Bathymetric Trends Research Articles

Reliability of CARD-FISH Procedure for Enumeration of Archaea in Deep-Sea Surficial Sediments

The enumeration of Archaea in deep-sea sediment samples is still limited, although different methodological procedures have been applied. Among these, catalysed reporter deposition-fluorescence in situ hybridisation (CARD-FISH) technique is a promising tool for estimation of archaeal abundance in deep-sea sediment samples. Comparing different permeabilisation treatments, the best results obtained both on archaeal pure cultures and on natural assemblages were with hydrochloric acid (0.1M) and proteinase K (0.004U/ml) treatments. The application of CARD-FISH on deep-sea sediments revealed that Archaea reach up to 41% of total prokaryotic cells. Specific probes for planktonic Archaea showed that marine Crenarchaea dominated archaeal seafloor communities. No clear bathymetric trends were observed for archaeal abundances and the morphology of continental margin (slope vs. canyon) seems not to have a direct influence on archaeal relative abundances. The site-specific sediment habitat-both abiotic environmental setting and sedimentary organic matter quality-explain up to 65% of variance of archaeal, crenarchaeal and euryarchaeal relative abundance, suggesting a wide ecophysiological adaptation to deep-sea benthic ecosystems. The findings demonstrate that Archaea are an important component of benthic microbial assemblages so far neglected, and hence they lay the groundwork for more focused research on their ecological importance in the functioning of deep-sea benthic ecosystems.

Balearic Islands vs Algeria: two nearby western Mediterranean elasmobranch assemblages with different oceanographic scenarios and fishing histories

SUMMARY: In this paper we compare the elasmobranch composition, depth-related trends of species and community descriptors (abundance, biomass, mean fish weight, species richness and diversity) of the Balearic Islands Archipelago and Algeria (north- and southwestern Mediterranean, respectively). The samples used in this study were collected in bottom trawl surveys between 36 and 779 m depth. Generalized linear models, linear regression, cluster and similarity percentage analyses, and generalized additive models were used to compare the two areas. Twenty-nine elasmobranch species were caught, 12 of them common to both areas, 7 appearing only in the Balearic Islands, and 10 only in Algeria. The bathymetric distributions of species were, in most cases, best fitted to uni-modal response curves. The models for species common to both areas showed similar bathymetric trends, except for Etmopterus spinax, which in Algeria showed a maximum abundance located 154 m shallower than in the Balearic Islands. Four bathymetric assemblages were identified in both areas with similar depth ranges but with different species composition. The mean values of the community descriptors were higher on the shelf in the Balearic Islands, whereas higher values were detected on the slope in Algeria. Different between-area bathymetric trends for all the descriptors were detected, with the exception of mean fish weight. The distinct environmental scenarios and fishing histories of the areas studied are discussed as underlying traits influencing the elasmobranch populations.

Influence of foundation species, depth, and location on diversity and community composition at Gulf of Mexico lower-slope cold seeps

Efforts to understand and preserve the seep communities of the deep Gulf of Mexico (GOM) begin with a comprehensive survey of the biodiversity of these communities. Previous studies have provided a conceptual model of the physiology, population, and community ecology of upper continental slope seeps. However, seeps at water depths below 1000m in the Gulf of Mexico remain relatively unknown. In this study, data from 47 samples of tubeworm- and mussel-associated communities at depths of 1005–2750m are examined. Other than tubeworms and mussels, 66 taxa of macro- and megafauna were collected, 43 of which appear to be restricted to water depths of over 1000m, and 39 that have not been reported previously from the Gulf of Mexico. Diversity in mussel beds was highest at mid-slope depths, but tubeworm-associated communities did not show clear bathymetric trends in diversity. Diversity was higher in tubeworm aggregations at the alpha level (per sample), but higher in mussel beds at the beta level (species turnover among collections). Although both community types were often numerically dominated by the endemic shrimp Alvinocaris muricola, broad differences in the communities hosted by tubeworm aggregations and mussel beds were apparent. The most important factors explaining community similarity within community type were the depth, relative abundance of different mussel species in a bed, and the average size of tubeworms in an aggregation. The high proportion of deep-seep species that were found for the first time in the Gulf of Mexico emphasizes the importance of conservation efforts for these patchy communities.

Biostratigraphical calibration of third order Ordovician sequences on the northern Gondwana platform

This study illustrates bathymetric trends across the northern Gondwana platform during the Ordovician. The sedimentary records of the Algerian Sahara, central Morocco, and western France are investigated to document related environmental changes through the period. Outcrop and subcrop sections have been selected with regard to their completeness and to the precision of the available biostratigraphical data, based on chitinozoans. This group provides the most continuous biostratigraphical record in the terrigenous Ordovician successions of northern Gondwana. For each area, the chitinozoan data have been assembled, updated and referred to one of the 26 Ordovician chitinozoan biozones defined in northern Gondwana regions. A sequential analysis based on the identification of genetic units is presented. The stacking pattern of these units is established for each locality, and the resulting curves express variations in sedimentary environments partly driven by relative sea-level changes. From successive smoothings of these curves, we define 16 main cycles at lower frequencies. Uncertainties concerning the precise chronostratigraphic position of some of these cycles are discussed. The proposed northern Gondwana relative sea-level variation curves are compared to the recently-published global Ordovician sea-level curve and to other regional curves available for the major Ordovician palaeoplates (Laurentia, Baltica, South China, north-eastern Gondwana).

The Ophiomorpha rudis ichnosubfacies of the Nereites ichnofacies: Characteristics and constraints

The Ophiomorpha rudis ichnosubfacies of the Nereites ichnofacies contains a low diversity (commonly 1–4 ichnotaxa) trace fossil assemblage that besides the eponymous ichnospecies commonly includes Ophiomorpha annulata and Scolicia, and rarely Nereites irregularis, Chondrites, graphoglyptids or other ichnotaxa. This ichnosubfacies occurs in channel and proximal depositional lobe facies of deep-sea fans or in thick-bedded facies of deep-sea clastic ramps. When considered with the Nereites and Paleodictyon ichnosubfacies, it can be used for determination of bathymetric trends. Specimens of O. rudis can also occur in overbank or fan-fringe facies in the Paleodictyon ichnosubfacies, in which ichnodiversity is distinctly higher. Ophiomorpha rudis ranges from the Tithonian but is rare in the Lower Cretaceous. It is distinctly abundant since the Turonian with a pronounced peak of abundance in the Eocene. After the Eocene, its abundance apparently declines. The occurrence of the O. rudis ichnosubfacies at present is stratigraphically limited to the Upper Cretaceous–Miocene. Ophiomorpha rudis is a very deep-feeding burrow system composed of oblique to vertical shafts and horizontal galleries. Probably, it was produced by shrimp-like crustaceans, which possibly fed by means of farmed microbes on decomposed phytodetritus close to or below the redox boundary. Tunnels of O. rudis were reinforced against collapsing, with irregular muddy sand granules. In more cohesive sediment, the burrows are smooth, without a wall, and in firmground sediment they are covered locally with casts of scratch ornament produced by the legs of the tracemaker.

Steeper biomass spectra of demersal fish communities after trawler exclusion in Sicily

AbstractSweeting, C. J., Badalamenti, F., D'Anna, G., Pipitone, C., and Polunin, N. V. C. 2009. Steeper biomass spectra of demersal fish communities after trawler exclusion in Sicily. – ICES Journal of Marine Science, 66: 195–202. The effects of trawling on Mediterranean demersal fish communities were assessed by comparing them with the normalized biomass spectra among three gulfs on the north Sicilian coast, one of which had been subject to 15 years of trawler exclusion. Comparisons were conducted across seasons and among depth strata. Biomass-spectra slopes were significantly steeper in the gulf that was closed to trawling than in the unprotected gulfs. This was attributed to the exclusion of trawlers, which lacked catch-size selectivity, and to the continued fishing by artisanal gears that are more size selective. The biomass of all size classes was higher in the protected gulf than in unprotected areas, and increases were greatest in smaller size classes. Community mean individual fish mass was similar among all areas with a wider range of body masses present in the trawl exclusion area, compensating for the greater abundance of small fish. Size-spectra slopes were generally shallower and midpoint heights lower with increasing depth and were greater in autumn than spring; the effect of these seasonal and depth factors was as great as that of protection. Depth patterns are explainable by bathymetric trends in within- and among-species fish size. Seasonal differences were attributed to variation in spawning behaviour and fishery recruitment, with seasonal differences being greater in unprotected locations as a result of recruitment overfishing.

Depth zonation and bathymetric trends of deep-sea megafaunal scavengers of the Hawaiian Islands

The deep sea has been shown to exhibit strong depth zonation in species composition and abundance. Examination of these patterns can offer ecological insight into how organisms adapt and respond to changing environmental parameters that co-occur with depth. Here we provide the first tropical study on bathymetric zonation and other depth-related trends (size, abundance, and species richness) spanning shelf to abyssal depths of scavenging megafauna. Baited time-lapse free-vehicle cameras were used to examine the deep-sea benthic and demersal scavenging communities of the Hawaiian Islands, an area for which the biology and ecology have remained poorly studied below 2000 m. Twenty-two deployments ranging in depth from 250 to 4783 m yielded 37 taxa attracted to bait, including the first known occurrence of the family Zoarcidae in the Hawaiian Islands. Cluster analysis of Bray–Curtis similarity of species peak abundance ( n max) revealed four main faunal zones (250–500, 1000, 1500–3000, and ⩾4000 m) with significant separation (ANOSIM, global R=0.907, p=0.001) between designated depth groups. A major faunal break was identified at the 500–1000 m transition where species turnover was greatest, coinciding with the location of the local oxygen minimum zone. Dominance in species assemblage shifted from decapod crustaceans to teleosts moving from shallow to deeper faunal zones. Significant size differences in total length with depth were found for two of the four fish species examined. A logarithmic decline was observed in scavenger relative abundance with depth. Evidence of interaction between scavenging species was also noted between Synaphobranchus affinis and Neolithodes sp. (competition) and Histiobranchus sp. and aristeid shrimp (predation), suggesting that interactions between scavengers could influence indices of abundance generated from baited camera data.

Spatial and temporal trends in condition of Atlantic cod Gadus morhua on the Icelandic shelf

Interannual (1993 to 2006), spatial and bathymetric trends in the hepatosomatic index (H) and relative body condition index (Kr) of Atlantic cod Gadus morhua in Icelandic waters were investigated from data collected during annual spring (March) groundfish surveys. Individual stom- ach content data were analysed to assess the relationship between condition and consumption of capelin Mallotus villosus. Liver condition was found to vary with region and depth, tending to be highest in deeper water and in the northern and eastern regions; where temperatures were relatively cold and capelin consumption relatively high. A continuous decline in condition of cod in waters off the east coast was observed throughout the study period. Mature cod were found to be in signifi- cantly better condition than immature cod of the same age, and mature females were in better condi- tion than mature males. Different patterns emerged from the 2 condition indices; little variation in Kr was observed whereas H was found to be a dynamic index of condition, suggesting that these met- rics are not equivalent measures of cod bioenergetic condition.

Bathymetric trends in distribution and size of demersal fish species in the north Aegean Sea

Seasonal experimental trawl surveys (summer 1990–winter 1993) were carried out in the north Aegean Sea, at depths from 16 to 500 m. A total of 192 demersal fish species was caught. Bathymetric distribution of the dominant species was investigated using the quantitative model of the “centre of gravity” (COG) and habitat width (HW), a measure of the distribution heterogeneity. Out of the 40 dominant species studied, 31 were fully included within the range of available depths and most of them were centred between 90 and 270 m. The analysis indicated that most of the species exhibited a wide distribution range within the study area, although few were restricted to the greatest depths. Size‐depth trends of the dominant species demonstrated significant positive relationships for most species (56%) examined. The average rate of increase in fish length with increasing depth was also estimated, while correlation analysis was performed between mean depth and minimum or maximum fish size. The results indicated both a tendency towards “larger‐deeper” and “smaller‐shallower” for most of the species, depending on the size range of different species, but the larger‐deeper trend predominated.

Tectonic control on peritidal carbonate parasequence formation: an investigation using forward tectono‐stratigraphic modelling

AbstractStudies of Quaternary extensional faults indicate that they have instantaneous amounts of throw (0·4 to 4 m), average slip rates (0·05 to 2·8 m kyr−1) and frequency of recurrence (<40 000 years) accounting for the accommodation space required for the accumulation of peritidal carbonate parasequences (PCPs). Hangingwall sites and graben are characterized by fault down‐dropping together with regional subsidence, and footwall sites and horsts by fault‐related uplift alternating with periods of regional subsidence. The relative sea‐level curves generated by these processes operating in a maritime rift setting are used as inputs to a forward stratigraphic modelling program SedTec2000 to simulate how fault‐related changes in accommodation space can account for high‐frequency PCP formation. Each instantaneous fault slip generates a flooding surface or aggradation in hangingwall and graben settings. High‐frequency cycles in hangingwall sites are either symmetric (deepening then shallowing upward) or asymmetric (shallowing‐upward). The major factor controlling cycle types is the balance between rates of carbonate accumulation and generation of accomodation space. High‐frequency cycles in footwall sites and horsts comprise shallow subtidal facies, with no distinctive bathymetric trends, capped by erosional boundaries generated by footwall uplift. The modelled cycles are of the same thickness, with bathymetric trends and frequency to cycles commonly interpreted to be due to orbitally driven eustatic sea‐level changes or autocyclic processes. These numerical experiments demonstrate that high‐frequency PCPs can be generated by tectonic, fault‐related processes, a hypothesis that is frequently discounted.

Geographic and bathymetric trends in abundance, biomass and body size of four grenadier fishes along the Iberian coast in the western Mediterranean

The present study is a mesoscale analysis of latitude and depth related trends in abundance, biomass and body size of the four grenadier species Caelorinchus caelorhincus, Hymenocephalus italicus, Nezumia aequalis and Trachyrinchus scabrus inhabiting the deep western Mediterranean. We have analysed data from seven annual bottom trawl surveys, carried out down to 800 m depth along the Iberian Mediterranean coast covering a distance of approximately 1200 km. The objectives were to establish general patterns in the mesoscale distribution of abundance, biomass and body size of deep-water grenadier fishes and also analyse the consistency of the bathymetric distribution of these parameters along a large latitudinal gradient. Five complementary series of analyses have been completed. The first focussed on describing the general patterns of abundance and size by correspondence canonical analysis, CCA, in the area. The second and third series focussed on the existence of temporal, geographical and bathymetric trends of abundance, weight and mean size by analysis of covariance, ANCOVA and multiple regression analysis. The fourth series compared the frequency distributions of body length. Finally, the last series focussed on the patterns of abundance versus size. The total number of individuals of all four grenadier species captured in 260 bottom trawls amounted to 27,435 and their weight was 1404 kg. No general trends for the four species have been observed between years. All four species showed a general pattern of increasing size with depth, which, except in the case of C. caelorhincus, was consistent along a large latitudinal gradient. Nezumia aequalis was unique in showing the same noticeable trend of increasing abundance with depth along the entire latitudinal range, but with clear differences in the intercepts. The abundance of N. aequalis and C. caelorhincus decreased significantly northwards. Hymenocephalus italicus was the least abundant species and had a homogeneous distribution without any specific trend along the entire latitudinal range analysed. The distribution of T. scabrus in the Mediterranean seemed to be more localised. Higher abundances were found to the north and south of the latitudinal gradient with lower values between. The grenadiers studied also showed a general trend of decreasing mean size northwards, except in the case of the smallest species, H. italicus. The relation between abundance and body size differed between sectors for the whole grenadier population and species-specific variations were also observed. The relationship between individual body mass and population density fit well to a second-order polynomial function rather than to a linear regression, showing a significant trend for density to increase with increasing size until some mid-point, then to decline with increasing size thereafter. The observed latitudinal gradient in the distribution patterns of grenadiers along the upper slope of the western Mediterranean can be discussed in relation to direct and indirect factors of biogeographic, environmental and anthropogenic origin.

The structural evolution of the Messinian evaporites in the Levantine Basin

The Levantine Basin in the South-eastern Mediterranean Sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load, because the Messinian evaporites are comparatively young, the sediment load varies along the basin margin, they are hardly tectonically overprinted, and the geometry of the basin and the overburden is well-defined. In this study we analyse depositional phases of the evaporites and their structural evolution by means of high-resolution multi-channel seismic data. The basinal evaporites have a maximum thickness of about 2 km, precipitated during the Messinian Salinity Crisis, 5.3–5.9 Ma ago. The evaporite body is characterized by 5 transparent layers sequenced by four internal reflections. We suggest that each of the internal reflection bands indicate a change of evaporite facies, possibly interbedded clastic sediments, which were deposited during temporal sea level rises. All of these internal reflections are differently folded and distorted, proving that the deformation was syn-depositional. Thrust angles up to 14° are observed. Backstripping of the Pliocene–Quaternary reveals that salt tectonic is mainly driven by the sediment load of the Nile Cone. The direction of lateral salt displacement is mainly SSW–NNE and parallel to the bathymetric trend. Apparent rollback anticlines off Israel result rather from differential subsidence than from lateral salt displacement. In the south-eastern basin margin the deposition of the Isreali Slump Complex (ISC) is coeval with the onset of salt tectonic faulting, suggesting a causal link between slumping processes and salt tectonics. The superposition of ‘thin-skinned’ tectonics and ‘thick-skinned’ tectonics becomes apparent in several locations: The fold belt off the Israeli Mediterranean slope mainly results from active strike-slip tectonics, which becomes evident in faults which reach from the seafloor well below the base of the evaporites. Owing to the wrenching of the crustal segments which are bounded by deep-rooted fault lines like the Damietta–Latakia, Pelusium and Shelf Edge Hinge line the setting is transpressional south of 32°N, where the fault lines bend further towards the west. This adds a component of ‘thick-skinned’ transpression to the generally ‘thin-skinned’ compressional regime in the basin. Above 1.5 km of evaporites, a mud volcano is observed with the mud source seemingly within the evaporite layer. At the eastern Cyprus Arc, the convergence zone of the African and the Anatolian plates, deep-rooted compression heavily deformed the base of the evaporites, whereas at the Eratosthenes Seamount mainly superficial compression affecting the Post-Messinian sediments and the top of the evaporites is observed.

Latitudinal and bathymetric trends in egg size variation: a new look at Thorson's and Rass's rules

AbstractThe inverse relationship between egg size in marine animals and water temperature was simultaneously described by two outstanding marine scientists: G. Thorson and T.S. Rass. This rule consists of two different phenomena. Thorson's rule describes ecological processes related to changes in larval biology and morphology that are caused by a selective pressure of natural selection on the different types of larval development. It belongs to the realm of macro‐evolution. Rass's rule describes physiological processes within populations and species, and between closely related species. This is not related to changes in reproductive strategy, and therefore belongs to the realm of micro‐evolution and to the early stages of macro‐evolution. Populations begin to produce larger eggs in colder environments because of phenotypic plasticity. Thorson's rule describes temperature‐dependent changes in the relative abundance of small‐ and large‐egged species, whereas Rass's rule describes a temperature‐dependent relative position of both groups within an adaptive range of reproductive strategies.

Spatial and bathymetric trends in Harpacticoida (Copepoda) community structure in the Northern Gulf of Mexico deep-sea

Harpacticoid copepod community structure was analyzed at 43 stations in the northern Gulf of Mexico deep-sea to test regional and bathymetric patterns of diversity in relation to environmental variables and topographic complexity of the continental slope. Depth, longitude, and proximity to the Florida Escarpment significantly affect average phylogenetic diversity, but basins and canyons do not. Multivariate analysis reveals a significant inverse relationship between diversity and POM flux, which is confirmed by significant region-scale depth and longitude differences. Although species richness declines linearly with increasing depth, the expected number of species (rarefraction) is maximized at approximately 1200 m, and average taxonomic and phylogenetic diversity continue to increase with depth, suggesting greater morphological or functional harpacticoid diversity with increasing depth. Most stations have unique species compositions, suggesting high regional (2200 species) and global (10 5–10 6 species) diversity by extrapolation. Therefore, processes maintaining harpacticoid diversity in the northern Gulf of Mexico deep-sea seem to rely on both small-scale dispersal and large-scale food supply mechanisms.

Bathymetric trends of northeastern Brazilian snappers (Pisces, Lutjanidae): implications for the reef fishery dynamic

The investigation of bathymetric distribution of five snappers caught along the Brazilian Northeastern coast by artisanal fleets through the analysis of the catch composition and relative abundance (CPUE) showed that, on the overall, fished mean size increased along depth and that particular species dominated the catch according to the depth strata. Mutton snapper, L. analis, yellowtail snapper, L. chrysurus, and dog snapper, L. jocu were mainly caught at intermediate depth (20-80m) whereas lane snapper, L. synagris, and silk snapper, L. vivanus, inhabit respectively shallow (<20m) and deep (>80 m) waters. Each fleet category exploited preferentially a particular combination of species and their size range. The fleet dynamic of the Northeast Brazil is technologically heterogeneous and determines the catch composition. Geographical distribution of the fishery and technical interaction between fleets and gears should be considered by the management of these species in order to maintain the sustainability of the stock and to guarantee the continuance of the resource.

“Plate‐like” subsidence of the East Pacific Rise–South Pacific superswell system

In previous studies the removal of small‐scale features such as seamounts and oceanic islands from bathymetry has revealed a large and unusually shallow region in the South Pacific Ocean, which, at 3000 km wide and up to 1 km high, has been dubbed a “superswell.” These studies use statistical techniques based on finding the modal depth of the bathymetry. Such an analysis, however, does not completely isolate these features, or their associated oceanic plateaus and localized hot spot swells, from the ridge‐generated regional bathymetry upon which they are superimposed. Accordingly, a technique is required that passes beneath topographic constructs rather than through them, as is the tendency of the mean, median, or mode. We have developed an algorithm, MiMIC, that reproducibly removes all these features and reveals the large‐scale bathymetric trends in a manner based upon and consistent with manual interpretation. Application of the algorithm to bathymetry data in the southwest Pacific shows that the depth anomaly with respect to a cooling plate model changes steadily from being too deep at the East Pacific Rise (EPR) crest to being too shallow at the superswell. The largest shallow anomaly of 712 ± 66 m occurs at 98 Ma, not 1300 m at 65 Ma, as has been previously suggested. Most significantly, the superswell appears to be part of a large‐scale, “plate‐like,” subsidence that extends to the EPR crest, rather than an isolated shallowing that reverses the subsidence and causes uplift. We interpret the plate‐like subsidence as due in part to cooling of the oceanic lithosphere and in part to a lateral temperature gradient in the underlying asthenosphere which is maintained by the flow of relatively hot material from beneath the superswell toward the relative cold material beneath the EPR. The best fit model implies a lateral temperature gradient of 0.014°C km−1 and is in general accord with the available effective elastic thickness, crustal thickness, heat flow, and seismic tomography data.

P4.013 Effects of donepezil on behavioral andpsychological symptoms in Korean patients with Alzheimer's disease

We analyzed patterns of α- and β-diversity in deep-sea bivalves collected by epibenthic sleds from the western North Atlantic south of New England, and from the eastern North Atlantic in the Rockall Trough, Porcupine Seabight and Porcupine Abyssal Plain. In the western North Atlantic, species diversity, measured as the normalized expected number of species, shows a unimodal bathymetric trend peaking at mid-bathyal depths. In the eastern North Atlantic, diversity increases monotonically with depth reaching a maximum at abyssal depths. We used Baselga's (2010) metrics to distinguish two separate components of β-diversity along depth gradients, species dissimilarity among sites due to spatial replacement (turnover) and species loss leading to nestedness. We also examined the rank order of nestedness with depth using Rodríguez-Gironés and Santamaría's (2006) BINMATNEST. The primary difference in β-diversity between west and east centers on the composition of abyssal communities. In the western North Atlantic, abyssal assemblages are nested subsets of bathyal assemblages. In the eastern North Atlantic, turnover dominates at all depths. These very fundamental differences in community structure between the basins may be attributable to differences in food supply, which is greater in the eastern North Atlantic region sampled. POC-flux to abyssal depths in the east may not reach levels low enough to depress species diversity as it does in the west. In the west, the abyssal fauna is largely an impoverished nested subset of the bathyal fauna that shows less endemism and may be maintained partly by source–sink dynamics.

Meiofauna towards the South Sandwich Trench (750–6300m), focus on nematodes

Abstract Meiobenthos (excluding foraminifers) from the South Sandwich Trench was studied in sediment samples collected by multiple core (MUC) or multiple grab (MG). Sampling stations were chosen along a depth transect that covered the continental slope and abyssal plain towards the trench (water depths from 747 to 6319 m). Total abundance and biomass of meiobenthos ranged between 354 and 1675 ind. 10 cm −2 , and between 16.3 and 80.8 μg C 10 cm −2 , respectively. Standing stock decreased, though not linearly, with increasing water depth. Biomasses and densities were situated above the world ocean's regression line of meiobenthic stocks against water depth, and higher on the trench floor (354–930 ind 10 cm −2 , 18.7 μg C 10 cm −2 at 6300 m) compared to most other oceans’ trench regions. This observation confirms earlier results from the Antarctic continental margins that Antarctic meiofauna is characterised by dense populations in which nematodes predominate over the other taxonomic groups (87–98% of total abundance). Taxonomic investigations at genus level revealed that Chromadoridae, Monhysteridae, Desmodoridae, Desmoscolecidae, Xyalidae and Cyatholaimidae were dominant. Most of the nematode genera (in total 94) occurred in all depths, with only a slight distinction between the “shallow” ( Daptonema , Dichromadora and Molgolaimus preferentially at 750–2300 m) and “deep” (with Tricoma preferentially from 3000 m on). The “shallow”communities were comparable to those from the Weddell Sea continental margin; the sediments at 2300–6300 m harboured in big lines similar compositions as abyssal and trench communities worldwide. Two main morph clusters were distinguished among the South Sandwich Trench nematodes: plump nematodes, with average L : W = 9 , belonging to the taxonomic similar selective deposit-feeding genera of the Desmoscolecida, and comparable slender nematodes ( L : W = 26 ; biomass size class −4 to −2) such as Monhystera , Acantholaimus , Daptonema , Dichromadora , Molgolaimus , Microlaimus and some species from Paracanthonchus , mixed among mainly selective and epistratum feeding modes. They formed the bulk of the trench community. The results did not fit well with the general decrease in standing stock with increasing water depth and distance from the continental shelf. Similarly, nematode size (length from 124 to 2991 μm, biomass from 0.023 to 0.042 μg dwt) did not show clear bathymetric trends. The lack of the usual deep-sea trends of structural characteristics of meiofauna in general (density, total biomass, taxon composition) and functional attributes of nematodes (morphometrics, biomass, trophic guild structure, and maturity index) is explained by the particularly complexity of the sedimentary environment of the South Sandwich Trench, which was the result of physical processes (turbidites), bioturbation activity by invertebrate taxa and food supply along the depth transect.

Coastal sponge communities of the West Indian Ocean: taxonomic affinities, richness and diversity

AbstractSponges assemblages were sampled in four coastal study regions (Malindi, Kenya; Quirimba Archipelago, northern Mozambique; Inhaca Island, Southern Mozambique and Anakao, Madagascar) in the west Indian Ocean. Sponge species were counted in multiple 0.5 m2 quadrats at depths of between 0 and 20 m at a number of sites within localities within each region. Despite the relatively small areas sampled, sponge samples comprised a total of 130 species and 70 genera of the classes Demospongiae and Calcarea. Sponges are clearly a major taxon in these regions in terms of numbers of species, percentage cover or biomass, although their ecology in the west Indian Ocean is virtually unknown. Nearly half of the genera, e.g. Iotrochota, found were species with a so‐called Tethyan distribution. Most of the other genera were cosmopolitan, e.g. Clathria, but some were cold water (Coelosphaera), Indo‐Australian (Ianthella) or circum‐African (Crambe). Many of the species encountered in the present study occurred in at least two study regions, many in more and could occupy large areas of substratum. Some of these, e.g. Xestospongia exigua, are commonly found throughout the Indo‐west Pacific region where they also occupy much space. The endemicity of the shallow water sponge faunas in East Africa (20–25%) seem to be high within the Indo‐Pacific realm but are lower than northern Papua New Guinea. The tropical regions (Kenya and Northern Mozambique) were more speciose than subtropical regions (southern Mozambique and Madagascar) but not significantly more diverse (Shannon H′). Although latitude was not a major influence on sponge community patterns, hard substratum assemblages did form a cline from the tropics to Southern Mozambique, linked by Madagascar. Substratum nature (habitat) was most important in influencing the suite and number of species present. Sponge assemblages of soft substrata were much more dissimilar, both within and between habitats, than those on hard substrata. There was a predictable variability in species richness between hard substratum habitats: coral reefs being speciose and caves being less so. Our findings showed that both patterns and influences on species richness may be decoupled from those influencing diversity. In our data species richness, but not diversity, showed striking regional and bathymetric trends. In addition, sponge species richness mainly split at coral reef vs. non‐reef habitats, whilst diversity divided principally into assemblages on hard and soft substrata. We consider this dichotomy of findings between species richness and diversity values to be important, as these are two principal measures used for the interpretation of biodiversity.

Overview of ASIAEX field experiments in the South and East China Seas

In the spring of 2001 the Asian Seas International Acoustics Experiment (ASIAEX) was performed in the South and East China Seas. The ASIAEX program originated from the Office of Naval Research’s initiative to develop a Sino-American cooperation in the field of ocean acoustics, and expanded to involve Taiwan, Korea, Singapore, and Japan. In the South China Sea, the emphasis was on lower frequency (50–600 Hz) acoustic propagation through complex oceanography along and across the shelfbreak. The oceanographic variability was driven at the mesoscale by the monsoonal wind stress, buoyancy fluxes from the Chinese coast, and by occasional Kuroshio intrusions through the Luzon Strait. Large, nonlinear internal waves also significantly affected the acoustics. In the East China Sea the emphasis was on low- to- midfrequency acoustic interaction with, and reverberation from, the sea floor and sea surface. The experimental site was chosen for flatness, to minimize the influence of bathymetric trends, and emphasize bottom roughness and subbottom structures, in the measurements. This talk will describe the scope of the ASIAEX experimental program, including the ocean acoustic and environmental characterization of the seafloor, sea surface, and water column. Results from various measurement programs will be described in separate papers.