Depth Segregation Research Articles

Vertical structure of Caribbean deep-reef fishes from the altiphotic to deep-sea boundary

While recent technical breakthroughs have enabled advances in the description of reefs down to 150 m, the structure and depth zonation of deep-reef communities below 150 m remains largely unknown. Here, we present results from over 10 years of deep-reef fish surveys using human-occupied submersibles at four locations across the Caribbean Sea, constituting one of the only continuous reef-fish surveys from 10 to 480 m (1 site) and 40 to 300 m (3 sites). We identify four vertically stratified deep-reef fish communities between 40 and 300 m bordered by an altiphotic (0–10 m) and a deep-sea (300–480 m) community. We found a strong faunal break around 150 m that separates mesophotic and rariphotic zones and secondary breaks at ~ 70 to 90 m and ~ 180 to 200 m subdividing these zones into upper and lower communities. From 300 to 480 m in Roatán, we found a single fish community dominated by deep-sea families, indicating that the lower boundary of the reef-fish realm occurs at 300 m. No differences were found between communities ranging from 20 to 60 m, suggesting that fishes from the lower altiphotic and upper mesophotic form an ecological continuum. While some variability was observed across sites, the overall depth zonation and key species characterizing depth zones were consistent. Most deep-reef species observed were depth specialists restricted to a single depth zone, but many shallow-reef species extended down to mesophotic depths. Depth segregation among species of a genus was found across ten reef-fish genera and likely constitutes one of the mechanisms driving community distinctiveness and thereby fish diversity across depths.

Management and ecology of the wedge clam (Donax trunculus) in the NW Mediterranean Sea: The case of Ebro Delta (NE Spain)

The wedge clam (Donax trunculus) is one of the most prized clam species fished in the EU. Clam fisheries have experienced a dramatic decline during the last decades on Spanish coasts resulting in the progressive closure of fishing grounds. The Ebro Delta (NW Mediterranean Sea) is one of the few areas of the Spanish coast where there is still some fishing activity. In this context, the main objectives of this study were: to provide novel data on the ecology of this species and to analyse the management of D. trunculus fisheries in the Ebro Delta. The results showed a depth segregation phenomenon and suggested that D. trunculus performs two migrations during its benthic life cycle, i.e., (1) the settlement of planktonic larvae occurs more intensely in the deepest part of its bathymetric distribution, where the survival was more intense. As clams progressively increase in size, they move to shallower areas; (2) adults tend to move back to the deepest part of their bathymetric distribution as they increase in size. The management of D. trunculus has improved significantly in the last decade. However, some issues are still unsolved (e.g., fishing gear limits are unclear; population boundaries do not coincide with political boundaries). Moreover, the shallower areas where juveniles are located concentrate the highest fishing pressure over the stock.

Spatiotemporal and bioecological distribution of four commercial Mullid species in an ultraoligotrophic Mediterranean gulf

This study provides baseline data on the mullid fish assemblages based on their morphometries on a shelf of the most oligotrophic water of the Mediterranean Sea, Antalya Gulf. The distribution of fish abundances, biomasses, total length, sex composition, growth parameters, and ecological fish assemblages was studied along three transects (each had a series of bottom depths of 10, 25, 75, 125, and 200 m) between spring 2014 and winter 2015, representing the winter, spring, summer and autumn seasons. Four different species of the Mullidae family: the red mullet (Mullus barbatus), the striped red mullet (M. surmuletus), the golden-banded goatfish (Upeneus moluccensis) and the Por's goatfish (U. pori) were found and subjected to distributional analyses. Excluding M. surmuletus, all of the mullid fish were commonly and abundantly found. There was a definite depth segregation among their distributions, but no seasonal differences occurred. Mediterranean meadows are attractive areas for mullid species, especially for M. surmelatus. The spatial distributional pattern of U. pori was in complete contrast to that of M. surmuletus. Overall, the females (F) outnumbered the males (M) significantly in space (region and depth) and time (season). The morphometric parameters (length-related and growth parameters) were estimated to increase comparatively from east to west in the Mediterranean Sea. Ecologically, the mullid assemblages depended on the seafloor depth, bottom type (habitat and sedimentary characteristics), water productivity and dissolved oxygen content and salinity, and benthic composition.

Revision of the 'dragon-head cusk eels of the genus Porogadus (Teleostei: Ophidiidae), with description of eight new species and one new genus.

The ophidiid genus Porogadus occurs between 800 and 5300 m in the tropical and subtropical world oceans. Fifteen nominal species have been described since 1878 and most of them until 1902. The genus has been highlighted as needing revision in recent compilations about ophidiiforms and here we present the first comprehensive review. Twelve of the previously described species are here accepted as valid with two being moved to the newly established genus Tenuicephalus n. gen. that encompasses fishes differing from those of Porogadus in the extremely weak ossification, the stout head, absence of head spines and absence of the triple lateral line system considered typical for Porogadus and a reduced dentition. In addition, eight new species are described: Porogadus caboverdensis, P. dracocephalus, P. lacrimatus, P. mendax, P. solomonensis, P. turgidus, Tenuicephalus multitrabs and T. squamilabrus. The species of Porogadus show a distinctive depth segregation with the majority of species having a demersal bathyal life-style between 800 and 3500 m and other species being more or less exclusively restricted to abyssal depths below 3000 m. The biogeographic distribution pattern of bathyal groups shows putative species pairs in the Atlantic versus the eastern Pacific and a clear separation of eastern Pacific from Indo-West Pacific species. The geographic effects and timing are being discussed that may have led to this speciation events. Generally, we found widely distributed species that are found far away from continental masses and others restrained to continental slopes and sometimes exhibiting regionalism. In abyssal depth, the Cabo Verde and Canary basins off NW-Africa have yielded three exclusive species, but it is uncertain at this stage whether this could represent a sampling bias with this area being extensively sampled by the Discovery research vessel (BMNH) over the years from 19701998. Another instance of a potentially endemic abyssal species is that of Porogadus melanocephalus in the Bay of Bengal. The latter has been caught with 45 specimens in a single trawl, representing the highest number of Porogadus specimens collected in any trawl and indicating that these fishes may actually not be as rare as one might assume from the literature.

Microevolutionary change in viscerocranial bones under congeneric sympatry in the Lake Tanganyikan cichlid genus Tropheus

The endemic Lake Tanganyika cichlid genus Tropheus lives at rocky shores all around the lake and comprises six species which are subdivided into about 120 morphologically similar but color-wise distinct populations. Typically, they live without a second Tropheus species, but there are some regions where two or even three sister species live in sympatry. We previously showed that there are morphological differences concerning head shape, eye size and insertion of fins among populations living alone compared to those living in sympatry with a second Tropheus. This study goes one step further to test if sympatry affects the shape of viscerocranial bones. By means of geometric morphometrics, we compare the shape of four bones among thirteen Tropheus populations, some of which in sympatry and some living alone. We quantify patterns of shape variation and estimate morphological disparity among the four bony elements in the study species and populations. We found consistent differences in the shape of one bony element among non-sympatric and sympatric populations, besides an extensive variation in the shape of viscerocranial bones within and among species. Furthermore, sexual dimorphism in Tropheus is clearly evident in the viscerocranial bones analyzed. We suggest that the relatively subtle morphological signal in sympatric vs. non-sympatric Tropheus populations is owed to the fact that the depth segregation does not yet represent a full shift in the trophic niche, albeit our data confirm that differences in ecologically relevant traits, such as bones of the preorbital region, play an important role in the process of niche separation and in the context of explosive diversification of cichlid fishes.

Speciation-by-depth on coral reefs: Sympatric divergence with gene flow or cryptic transient isolation?

The distributions of many sister species in the sea overlap geographically but are partitioned along depth gradients. The genetic changes leading to depth segregation may evolve in geographic isolation as a prerequisite to coexistence or may emerge during primary divergence leading to new species. These alternatives can now be distinguished via the power endowed by the thousands of scorable loci provided by second‐generation sequence data. Here, we revisit the case of two depth‐segregated, genetically isolated ecotypes of the nominal Caribbean candelabrum coral Eunicea flexuosa. Previous analyses based on a handful of markers could not distinguish between models of genetic exchange after a period of isolation (consistent with secondary contact) and divergence with gene flow (consistent with primary divergence). Analyses of the history of isolation, genetic exchange and population size based on 15,640 new SNP markers derived from RNAseq data best support models where divergence began 800K BP and include epochs of divergence with gene flow, but with an intermediate period of transient isolation. Results also supported the previous conclusion that recent exchange between the ecotypes occurs asymmetrically from the Shallow lineage to the Deep. Parallel analyses of data from two other corals with depth‐segregated populations (Agaricia fragilis and Pocillopora damicornis) suggest divergence leading to depth‐segregated populations may begin with a period of symmetric exchange, but that an epoch of population isolation precedes more complete isolation marked by asymmetric introgression. Thus, while divergence‐with‐gene flow may account for much of the differentiation that separates closely related, depth‐segregated species, it remains to be seen whether any critical steps in the speciation process only occur when populations are isolated.

Diel vertical migration of copepods and its environmental drivers in subtropical Bahamian blue holes

Diel vertical migration (DVM) is the most common behavioral phenomenon in zooplankton, and numerous studies have evaluated DVM under strong seasonality at higher latitudes. Yet, our understanding of the environmental drivers of DVM at low latitudes, where seasonal variation is less pronounced, remains limited. Therefore, we here examined patterns of vertical distribution in copepods in six subtropical Bahamian blue holes with different food web structure and tested the role of several key environmental variables potentially affecting this behavior. Day and night samplings showed that copepods generally performed DVM, characterized by downward migration to deeper depths during the day and upward migration to surface waters at night. Across all blue holes, the daytime vertical depth distribution of calanoid copepods correlated positively with both predation risk and depth of food resources (Chlorophyll a), but was less affected by ultraviolet radiation (UVR). A potential explanation is that since UVR is a continuous threat across seasons, zooplankton have established photoprotective pigmentation making them less vulnerable to this threat. The copepods also showed a size-structured depth segregation, where larger individuals were found at deeper depths during the day, which further strengthens the suggestion that predation is a major driver of DVM in these systems. Hence, in contrast to studies performed at higher latitudes, we show that despite the constant exposure to UVR, predator avoidance and food availability are the most pronounced drivers of copepod DVM at those low latitudes, suggesting that the main driver of DVM may vary among systems, but also systematically by latitude.

Reproductive strategy of Scyliorhinus canicula (L., 1758): a holistic approach based on macroscopic measurements and microscopic observations of the reproductive organs

Understanding reproductive features of elasmobranchs that affect population recovery and natural mortality is essential for conservation management planning. Considering macroscopic and microscopic observations of the reproductive tract in 2253 individuals, sampled in Hellenic waters over a 7-year period, four reproductive stages were described. The presence of advanced spermatocyst stages in immature testes supported the early gamete development and long maturation process. The simultaneous presence of follicles of all developmental stages in mature ovaries indicated a protracted egg-laying season. An extended reproductive period was also supported by monthly records of egg-laying females, sexually active males, large egg cases and high values of the gonadosomatic (GSI) and hepatosomatic (HSI) indices. Size at maturity was similar for both sexes. Females and males exhibited no depth segregation compared with individuals of different maturity stages regardless of sex. Sex, size and maturity stage significantly affected GSI, HSI and the relative condition factor. All three somatic indices showed a similar monthly variation, supporting a fat assimilation rate that follows maturation rate, with both affecting physiological condition. The severe population decline that Scyliorhinus canicula has recently undergone should focus our attention on future research supporting robust population modelling to help management of the species.

Deep stocks avoid competition migrating horizontal and vertically: The example of two scabbardfishes (Aphanopus spp.) targeted by long-liners in grounds next to an oceanic archipelago

Fishing is occurring all over the globe, with an increase trend of exploiting deep stocks. Several species are currently targeted from the deep ocean, and some artisanal fisheries developed fishing gears, e.g. long lines, with limited impact to the environment but scarce information is available on biological aspects of these exploited stocks. In the Macaronesian region and specifically in Madeira archipelago, two Aphanopus sympatric species have been extensively exploited for decades but no detailed information is available on the spatial and vertical distribution of both species (Aphanopus carbo and Aphanopus intermedius). Currently, they represent an important percentage of landings from artisanal fishermen of Madeira (27% of the total catches in 2017). We herein observed that they showed a pattern of depth segregation, where adults of both species are more abundant (ca. 80%) at deeper seafloor (> 2500 m). A. intermedius was more numerous in fishing areas with greater seafloor depth (> 4500 m) compared to A. carbo. This pattern may be explained by a food source overlap between both species, and also the vertical segregation within the same species may be considered as a pattern to avoid cannibalism. Also, migration patterns were found in both species being more pronounced for A. intermedius where > 86% of individuals were collected offshore (> 12 n.m.). The present results constitute a step forward to start developing integrative management actions to preserve stocks of both species in the medium and long term in the study region.

Macroevolutionary analysis of the tempo of diversification in snappers and fusiliers (Percomorpha: Lutjanidae)

The percomorph fish family Lutjanidae (snappers and fusiliers) includes about 135 reef-dwelling species, mainly confined to tropical and subtropical marine waters. The great majority of snappers are active predators feeding on fishes or crustaceans, even though some species, including the fusiliers (Caesioninae), have evolved zooplanktivory. Lutjanids show a great diversity of habitat preferences, based on depth segregation and distribution across reef and associated habitats (e.g., mangroves, seagrass beds, estuaries). In spite of their great ecological and economic importance little is known about the tempo of evolution in this group. The present study provides the most comprehensive molecular phylogeny to date for lutjanids, including 70% of extant species and 19 of the 21 currently described genera. We time-calibrated our molecular tree using the oldest described lutjanid fossils, and show how this group most likely originated during the Late Cretaceous or Early Paleocene. Lutjanids experienced a significant radiation during the Late Eocene and Early Oligocene, in contrast to a pattern of Late Oligocene/Miocene radiation observed in many other reef-associated groups. The time-tree allows us to investigate the tempo of diversification, and our results suggest a variation in the rate of speciation during the evolution of the major clade formed by “lutjanins and caesionins”. Variation in diet and life history strategies could explain this clade-specific dynamic, although future phylogenetic comparative studies combining additional ecological and morphological data are needed to test this hypothesis.

Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic

We diagnose the relative influences of local-scale biogeochemical cycling and regional-scale ocean circulation on Atlantic barium cycling by analysing four new depth profiles of dissolved Ba concentrations and isotope compositions from the South and tropical North Atlantic. These new profiles exhibit systematic vertical, zonal and meridional variations that reflect the influence of both local-scale barite cycling and large-scale ocean circulation. Epipelagic decoupling of dissolved Ba and Si reported previously in the tropics is also found to be associated with significant Ba isotope heterogeneity. As such, we contend that this decoupling originates from the depth segregation of opal and barite formation but is exacerbated by weak vertical mixing. Zonal influence from isotopically-‘heavy’ water masses in the western North Atlantic evidence the advective inflow of Ba-depleted Upper Labrador Sea Water, which is not seen in the eastern basin or the South Atlantic. Meridional variations in Atlantic Ba isotope systematics below 2000m appear entirely controlled by conservative mixing. Using an inverse isotopic mixing model, we calculate the Ba isotope composition of the Ba-poor northern end-member as +0.45‰ and the Ba-rich southern end-member +0.26‰, relative to NIST SRM 3104a. The near-conservative behaviour of Ba below 2000m indicates that Ba isotopes can serve as an independent tracer of the provenance of northern- versus southern-sourced water masses in the deep Atlantic Ocean. This finding may prove useful in palaeoceanographic studies, should appropriate sedimentary archives be identified, and offers new insights into the processes that cycle Ba in seawater.

Drivers and patterns of iron redox cycling from surface to bedrock in a deep tropical forest soil: a new conceptual model

Iron (Fe) reduction and oxidation are important biogeochemical processes coupled to decomposition, nutrient cycling, and mineral weathering, but factors controlling their rates and spatial distribution with depth are poorly understood in terrestrial soils. In aquatic ecosystems, Fe reduction often occurs below a zone of oxic sediments. We tested an alternative conceptual model for Fe redox cycling in terrestrial soils using a deep humid tropical forest soil profile. We hypothesized that Fe reduction in anaerobic microsites scales with depth variation in labile C and Fe availability, as opposed to bulk oxygen (O2). We measured bulk O2 at multiple depths from 0.1 to 5 m quasi-continuously over 18 months and sampled soils from surface to bedrock (~7 m). Median O2 mixing ratios declined from 19.8 ± 1.2 % at 0.25 m to 16.1 ± 1.0 % at 1 m, but did not consistently decrease below 1 m, challenging a recent model of regolith development. Reduced Fe (Fe(II)) extractable in 0.5 M hydrochloric acid was greatest in 0–0.1 m soil and declined precipitously with depth, and did not correspond with visible gleying in B horizons. We observed similar depth trends in potential Fe reduction under anaerobic conditions. Depth trends in Fe(II) also closely mirrored short-term soil respiration and bulk soil C. Labile C stimulated Fe reduction at 0–0.1 m depth, whereas addition of short-range-ordered Fe oxides had no effect. Cultivable Fe-reducing bacterial abundance was four orders of magnitude greater in surface soil (0–0.1 m) than below 1 m. Although cultivable Fe oxidizing bacteria were typically also more abundant in surface soil, addition of labile C and nitrate stimulated Fe oxidizers in deep soil by two orders of magnitude under anaerobic conditions. This implies that infiltration of nitrate (and possibly C) from shallow soil water could potentially promote biotic Fe oxidation, a critical step in bedrock weathering, 7 m below. Together, these data suggest that C, Fe, and nutrient availability increase microbial Fe reduction and oxidation in surface (vs deeper) soil microsites despite high bulk O2, in contrast to the depth segregation of electron accepting processes often observed in aquatic ecosystems. Furthermore, the greatest capacity for Fe redox cycling can occur in A horizons that do not display gleying or mottling.

Depth segregation and diet disparity revealed by stable isotope analyses in sympatric herbivorous cichlids in Lake Tanganyika.

BackgroundLake Tanganyika in the African Great Rift Valley is known as a site of adaptive radiation in cichlid fishes. Diverse herbivorous fishes coexist on a rocky littoral of the lake. Herbivorous cichlids have acquired multiple feeding ecomorphs, including grazer, browser, scraper, and scooper, and are segregated by dietary niche. Within each ecomorph, however, multiple species apparently coexist sympatrically on a rocky slope. Previous observations of their behavior show that these cichlid species inhabit discrete depths separated by only a few meters. In this paper, using carbon (C) and nitrogen (N) stable isotope ratios as markers, we followed the nutritional uptake of cichlid fishes from periphyton in their feeding territories at various depths.Resultsδ15N of fish muscles varied among cichlid ecomorphs; this was significantly lower in grazers than in browsers and scoopers, although δ15N levels in periphyton within territories did not differ among territorial species. This suggests that grazers depend more directly on primary production of periphyton, while others ingest animal matter from higher trophic levels. With respect to δ13C, only plankton eaters exhibited lower values, suggesting that these fishes depend on production of phytoplankton, while the others depend on production of periphyton. Irrespective of cichlid ecomorph, δ13C of periphyton correlated significantly with habitat depth, and decreased as habitat depth became deeper. δ13C in territorial fish muscles was significantly related to that of periphyton within their territories, regardless of cichlid ecomorph, which suggests that these herbivorous cichlids depend on primary production of periphyton within their territories.ConclusionsCarbon and nitrogen stable isotope ratios varied among ecomorphs and among cichlid species in the same ecomorphs sympatrically inhabiting a littoral area of Lake Tanganyika, suggesting that these cichlids are segregated by nutrient source due to varying dependency on periphyton in different ecomorphs (especially between grazers and browsers), and due to segregation of species of the same ecomorph by feeding depth, grazers and browsers in particular.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-015-0016-1) contains supplementary material, which is available to authorized users.

Molecular biological and isotopic biogeochemical prognoses of the nitrification‐driven dynamic microbial nitrogen cycle in hadopelagic sediments

There has been much progress in understanding the nitrogen cycle in oceanic waters including the recent identification of ammonia-oxidizing archaea and anaerobic ammonia oxidizing (anammox) bacteria, and in the comprehensive estimation in abundance and activity of these microbial populations. However, compared with the nitrogen cycle in oceanic waters, there are fewer studies concerning the oceanic benthic nitrogen cycle. To further elucidate the dynamic nitrogen cycle in deep-sea sediments, a sediment core obtained from the Ogasawara Trench at a water depth of 9760 m was analysed in this study. The profiles obtained for the pore-water chemistry, and nitrogen and oxygen stable isotopic compositions of pore-water nitrate in the hadopelagic sediments could not be explained by the depth segregation of nitrifiers and nitrate reducers, suggesting the co-occurrence of nitrification and nitrate reduction in the shallowest nitrate reduction zone. The abundance of SSU rRNA and functional genes related to nitrification and denitrification are consistent with the co-occurrence of nitrification and nitrate reduction observed in the geochemical analyses. This study presents the first example of cooperation between aerobic and anaerobic nitrogen metabolism in the deep-sea sedimentary environments.

Depth segregation of deepwater ciscoes (Coregonus spp.) in Lake Michigan during 1930–1932 and range expansion of Coregonus hoyi into deeper waters after the 1990s

Depth segregation of deepwater ciscoes (Coregonus spp.) in Lake Michigan during 1930–1932 and range expansion of Coregonus hoyi into deeper waters after the 1990s

Quantitative analysis of conodont tooth wear and damage as a test of ecological and functional hypotheses

Analysis of dental wear and damage is becoming an increasingly important tool in unraveling the trophic ecology of a wide range of vertebrates, and when applied to fossils it can provide evidence of both diet and feeding kinematics that is independent of morphological analysis. Conodonts have the best fossil record among vertebrates and their skeletal elements are known to exhibit surface wear and damage generated in vivo as a consequence of their function as teeth. We report the results of the first systematic survey and analysis of the frequency and extent of this wear and damage in conodonts (based on P1elements from a range of Carboniferous genera). This has revealed that wear and damage are remarkably common, present in all conodont elements sampled. Multivariate analysis reveals that patterns of wear and damage differ significantly among different conodont taxa, and exploratory ANOVA and linear discriminant analyses show that wear and damage differ according to the position of taxa in an onshore-offshore gradient, and whether they are likely to have had a benthic or pelagic mode of life. The incidence of denticle tip spalling in particular is higher in more-offshore environments and in taxa likely to have had a pelagic mode of life. Aspects of the data also reflect the occlusal kinematics of the elements, providing a means of testing hypotheses of element function. Our results have wide-ranging implications for unlocking the fossil record of conodonts, by, for example, furnishing direct evidence of the diet-mediated processes that may have driven observed patterns of evolutionary change, and reducing the confounding effects of depth segregation when using conodonts in isotope-based paleotemperature studies.

Vertical distribution of two sympatric labrid fishes in the Western Mediterranean and Eastern Atlantic rocky subtidal: local shore topography does matter

Changes in the shore topography (e.g. slope) occur at a scale of hundreds of meters in several locations in the Lusitanian and the Mediterranean Sea provinces. We tested whether differences in the bottom inclination might affect the vertical distribution patterns of two sympatric coastal labrid fishes, the rainbow wrasse Coris julis and the ornate wrasse Thalassoma pavo. Visual censuses were used to determine the distribution and abundance of these labrid species in high (≥30°) and low (≤3°) slope rocky substrates covered by brown macroalgae and at two different depths (shallow, 4–7 m, and deep 14–20 m). Pectoral fin aspect ratio was used as an estimate of swimming performance to potentially explain the patterns observed. Despite the intrinsic biogeographical differences in the overall density of T. pavo and C. julis, on steep coasts the ornate wrasse dominated in shallow waters, whereas the two species coexisted both in shallow and deeper depths on gentle slope coasts. These distribution patterns were consistent across locations, and fin aspect ratio was not a good predictor of between-habitat use for wrasses. We show that, under specific topographical conditions, the depth segregation pattern seems to be an interactive segregation (likely related to resource competition) rather than a result of selective segregation due to morphological differences in the pectoral fin. Significant ecological changes might occur in locations where the density of T. pavo has recently increased as a result of water warming.

Investigation of fullerene depth distribution in PMMA‐C60 blends using dual beam ToF‐SIMS

AbstractNanocomposites, and in particular, Polymer–Fullerene blends, have recently drawn strong attention owing to their properties and their numerous applications in new‐generation electronic and optoelectronic devices. The fullerene concentration in the material is critical since it dictates its electrical behavior. In this context, precise knowledge of the fullerene depth distribution in the blends is needed. Here, we investigate the capability of the ToF‐SIMS technique to provide quantitative information on PMMA‐C60 blends with extremely small C60 concentrations. Smooth PMMA layers of ∼130 nm thickness ranging from 0 to 0.04 wt% C60 were deposited on Si wafers. Samples were analyzed with an ION‐TOF TOF SIMS V instrument in negative mode. Using low‐energy Cs+ sputtering (250 eV) and Bi3+ as the analysis ion allowed monitoring of C60 characteristic secondary ions, namely C60− and its isotopes at m = 720,721,722,723,724,725 u. Operating the beams in noninterlaced mode enabled successful depth profiling of samples with very little signal decay. Improvement of depth resolution was achieved by cooling the sample while profiling; AFM study of crater bottoms showed reduced roughness at low temperature, justifying the improvement. Segregation in depth of C60 against PMMA was not observed, in agreement with surface free energy values determined by a contact angle method. Point‐by‐point normalization of C60 signal (C60−, m = 720 u) to PMMA monomer signal (C5H9O2−, m = 101 u) was found to give a linear function of C60 concentration with excellent regression coefficient. Copyright © 2010 John Wiley & Sons, Ltd.

Biogeography and Potential Exchanges Among the Atlantic Equatorial Belt Cold-Seep Faunas

Like hydrothermal vents along oceanic ridges, cold seeps are patchy and isolated ecosystems along continental margins, extending from bathyal to abyssal depths. The Atlantic Equatorial Belt (AEB), from the Gulf of Mexico to the Gulf of Guinea, was one focus of the Census of Marine Life ChEss (Chemosynthetic Ecosystems) program to study biogeography of seep and vent fauna. We present a review and analysis of collections from five seep regions along the AEB: the Gulf of Mexico where extensive faunal sampling has been conducted from 400 to 3300m, the Barbados accretionary prism, the Blake ridge diapir, and in the Eastern Atlantic from the Congo and Gabon margins and the recently explored Nigeria margin. Of the 72 taxa identified at the species level, a total of 9 species or species complexes are identified as amphi-Atlantic. Similarity analyses based on both Bray Curtis and Hellinger distances among 9 faunal collections, and principal component analysis based on presence/absence of megafauna species at these sites, suggest that within the AEB seep megafauna community structure is influenced primarily by depth rather than by geographic distance. Depth segregation is observed between 1000 and 2000m, with the middle slope sites either grouped with those deeper than 2000m or with the shallower sites. The highest level of community similarity was found between the seeps of the Florida escarpment and Congo margin. In the western Atlantic, the highest degree of similarity is observed between the shallowest sites of the Barbados prism and of the Louisiana slope. The high number of amphi-atlantic cold-seep species that do not cluster according to biogeographic regions, and the importance of depth in structuring AEB cold-seep communities are the major conclusions of this study. The hydrothermal vent sites along the Mid Atlantic Ridge (MAR) did not appear as “stepping stones” for dispersal of the AEB seep fauna, however, the south MAR and off axis regions should be further explored to more fully test this hypothesis.

Ecological correlates of species differences in the Lake Tanganyika crab radiation

The endemic crabs of Lake Tanganyika include a phenotypically diverse clade that exhibits recent divergence and low phylogenetic species resolution. There are indications that ecological niche segregation has played a prominent role in the divergence of this clade. We used habitat surveys, gut content analyses and stable isotope analyses to test the extent to which morphological species are ecologically different. Our data show some interspecific segregation in depth, substrate type and mean stable isotope signatures. At the same time, a considerable level of ecological niche overlap is evident among species of Platythelphusa that coexist in rocky littoral habitats. We consider these results in the framework of adaptive radiation theory, and we discuss general ramifications for the maintenance of species diversity in Lake Tanganyika.