Benthic response to chronic natural physical disturbance by glacial sedimentation in an Arctic fjord

摘要

The activity of Arctic tidal glaciers results in high turbidity, high rate of inorganic particulate sedimentation and sedimentary instability in near-glacier marine basins. The chronic physical disturbance of sediments is accompanied by low input levels of organic matter. The response of soft-bottom macrofauna to glacial disturbance was studied in Kongsfjord, Svalbard. The quantitative characteristics of the macrofauna of 4 associations located along a gradient of glacier-induced disturbance were examined. Benthic biomass decreased with increased proximity to the glacier (from 10.9 g wet weight (ww) m~(-2) in the outermost association to 2.7 g ww m~(-2) in the glacial bay). Faunal density was highest in the transitional zone (592 ind. 0.1 m~(-2)) between the central basin (425 ind. 0.1 m~(-2)) and the inner glacial bay (442 ind. 0.1 m~(-2)). The average individual biomass was lowest in the glacial bay as a result of the smaller body size of organisms. A decrease in the size of organisms in disturbed sites was not accompanied by a classical shift from 'equilibrium' to 'opportunistic' species. The functional structure of the faunal associations was simplified in the impoverished glacial bay association where 1 guild, the mobile surface-detritus feeders, strongly dominated. Average species number per sample was lowest in the glacial bay (22 species) and highest in the transitional association (42 species). Species diversity expressed by the Shannon-Wiener and Hurlbert rarefaction indices and evenness expressed by the Pielou index was lower in the glacial bay than in the remaining associations. The decrease in biomass, mean size of organisms, species diversity and evenness as well as the peaked distribution (i.e. maximum in the transitional zone) of density and species richness are consistent with patterns reported in studies of different natural and anthropogenic disturbances. Some distinct features of the case of glacial-induced disturbance include relatively high taxonomic distinctness and low beta diversity and low faunal dispersion in the near-glacier association.