366 resultados para CHITONS MOLLUSCA
Resumo:
The PELMED-ECOPEL dataset contains mesozooplankton data collected in 1995-1996 in the Gulf of Lion (North Western Mediterranean Sea) between 43°35' N, 2°50' E and 42°15' N, 6°15' E. Zooplankton taxonomy-related abundance per unit volume of the water column.
Resumo:
The MARECHIARA-mesozooplankton dataset contains mesozooplankton data collected in the ongoing time-series at Sation MC (40°48.5' N, 14°15' E) in the Gulf of Naples. This dataset spans over the period 1984-2006 and contains data of mesozooplankton abundance and species composition as well as biomass (as dry weight). Mesozooplankton was regularly sampled in 1984-1990 and 1995-2006, only a few samples were collected in 1991-1992 and no samples in 1993-1994. During the first period of the series sampling frequency was fortnightly, and weekly since 1995.
Resumo:
We studied the effects of changed quality of inflow water of aquaculture ponds on three aquatic communities, phytoplankton, zooplankton and zoobenthos, during two seasons of rearing common carp (Cyprinus carpio). The new water source coming from a deep tube well was markedly different in water chemistry from the surface water sources previously used to maintain the investigated fish ponds. Ponds supplied by the tube well water were characterized by lower oxygen and water hardness, and higher total ammonia and conductivity reaching subsaline conditions. Multivariate analysis (co-inertia) revealed that all investigated groups, except Mollusca (zoobenthos), decreased in species richness, abundance and biomass due to changed water chemistry, but differed in the level of susceptibility to stressors. Assemblages of Rotifera and Cladocera were the most affected showing a sharp decline in density and number of species since 29 out of 44 species disappeared from the ponds. The abundance of Copepoda (Cyclopoida) was relatively high although significantly lower in new environmental conditions (P<0.05), with adults being more tolerant to changed inflow water than larvae. Phytoplankton, except Bacillariophyta, had a highest potential to replace previous species with newcomers more adapted to changed inflow water, providing 36 immigrant species while 49 became extinct. Although mainly influenced by fish predation, Chironomidae (zoobenthos) were undoubtedly affected by changed water chemistry, decreasing from 11 to only 3 species. These results suggest that this pattern was a result of the shift from freshwater to subsaline conditions.
Resumo:
Seven cores from the West African continental margin in 12-18° N have been investigated by means of a coarse fraction analysis. Four of the seven cores contain allochthonous material: turbidites and debris flow deposits. The source of the allochthonous material is in about 300-600 m water depth. The age of the slide induced debris flow deposits is at the end of oxygen isotope stage 2. One debris flow deposit is covered by a turbidite (core GIK13211-1). The turbidites in the deep-sea core GIK13207-3 originate from river-influenced sediments from the West-African continental margin, whereas the autochthonous sequences are influenced by volcanic material from the Cape Verde Islands. Particle by particle supply from upper slope areas has been found in all four cores from the continental slope. Current sorting occurs on the submarine diapir (core GIK13289-3), whereas core GIK13291-1 on the NW-flanc, 200 m below core GIK13289-3, has no current sorting, except for stage 1 and parts of stage 5. The current sorting is reflected by parallel variations of median diameters of whole tests and of fragments of planktonic foraminifers, by higher median diameters of foraminifers on top of the diapir, by reduced accumulation rates and increased sand fraction percentages in core GIK13289-3 compared to core GIK13291-1. The Late Quarternary climatic history of the West-African near coastal area (12-18° N) has been redrawn: - in oxygen isotope stage 1 a humid climate is found in 12-18° N (This "humid impression" in 18° N, which is actually an arid area, is due to the poleward directed undercurrent, which transports Senegal river material to the north). - in oxygen isotope stage 2 an arid climate existed in 14-18° N, whereas in 12° N river discharfe persisted. But within stage 2 dune formation occured in 12° N on the (dry) shelf, additionally to fluviatile sediment input. - Older periods are preserved in autochthonous sediments of core GIK13289-3 and GIK13291-1, where oxygen stage 3,5 and 7 (the latter only in core GIK13289-3 present) show a humid climate (as well as in stage 5 of core GIK13255-3), interrupted by short arid intervals in core GIK12389-3, and stage 4 and 6 show an arid climate, interrupted by short humid periods The allochthonous stage 5 sediment in core GIK13211-1 also reflects a humid climate. The dissolution of planktonic foraminifers is strongest in th eLate Holocene and shows a minimum in the early Holocene, where also pteropods are preserved. The degree of carbonate dissolution is related mainly to the fine matter content (< 63 µm) whereas water depth is a less decisvive factor.