Growth and production of sea urchin Strongylocentrotus droebachiensis in a high-Arctic fjord, and growth along a climatic gradient (64 to 77°N)

Abstract

Density, growth and production of Strongylocentrotus droebachiensis were investigated in the outer parts of a high-Arctic fjord (74° 18' N, 20° 15' W) in Northeast Greenland based on a com- bination of high resolution underwater photographs of the sea floor, dredge collections, and age determinations. The average density of 1.8 ind. m -2 (ranging from 0 to 16) from 10 to 60 m water depth was correlated with depth and amount of rocky substrate. The size structure of S. droebachien- sis in summer 2004 was unimodal with highest frequencies of individuals between 20 and 50 mm in diameter. Age estimated from growth increments in the interambulacral and genital plates revealed that growth was slow and that life span reached 45 yr. Annual production was estimated at 0.307 g ash-free dry weight (AFDW) m -2 , of which gonad production made up ~67%, thereby greatly influ- encing the production-to-biomass ratio of 0.29. The annual carbon demand of S. droebachiensis was estimated at ~37 t C in the outer part of the fjord (76 km 2 ; average = 0.49 g C m -2 ), corresponding to 3.5% of the total benthic and pelagic primary production, or 2.9% of the sedimentation of organic carbon within this area. Collections of S. droebachiensis from 7 populations from sub- to high-Arctic areas revealed a decline in growth performance along a south-north climate gradient in Greenland (64 to 77° N). Difference in length of the productive open-water period explained more than 80% of the variability in growth (p < 0.01) between populations and these findings are discussed in relation to predictions of future reductions in Arctic sea ice cover.