The colour patterns of cypraeid gastropods

Colour patterns on mollusc shells are usually controlled by one-dimensional morphogenetic programmes. In adult cypraeids, by comparison, colour patterns are two-dimensional in morphogenesis and three-dimensional in structure. Visible patterns usually result from the uneven thickness of a pigmented layer, rather than from a spatially uneven concentration of pigment. Specialized sculptures in a few cypraeids may be regarded as extreme examples of three-dimensional colour patterns. Morphogenesis of some patterns is controlled by three-dimensional relief of the underlying shell surface. Computer models successfully reproduce key characteristics of cypraeid colour patterns. Since most cypraeids possess colour patterns, while few of the combinations of factors controlling these programmes yield a pattern, these patterns can be expected to have a yet undemonstrated adaptive value.     

The benthic foraminiferal communities of the northern Adriatic continental shelf

Off the Po Delta in the northern Adriatic, three different foraminiferal associations were identified in the fraction >0.125 mm of 25 sediment samples. The first association concerns sample stations between depths of 5 and 13.5 m in the shallow, nutrient-rich belt and is characterised by dominant Ammonia beccarii. The second occupies the 29.5–38.5-m-deep, nutrient-rich zone of clay-rich sediment, where inputs from the Po are concentrated, and is dominated by Nonionella opima. The third association, in the 21–46-m-deep and nutrient-poor zone, is dominated by Textularia agglutinans. The same distribution of communities was obtained using total associations (living and dead specimens) and biocenosis (stained individuals). The good correspondence with the foraminiferal distributions described in the past indicates that, in spite of the occurrence of anoxic and dysoxic events, the environmental state in the northern Adriatic may be considered stable.     

Geographical patterns in species richness of the benthic polychaetes in the continental shelf of the Gulf of California, Mexican Pacific

The present study is the first attempt to describe meso-scale patterns in the species richness of polychaetes along the Gulf of California, which stretches from about 23°N to 31°N. We examine herein the spatial changes in species distribution and explore the overlapping of species’ ranges towards the centre of the Gulf, to test whether the mid-domain effect (MDE) could explain an expected mid-domain peak in species richness. The faunal composition and the latitudinal range of 244 species of polychaetes recorded along the continental shelf of the Gulf of California were analysed in latitude bands of 1°. The species composition changes around the Gulf’s archipelago (~29°N), and the highest values of species richness are found at the 25° (197 species) and 26° (193 species) of latitude. Although the species richness pattern could be described by a parabolic shape, the regional trend was not strongly consistent with the peak of diversity at 27°N (176–191 species) predicted by the mid-domain effect: the random sorting of species’ ranges within spatial domain does not explain satisfactorily the geographical patterns of diversity. Nevertheless, a partial contribution of MDE to these natural patterns of diversity could be detected, and the increase in species richness towards middle latitudes was basically determined by species with distribution ranges larger than 6°. The low level of significance between the empirical species richness pattern and the mid-domain model prediction for polychaetes in the Gulf does not restrict their use as a model for exploring the randomness of the diversity patterns.     

Patterns in the benthic communities on the shelf of the sub-Antarctic Prince Edward Islands

Summary Benthic communities at the sub-Antarctic Prince Edward Islands were sampled qualitatively with an epi-benthic sled at 57 stations over a five year period. Additional information on these communities was obtained from replicate underwater photographs. In total, 546 macrofaunal species were found. Despite the extreme isolation and geological youth of the islands, there seems to have been a diverse colonisation. A cluster-analysis based on species abundance aggregated most stations into 8 groups. Each of these groups had a unique depth and substratum combination. Thourella variabilis (Octocoralea), and Cabarea darwinii (Bryozoa) characterised deep rocky assemblages and Serpula vermicularis, Lanice conchilega (Polychaeta) and Magellania kerguelenensis (Brachiopoda) characterised soft substrata. Indicator species separating each of the 8 clusters are given. Trends in percentage cover and densities of major taxa with respect to depth and substratum, as shown by photographs, are described. Deep, rocky substrata were dominated by Porifera, Bryozoa and Cnidaria, while soft-substrata were dominated by Polychaeta, Bivalvia and Brachiopoda. Errant forms consisted predominantly of Echinodermata, with Crustacea being important in shallower habitats. Filter-feeders dominated the benthos of the islands in all habitats.     

Meiobenthic stocks and benthic activity on the NE-Svalbard shelf and in the Nansen Basin

Summary High Arctic meiofaunal distribution, standing stock, sediment chemistry and benthic respiratory activity (determined by sediment oxygen consumption using a shipboard technique) were studied in summer 1980 on the NE Svalbard shelf (northern Barents Sea) and along a transect into the Nansen Basin, over a depth range of 240–3920 m. Particulate sediment proteins, carbohydrates and adenylates were measured as additional measures of benthic biomass. To estimate the sedimentation potential of primary organic matter, sediment bound chloroplastic pigments (chlorophylls, pheopigments) were assayed. Pigment concentrations were found comparable to values in sediments from the boreal and temperate N-Atlantic. Meiofauna, which was abundant on the shelf, decreased in numbers and biomasses with increasing depth, as did sediment proteins, carbohydrates, adenylates and sediment oxygen consumption. Meiofaunal abundances and biomasses within the Nansen Basin were comparable with those observed in abyssal sediments of the North Atlantic. Nematodes clearly dominated in metazoan meiofauna. Protozoans were abundant in shelf sediments. Probably in response to the sedimentation of the plankton bloom, meiofauna abundance and biomass as well as sediment proteins, carbohydrates and adenylates were significantly correlated to the amount of sediment bound chloroplastic pigments, stressing the importance of food quantity to determine benthic stocks. Ninety-four percent of the variance in sediment oxygen consumption were caused by chloroplastic pigments. Benthic respiration, calculated per unit biomass, was 3–10 times lower than in the East Atlantic, suggesting low turnover rates in combination with a high standing stocks for the high Arctic benthos.     

Distribution of the twenty seven dominant species of shelf benthic foraminifers on the continental shelf, north of Dakar (Senegal)

One hundred and thirty-one samples were collected on the shelf and on the uppermost slope (down to 180 m) off Northern Senegal, between 14 °50′ and 16 °20′ N latitude.Two hundred and three species of benthic foraminifers were recognized. Most of them were reported in previous works, along the coast of Africa. Twenty seven species are selected for detailed analysis and distribution maps are given for each of them. Q mode and R mode statistical analyses were performed on these selected species. The distribution is mainly related to depth; the second factor of distribution is the nature of the sediments: about 30% of the study area is covered by the muddy sediments of the pro-delta of the Senegal river. Hierarchical analysis shows that the main limit in the pattern of change of these 27 species with depth is about 60–65 m.A depth index Di, calculated on the basis of twelve selected species, gives a depth indication with a precision of about 40 m over the shelf. It is possible to envisage a possible use of this index for the investigation of Quaternary sea-level changes.     

AUV-based classification of benthic communities of the Ningaloo shelf and mesophotic areas

Coral Reefs - Despite a growing understanding of the importance of mesophotic ecosystems, they remain relatively unexplored globally, and particularly in the Indian Ocean. The composition of...     

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on the continental shelf of the Pacific Northwest, using video footage collected by ROV, to more finely characterize these assemblage–habitat associations. Four main associations were found: pure mud/sand dominated by sea whips and burrowing brittle stars; mixed mud–rock (which may be further divided based on size of mixed-in rocks) characterized by various taxa at small densities; consolidated rocks characterized by high diversity and density of sessile or motile mega-invertebrates; and rubble rocks showing less diversity and density than the consolidated rocks, possibly due to the disturbance generated by movement of the unconsolidated rocks. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.     

Influence of benthic macrofauna on microbial production of methylmercury in sediments on the New England continental shelf

Microbial methylation processes in sediment are an important source of toxic monomethylmercury (MMHg) to aquatic ecosystems. Although bioturbation activities (feeding, digging of galleries, excavations, bioirrigation) by benthic fauna are known to affect many biogeochemical processes, their influence on benthic MMHg production is poorly understood. We investigated the effect of benthic fauna on the microbial production of MMHg in sediments on the continental shelf of the northwest Atlantic Ocean in September 2009. Replicate cores of sieved (control) and unaltered sediment containing native macrofauna were incubated to examine the influence of benthic macrofauna on net MMHg production, potential gross rates of Hg methylation, sediment reworking, dissolved oxygen and organic carbon concentrations, and microbial metabolic activities. The presence of macrofauna stimulated aerobic microbial respiration and net MMHg production, but had no observed effect on short-term gross rates of Hg methylation. This suggests that bioturbation may promote net MMHg production by inhibiting demethylating microorganisms, although overall community metabolism was increased. Results from this work emphasize the need to enhance our knowledge and understanding of the interactions among benthic fauna, microorganisms, and geochemistry in affecting MMHg production.     

Taxonomic relatedness and spatial structure of a shelf benthic gastropod assemblage

Aim Phylogenetically related species share attributes that lead to common responses to environmental conditions, but which could also produce the exclusion of species by its relatives. These processes could generate the patterns of phylogenetic attraction or repulsion in local communities, where related species would tend to coexist more or less than expected by chance. This paper aims to (1) analyse the phylogenetic structure of a benthic gastropod assemblage in the south‐western Atlantic Ocean (SAO); (2) explore the linkages between phylogenetic structure and spatial distribution patterns; (3) compare outcomes driven by the analysis of presence‐only data and predictive species distribution models; and (4) explore which aspects of the gained knowledge can be useful to the design of sound conservation and/or management actions. Location Uruguayan shelf and slope in the SAO. Methods Spatial patterns in taxonomical relatedness were assessed using (1) raw presence/absence data (i.e. realized niche approach) and (2) reconstruction of the potential composition of the assemblage from niche modelling (i.e. fundamental niche approach). Null models were used to test hypotheses on assemblage structure. Results Significant departures from the null hypothesis that all species were drawn from the same assemblage were observed irrespectively of the approach, indicating the existence of non‐random structures. However, a high proportion of local communities can be thought as random subsets of the regional species pool. This lack of a strong signal of a taxonomic effect could be related to the absence of a linkage between taxonomic distances and ecological similarities. Main conclusions Our results suggest a random assembly of local communities from the regional species pool and/or niche filtering independent of phylogeny as main determinants of local community composition. We also suggest that local assemblages displaying significantly higher (or lower) than expected taxonomic relatedness should be taken into consideration for designing spatially explicit conservation measures.     

Potential impact of the main benthic amphipods on the eastern Weddell Sea shelf ecosystem (Antarctica)

As they represent one of the most diversified taxonomic groups on Antarctic bottoms, amphipods are likely to play a complex role in biogeochemical fluxes that occur within benthic ecosystems. The aim of this paper is to present, using both digestive tract analyses and relative species abundance data, the impact of amphipod feeding on different potential preys of the Weddell Sea. The study is based on data obtained for 29 representative amphipod species collected at 130 stations distributed along the eastern shelf of the Weddell Sea (depth range: 60-2,000 m) during three summer cruises, from 1989 to 1998. Sedimenting plankton particles (10-27%), crustaceans (22-32%) and fish carrion (5-18%) are the main food resources. Other abundant potential preys, such as molluscs or tunicates, do not seem to be consumed. Variations in the proportions of the different preyed food items are observed, mainly related to differences in relative amphipod species composition in samples. Presented results will help in refining ecological models of the prospected area, but also underline the need for accurate and reliable measurements of the feeding rates of Antarctic benthic organisms.     

Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea

The distribution of recent shallow-water benthic foraminifera in surface sediment samples from cool-water carbonate environments of the Oran Bight, Alboran Platform and Mallorca Shelf in the Western Mediterranean Sea was studied. Multivariate statistical analyses resulted in the identification of species assemblages, representing different environmental settings. In all three regions the assemblages show a distinct bathymetric zonation that is mainly attributed to the distribution of rhodoliths and related substrates, but also to water turbulence and the availability of food at the sea floor. The live assemblages (Rose Bengal stained individuals) are characterised by rather low diversity and low standing stocks, likely reflecting seasonal population dynamics. In the Oran Bight, elevated standing stocks of “high food”-taxa suggest the impact of anthropogenic eutrophication on the near-coastal benthic ecosystems of this area. The diversity of the dead assemblages is higher than in siliclastic shelf ecosystems of the Mediterranean Sea but lower when compared to carbonate environments of the Levantine Sea. This regional difference is mainly attributed to lower sea surface temperatures and the lack of Lessepsian invaders in the western Mediterranean Sea. In all study areas, a distinct faunal change occurs between approximately 80–90 m water depth. This change coincides with the lower distribution limit of living rhodoliths at the shelf of Mallorca, providing coarse-grained substrates that are dominated by attached taxa. Below this depth interval, the fauna shows regional differences depending on the grain-size and related accumulation of organic material. Fine-grained substrates with infaunal niches are restricted to low-energy environments on the deeper shelf southwest off Mallorca.     

Seasonal benthic nitrogen cycling in a temperate shelf sea: the Celtic Sea

Spring runoff often comprises the majority of annual discharge and riverine phosphorus (P) export due to sustained high flow, and the magnitude of spring runoff can be a strong predictor of receiving water summer harmful algal bloom severity. Yet the loading of reactive forms of P during this time period remains poorly-characterized in time, space and geochemical partitioning. Here, we explore the hypothesis that riverine dissolved and suspended sediment P loads during spring runoff have a particularly high proportion of potentially reactive species due to unique hydrologic pathways and P association with iron (Fe).The concentration, distribution and temporal dynamics of dissolved P (DP), dissolved and colloidal Fe, and redox sensitive suspended sediment P (RSP) and Fe during spring runoff and summer storms were compared in forested and agricultural catchments of the same watershed. The dominant carrier of RSP was Fe (oxy)hydroxides across land cover and season, but Fe (oxy)hydroxide particles and colloids in agricultural catchments were strongly enriched in RSP and DP during spring runoff and summer storms, particularly at the onset of snowmelt. In 2014, 83% of DP and 74% of RSP were delivered to Missisquoi Bay during spring runoff. Suspended sediment was significantly more redox sensitive than typically input to limnological models, suggesting that the reactivity of this load may be systematically underestimated. Changes in the timing, provenance and severity of spring runoff associated with climate or land cover change will have dramatic impacts on total riverine P loads and their potential reactivity in receiving water ecosystems.     

Global patterns in the impact of marine herbivores on benthic primary producers

Despite the importance of consumers in structuring communities, and the widespread assumption that consumption is strongest at low latitudes, empirical tests for global scale patterns in the magnitude of consumer impacts are limited. In marine systems, the long tradition of experimentally excluding herbivores in their natural environments allows consumer impacts to be quantified on global scales using consistent methodology. We present a quantitative synthesis of 613 marine herbivore exclusion experiments to test the influence of consumer traits, producer traits and the environment on the strength of herbivore impacts on benthic producers. Across the globe, marine herbivores profoundly reduced producer abundance (by 68% on average), with strongest effects in rocky intertidal habitats and the weakest effects on habitats dominated by vascular plants. Unexpectedly, we found little or no influence of latitude or mean annual water temperature. Instead, herbivore impacts differed most consistently among producer taxonomic and morphological groups. Our results show that grazing impacts on plant abundance are better predicted by producer traits than by large-scale variation in habitat or mean temperature, and that there is a previously unrecognised degree of phylogenetic conservatism in producer susceptibility to consumption.     

Contrasting demographic history and phylogeographical patterns in two Indo-Pacific gastropods

Marine species with ranges that span the Indo-Australian Archipelago (IAA) exhibit a range of phylogeographical patterns, most of which are interpreted in the context of vicariance between Indian and Pacific Ocean populations during Pliocene and Pleistocene low sea-level stands. However, patterns often vary among ecologically similar taxa, sometimes even within genera. This study compares phylogeographical patterns in two species of highly dispersive neritid gastropod, Nerita albicilla and Nerita plicata, with nearly sympatric ranges that span the Indo-Pacific. Mitochondrial COI sequences from >1000 individuals from 97 sites reveal similar phylogenies in both species (two divergent clades differing by 3.2% and 2.3%, for N. albicilla and N. plicata, respectively). However, despite ecological similarity and congeneric status, the two species exhibit phylogeographical discordance. N. albicilla has maintained reciprocal monophyly of Indian and Pacific Ocean populations, while N. plicata is panmictic between oceans, but displays a genetic cline in the Central Pacific. Although this difference might be explained by qualitatively different demographic histories, parameter estimates from three coalescent models indicate that both species have high levels of gene flow between demes (2Nem>75), and share a common history of population expansion that is likely associated with cyclical flooding of continental shelves and island lagoons following low sea-level stands. Results indicate that ecologically similar, codistributed species may respond very differently to shared environmental processes, suggesting that relatively minor differences in traits such as pelagic larval duration or microhabitat association may profoundly impact phylogeographical structure.     

Pelagic larvae of benthic gastropods from shallow Antarctic waters of Admiralty Bay,King George Island

The occurrence, distribution and summer variation of pelagic larvae of benthic gastropods in the shallow coastal area of Admiralty Bay were determined for the summers of 1993/1994, 1994/1995 and 1996/1997 from plankton samples taken at 15- to 30-m depths in 12 stations. Significant differences were found among years at the end of January and February. Results of Principal Component Analysis showed the inverse relation of high wind speed and abundance of gastropod larvae in the three austral summers sampled, and suggested that environmental conditions prevalent during 1994/1995 and 1995/1997 were similar and differed from those of 1993/1994, which may have influenced the number of larvae observed.     

Biogeographical patterns of benthic macroinvertebrates in the Southeastern Pacific littoral

Aim To use new collections and taxonomic reviews of the Chilean coastal biota, and studies on biodiversity on a reappraisal of Southeastern Pacific littoral biogeography. Location The temperate coastline of the Southeastern Pacific, extending over 6000 km from northern Peru to the southern tip of Chile. Methods Records of coastal macroinvertebrates were assigned to ten geographic zones along the Chilean coast. The Spearman rank correlation coefficient, ρ, was used to establish the relationship between the total number of species and the number of single records for each zone. Regions and underlying faunal gradient were verified via an unweighted paired group method using arithmetic averages (UPGMA), and ordination non-metric multidimensional scaling (nMDS) analysis based on a disagreement distance matrix of presence/absence data. Abundance down-weighting was preferred to rare species down-weighting, owing to the nature of the records, where a larger number of references for a given taxon did not necessarily indicate a greater abundance or commonness. The dissimilarity matrices between the different zones were used to establish the degree of agreement between the different levels of analysis, using a weighted Spearman rank correlation coefficient ρ_w. Statistical significance was established using a randomization (permutation) test. Main conclusions Analysis of new macroinvertebrate data and taxonomic reviews of the Chilean coastal fauna indicates a Transitional-Temperate Region for the Southeastern Pacific littoral, located between 35°S and 48°S where a gradual mixing and replacement of species negates previous hypotheses on the existence of a marked distributional break at 42°S.