Textularia

Abstract: Benthic foraminiferal populations through 1991–94 were investigated by taking cores and in situ observations from the submersible Shinkai 2000 in Sagami Bay, Japan (1450 m water depth). At this location, a strong spring bloom causes seasonal deposition of phytodetrital material to the sea floor. The population size of benthic foraminifera is mainly controlled by this seasonal flux of organic matter, which triggers rapid, opportunistic reproduction of the shallow infaunal taxa Bolivia pacifica and Textularia kattegatensis. We propose that these species have a one-year life cycle. The deep infaunal taxa Globobulimina affinis and Chilostomella ovoidea show less pronounced seasonal fluctuations in population size, and seem to have a life cycle longer than two years. The foraminifera migrate vertically through the sediment, down to the maximum depth to which the sediment is oxygenated. The seasonal flux of organic matter thus is the most important determinant of population size, microhabitats, and reproduction in Sagami Bay. Such foraminifera are extremely relevant in the functioning of the global carbon cycle, especially at the interface of the hydrosphere and lithosphere.

Abstract: Benthic foraminiferal food sources were examined in the central part of Sagami Bay, Japan (water depth 1450 m) based on an in situ feeding experiment with 13 C-labeled food materials. In this study, 3 different 13 C-labeled food materials were used: the unicellular marine algae Dunaliella tertiolecta, the marine diatom Chaetoceros sociale, and the marine bacterium Vibrio algi- nolyticus. The first two are representatives of phytodetritus and the third of organic matter produced in the sediments. Each type of food material was injected into a series of in situ culture cores and incubated for up to 21 d. We observed that some benthic foraminiferal species selectively ingested 13 C-labeled algae from the sedimentary organic matter. On the other hand, benthic foraminifera ingested 13 C-labeled bacteria unselectively from sedimentary organic matter. Total benthic forami- nifera assimilated 8.8 mg C m -2 d -1 of sedimentary organic matter without phytodetritus assimilation. Based on the assimilation rates estimated in this experiment, we recognized 3 types of feeding strat- egy among deep-sea benthic foraminifera in Sagami Bay. There are those that ingest (1) fresh phyto- detritus selectively (phytophagous species: Uvigerina akitaensis, Bolivina spissa, Bolivina pacifica); (2) fresh phytodetritus selectively but sedimentary organic matter as well when phytodetritus is absent (seasonal-phytophagous species: Bulimina aculeata, Textularia kattegatensis, Globobulimina affinis); and (3) sedimentary organic matter at random (deposit feeders: Cyclammina cancellata, Chilostomella ovoidea). These different types of carbon utilization should be considered not only for understanding modern ecosystems on the deep-sea floor but also for paleoceanographic reconstruc- tions using the abundance and distribution, or isotopic composition, of benthic foraminifera.

Abstract: Benthic foraminifera were investigated from 20 grab samples collected from a large marine embayment, Disko Bugt, along the west Greenland margin. Agglutinated and calcareous foraminifera were found throughout Disko Bugt, with agglutinated species dominating 19 out of the 20 samples. The most common species are Adercotryma glomerata, Spiroplectammina biformis, Textularia earlandi, Cribrosto- moides crassimargo and Reophax fusiformis. Six faunal assemblage zones were identified from cluster analysis and detrended correspondence analysis. The relationship between the foraminifera and environmental variables was investigated using canonical correspondence analysis. From this analysis, bottom water salinity and water depth were identified as the most important environmental variables explaining the fora- miniferal assemblages. This result suggests water mass characteristics in Disko Bugt are an important control on the benthic foraminiferal assemblage zones. Where the warm and saline West Greenland Current water mass impinges on the seafloor, the assemblage is dominated by A. glomerata, T. earlandi, R. fusiformis and Reophax pilulifer. Sites with the cold, lower salinity Polar Water mass at the seafloor are dominated by S. biformis and A. glomerata, with common Cuneata arctica and C. crassimargo. In shallow locations with a relatively warm and low salinity surface water mass and coarse sediments the fauna is dominated by Cibicides lobatulus. In similar hydrographic locations with fine-grained sediments a mixed faunal assemblage dominated by Ammos- calaria pseudospiralis and Eggerella advena is found.