A temporal comparison of a benthic infaunal community southwest of St. Lawrence Island, Bering Sea between 2006 and 1970–1974

Benthic infaunal biomass and abundance may be changing in Bering Sea communities. This study compared benthic infaunal biomass, abundance, and community composition southwest of St. Lawrence Island in an important forage area for benthic-feeding birds and mammals between 1970–1974 and 2006. Invertebrate biomass and abundance were significantly greater in 2006 than in 1970–1974 primarily due to high nuculid (Bivalvia) biomass and abundance that contributed 13.2% (biomass) and 8.5% (abundance) to differences in community structure between the sampling periods. This is in contrast to St. Lawrence Island Polynya studies conducted in the 1980s and 1990s that documented decreases in benthic biomass and abundance. Spatial scale of sampling, selective predation, a strong recruitment event, and/or sampling design may account for the difference in trends among the studies.     

Effects of UV radiation on the structure of Arctic macrobenthic communities

At present, information on the effects of ultraviolet radiation (UVR) on structure and diversity of polar, in particular Arctic, benthic communities is scarce. It is unclear whether and to what extent communities of different successional age are susceptible to UVR and whether UVR effects known to be detrimental at the species level can be buffered at the community level. In a subtidal field study on Spitsbergen (Norwegian Arctic), we investigated the potential effect of distinct UVR regimes on macrobenthic communities of different successional ages, grown on ceramic tiles. Total taxon cover, taxon composition, evenness, and richness were assessed after experimental exposure of 4 and 8 weeks. Overall, 17 algal and invertebrate taxa were encountered in the study and diatoms dominated the communities regardless of successional age or radiation treatment. UVR effects were dependent on both exposure time and community age. We did not find overall detrimental UVB effects. In contrast, abundance of several species increased in UVR-exposed communities. Especially, UVA seemed to have a beneficial effect in that several green and brown algal taxa increased in abundance (e.g. Ulothrix flacca, Chlorophyta, and Desmarestia sp., Phaeophyceae). In general, UVR effects depended on species composition and thus on successional age of communities, with later successional communities likely to be able to buffer and alleviate possible negative effects of UVR at species level. Overall, the presented study provides a first insight into the complex role UVR plays in structuring Arctic epibenthic communities.     

Microphytobenthic Primary Production and Sedimentary Carbohydrates Along Salinity Gradients in the Lagoons of Grado and Marano (Northern Adriatic Sea)

Primary production of the microphytobenthic community and carbohydrates concentrations were studied in the lagoonal system of Grado and Marano, located in the Northern Adriatic coast. Sediment samples were collected along a salinity gradient. Abundance and species composition of the microphytobenthic communities were analysed and the benthic microalgal biomass was estimated as Chlorophyll a (Chl a). Primary production of benthic diatoms was estimated using ¹⁴C-tracer. Extracellular carbohydrates were extracted from the sediment and separated in two operationally defined fractions (colloidal and EDTA-extractable). Salinity was higher in the Grado lagoon, where the benthic microalgal community was mainly composed of marine diatoms. In the Marano lagoon, which has a lower salinity, freshwater species were also found. In both lagoons, photosynthetic efficiency showed an inverse relationship with salinity and a direct relationship with the main biological variables. Photosynthetic activity was directly related to Chl a and abundance of benthic microalgae, suggesting that in the benthic system microalgal community is responsible for primary production. Overall, salinity was also influent on the microphytobenthic primary production, which was greater in the more saline Grado lagoon.     

Salinity drives meiofaunal community structure dynamics across the Baltic ecosystem

Coastal benthic biodiversity is under increased pressure from climate change, eutrophication, hypoxia, and changes in salinity due to increase in river runoff. The Baltic Sea is a large brackish system characterized by steep environmental gradients that experiences all of the mentioned stressors. As such it provides an ideal model system for studying the impact of on‐going and future climate change on biodiversity and function of benthic ecosystems. Meiofauna (animals < 1 mm) are abundant in sediment and are still largely unexplored even though they are known to regulate organic matter degradation and nutrient cycling. In this study, benthic meiofaunal community structure was analysed along a salinity gradient in the Baltic Sea proper using high‐throughput sequencing. Our results demonstrate that areas with higher salinity have a higher biodiversity, and salinity is probably the main driver influencing meiofauna diversity and community composition. Furthermore, in the more diverse and saline environments a larger amount of nematode genera classified as predators prevailed, and meiofauna‐macrofauna associations were more prominent. These findings show that in the Baltic Sea, a decrease in salinity resulting from accelerated climate change will probably lead to decreased benthic biodiversity, and cause profound changes in benthic communities, with potential consequences for ecosystem stability, functions and services.     

Bacterial Diversity in the South Adriatic Sea during a Strong,Deep Winter Convection Year

The South Adriatic Sea is the deepest part of the Adriatic Sea and represents a key area for both the Adriatic Sea and the deep eastern Mediterranean. It has a role in dense water formation for the eastern Mediterranean deep circulation cell, and it represents an entry point for water masses originating from the Ionian Sea. The biodiversity and seasonality of bacterial picoplankton before, during, and after deep winter convection in the oligotrophic South Adriatic waters were assessed by combining comparative 16S rRNA sequence analysis and catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). The picoplankton communities reached their maximum abundance in the spring euphotic zone when the maximum value of the chlorophyll a in response to deep winter convection was recorded. The communities were dominated by Bacteria, while Archaea were a minor constituent. A seasonality of bacterial richness and diversity was observed, with minimum values occurring during the winter convection and spring postconvection periods and maximum values occurring under summer stratified conditions. The SAR11 clade was the main constituent of the bacterial communities and reached the maximum abundance in the euphotic zone in spring after the convection episode. Cyanobacteria were the second most abundant group, and their abundance strongly depended on the convection event, when minimal cyanobacterial abundance was observed. In spring and autumn, the euphotic zone was characterized by Bacteroidetes and Gammaproteobacteria. Bacteroidetes clades NS2b, NS4, and NS5 and the gammaproteobacterial SAR86 clade were detected to co-occur with phytoplankton blooms. The SAR324, SAR202, and SAR406 clades were present in the deep layer, exhibiting different seasonal variations in abundance. Overall, our data demonstrate that the abundances of particular bacterial clades and the overall bacterial richness and diversity are greatly impacted by strong winter convection.     

Food selection of Coregonus lavaretus in a brackish water ecosystem

This study examined how variability in the abundance and biomass structure of benthic invertebrates affected the feeding choice of the whitefish Coregonus lavaretus on a hard bottom habitat of the brackish Baltic Sea. In general, crustaceans such as Idotea balthica and Gammarus spp. were preferred over molluscs. Although being the most numerous taxon in the invertebrate samples, Mytilus trossulus was the lowest ranking in C. lavaretus food preference. The availability of benthic invertebrate prey set the dietary range of fish but the selectivity largely described fish feeding within this range. There was no clear link between fish predation and the dominance structure of benthic invertebrate communities, suggesting that species composition, abundance and biomass of invertebrate species had no impact on the feeding selectivity of the fish. Thus, while fish predation may not affect the dominant species within a benthic community, due to strong selectivity fish may impose strong pressure on some rarer but highly preferred invertebrate prey species.     

Meiofauna response to iceberg disturbance on the Antarctic continental shelf at Kapp Norvegia (Weddell Sea)

The impact of iceberg scouring on meiofauna communities, especially nematodes, was studied on the Kapp Norvegia shelf in the Weddell Sea, Antarctica. Three stations with different stages of recolonisation following scour were selected on the basis of seafloor video images, sediment characteristics and faunal occurrences. These stations comprised a fresh scour, an older scour, and an undisturbed control site where a sponge spicule mat covered the sediment with dense epifauna. Meiofaunal abundance and taxonomic diversity of meiofauna groups were significantly reduced in the fresh scour. The highest abundance and diversity were found in the older scour as compared with the undisturbed site. The abundance and diversity of nematodes also decreased due to scouring. The abundance in the older scour recovered to the level of the undisturbed site whereas the diversity remained low. Scouring also changed the nematode community structure, with the suborders Desmoscolecina and Leptolaimina as the most sensitive groups. In addition, scouring resulted in the decrease of selective deposit feeders and the Maturity Index. The low diversity and the change in nematode generic composition in the older scour compared with the undisturbed site, despite the complete recovery in terms of abundance, suggest that the deep continental shelf nematode community in this area is sensitive to iceberg disturbance.     

南黄海冬季小型底栖生物丰度和生物量

分别于2003年1月和2004年1月在南黄海广大陆架浅海水域进行小型底栖生物调查.结果表明,两个航次的小型底栖生物平均丰度分别为 (954.20±269.47) ind·10 cm^-2和(1 186.12±486.07) ind·10 cm^-2;平均生物量分别为(954.38±403.93)μg·10 cm^-2和(1 120.72±487.21) μg·10 cm^-2.两个航次小型底栖生物丰度值、生物量和生产力均无显著变化(P>0.05).共鉴定出20个小型底栖生物类群,按丰度,自由生活海洋线虫为最优势类群,两个航次的优势度分别为87%和90%,其他优势类群依次为桡足类、多毛类和动吻类;按生物量依次为线虫34%～38%,多毛类25%～33%,介形类9%～22%,桡足类8%.96.64%的小型生物分布在0～5 cm的表层沉积物内,线虫和桡足类分布在0～2 cm的比例分别为72.48%和89.46%.小型底栖生物的生物量与沉积物砂含量(%)、粉砂含量(%)和叶绿素a含量呈显著相关.代表性站位的种类组成和多样性分析显示了沿岸、黄海冷水团和东、黄海交汇区3个不同的底栖生物群落.     

Benthic diatom community composition in three regions of the Great Barrier Reef,Australia

Despite their ecological importance, very little is known about the taxonomy and ecology of benthic diatoms in coral-reef ecosystems. Diatom densities and community compositions were investigated in three distinct regions of the Great Barrier Reef (GBR): (a) Wet Tropics (WT), (b) Princess Charlotte Bay (PCB), and (c) the Outer Shelf (OS). About 209 taxa were observed in the GBR sediments studied, with an average abundance of 2.55 × 10⁶ cells ml⁻¹ in the upper 1 cm of sediment. Total diatom abundances were about twice as high in inshore reefs of PCB and WT compared with OS reefs. A redundancy analysis (RDA) of diatom composition clearly grouped the three regions separately but showed little influence of grain size, nitrogen and organic carbon content of the sediments. The only distinct correlates were inorganic carbon and the distance to the mainland associated with OS communities. Analysis of similarity (ANOSIM) of diatom community composition revealed significant differences between all three regions. Indicator values showed that most highly abundant taxa occurred in all regions. However, several taxa were clearly identified as characteristic of particular regions. It is hypothesised that variations in nutrient and light availability are the most likely explanation for the observed differences in community composition.     

Parasite communities of Adriatic cage-reared fish

From June 2001 to March 2002, 7 semi-offshore facilities in the Adriatic Sea rearing sea bass Dicentrarchus labrax, sea bream Sparus aurata, sharpsnout bream Diplodus puntazzo and red sea bream Pagellus bogaraveo aged 1+, were monitored for the presence of protozoan and metazoan parasites. Obtained data sets of abundance and prevalence were used to evaluate the structure and dynamic of infra- and component parasite communities. In all hosts, except the red sea bream, dominant parasites were monogenean specialists, showing clear seasonality. Average infracommunity richness was very low, ranging from 1 to 3 parasites per fish, while at component community level, values ranged from 3 to 8, depending on host species. Based on low diversity indices and a moderate to high similarity coefficient between different facilities, it can be concluded that the parasitofauna of Adriatic cage-reared fish is a stable and impoverished stochastic assemblage, with monogeneans as the predominant parasitic group.     

Organic aggregates formed by benthopleustophyte brown alga Acinetospora crinita (Acinetosporaceae,Ectocarpales)

This work presents the elemental, polysaccharide, and fatty acid compositions of benthic aggregates formed by the filamentous brown alga Acinetospora crinita, which are widely spread on the rocky bottoms of the Mediterranean Sea. The aggregates can be characterized as mineralized centers in which regeneration of nutrients and recycling of dissolved organic matter actively occur and favor the development of an abundant phytoplankton community. Analyses of the stable isotopes of C and N display their marine origin and could provide evidence of the processes that occur inside/outside of the aggregates. The monosaccharide compositions of Adriatic and Tyrrhenian mucilages produced by brown alga A. crinita were quite similar. In particular, the Adriatic sample compositions resembled the average composition of the Tyrrhenian high molecular weight exopolymers, and the observed differences could be ascribed to different degradation stages. The fatty acid patterns found for the aggregates were similar to those observed in the isolated A. crinita algae with variable contributions from embedded diatom species. The bacterial contribution to the fatty acid pool was quite low, most likely due to the known poor conditions for their heterotrophic growth.     

Cold winter effects on benthic macrofauna communities in near- and offshore regions of the North Sea

In order to investigate the effect of severe winters on the long-term variability of benthic macrofauna communities four stations from the inner German Bight towards the Dogger Bank (North Sea) were sampled in March 1990 and from May 1995 to 2002. The stations were chosen to reflect a gradient in the hydrographic regime, temperature and organic matter supply. We initially hypothesized that the effect of severe winters on benthic communities will be more pronounced in the offshore more stable environment than in the nearshore regions. Our results clearly showed the opposite pattern. The benthic communities at the nearshore stations in the German Bight changed dramatically in species abundance and community structure after the severe winter 1995/1996. But the community structure in the German Bight returned to the previous stage within 2 years. In contrast, the offshore stations in the Oyster Ground and at the Dogger Bank remained rather unaffected by the severe winter and changed gradually during the study period. The results are discussed concerning the ecological importance of severe winters for benthic communities and the utility of our results for interpreting long-term changes.     

基于高通量测序分析西藏北部高寒草甸不同深度土壤线虫群落分布特征

为了研究藏北高寒草甸土壤线虫多样性,于2017年8月,采用Illumina MiSeq测序技术,研究了西藏北部高寒草甸0—25 cm范围内不同深度土层的土壤线虫群落组成与结构特征。结果表明:5个不同深度共获得OTU 990个,隶属于3个纲,7个目,25个科,30个属,刺嘴纲Enoplea为共有优势土壤线虫群落;对样品进行Alpha多样性评价,计算Chao 1指数、Shannon指数和Ace指数,发现5—10 cm的土壤样品群落有较高的丰富度;属水平Heatmap图分析可知20—25、15—20、0—5、5—10、10—15 cm土壤线虫群落的组成相似性有一个递增的趋势。与不同深度藏北高山嵩草(盛长期)线虫群落结构相关性较大的土壤化学指标是K~+、含水率、有机质和Zn~(2+)。研究发现不同深度土壤线虫种类及丰度存在一定的差异,可为研究藏北高寒草地土壤线虫群落特点提供依据。     

Macrofauna communities of the Dogger Bank (central North Sea) in the late 1990s: spatial distribution,species composition and trophic structure

Macrofauna samples were taken in May 1996–1998 at 28 stations on the Dogger Bank (central North Sea) to describe species composition, spatial distribution and trophic structure of the macrofaunal communities. In general, five communities could be distinguished depending on the influence of different water masses, depth, type of sediment and food availability. Except for those species which feed in the sediment, macrofauna communities did not show any correlation to the measured sediment variables. In fact, macrofauna communities of the Dogger Bank were mainly structured by lateral food supply via frontal systems. This was indicated by the dominance of interface feeders foraging in the benthic boundary layer, which are able to switch from surface deposit to suspension feeding depending on flow conditions. The importance of sandlickers in the shallowest parts of the Dogger Bank hints at an important contribution of benthic primary production to the nutritional and energetic needs of the benthic community. Electronic Publication     

Above- and belowground insect herbivores differentially affect soil nematode communities in species-rich plant communities

Interactions between above‐ and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above‐ and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial‐feeding and 3) reduce plant‐feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species‐rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni‐carnivorous nematodes were evaluated in relation to plant community composition. Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom‐up control of the nematodes. However, our results show that above‐ and belowground insect herbivores may facilitate root‐feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores.     

Alpha and beta diversity of connected benthic–subsurface invertebrate communities respond to drying in dynamic river ecosystems

Drying disturbances are the primary determinant of aquatic community biodiversity in dynamic river ecosystems. Research exploring how communities respond to disturbance has focused on benthic invertebrates in surface sediments, inadequately representing a connected community that extends into the subsurface. We compared subsurface and benthic invertebrate responses to drying, to identify common and context‐dependent spatial patterns. We characterized community composition, alpha diversity and beta diversity across a gradient of drying duration. Subsurface communities responded to drying, but these responses were typically less pronounced than those of benthic communities. Despite compositional changes and in contrast to reductions in benthic alpha diversity, the alpha diversity of subsurface communities remained stable except at long drying durations. Some primarily benthic taxa were among those whose subsurface frequency and abundance responded positively to drying. Collectively, changing composition, stable richness and taxon‐specific increases in occurrence provide evidence that subsurface sediments can support persistence of invertebrate communities during drying disturbances. Beta‐diversity patterns varied and no consistent patterns distinguished the total diversity, turnover or nestedness of subsurface compared to benthic communities. In response to increasing drying duration, beta diversity increased or remained stable for benthic communities, but remained stable or decreased for subsurface communities, likely reflecting contrasts in the influence of mass effects, priority effects and environmental filtering. Dissimilarity between subsurface and benthic communities remained stable or increased with drying duration, suggesting that subsurface communities maintain distinct biodiversity value while also supporting temporary influxes of benthic taxa during drying events. As temporary rivers increase in extent due to global change, we highlight that recognizing the connected communities that extend into the subsurface sediments can enable holistic understanding of ecological responses to drying, the key determinant of biodiversity in these dynamic ecosystems.     

Benthic ecology of <Emphasis Type="Italic">Vibrio</Emphasis> spp. and pathogenic <Emphasis Type="Italic">Vibrio</Emphasis> species in a coastal Mediterranean environment (La Spezia Gulf,Italy)

We carried out a 16-month in situ study to investigate the ecology of Vibrio spp. and pathogenic Vibrio species in coastal sediments of the Mediterranean Sea, employing multiple-regression analysis to reveal the major environmental factors controlling their occurrence in the benthic environment. In addition, association between vibrios and sediment-inhabiting meiofauna, which is a major component of benthic ecosystems, was investigated. Culturable and total Vibrio spp. estimates by most-probable-number technique coupled with standard polymerase chain reaction (PCR) and real-time PCR methods, respectively, were at least one order of magnitude higher in sediment than in seawater. In addition, potential human pathogenic species Vibrio cholerae, Vibrio vulnificus and Vibrio parahaemolyticus occurred in the sediment with V. parahaemolyticus being the most frequently found. In the pelagic environment, 60% of total variance in culturable Vibrio data was explained by sea surface temperature (40%), salinity (13%) and organic matter concentration (7%). In the benthic environment, sea surface temperature was the only factor that significantly affected culturable Vibrio occurrence although it explained only 25% of total variance, suggesting that additional unexplored factors may play a role as well. No correlation was found between culturable Vibrio spp. concentrations and the abundance of harpacticoid copepods in the sediment whilst a negative correlation was found between Vibrio spp. and nematode abundance which accounted for almost 90% of the total meiofaunal density. Taxonomic analysis revealed that selective bacterial feeders accounted for nearly 50% of the total nematode community and included genera such as Terschellingia, Molgolaimus and Halalaimus, suggesting that top-down control by nematode grazing may be an important factor affecting Vibrio occurrence in these sediments. It is concluded that the benthic marine environment may function as a reservoir of Vibrio spp. and potential pathogenic vibrios whose ecological features appeared substantially different from the ones recognised in the pelagic environment.     

Cartography of littoral rocky-shore communities (CARLIT) as a tool for ecological quality assessment of coastal waters in the Eastern Adriatic Sea

Littoral cartography is a valuable tool which uses shallow water macroalgal communities for monitoring ecosystem health and water quality. Cartography of littoral rocky-shore communities (CARLIT) is a European Union Water Framework Directive-compliant monitoring method widely used in the Western Mediterranean Sea. This non-destructive method is based on a visual observation of the type and length of coast occupied by rocky-shore communities in the upper-sublittoral zone. Here we present the first wide-scale application of CARLIT in the Adriatic Sea. The reference values calculated specifically for the Croatian coast (Eastern Adriatic Sea) ensure accurate calculation of the ecological status. The measured ecological quality ratio values (EQR) show a good linear relation with the Land Uses Simplified Index (LUSI) and appropriately reflect an increase in nutrient concentrations. The results suggest that this method can be used as a reliable biomonitoring tool in the Eastern Adriatic Sea. This study highlighted that Cystoseira forests thrive in 39% of the surveyed coastline and 23% of the coastline seems to be subjected to overgrazing by sea urchins. Our results provide a spatially accurate information on the abundance of different upper-sublittoral communities and the associated ecological status, which can be used in future management plans for improving water quality.