and Ecnomus puro) made up approximately 75.49% of the total male abundance. Canonical correspondence analysis (CCA) showed that nitrate-nitrogen, ammonia-nitrogen, sulfate, pH, and dissolved oxygen were the most influential environmental parameters on Trichoptera assemblages. Caddisfly species Ecnomus puro, E. mammus, and E. utto were positively related to sulfate, whereas Leptocerus lampunensis, Setodes melanippos, and Cheumutopsyche schwendingeri were negatively related. Species of Paduniella sampati, Pseudoneureclipsis tramot, Setodes gangaya, and Leptocerus dirghachuka were positively related to nitrate-nitrogen. The results of this study revealed that the order Trichoptera, identified by species, can be potentially used to assess environmental water quality status in freshwater ecosystems.

Seasonal Dietary Shifts of the Gammarid Amphipod Gondogeneia antarctica in a Rapidly Warming Fjord of the West Antarctic Peninsula

The amphipod Gondogeneia antarctica is among the most abundant benthic organisms, and a key food web species along the rapidly warming West Antarctic Peninsula (WAP). However, little is known about its trophic strategy for dealing with the extreme seasonality of Antarctic marine primary production. This study, using trophic markers, for the first time investigated seasonal dietary shifts of G. antarctica in a WAP fjord. We analyzed δ13C and δ15N in G. antarctica and its potential food sources. The isotopic signatures revealed a substantial contribution of red algae to the amphipod diet and also indicated a significant contribution of benthic diatoms. The isotope results were further supported by fatty acid (FA) analysis, which showed high similarities in FA composition (64% spring–summer, 58% fall–winter) between G. antarctica and the red algal species. G. antarctica δ13C showed a small shift seasonally (−18.9 to −21.4‰), suggesting that the main diets do not change much year-round. However, the relatively high δ15N values as for primary consumers indicated additional dietary sources such as animal parts. Interestingly, G. antarctica and its potential food sources were significantly enriched with δ15N during the fall–winter season, presumably through a degradation process, suggesting that G. antarctica consumes a substantial portion of its diets in the form of detritus. Overall, the results revealed that G. antarctica relies primarily on food sources derived from benthic primary producers throughout much of the year. Thus, G. antarctica is unlikely very affected by seasonal Antarctic primary production, and this strategy seems to have allowed them to adapt to shallow Antarctic nearshore waters.

Natural Recovery of the Crab Ucides cordatus (Ocypodidae) in Replanted Mangroves on the Brazilian Amazon Coast

The recovery of degraded mangroves may favor the reestablishment of the diversity and abundance of benthic organisms, including those of commercial importance. Here, we assessed (i) the degree of population recovery of the exploited mangrove crab Ucides cordatus in nine areas of replanted mangroves, and (ii) the influence of dominant mangrove species on density and population parameters of this species. Our results indicate that the U. cordatus population has been reestablished successfully in all replanted areas. A total of 1620 inhabited burrows (1.8 ± 0.5 burrows m−2) were counted, and 423 crabs were captured (57.7% males and 42.3% females). Almost a third (33.2%) of the male crabs was of legally harvestable size (6.4 ± 0.3 cm carapace width), while the others (66.8%; 5.0 ± 0.8 cm) can be considered for future fishery. The densities of burrows were higher in areas dominated by R. mangle and L. racemosa. Both males and females were larger in areas dominated by L. racemosa, while they were heavier at the sites dominated by R. mangle and L. racemosa. The return of the local crab population exhibiting density and structure similar to those found in preserved habitats highlights the success of the rehabilitation of impacted mangroves.

Abundance and diversity of black flies (Diptera: Simuliidae) in rivers of the Andean Eastern Hills of Bogotá (Colombia),

Black flies are abundant benthic organisms in well-oxygenated running water and are considered effective bioindicators of water quality. Information on the ecology of these organisms at the species level is important, since up to now information has mainly been available on a family level. The aim of this study was to evaluate the composition of black flies and their relationships to a group of physical and chemical factors in four small rivers of the Eastern Hills around Bogotá, Colombia. These headwaters are protected by the Empresa de Acueducto y Alcantarillado de Bogotá. Black fly larvae and pupae were collected during four sampling periods during the dry season to the early rainy season of 2012. Multivariate methods were used to determine the presence of each species in relation to dissolved oxygen, nitrates, pH, temperature, and water velocity. PCA ordination revealed a physicochemical environment with a tendency towards a certain homogeneity in the fourrivers studied. The DCA ordination confirmed that in La Vieja River the G. ortizi complex dominated while S. muiscorum was dominant in the other three rivers. Similarly, according to the NMDS, the composition of black flies in Arzobispo and Chorro de Padilla rivers was similar, while that of El Delirio and La Vieja rivers were different, especially in this last river. The rivers hadlow species richness (four species and one species complex). Simulium muiscorum was negatively correlated with dissolved oxygen, temperature and current velocity while S. ignescens was associated with slightly more oxygenated waters and S. furcilatum with fastercurrents.The low species diversity and richness for the four rivers is consistent with previous report sof low Neotropical diversity of black flies. Results showed that simuliid species could possibly be good indicators of the environmental conditions of Eastern Hills rivers around Bogotá.

The impact of trawling on the epibenthic megafauna of the west Greenland shelf

Benthic habitats are important elements of polar marine environments, but can be vulnerable to anthropogenic influences such as trawling. Bottom trawling can reduce diversity and alter communities, although some habitats show resilience. The shrimp trawl fishery of West Greenland is a significant part of Greenland's economy. It operates along the west coast from the narrow rockier shelf of the south, up to deeper, muddy areas around Disko Bay. Here we use a benthic drop camera to sample 201 sites between latitudes 60–72°N and depths of 61–725m. Linear models examined relationships of taxon abundance and diversity with bottom trawling intensity and environment (depth, temperature, current, iceberg concentration). Trawling intensity is the most important factor determining the overall abundance of benthic organisms, accounting for 12–16% of variance, although environmental conditions also show significant associations. Sessile erect organisms such as corals show a significant negative response to trawling. Soft sediment communities show a higher resilience than rocky areas. On soft sediments significantly lower abundance characterises sites trawled under five years ago. On hard/mixed ground reduced abundance remains characteristic of sites trawled a decade ago. Continued monitoring of benthic habitats is an essential part of evaluating the ongoing impacts of trawl fisheries.

Impact on bird fauna of a non-native oyster expanding into blue mussel beds in the Dutch Wadden Sea

Intertidal mussel beds are important for intertidal ecosystems, because they feature a high taxonomic diversity and abundance of benthic organisms and are important foraging grounds for many avian species. After the introduction of the Pacific oyster (Crassostrea gigas) into the European Wadden Sea, many mussel beds developed into oyster dominated bivalve beds. Despite the fact that oysters have been colonizing many European intertidal areas for about two decades, their impact on the ecosystem is still poorly understood. Here, we investigated the impact of oysters on the condition of mussels and on the spatial distribution of birds on 18 bivalve beds with different grades of oyster occurrence throughout the Dutch Wadden Sea. Moreover, in comparing bird densities on bivalve beds with densities expected on the total intertidal area, we could detect which species exhibit a preference for the structured habitat. Overall, 50 different bird species were observed on the beds, of which about half regularly frequent intertidal flats. Most of these species showed a preference for bivalve beds. The condition of mussels decreased with the oyster dominance, whereas the majority of bird species was not affected by the oyster occurrence. However, three of the four species that were negatively affected depend on intertidal mussels as food source. Even though the Pacific oyster is a nonnative species, attempts to fight it may do more harm to avian biodiversity than good.

Benthic Ecology of Northern Quahog Beds with Different Hydraulic Dredging Histories in Long Island Sound

Mercaldo-Allen, R.; Goldberg, R.; Clark, P.; Kuropat, C.; Meseck, S.L., and Rose, J.M., 2016. Benthic ecology of northern quahog beds with different hydraulic dredging histories in Long Island Sound. This paper evaluates benthic community composition of four shellfish beds in Long Island Sound near Milford, Connecticut, where northern quahog or hard clams, Mercenaria mercenaria (Linnaeus 1758), were harvested by hydraulic dredge. These leased beds reflect a variety of dredging histories; 0 year (dredged just before sampling began), 1 year postharvest, 2 years postharvest, and an inactive clam bed left fallow for at least 10 years. Benthic sediment was sampled at 1- to 2-week intervals from June to October 2011 using a Smith–McIntyre grab. Benthic community composition was significantly influenced by dredging history and sampling month. Abundance of benthic organisms (number of individuals and biovolume) and total organic matter concentrations were significantly greater at the 0-year site than at the 1-, 2-, and 10 -year sites, and significantly greater at the 1- and 2-year sites than at the 10 -site. Newly settled bivalves, primarily Nucula spp. and Yoldia limulata, were significantly more prevalent on the recently harvested 0-, 1-, and 2-year sites vs. the 10 -year site and highest at the 0-year site. A significantly greater number of species was observed on the 1- and 2-year sites vs. the 0- and 10 -year locations. Species richness at the 0-year site was significantly lower than at the 1-, 2-, and 10 -year sites, whereas diversity and evenness at the 0-year site was significantly lower than at the 10 -year site. This study observed successional changes in community structure of inshore clam beds related to the length of time elapsed after harvest dredging.

Benthic Faunal Assemblage of the Arctic Kongsfjorden System, Norway

Kongsfjord is an open glacial fjord on the west coast of Svalbard, located northwards to Norway. Benthic samples were collected from seven selected locations as a part of summer Phase III group 2 – Indian Arctic Expedition 2011. The characteristic macro benthic fauna observed in the soft bottom glacial community include Foraminifera, Nematoda, Polychaeta, Bivalvia, Amphipoda, Calanoid copepoda and Ostracoda, out of which polychaetes (59%) and nematodes (21%) were abundant. The meio benthic group was constituted by Nematoda, Foraminifera, Bivalvia, Polychaeta, Harpacticoid copepoda, Gastrotricha, and Kinoryncha, of which nematodes (54%) followed by foraminferans (37%) were the dominant group. A significant difference in the distribution of meio benthos between the inner and outer fjords was observed. Multivariate analysis of macro and meio fauna showed an overall similarity of ~ 80% among stations. The inner and outer fjords were similar in terms of granulomertic composition and were also silt dominated in the entire Kongsfjorden system. Total carbon (TC) and total organic carbon (TOC) were higher in the outer fjord, but the total inorganic carbon (TIC) was slightly higher in the inner fjord. The diversity and abundance of benthic organisms was strongly influenced by sediment characteristics, glacial inputs and Atlantic water mass movements making the ecosystem unpredictable.

Oligochaetes (Annelida, Clitellata) in the Anzali International Wetland, north-western Iran

INTRODUCTION Transitional waters, for example lagoons, represent important but fragile ecosystems in the coastal landscape, providing key ecosystem services such as water quality improvement, fisheries resources, habitat and food for migratory and resident animals, and recreational areas for human populations. The Anzali International Wetland was registered in the Ramsar Convention in 1975 as Ramsar Site #40, Wetlands International Site Reference No. 2IR005 (JICA 2005). The Anzali Wetland complex comprises large, shallow, eutrophic freshwater lagoons, shallow impoundments, marshes, and seasonally flooded grasslands at the south-western coast of the Caspian Sea (Fig. 1). It consists of different aquatic and dry land ecosystems and is a good example of a natural habitat supporting an extremely diverse wetland flora and fauna (Ayati 2003). Oligochaete annelids have a worldwide distribution, being frequently the most abundant benthic organisms in freshwater ecosystems; many species are cosmopolitan (Brinkhurst and Jamieson 1971). They are used in biodiversity studies, pollution surveys, and environmental assessment and have also economic importance (Mason 1996; Wetzel et al. 2000; Rodriguez and Reynoldson 2011). Although many researchers have studied the Anzali Wetland from the pollution-related, faunistic, and ecological points of view (e.g. Ayati 2003; JICA 2005; Charkhabi and Sakizadeh 2006; Akbarzadeh et al. 2008; Jafari 2009; Tahershamsi et al. 2009; Mirzajani et al. 2010; Pourang et al. 2010; Jamshidi-Zanjani and Saeedi 2013), there are no data on the species diversity of the Oligochaeta of the region, except the single record of Tubifex tubifex by Pourang (1996). The aquatic Oligochaeta species of Iran are mentioned only in a few papers: Stephenson (1920), Egglishaw (1980), Aliyev and Ahmadi (2010), Ahmadi et al. (2011, 2012), Ardalan et al. (2011), Jablonska and Pesic (2014). Until now 19 species of aquatic oligochaetes occurring in inland waters of Iran have been recorded. The aim of this study was to evaluate the diversity and distribution of this group and to contribute to the Oligochaeta fauna of both the Anzali Wetland and Iran. MATERIAL AND METHODS Study area The Anzali International Wetland (37[degrees]28' N, 49[degrees]25' W), one of the largest freshwater coastal wetlands of Iran, is located in the Guilan Province at the south-western coast of the Caspian Sea and covers an area of 193 [km.sup.2] (Pourang et al. 2010) (Fig. 1). The main wetland covers about 11 000 ha; it comprises an open freshwater lagoon with a length of 26 km and a width of 2.0-3.5 km, surrounded by reed beds extending its eastern border for another 7 km. Eleven rivers and groundwater seeps feed the wetland. The wetland complex is separated from the Caspian Sea by a dune system; the passage to the sea has a width of 426 m. The wetland supports extensive reed beds and an abundant submerged and floating macrovegetation. Its permanently aquatic portion is surrounded by seasonally flooded marshes and water impoundments, which are also fringed by reed beds and damp grassland. The southern part of the wetland is mainly adjacent to rice fields and patches of woodland, while the northern part borders on sand dunes with grassland and a scrubby vegetation. The wetland consists of four main parts: the western, the central (Sorkhankol Wildlife Refuge), the south-western (Siahkeshim Protected Area), and the eastern; the last part has different physico-chemical, morphologic, phytoecological, and geographical characteristics, including a higher anthropogenic pressure (Ayati 2003). [FIGURE 1 OMITTED] Total precipitation in the Anzali Wetland is about 1500 to 2000 mm [y.sup.-1]. Maximum water depth is about 3 m but it is fluctuating (Jafari 2009). The water depth has decreased, owing to solid sedimentation, in some parts to less than 0.5 m (Ayati 2003). In the last ten years, salinity has slightly increased with the rise of the level of the Caspian Sea, which has caused more intensive mixing of water, as well as with the inflow of salt from increased upstream irrigation. …

Diet of the queen angelfish Holacanthus ciliaris (Pomacanthidae) in São Pedro e São Paulo Archipelago, Brazil

Holacanthus ciliaris is an important benthic-feeding reef fish but the relationship between the composition of its diet and prey availability is still unknown. Here we determined the quantitative composition of the gut contents of H. ciliaris in São Pedro e São Paulo Archipelago, Brazil (SPSPA), and compared it to the abundance of benthic organisms in the area. Holacanthus ciliaris has a relatively diversified diet with more than 30 prey species in SPSPA, especially sponges (13 spp., average 68% of gut contents total weight), algae (12 spp., 25%) and bryozoans (3 spp., 5%). In contrast, the benthic community is composed mainly of algae (average 81% of total cover) and followed by sponges (13%), bryozoans (5%), cnidarians (0.5%), polychaetes (0.5%) and tunicates (0.5%). The most common species were the algae Caulerpella ambigua and Caulerpa racemosa var. peltata; the bryozoan Margaretta buski; and the sponges Scopalina ruetzleri, Chondrosia collectrix and Clathria calla. The Manly resource selection function showed that H. ciliaris preferred the sponges Geodia neptuni, Erylus latens, Clathria calla and Asteropus niger, among others, and avoided common species such as the sponges Scopalina ruetzleri, Dysidea etheria and Hemimycale insularis and the algae Caulerpella ambigua, Bryopsis plumosa and Neomeris annulata. Kendall's rank correlation index showed no significant correlation between prey abundance in the field and in the diet of H. ciliaris, which seems to actively choose relatively rare and less defended prey.

Geochemical and palaeoecological record of the Cenomanian–Turonian Anoxic Event in the carbonate platform of the Preafrican Trough, Morocco

Geochemical analyses (major and trace elements) and palaeontological studies were carried out based on rock samples and thin sections collected from three outcrop sections (Goulmima, Ziz and Tazzouguert) in the upper Cenomanian–lower Turonian in the carbonate platform of the Preafrican Trough (South Morocco), in order to determine if oxygen-depleted conditions affected the platform, and to highlight the possible impact of oxygen variation on carbonate production, particularly during the Oceanic Anoxic Event 2 (OAE2), which took place in the late Cenomanian.During this interval, the carbonate platform was composed of two contrasting environments. A shallow-water environment (peritidal to mid-ramp) was developed in the East (Ziz and Tazzouguert sections), characterized by a high diversity and abundance of benthic organisms, and in some cases, by a high diversity of planktonic organisms, associated with low concentrations of authigenic markers (U, Mo, V and Cr: redox proxies), indicating oxic conditions. In the West (Goulmima section), the environment was deeper (mid ramp/outer ramp) and redox proxies record a high enrichment, an indicator of reducing conditions, associated with a low diversity and abundance of organisms and the presence of Buliminidae. Bottom waters were dysoxic and the palaeoproductivity was low at the sea surface. Thus, during the late Cenomanian, oxygenation conditions were relatively good over the area of the Preafrican Trough, even during the OAE2, except in the deeper environments toward the West, where bottom waters were depleted in oxygen. During the Cenomanian transgression, and more precisely during the OAE2, this dysoxia was linked to the influx of poorly-oxygenated waters from the deeper anoxic basins of the Atlantic and/or Tethys oceans.Geochemical, palaeontological and sedimentological disturbances are recorded in the lower Turonian everywhere in the outer-ramp environments of the platform. Palaeontological proxies show a huge decrease in group diversity, with the disappearance of benthic foraminifera – except for the Buliminidae which proliferated – and only shallow-water planktonic foraminifera survived. Geochemical proxies of redox conditions and palaeoproductivity show a marked enrichment in all three outcrop sections, with higher values in the West. This dysoxia occurred in response to a climatic change, from warm with contrasting seasons to hot and wet, which induced an increase of chemical weathering in the Anti-Atlas to the southwest of the platform. This substantial input of nutrients increased the palaeoproductivity, which finally enhanced the consumption of O2 owing to the decay of organic matter. Moreover, the late Cenomanian transgression led to the supply of additional nutrients to the platform, due to the leaching of soils.

Cumulative ecological impacts of two successive annual treatments of imidacloprid and fipronil on aquatic communities of paddy mesocosms

Agricultural landscapes, including paddies, play an important role in maintaining biodiversity, but this biodiversity has been under the threat of toxic agro-chemicals. Our knowledge about how aquatic communities react to, and recover from, pesticides, particularly in relation to their residues, is deficient, despite the importance of such information for realistic environmental impact assessment of pesticides. The cumulative ecological impacts on aquatic paddy communities and their recovery processes after two successive annual applications of two systemic insecticides, imidacloprid and fipronil, were monitored between mid-May and mid-September each year. The abundance of benthic organisms during both years was significantly lower in both insecticide-treated fields than in the controls. Large-impacts of fipronil on aquatic arthropods were found after the two years. Growth of medaka fish, both adults and their juveniles, was affected by the application of the two insecticides. A Principal Response Curve analysis (PRC) showed the escalation and prolongation of changes in aquatic community composition by the successive annual treatments of each insecticide over two years. Residues of fipronil in soil, which are more persistent than those of imidacloprid, had a high level of impact on aquatic communities over time. For some taxonomic groups, particularly for water surface-dwelling and water-borne arthropods, the second annual treatment had far greater impacts than the initial treatment, indicating that impacts of these insecticides under normal use patterns cannot be accurately assessed during short-term monitoring studies, i.e., lasting less than one year. It is concluded that realistic prediction and assessment of pesticide effects at the community level should also include the long-term ecological risks of their residues whenever these persist in paddies over a year.

The impact of coastal urbanization on the structure of phytobenthic communities in southern Brazil

The anthropogenic pressures on coastal areas represent important factors affecting local, regional, and even global patterns of distribution and abundance of benthic organisms. This report undertakes a comparative analysis of the community structure of rocky shore intertidal phytobenthos in both pristine like environments (PLE) and urbanized environments (UBE) in southern Brazil, characterizing variations on different spatial scales. Multivariate analysis of variance indicated that the PLE is characterized by a larger number of taxa and an increased occurrence of Rhodophyta species in relation to UBE. In contrast, UBE were dominated by opportunistic algae, such as Cladophora and Ulva spp. Significance tests further indicated higher species richness and Shannon–Wiener diversity on the PLE in relation to UBE. Here we provide data showing the magnitude of seaweed biodiversity loss and discuss direct and indirect consequences of unplanned urbanization on these communities.

Life in the sublittoral zone of long-lived Lake Pannon: paleontological analysis of the Upper Miocene Szák Formation, Hungary

Life and depositional environments in the sublittoral zone of Lake Pannon, a large, brackish Paratethyan lake from the Late Miocene, were reconstructed from fossils and facies of the Szák Formation. This formation is exposed in several, roughly coeval (9.4–8.9 Ma) outcrops, located along strike of the paleo-shelf-break in northwestern Hungary. The silty argillaceous marl of the formation was deposited below storm wave base, at 20–30 to 80–90 m water depth. The abundance of benthic organisms indicates that the bottom water was usually well oxygenated. Interstitial dysoxia, however, may have occurred immediately below the sediment–water interface, as evidenced by occasional preservation of trace fossils such as Diplocraterion. The fauna comprised endemic mollusks, including brackish cockles of the subfamily Lymnocardiinae, dreissenid mussels (Congeria), and highly adapted, uniquely large-sized deep-water pulmonate snails (planorbids and lymnaeids). Ostracods were dominated by endemic species and, in some cases, endemic genera of candonids, leptocytherids, cypridids, and loxoconchids. Fish remnants include a sciaenid otolith and the oldest skeletal occurrence of Perca in Europe. The phytoplankton comprised exclusively endemic coccolithophorids, mostly endemic dinoflagellates (prevailingly Spiniferites), and cosmopolitan green algae. The Late Miocene fauna and flora of Lake Pannon were in many ways similar to the modern Caspian biota, and in particular cases can be regarded as its precursor.

Role of peat organic matter on isotopic composition of most abundant benthic organisms in intertidal habitats of SW Iceland

The transfer of peat organic matter (OM) from tidal pools of upper littoral to downstream rocky shores and its potential incorporation into marine biota were investigated using the stable isotope approach. Samplings were carried out in September 2004 in two SW Icelandic sites (Osar and Hvassahraun), where we selected (1) areas with shores where grass gently declined towards rocks and, on reaching the sea line, formed small tidal peat pools and (2) areas where grass and rocky shores were not contiguous, rather the grass lower limits were several hundreds of meters back from the shore. In both grass and no grass areas, in the intertidal zone, all benthic organisms and all potential OM sources were sampled. Dominant macroalgae were Ascophyllum nodosum ([Linnaeus] Le Jolis) and Fucus vesiculosus Linnaeus. In grass sites, organisms partially reflected the isotopic composition of peat OM, while in no grass sites, peat represented only a negligible amount of available OM, or its signal was totally absent from the environment. Intertidal organisms could rely on peat both directly by suspension feeding, grazing or scavenging and indirectly by predation (crabs) on low level consumers (barnacles).

Study of Benthic Fauna in the Discharge Lagoon of a Shrimp Farm With Special Emphasis on the Polychaetes

A study of benthic fauna, with special emphasis on polychaetes, was made in the discharge lagoon of an experimental shrimp farm and a pond of the farm. The discharge lagoon was divided into three sections and stocked with shrimp at low density (6 Pl/m2). Neither formulated feed nor fertilization was used in these sections. The control pond was stocked with shrimp at high density (32 Pl/m2). The pond was fertilized and fed with a commercial shrimp diet. Enclosures of 4 m 2 were made in the sections and control ponds with plastic nets to exclude shrimp. Water quality parameters (temperature, salinity, dissolved oxygen, pH and organic matter) and the nutrients (N-NO2, N-NO3, TAN and P-PO4), were recorded during the study. Abundance and composition of benthic fauna were recorded biweekly in sections and pond. Significant differences in nutrients and organic matter were found among control pond and the discharge sections, with the highest values in the pond. The main benthic groups collected during the study were Chironomidae insect larvae, polychaete worms (Polydora socialis), gammarid crustaceans and gasteropods (Cerithidea sp). Total abundance of benthic organisms was greater in the discharge sections (5657 to 6202) compared with the control pond (5336). The abundance of polychaetes showed the same tendency (2318 to 2681 versus 1697). Total benthic abundance was always lower in sections and pond than in the respective enclosures (6882 to 7606 organisms). The same pattern was found for polychaetes abundance (3386 to 4006 organisms). Temporal variation of polychaetes abundance was mainly related to shrimp predation as confirmed by the more abrupt abundance decline in pond as compared to sections and in pond and sections as compared to the respective enclosures.

Biodiversity and food chains on the littoral bottoms of Lakes Baikal, Biwa, Malawi and Tanganyika: working hypotheses

Boreal Lake Baikal, temperate Lake Biwa, and tropical Lakes Malawi and Tanganyika each possess high biodiversities of benthic organisms in their littoral areas. Two general mechanisms influencing the evolutionary development of these high biodiversities can be hypothesized; i.e., a bottom-up constraint depending on the availability of food resources, and a top-down effect exerted by predators especially within the fish assemblage. The bottom-up constraint may be prominent where the abundance of benthic organisms in the grazing-food-chain is restricted by a seasonally lowest production, referring chiefly to attached algae, and large fluctuations in the abundance of primary producers provide a resource that is eventually utilized by benthic organisms of the detritus-food-chain. The top-down effect may be realized where the most of benthic organisms are supported by a constantly large primary production. These hypotheses help to explain, for the lakes we cite, the facts that diverse grazing-food-chain organisms live on the littoral bottom of tropical lakes where there is relatively constant large algal production due to suitable conditions of water temperature and light penetration through the year; while on the other hand, detritus-food-chain organisms are predominant on the littoral bottom of a boreal lake with seasonally fluctuating algal production and its pronounced lowest production in a year. In fish communities, segregations in habitat and food resource are important mechanisms allowing development of high species packing, while cohabitation within predatory fishes increases their feeding success due to the decrease of defensive efficiency by the threat of a variety of attacking methods. A further top-down effect may be exerted by scale-eating fishes, especially in Lake Tanganyika. The presence of such predatory and harmful members may promote more dense packing of prey members to increase their mutual defense efficiency.

The benthic community in the profundal of Lake Brunnsee: seasonal and spatial patterns

The seasonal distribution of bacteria, flagellates, ciliates, and selected metazoan organisms was investigated in the profundal sediment (18 m depth) of oligotrophic Lake Brunnsee (Germany) over a period of one year (April 1997 to April 1998). Most of the organisms displayed seasonal fluctuation with high abundance in summer and lower spring and autumn densities. Bacteria reached densities up to 2.1 x 10(10) cells/ml, with highest production values in July. Flagellates and ciliates had densities up to 151000 and 4100 cells/ml, respectively. Metazoan organisms were dominated by nematodes with a relative proportion of 76.4%, followed by rotifers with 6.5%. Other benthic taxa contributed less than 5% to overall abundance. Biotic and abiotic variables were tested for their ability to explain the variance in abundance of benthic organisms by means of multiple regression analyses. Vertical distribution of the metazoan organisms was recorded to a sediment depth of 4 cm. Most organisms preferred the uppermost centimetre. Rotifers and gastrotrichs have rarely been found (<15%) below 1 cm depth, while copepods and mites penetrate deeper (more than 60% have been found between 1 and 4 cm sediment depth). Spatial variation in abundance was recorded at a single sampling occasion by taking 16 sediment cores from the profundal of the lake. The spatial variation (differences between the cores) was highest for ciliates and bacteria and low for organic carbon, bacterial production, and bacterial extracellular activity.

Phylogeny of Antarctic Epimeria (Epimeriidae: Amphipoda)

Amphipoda belong to the most abundant benthic organisms of Antarctica, the Epimeriidae being one of the most dominant families. Morphological characters are used to explore relationships between the species of all Antarctic Epimeria , the genus representing 70% of Antarctic epimeriid species. Additional Epimeria from the deep sea off Brazil, the Tasman Sea and from shallow Norwegian waters are analysed. Species of Epimeriella and Metepimeria , as well as iphimedoid taxa are also considered. High intraspecific variation was observed, which was not related to size, sex, or locality and may indicate recent speciation of some Antarctic epimeriids. The small number of taxa studied from the deep sea and the northern hemisphere and difficulty in defining apomorphic and plesiomorphic states does not allow us to present final conclusions about the origin of Antarctic Epimeria living on the Antarctic shelf. Nonetheless, deep-sea species from the mid-Atlantic form a clade with deep-sea species from the western Pacific and two of the three studied North Atlantic species. This supports the Watling & Thurston (1989) hypothesis that Antarctica acts as an evolutionary incubator.

Low abundances and diversities of benthic faunas of shallow, coastal sediments in the Solomon Islands and their implications for assessing environmental impacts of logging

The diversity and abundance of benthic organisms were examined in relation to logging impacts in Western Province, Solomon Islands. Organisms occupying sediments offshore from the mouths of logged and unlogged streams in two areas were sampled at three depths during a single survey. Overall abundances of organisms were low, and patterns varied between areas. At Kolombangara, ANOVA showed that numbers of molluscs and crustaceans were higher at mouths of rivers with unlogged catchments than with logged catchments, but numbers of individuals, taxa, and polychaetes differed among river mouths within treatments. At Vangunu, numbers of taxa varied inconsistently among depths in the different logging treatments, whereas numbers of individuals were greater at river mouths of unlogged than logged catchments. Multivariate analyses (MDS, ANOSIM) showed differences among river mouths within treatments but not among treatments. In general, there were indications of logging impacts but the effects were not consistent across taxa. Because of this inconsistency, the low abundance and diversity of animals, and the relatively high cost of processing samples, benthic macrofaunal variables were not considered to be cost-effective measurement variables for longer term monitoring of the effects of run-off from logging operations on inshore marine habitats at these study sites.