A population model for the alkali fly at Mono Lake: depth distribution and changing habitat availability

The densities of alkali fly larvae and pupae were measured in relation to depth and substrate type at six locations around Mono Lake. Samples representing a mixture of different bottom features were taken to a depth of 10 m (33 ft) using SCUBA. This is at or near the depth limit of fly larvae and pupae. The biomass of larvae and pupae on hard substrate were maximum and approximately equal at depths of 0.5 m and 1 m, substantially lower at intermediate depths of 3 m and 5 m, and over an order of magnitude further reduced at 10 m. Densities of flies on hard or rocky substrates (mainly calcareous tufa deposits), were significantly greater than those found on soft substrates such as mud or sand, at all but the greatest depth surveyed.Bathymetric maps of the areas of hard and soft substrate occurring at different lake depths were used to estimate the fly population size over the whole lake, based on the density distribution of larvae and pupae with depth on different substrates. The mapped areas of soft and hard substrates were also calculated for different lake levels, and applying the same procedure, a population model comparing the abundance of flies at different lake levels was developed. This habitat-based population model predicts that the abundance of the alkali fly is maximized at 6380 ft (1945 m) lake surface elevation. Most of the tufa substrate submerged at this lake level will become exposed and unavailable as habitat as the lake declines to 6370 ft (1942 m). In late 1991, the lake level was just over 6374 ft (1943 + m).     

Modern distribution of ostracodes and other limnological indicators in southern Lake Malawi: implications for paleocological studies

This modern distribution study from the southwest arm of Lake Malawi quantitatively relates variables of the lake environment to surficial assemblages of ostracodes and other paleoenvironmental indicators (molluscs, Botryococcus, fish, and charcoal) from 102 sites, across a gradient of littoral to shallow profundal conditions. The goal of this research is to use the resultant relationships to help quantify paleoecological interpretations of the fossil record from sediment cores. Site locations varied by depth (1–60 m) and adjacent shoreline environment. Thirty-three ostracode species are identified from 54 sites including four new, undescribed species of Cypridopsinae (2) and Limnocythere (2). Ostracodes are extremely abundant between 1 and 25 m water depth, but are rare to absent between 30 and 60 m. This disappearance is probably taphonomically controlled, with carbonate dissolution in the death assemblage since abundant live ostracodes have been found in the lake at greater than 30 m depth, where bottom sediments lack calcium carbonate. Constrained correspondence analysis (CCA) of ostracode species abundance suggests depth and dissolved oxygen (DO) content to be the primary environmental variables affecting their distribution. Additional CCA models using all biological indicators suggest limnologic variables correlated with depth (e.g., bottom water temperature and DO) and adjacent shoreline environment were most significant.     

Spatial and temporal structure of the trematode component community in Valvata macrostoma (Gastropoda, Prosobranchia)

We conducted the first comprehensive study on the spatiotemporal structure of trematode communities in the large-mouthed valve snail, Valvata macrostoma. A total of 1103 snails were examined monthly between May and October 2007 from Lake Konnevesi, Central Finland, from a shallow (1-2 m deep) and an offshore site (5-6 m deep), located ca. 50-70 m apart. Snails were infected by 10 trematode species. The species composition and prevalence were strikingly different between the sites with high species diversity in the shallow site (all 10 species; total prevalence of sporocysts/rediae 12.1%, metacercariae 55.4%) compared to the deeper site (3 species; prevalence 15.0% and 1.9%, respectively). This difference persisted throughout our study and is probably related to the spatial distribution of bird definitive hosts, whereas the seasonal parasite dynamics are likely to be affected by changes in the age-structure of the snail population. The probability of sporocyst infections increased with snail size, but no such trend was observed in redial or metacercarial infections which decreased with host size. Our results show that generally well-described spatiotemporal differences in trematode infection of molluscs can emerge in very narrow spatial and temporal scales, which emphasizes the importance of these factors in community studies.     

Gastropods and bivalves taken as by-catch in the deep-water shrimp trawl-fishery along the Pacific coast of Costa Rica,Central America

Deep-water habitats are among the least studied but most vulnerable environments. By-catch data from deep-water fisheries in Latin America are limited, and detailed reports on associated molluscs are scarce. This study provides information on deep-water shelled molluscs collected between 2010 and 2011 by commercial shrimp trawling fisheries along the Pacific coast of Costa Rica at depths from 112 to 271?m. Twenty-six species were identified, 23 gastropods and three bivalves. Our data extend the depth range of 14 species, and Homalopoma cf. grippii is reported for the first time for Costa Rica. The most common species were the gastropods Fusinus spectrum, Polystira nobilis and Solenosteira gatesi. Only one species (Sinum debile) was captured below 250?m. The catch of molluscs per unit effort was influenced by depth, but not by seasonality or geographic area. It is speculated that these long-lasting bottom-trawling activities have caused negative effects on species diversity and mollusc biomass. Nevertheless, a monitoring program is recommended to assess possible impacts of this type of fishery on mollusc diversity and biomass.     

Community structure and biogeography of shore fishes in the Gulf of Aqaba,Red Sea

Shore fish community structure off the Jordanian Red Sea coast was determined on fringing coral reefs and in a seagrass-dominated bay at 6 m and 12 m depths. A total of 198 fish species belonging to 121 genera and 43 families was recorded. Labridae and Pomacentridae dominated the ichthyofauna in terms of species richness and Pomacentridae were most abundant. Neither diversity nor species richness was correlated to depth. The abundance of fishes was higher at the deep reef slope, due to schooling planktivorous fishes. At 12 m depth abundance of fishes at the seagrass-dominated site was higher than on the coral reefs. Multivariate analysis demonstrated a strong influence on the fish assemblages by depth and benthic habitat. Fish species richness was positively correlated with hard substrate cover and habitat diversity. Abundance of corallivores was positively linked with live hard coral cover. The assemblages of fishes were different on the shallow reef slope, deep reef slope and seagrass meadows. An analysis of the fish fauna showed that the Gulf of Aqaba harbours a higher species richness than previously reported. The comparison with fish communities on other reefs around the Arabian Peninsula and Indian Ocean supported the recognition of an Arabian subprovince within the Indian Ocean. The affinity of the Arabian Gulf ichthyofauna to the Red Sea is not clear. Received in revised form: 2 November 2001 Electronic Publication     

The benthic macrofauna community of Kenyan waters of Lake Victoria

The benthic macroinvertebrates in the Kenya waters of Lake Victoria (ca. 1400 km²) were surveyed during four 10 day sampling periods in February, April, August and November 1984. Fourty three taxonomic groups were recorded. Oligochaetes, molluscs and dipteran larvae were the most abundant and widely distributed groups. The dominant oligochaetes were Branchiura sowerbyii Beddard and the swamp worm Alma emini Michaelsen, which were abundant in all silty and soft mud areas in both littoral and open water zones. Melanoides tuberculata Müller, Bellamya unicolor Olivier and Caelatura spp. were the most abundant molluscs. Different patterns were observed between near-littoral stations (<8 m deep) and deep water stations (8–40 m deep). After 10 years (1994), the macroinvertebrates of Lake Victoria were examined again. No evidence was found of seasonal changes in the composition or benthos density, although local changes occurred in some species which were attributed to swarming behaviour or larval settlement patterns. The spatial distribution of the fauna may be influenced primarily by oxygen availability and industrial effluent discharged from paper mill and agro-based industries in the catchment of the lake. There has been a shift in abundance, from an Oligochaeta and Insecta dominated community in 1984, to the present community dominated by Mollusca and Oligochaeta. The ecological role of the benthic community and its recent changes to fisheries production in the lake is discussed.     

Biodiversity of peracarid crustaceans(Malacostraca) from the shelf downto the deep Arctic Ocean

During three expeditions with the RVs Meteor and Polarstern more than sixty thousand peracarids were sampled from the deep Arctic Ocean (northern North Atlantic) by means of an epibenthic sledge. Sampling areas were the Kolbeinsey Ridge north of Iceland (800–1100 m), the Northeast Water Polynya, off Greenland (45–517m), and 75°N east of Greenland (197–2681m). Until now 288 species of Peracarida have been identified to species level. These 288 species comprise 152 genera and 59 families of Amphipoda, Cumacea, Isopoda, Mysidacea and Tanaidacea. Thirty-eight genera were very frequent and were sampled at each expedition (these were 22 species of Isopoda, seven species of Cumacea, three species of Amphipoda and Mysidacea, each, and two species of Tanaidacea). Sixty genera are eurybathic, occurring at least over a depth range of 1000m, some even from the shelf up to 2681m depth. Only 10 genera are stenobathic, occurring only in the deep sea. No significant decrease in species number with depth or latitude could be observed. The influencing factors probably causing different community structures are diverse, ranging from food availability over substrate or hydrographical qualities to interspecific competition.     

Food of Iago omanensis, a deep water shark from the northern Red Sea

Stomach contents of 252 lago omanensis were examined. Sharks were collected in deep water between 150 and 450 m depth off the Marine Laboratory of Eilat. This species feeds on benthopelagic fishes, deep water cephalopods, crustaceans, benthic molluscs and polychaetes. Cephalopods were the main food of I. omanensis , except during the summer when fishes (mainly myctophids) were ingested in greater quantity. Stomachs also contained terrigenous plant matter, animal remains and large quantities of mud. Prey taxa included two new cephalopod records for the Red Sea.     

Diversity and spatial pattern of coral communities in the Red Sea upper twilight zone

Summary This is the first study based on numerical analysis of the abundance of 11 scleractinian corals of depths at between 100–210 m in the Red Sea twilight zone. Two distinct coral communities were found: a Leptoseris fragilis community at a depth of 100–130 m (zone 1) and a Dendrophillia horsti community below 130 m (zone 2, 3). Population densities and coral coverage are very low; distribution of individuals is highly clumped. Highest observed densities on 100 m² were 2720 individuals for L. fraglis, 2720 for D. horsti and 2260 for Javania insignis. Calculated coverage rates were maximally 3.6% (L. fragilis), 0.08% (D. horsti) and 0.11% (J. insignis). L. fragilis, the only symbiont bearing coral, was very abundant. It has an unusual depth range for a photosynthesising coral. Coral density is only weakly correlated with hard bottom coverage. Species diversity with an average of 8 species is highest at 120–170 m and decreases in shallower and deeper water. The study depth range is a transient zone for coral distribution. It contains the upper distribution limits of a few deep sea corals and the lower ones of several shallower water species. Ahermatypic corals, collected at 160–170 m depth, were transplanted from their original depth to 159, 118, 70 and 40 m; after one year most species survived transplantation far beyond their upper distributional limits. The symbiotic L. fragilis, collected at 120 m, survived transplantation to deep water (159 m) as well as shallow zones (90, 70 and 40 m). The study demonstrates the feasibility of line-transect methods for coral community studies with a submersible.     

A comparison of the abilities of three sympatric species of Petrotilapia (Cichlidae,Lake Malawi) to penetrate deep water

Synopsis The ability of three sympatric species ofPetrotolapia, from Monkey Bay, Lake Malawi, to penetrate deep water was tested using pressure chambers. The three species were found to differ in terms of the maximum pressure (= depth) to which each was able to equilibrate. Mean maximum equilibration pressures were for the form designated MOL 39.0 m, for MBB 35.5 m and for the form MOC 30.4 m. The rate of compensation to pressure changes was slower in MBB (2.59 m day^–1) than in other two forms (MOL = 3.97 m day^–1, MOC = 3.98 day^–1). Natural depth distribution of all three forms, in particular MBB and MOC, is not determined by limits imposed by swin bladder physiology.     

Fish assemblages of Cais do Carvão Bay (Madeira Island) determined by the visual census technique

Fish assemblages in Cais do Carvão Bay, Madeira Island, a proposed marine protected area (MPA), were determined from a diver visual census. A total of 32 transect counts were performed. Habitats sampled included sandy bottom, rocky boulders, vertical walls and rocky outcrops. Species richness, diversity, density, trophic structure, size and spatial organization were documented for the fish assemblages. Forty‐four species from 23 families were encountered; 32% belonged to Sparidae (10) and Labridae (four). The greatest species richness (25) was observed in rocky boulder habitat at 10–15 m depth, while the lowest (five) occurred over a deeper sand habitat. The greatest density (760·5 individuals per 100 m²) was recorded over rocky outcropping (20–25 m deep), and the lowest of 11·6 individuals per 100 m² was over a sand bottom at 10–15 m depth. Thalassoma pavo , Abudefduf luridus and Chromis limbata had higher densities on hard bottoms, while Heteroconger longissimus was the most abundant species in sand bottom habitats. No significant differences were detected for all indices calculated among depth intervals for sand and rocky boulder stations. Sand and rock boulder substratum, however, differed significantly for the 10–15 m depth stratum.     

Depth-related radiolarian assemblage in the water-column and surface sediments of the Japan Sea

Plankton tows and surface sediments from the Japan Sea, a marginal sea of the northwestern Pacific, were examined to study the depth distribution of modern radiolarians. The depth distribution patterns between the living assemblage in the water-column and the thanatocoenose in surface sediments are similar to each other, indicating that the depth-related assemblage in sediments is closely related to the living depths of major species. Four clear restrictions of many species to discrete depth zones are recognized in the water-column, from the surface down to 2000 m: (1) upper subsurface-water species, which are abundant from 40 to 120 m (Larcopyle butschlii juvenile form, Spirocyrtis subscalaris, Spongodiscus resurgens and Lipmanella virchowii); (2) lower subsurface-water species, which are abundant from 40 to 300 m (Larcopyle butschlii adult form, Ceratocyrtis histricosa and Spongotrochus glacialis); (3) intermediate-water species, which have population maxima from 160 to 300 m (Ceratospyris borealis); and (4) deep-water species, which have maxima between 1000 and 2000 m (Cycladophora davisiana and Actinomma boreale). Only a few specimens of A. boreale were found in the water-column ranging from 1000 to 2000 m depth, although this is a dominant species in surface sediments from depths below 2000 m of which the dominance increases with water depth. A. boreale may live mainly in the bottom water. Cycladophora davisiana and A. boreale, which characterize the Japan Sea deep assemblage, are naturally shallow or intermediate dwellers in other oceans. On the other hand, the typical deep-dwellers (e.g. Cornutella profunda, Cyrtopera languncula and Peripyramis circumtexta) of other oceans have not been found in the Japan Sea. Such a peculiar deep assemblage is a result of the deep circulation system in the Japan Sea and the shallow depths of the sills around it.     

Diversity and distribution of symbiodinium associated with seven common coral species in the Chagos Archipelago, central Indian Ocean

The Chagos Archipelago designated as a no-take marine protected area in 2010, lying about 500 km south of the Maldives in the Indian Ocean, has a high conservation priority, particularly because of its fast recovery from the ocean-wide massive coral mortality following the 1998 coral bleaching event. The aims of this study were to examine Symbiodinium diversity and distribution associated with scleractinian corals in five atolls of the Chagos Archipelago, spread over 10,000 km(2). Symbiodinium clade diversity in 262 samples of seven common coral species, Acropora muricata, Isopora palifera, Pocillopora damicornis, P. verrucosa, P. eydouxi, Seriatopora hystrix, and Stylophora pistillata were determined using PCR-SSCP of the ribosomal internal transcribed spacer 1 (ITS1), PCR-DDGE of ITS2, and phylogenetic analyses. The results indicated that Symbiodinium in clade C were the dominant symbiont group in the seven coral species. Our analysis revealed types of Symbiodinium clade C specific to coral species. Types C1 and C3 (with C3z and C3i variants) were dominant in Acroporidae and C1 and C1c were the dominant types in Pocilloporidae. We also found 2 novel ITS2 types in S. hystrix and 1 novel ITS2 type of Symbiodinium in A. muricata. Some colonies of A. muricata and I. palifera were also associated with Symbiodinium A1. These results suggest that corals in the Chagos Archipelago host different assemblages of Symbiodinium types then their conspecifics from other locations in the Indian Ocean; and that future research will show whether these patterns in Symbiodinium genotypes may be due to local adaptation to specific conditions in the Chagos.     

Alien molluscs affect the composition and diversity of native macroinvertebrates in a sandy flat of Lake Neuchâtel,Switzerland

The spread of alien molluscs is a serious threat to native biodiversity in fresh waters. Alien freshwater molluscs may deplete the resources of native species and alter the physical structure of the habitat through their shell mass. These changes might have both positive and negative effects on native community members. We investigated the native macroinvertebrate community in relation to the densities of four alien mollusc species (Corbicula fluminea, Dreissena polymorpha, Potamopyrgus antipodarum and Lithoglyphus naticoides) in a sandy flat of Lake Neuchatel, Switzerland. The habitat examined was dominated by these alien mollusc species. The abundance of the alien molluscs did not directly impact the native community assembly. However, C. fluminea and D. polymorpha influenced the composition and diversity of native macroinvertebrates by transforming the sandy substratum into a partly hard substratum habitat. Substantial differences in community composition between shallow (<3.5 m) and (≥5 m) deep sites were recorded. At shallow sites, the abundance of D. polymorpha was significantly reduced as a result of depth-selective feeding of ducks. A controlled shell decay study revealed that shells of alien molluscs (C. fluminea, D. polymorpha) persist for a longer period in the sediment than those of native molluscs. Consequently, shells of alien molluscs have a long-lasting impact by modifying the sandy habitat. This form of ecosystem engineering favours the occurrence of several native taxa, but is disadvantageous for other taxa with specific habitat requirements, and thus can be regarded as an indirect impact of competition.     

The Diversity and Biogeography of Western Indian Ocean Reef-Building Corals

This study assesses the biogeographic classification of the Western Indian Ocean (WIO) on the basis of the species diversity and distribution of reef-building corals. Twenty one locations were sampled between 2002 and 2011. Presence/absence of scleractinian corals was noted on SCUBA, with the aid of underwater digital photographs and reference publications for species identification. Sampling effort varied from 7 to 37 samples per location, with 15 to 45 minutes per dive allocated to species observations, depending on the logistics on each trip. Species presence/absence was analyzed using the Bray-Curtis similarity coefficient, followed by cluster analysis and multi-dimensional scaling. Total (asymptotic) species number per location was estimated using the Michaelis-Menten equation. Three hundred and sixty nine coral species were named with stable identifications and used for analysis. At the location level, estimated maximum species richness ranged from 297 (Nacala, Mozambique) to 174 (Farquhar, Seychelles). Locations in the northern Mozambique Channel had the highest diversity and similarity, forming a core region defined by its unique oceanography of variable meso-scale eddies that confer high connectivity within this region. A distinction between mainland and island fauna was not found; instead, diversity decreased radially from the northern Mozambique Channel. The Chagos archipelago was closely related to the northern Mozambique Channel region, and analysis of hard coral data in the IUCN Red List found Chagos to be more closely related to the WIO than to the Maldives, India and Sri Lanka. Diversity patterns were consistent with primary oceanographic drivers in the WIO, reflecting inflow of the South Equatorial Current, maintenance of high diversity in the northern Mozambique Channel, and export from this central region to the north and south, and to the Seychelles and Mascarene islands.     

Distribution pattern of groundfishes hooked along a row of setline in the shallower part of the continental slope in the Bering Sea 2 bathymetric difference in relative abundance in relation to distribution pattern

1. This report demonstrates the well-defined bathymetric distribution of relative abundance of groundfishes in relation to the distribution pattern conjectured from the records of catch along a row of setline with remarkably large variation in the settled depth (from shallower than 350 m to deeper than 700 m) observed around 58⁰ 18′ N and 175⁰ 28′ W on Aug. 24, 1962.
2. The results of the analyses are depicted in Fig. 1. It is found that halibut, true cod and Sebastodes sp. (or Menuke in Japanese) show sharp or abrupt decrease in the relative abundance in accordance with depth whereas sablefish and rattail increase sharply. Arrow toothed halibut and ray do not show any clear bathymetric change in relative abundance and Pacific ocean perch shows decrease in the density in accordance with the disparity in the depth from the 500 m isobath.
3. The patterns conjectured from this example are compared with either those shown in other reports, the results of the observations on other examples or general view of our fishermen. And many proofs to the high reliability and wide universality of the conjectured pattern of the first four species are found out. But, for the last three species, the present results differ more or less from the general view of our fishermen and the observations on other examples.
4. For the distribution pattern, most of groundfishes incline to show chance distribution in the shallower part of the continental slope (350 m to 700 m deep) and only the species showing sharp decrease in density with increase in the depth are distributed contagiously on the shallower bottom (not deeper than 450 m).

     

Faunal change and bathymetric diversity gradient in deep-sea prosobranchs from Northeastern Atlantic

Despite the plethora of studies, geographic patterns of diversity in deep sea remain subject of speculation. This study considers a large dataset to examine the faunal change and depth-diversity gradient of prosobranch molluscs in the Porcupine Seabight and adjacent Abyssal Plain (NE Atlantic). Rates of species succession (addition and loss) increased rapidly with increasing depth and indicated four possible areas of faunal turnover at about 700, 1600, 2800 and 4100 m. Depth was a significant predictor of diversity, explaining nearly a quarter the variance. There was a pattern of decreasing diversity downslope from ~250 m to ~1500–1600 m, followed by an increase to high values at about 4000 m and then again, a fall to ~4915 m. Processes causing diversity patterns of prosobranchs in the Porcupine Seabight and adjacent Abyssal Plain are likely to differ in magnitude or type, from those operating in other Atlantic areas.     

The benthic and weed-bed faunas of Lake Awasa (Rift Valley,Ethiopia)

The community structures of the benthic and weed-bed faunas of Lake Awasa, Ethiopia Rift Valley, are described and related to the various types of substratum present. L. Awasa is non-saline (conductivity 860 µS cm^-1), and lies in a shallow basin with maximum depths of 21–22 m. It supports an important commercial fishery mainly based on the tilapia Oreochromis niloticus.The large weed beds of the lake extend out to the 4 m. isobath in most places; they consist mainly of the grass Paspalidium geminatum. Below the 6–8 m isobaths the bottom is covered with a deep layer of flocculant mud, with organic matter constituting about one third of the dry weight. No benthic animals are able to colonize this mud. In shallower regions the bottom consists of hard sand covered with a thin layer of organic detritus, except for a narrow region around the 6 m isobath where the sand is covered with a layer of ostracod shells up to 25 cm deep. All this firmer bottom is colonized by a benthic community consisting mainly of cyclopoids, ostracods, Limnodrilus and chironomids; there are no prosobranch or bivalve molluscs. The weed-bed community consists mainly of Cladocera, ostracods, Ephemeroptera, Heteroptera, chironomids and pulmonate molluscs. These communities are compared with those of other Afro-tropical lakes, and are shown to have much in common with that of Lake Chad (Dejoux, 1983), specially the chironomids (Dejoux, 1976) but L. Awasa has fewer species, the most noticeable absentees being the decapod Crustacea.