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.     

Estimating denitrification in North Atlantic continental shelf sediments

A model of coupled nitrification/denitrification was developed for continental shelf sediments to estimate the spatial distribution of denitrification throughout shelf regions in the North Atlantic basin. Using data from a wide range of continental shelf regions, we found a linear relationship between denitrification and sediment oxygen uptake. This relationship was applied to specific continental shelf regions by combining it with a second regression relating sediment oxygen uptake to primary production in the overlying water. The combined equation was: denitrification (mmol N m^–2 d^–1)=0.019^* phytoplankton production (mmol C m^–2 d^–1). This relationship suggests that approximately 13% of the N incorporated into phytoplankton in shelf waters is eventually denitrified in the sediments via coupled nitrification/denitrification, assuming a C:N ratio of 6.625:1 for phytoplankton. The model calculated denitrification rates compare favorably with rates reported for several shelf regions in the North Atlantic.The model-predicted average denitrification rate for continental shelf sediments in the North Atlantic Basin is 0.69 mmol N m^{– 2} d^–1. Denitrification rates (per unit area) predicted by the model are highest for the continental shelf region in the western North Atlantic between Cape Hatteras and South Florida and lowest for Hudson Bay, the Baffin Island region, and Greenland. Within latitudinal belts, average denitrification rates were lowest in the high latitudes, intermediate in the tropics and highest in the mid-latitudes. Although denitrification rates per unit area are lowest in the high latitudes, the total N removal by denitrification (53 × 10¹⁰ mol N y^–1) is similar to that in the mid-latitudes (60 × 10¹⁰ mol N y^–1) due to the large area of continental shelf in the high latitudes. The Gulf of St. Lawrence/Grand Banks area and the North Sea are responsible for seventy-five percent of the denitrification in the high latitude region. N removal by denitrification in the western North Atlantic (96 × 10¹⁰ mol N y^–1) is two times greater than in the eastern North Atlantic (47 × 10¹⁰ mol N y^–1). This is primarily due to differences in the area of continental shelf in the two regions, as the average denitrification rate per unit area is similar in the western and eastern North Atlantic.We calculate that a total of 143 × 10¹⁰ mol N y^–1 is removed via coupled nitrification/denitrification on the North Atlantic continental shelf. This estimate is expected to underestimate total sediment denitrification because it does not include direct denitrification of nitrate from the overlying water. The rate of coupled nitrification/denitrification calculated is greater than the nitrogen inputs from atmospheric deposition and river sources combined, and suggests that onwelling of nutrient rich slope water is a major source of N for denitrification in shelf regions. For the two regions where N inputs to a shelf region from onwelling have been measured, onwelling appears to be able to balance the denitrification loss.     

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.     

Prokaryotic metabolic activity and community structure in Antarctic continental shelf sediments

The prokaryote community activity and structural characteristics within marine sediment sampled across a continental shelf area located off eastern Antarctica (66 degrees S, 143 degrees E; depth range, 709 to 964 m) were studied. Correlations were found between microbial biomass and aminopeptidase and chitinase rates, which were used as proxies for microbial activity. Biomass and activity were maximal within the 0- to 3-cm depth range and declined rapidly with sediment depths below 5 cm. Most-probable-number counting using a dilute carbohydrate-containing medium recovered 1.7 to 3.8% of the sediment total bacterial count, with mostly facultatively anaerobic psychrophiles cultured. The median optimal growth temperature for the sediment isolates was 15 degrees C. Many of the isolates identified belonged to genera characteristic of deep-sea habitats, although most appear to be novel species. Phospholipid fatty acid (PLFA) and isoprenoid glycerol dialkyl glycerol tetraether analyses indicated that the samples contained lipid components typical of marine sediments, with profiles varying little between samples at the same depth; however, significant differences in PLFA profiles were found between depths of 0 to 1 cm and 13 to 15 cm, reflecting the presence of a different microbial community. Denaturing gradient gel electrophoresis (DGGE) analysis of amplified bacterial 16S rRNA genes revealed that between samples and across sediment core depths of 1 to 4 cm, the community structure appeared homogenous; however, principal-component analysis of DGGE patterns revealed that at greater sediment depths, successional shifts in community structure were evident. Sequencing of DGGE bands and rRNA probe hybridization analysis revealed that the major community members belonged to delta proteobacteria, putative sulfide oxidizers of the gamma proteobacteria, Flavobacteria, Planctomycetales, and Archaea. rRNA hybridization analyses also indicated that these groups were present at similar levels in the top layer across the shelf region.     

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.     

Influence of benthic organisms on solute transport in lake sediments

Increased inputs of nutrients into the waters of Lake Okeechobee has raised concern that the lake is becoming hypereutrophic. One aspect in understanding the overall cycling and dynamics of the nutrients in the system is the effect of benthic organisms on solute transport. Various diffusional models have been used to approximate the effect of benthic organisms on solute transport within sediments using diffusion coefficient values which represent the pooled contributions of molecular diffusion (D _s ) and enhanced solute mixing due to macrobenthos activity (D _i ). The objective of this study was to investigate the impact of benthic activity on solute transport by measuringD _s (i.e., no benthic activity) and an apparent-dispersion or mixing coefficientD _m (i.e., with benthic activity) for the four major sediment types of Lake Okeechobee, Florida using a reservoir technique. This method involved monitoring the depletion of a conservative tracer (tritiated water) from the overlying water (reservoir) resulting from transport into sediments using disturbed sediments repacked in cores (3.2 cm diam.) and undisturbed cores (3.2 to 12 cm diam.) obtained from the lake. Additional estimates ofD _m andD _s were also obtained by measuring tracer concentration profiles in the sediment cores at the end of a specified diffusion period. Molecular diffusion coefficients (D _s ) measured forrepacked cores of sand, littoral, mud and peat sediments ranged from 0.90 to 1.29 cm² d⁻¹, and estimates ofD _s were slightly higher in undisturbed cores without benthic organisms.D _m values for undisturbed cores of mud, sand and littoral sediments having macrobenthic populations ranged from 2.09 to 24.78 cm² d⁻¹; values that were 1.6 to 15 times higher than those in sediments without benthic activity. Undisturbed cores of varying diameter from mud sediments had similar estimates ofD _m for tritium; however, the undisturbed cores with larger diameters from littoral sediments yielded larger estimates ofD _m , reflecting the heterogeneity of benthic population densities and activity. Therefore,D _s estimates may not adequately represent transport processes for mud, sand and littoral sediments of Lake Okeechobee; hence careful consideration should be given to the role of benthic organisms in the overall transport of solutes across the sediment-water interface. A contribution of the Florida Agricultural Experiment Station Journal Series No. R-01150. A contribution of the Florida Agricultural Experiment Station Journal Series No. R-01150.     

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

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 three rocky reefs on the continental shelf of the Pacific Northwest, using video footage collected by remotely operated vehicle, to more finely characterize these assemblage–habitat associations. Benthic assemblages appeared to first group by depth (50–80 vs. 100–120 m), then by relief (consolidated rocks vs. unconsolidated rocks and soft sediments). Consolidated rocks were characterized at each site by a combination of various sponges, gorgonians, sea anemones and echinoderms; unconsolidated rocks were characterized at Grays Bank by sea anemones and burrowing brittle stars, and at Bandon-Arago by sponges and echinoderms; soft sediments were characterized at Grays Bank and Siltcoos Reef by sea whips and burrowing brittle stars, as well as pink shrimps and sea stars at Siltcoos Reef, and at Bandon-Arago by sponges, gorgonians and echinoderms. 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.     

Performance of predictive models in marine benthic environments based on predictions of sponge distribution on the Australian continental shelf

This study tested the performance of 15 predictive models in predicting the distribution of sponge assemblages on the Australian continental shelf using a common set of marine environmental variables. The models included traditional regression and more recently developed machine learning models. The results demonstrate that the spatial distribution of sponge assemblages can be successfully predicted, although the effectiveness of predictions varied among models. Overall, machine learning models achieved the best prediction performance. The direct variable of bottom-water temperature and the resource variables that describe bottom-water nutrient status were found to be useful surrogates for the distribution of sponge assemblages at the broad regional scale. A new method of deriving pseudo-absence data (weighted pseudo-absence) was compared with random pseudo-absence data — the new data were able to improve modelling performance for all the models both in terms of statistics (~ 10%) and in the predicted spatial distributions. Results from this study will further refine modelling methods used to predict the spatial distribution of marine biota at broad spatial scales, an outcome especially relevant to managers of marine resources.     

Primary production of ice algae on a seasonally-ice-covered,continental shelf

Summary Ice algae samples were collected from the winter pack ice off Labrador during March 1984. The population was dominated by centric diatoms. Chlorophyll concentrations ranged from 40 to 190 mg m^–3, and particulate organic carbon from 2 to 10 g m^–3. Assimilation numbers for the ice algae ranged from 1.4 to 2.8 mg C (mg chl)^–1 h^–1 with a mean of 2.3, and were not significantly different from the assimilation numbers of the pelagic community beneath the ice. The ice algae were not photoinhibited at light intensities approaching surface light intensities. It is postulated that the dynamic nature of the ice field permits near-surface light intensities to reach the ice algae community at irregular intervals thereby suppressing photoinhibition.     

Diversity of nitrous oxide reductase (nosZ) genes in continental shelf sediments

Diversity of the nitrous oxide reductase (nosZ) gene was examined in sediments obtained from the Atlantic Ocean and Pacific Ocean continental shelves. Approximately 1,100 bp of the nosZ gene were amplified via PCR, using nosZ gene-specific primers. Thirty-seven unique copies of the nosZ gene from these marine environments were characterized, increasing the nosZ sequence database fourfold. The average DNA similarity for comparisons between all 49 variants of the nosZ gene was 64% +/- 10%. Alignment of the derived amino acid sequences confirmed the conservation of important structural motifs. A highly conserved region is proposed as the copper binding, catalytic site (CuZ) of the mature protein. Phylogenetic analysis demonstrated three major clusters of nosZ genes, with little overlap between environmental and culture-based groups. Finally, the two non-culture-based gene clusters generally corresponded to sampling location, implying that denitrifier communities may be restricted geographically.     

Distribution of sponges on the Mauritanian continental shelf

Transect sampling on the continental shelf off the Banc d'Arguin, Mauritania, revealed a patchy distribution of sponge species and populations. Major sponge habitats are inshore coastal sandstone flats harbouring a diverse infaunal sponge fauna, and the moving substrate of shells of live gastropods or empty shells occupied by hermit crabs which harbour a numerically important but species-poor incrusting sponge fauna. The latter forms occur over most of the depth profile. Horizontal distribution of the sponges shows a distinct gap in species and numbers associated with a muddy bottom area where the sediment-rich Banc d'Arguin run-off is found. North and south of this gap the specific composition of the infaunal sponges is considerably different and this is explained as evidence for limitation of range extensions, notably of the southern sponge fauna, by the muddy area.     

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.     

Spatial and temporal distribution of benthic Polychaeta from the continental shelf of Tamaulipas, Gulf of Mexico]

In three oceanographic cruises off southern Tamaulipas (May, July and November, 1992), a total of 102 sediment samples were collected by autonomous diving at depths of 2.5 to 20.5 m, with a cylindrical 4 liter acrylic tube. The samples were sieved (aperture size 0.5 and 1.0 mm). In total, 88 species of polychaete annelids were determined (33 families); 15 species are first records for Mexico and three for the Gulf of Mexico. The dominant species were Paraprionospio pinnata, Scoletoma verrilli, Ceratocephale oculata, Aricidea finitima, Apoprionospio pygmaea, Onuphis eremita oculata and Prionospio cristata; P. pinnata was the most abundant (14.4% of the total). Highest abundance and diversity of species was in May (63 species and 622 organisms), followed by July (48 species and 401 organism); November was lowest (47 species and 217 organisms). Most diversity and abundance were found in the sandy bottoms.     

黄东海陆架区沉积物中磷的形态分布及生物可利用性

采用1992年Ruttenberg连续提取法(SEDEX)将黄东海陆架区沉积物中的磷分为交换态磷(Ex-P),Fe结合态磷(Fe-P),自生磷(Au-P),碎屑磷(De-P),有机磷(Or-P),分析了各形态磷的平面和垂直分布特征;利用沉积物年代序列测定的结果,探讨了柱状沉积物中不同形态磷的含量变化,并进一步分析了该区域磷形态的生物可利用性.结果表明,黄东海陆架区表层沉积物各形态磷平均含量为:Au-P(140.72 μg/g)＞De-P(59.23 μg/g)＞Or-P(32.69 μg/g)＞Fe-P(29.91 μg/g)＞Ex-P(5.92 μg/g);各形态磷在沉积时间序列上分布不同,反映了不同时期人类活动和气候环境等因子对磷埋藏量影响的不同,其中Au-P在长江口H1-18站位含量比南黄海中部3个站位要低得多;调查区表层潜在生物有效磷为13.55％左右,仅仅占沉积磷中的一小部分.     

Benthic macrofauna and sediments in the Severn Estuary

In the Severn Estuary and Bristol Channel, a multivariate analysis indicated eight groupings of macrobenthic fauna, each associated with a different physical habitat. Samples were faunistically impoverished, especially in sublittoral areas, but greater species richness was associated with reefs of Sabellaria alveolata , which extended well into the estuary.     

Coexistence patterns of benthic gastropods on the Uruguayan shelf

Community assembly rules theory attempt to understand the processes that determine the composition of local communities from a regional species pool. Nestedness and negative co‐occurrence are two of the most commonly reported meta‐community patterns, but almost exclusively from terrestrial and freshwater ecosystems. Here we analyzed the structure of species coexistence in six datasets containing presence/absence data for 120 marine benthic gastropod species in 249 sampling units on the Uruguayan continental shelf and Río de la Plata estuary. The ecological features of this system, such as the idiosyncratic nature of the biogeographic and oceanographic realms, are clearly different from those observed in other systems previously targeted by studies on coexistence structure. Community patterns were evaluated using null models and four structure indices. The existence of patterns in community assembly, and in particular segregated co‐occurrence, was verified only when analyzing the number of checkerboard units (CH index). This indicates more mutually exclusive species pairs than expected by chance. Nestedness, on the other hand, was not detected in any dataset. Storage and rescue effects related to overall high immigration and low local extinction rates are plausible mechanisms to account for the general pattern of random species coexistence, while the segregated co‐occurrence pattern depicted by the CH index may be related to differential habitat requirements within species pairs. Our study highlights the importance of analyzing metacommunity structures in alternative biological, environmental, and historical contexts in order to advance on the construction of a general ecological theory, relating patterns with the processes dominating in particular ecosystems.     

Effect of seasonal hypoxia on the benthic foraminiferal community of the Louisiana inner continental shelf: The 20th century record

A species census in sediment core samples reveals significant changes in the composition of the Louisiana-shelf benthic foraminiferal community in the past century; these changes can be explained by an increase in the severity of seasonal hypoxia in bottom waters. Agglutinated and porcelaneous orders living in water depths less than 60 m suffered a noticeable decline during this time. In particular, the genus Quinqueloculina was severely affected by the progression of hypoxia, and nearly disappeared from parts of the study area. In contrast, several hyaline taxa, especially Nonionella basiloba, Buliminella morgani, and Epistominella vitrea, tolerated the progressive oxygen depletion well. Results of cluster and principal components analyses of the foraminiferal assemblage data match the observed species distribution trends and indicate that seasonal hypoxia on the Louisiana shelf, related to eutrophication and water stratification, worsened in the past century, even near the outer edge of the present-day zone of spring and summer oxygen depletion. The temporal trends in the foraminiferal record correspond to that of fertilizer use in the U.S. and nitrogen loading in the Mississippi River, suggesting that the anthropogenic factor has been particularly strong in the development of coastal hypoxia since the early 1940s.     

Polychaete distribution on the southwestern Atlantic continental shelf

Diversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30?m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.     

The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf

Species diversity includes two aspects, the number of species (species richness) and the proportional abundances of the species (heterogeneity diversity). Species richness and heterogeneity diversity can be measured over different scales; a single point, samples, large scales, biogeographical provinces and in assemblages and habitats. In the literature, the terminology of these scales is confused. Here, scales are given a uniform notation. Scales of species richness and heterogeneity diversity are distinguished from turnover (beta) diversity, which is the degree of change in species composition along a gradient. Methods of measurement of the scales of species richness, heterogeneity diversity, turnover diversity and for estimating total species richness are reviewed. Two methods for measuring heterogeneity diversity are recommended Exp H′ (where H′ is the Shannon-Wiener index) and 1/Simpson’s index, together with an equitability index J′. The reviewed methods are then applied to a data set from the Norwegian continental shelf to illustrate the advantages of the recommended methods. Finally, the application of the methods to assessment of effects of disturbance, to studies of gradients of species richness and to conservation issues are discussed.