Masters Theses

Date of Award

5-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

Jacqueline M. Grebmeier

Committee Members

Lee Cooper, Dewey Bunting

Abstract

Benthic macrofaunal invertebrates were collected at 22 stations during an August-September 1995 cruise in the East Siberian and Chukchi Seas. The study area extended from the mouth of the Kolyma River east to Bering Strait. Benthic biomass and species composition were studied in relation to sediment characteristics and hydrographic parameters. Taxon-abundance and biomass based station groups were identified by cluster analysis and ordination techniques. Benthic macrofaunal biomass was found to be greatest in the eastern part of the study area and generally decreased from east to west and from offshore to nearshore. The highest benthic biomass, found in the Chukchi Sea, averaged 48.4 g Cm-2 (s.d.= +/-19.2). A diverse fauna exists at these stations with bivalves (F. Nuculanidae: Nuculana radiata and F. Tellinidae: Macoma calcarea) and amphipods (F. Ampeliscidae: Byblis sp. and Ampelisca sp.) dominating the biomass with other species of polychaetes, bivalves and amphipods also present. The lowest benthic biomass was found at stations in the East Siberian Sea, particularly near the Kolyma River mouth. These stations averaged 2.3 g Cm-2 (s.d.= +/-1.1), were dominated by isopods (F. Idoteidae: Idotea ochotensis) and small bivalves (F. Nuculidae: Nucula belloti) and showed low species diversity. The Kolyma River discharges freshwater onto the shallow continental shelf of the East Siberian Sea and this water is then carried to the east, during most years, by the Siberian Coastal Current. Freshwater inflow of the Kolyma River and the relatively high biological productivity of the more productive Chukchi Sea appear to be dominant oceanographic features. Organic carbon of terrestrial origin and lower nutritional value for the marine benthic community is more prevalent in the East Siberian Sea. Indications from the δ-13C values and C/N ratios of the organic carbon in the sediments suggest a progressive increase, west to east, in the relative contribution of marine vs. terrestrial origin of particulate organic carbon available to the benthos. Organic δ-13C values reached a minimum of -25.5% in the East Siberian Sea and increased to a maximum of -20.3% in the Chukchi Sea. C/N ratios (wt./wt.) ranged from a maximum of 8.3 in the East Siberian Sea and decreased to a minimum of 5.2 in the Chukchi Sea. The results of the study indicate that higher biomass of the study area is related to the marine origin of available organic carbon and the production of the overlying water column while benthic community structure is affected by sediment characteristics and the influence of the Kolyma River plume.

In addition to the ecologically oriented investigations, twenty-eight samples representing 16 stations were analyzed to assess the activities of accumulated natural and anthropogenic radionuclides. The samples counted were chosen to best represent the various animal types, feeding strategies, and geographic locations of invertebrates. The assays of gamma-emitting radionuclides in this study indicate that benthic macrofaunal invertebrates in the East Siberian and Chukchi Seas have not concentrated anthropogenically introduced radionuclides in detectable amounts with two exceptions. These exceptions were collected from two stations in the East Siberian Sea that contained only trace quantities of 137Cs that produced a positive signal, but had large uncertainties. Activities, on a wet weight basis, of the natural radioactive isotope 40K, were not concentrated in the tissues of benthic macrofaunal invertebrates above levels that can be reasonably attributed to absorption from the underlying sediment or the overlying water.

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