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Shallow Arctic banks have been observed to harbour rich communities of epifaunal organisms, but have not been well-studied with respect to composition or function due to sampling challenges. In order to determine how these banks function in the Barents Sea ecosystem, we used a combination of video and trawl/dredge sampling at several locations on a heavily trawled bank, Tromsøflaket — located at the southwestern entrance to the Barents Sea. We describe components of the benthic community, and calculate secondary production of dominant epifaunal organisms. Forty-six epibenthic taxa were identified, and sponges were a significant part of the surveyed benthic communities. There were differences in diversity and production among areas, mainly related to the intensity of trawling activities. Gamma was the most diverse and productive area, with highest species abundance and biomass. Trawled areas had considerably lower species numbers, and significant differences in epifaunal abundance and biomass were found between all trawled and untrawled areas. Trawling seems to have an impact on the sponge communities: mean individual poriferan biomass was higher in untrawled areas, and, although poriferans were observed in areas subjected to more intensive trawling, they were at least five times less frequent than in untrawled areas.
A detailed ecological study was conducted for three years (2001–03) on a 5 km stretch of well-developed coral reef facing an industrial site in the southernmost section of the Jordanian coast of the Gulf of Aqaba, Red Sea. The degree of modification associated with the prevailing ecological factors was assessed with respect to species diversity and abundance of the major groups of the macrobenthic community: corals, bivalves, hydrozoans, echinoderms, sponges and macroalgae. Three locations of two depths each – 6 and 12 m – were selected and surveyed using the visual census point-intercept method. The actual area of the survey covered about 2250 m2. Macrobenthic communities occurring close to the industrial jetty were characterized by low diversity and the obvious dominance of soft coral (16–30% cover). In the deep transects (12 m) hard coral cover was higher than that in the shallow transects (30–55%). Correlation analyses indicated that species richness increased with increasing distance from the industrial jetty. Species richness of other macrobenthos was also higher as depth increased. The results revealed that the distribution and abundance of coral, echinoderms, hydrozoans and macroalgae were correlated with the relative importance of bottom modification within the various locations in the entire study area. However, no distinct influence of location or depth on the identities of most macrobenthic species was indicated.
Two different assemblages of skeletonized microfossils are recorded in bioclastic shoals that cross the Lower–Middle Cambrian boundary in the Esla nappe, Cantabrian Mountains. The uppermost Lower Cambrian sedimentary rocks represent a ramp with ooid−bioclastic shoals that allowed development of protected archaeocyathan−microbial reefs. The shoals yield abundant debris of tube−shelled microfossils, such as hyoliths and hyolithelminths (Torellella), and trilobites. The overlying erosive unconformity marks the disappearance of archaeocyaths and the Iberian Lower–Middle Cambrian boundary. A different assemblage occurs in the overlying glauconitic limestone associated with development of widespread low−relief bioclastic shoals. Their lowermost part is rich in hyoliths, hexactinellid, and heteractinid sponge spicules (Eiffelia), chancelloriid sclerites (at least six form species of Allonnia, Archiasterella, and Chancelloria), cambroclaves (Parazhijinites), probable eoconchariids (Cantabria labyrinthica gen. et sp. nov.), sclerites of uncertain affinity (Holoplicatella margarita gen. et sp. nov.), echinoderm ossicles and trilobites. Although both bioclastic shoal complexes represent similar high−energy conditions, the unconformity at the Lower–Middle Cambrian boundary marks a drastic replacement of microfossil assemblages. This change may represent a real community replacement from hyolithelminth−phosphatic tubular shells to CES (chancelloriid−echinoderm−sponge) meadows. This replacement coincides with the immigration event based on trilobites previously reported across the boundary, although the partial information available from originally carbonate skeletons is also affected by taphonomic bias.
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