Plankton community structure and variability in the Scotia Sea: austral summer 2003

first_imgPlankton community structure in the Scotia Sea was investigated during January/earlyFebruary 2003 based on phytoplankton cell counts from 20 m depth and mesozooplankton countsfrom 0 to 400 m net hauls. Cluster analysis and multi-dimensional scaling revealed 4 major groups ofstations within each ordination that broadly corresponded geographically. A grouping of stations tothe east of the Antarctic Peninsula was characterised by low phytoplankton cell counts. The correspondinggrouping of stations in the mesozooplankton data were characterised by low abundance,overwintered state of many species, low egg production rates, and low carbon mass of copepodinstars. In contrast, groupings of stations in the northern part of the Scotia Sea were characterised aschlorophyll and mesozooplankton rich, and the summer generation was well advanced. Latitude wasmost strongly correlated with mesozooplankton community pattern (rank correlation ρ = 0.608),whereas surface chlorophyll a was a weaker correlate (ρ = 0.344) but along with measures of sizefractionedchlorophyll contributed towards explaining variation in species stages carbon mass andegg production rates. Additional hauls to 1000 m with an LHPR indicated copepod populations werebroadly in an overwintered state in the south of the region, whereas to the north of South Georgiarecruitment had been completed and some species were undergoing a seasonal descent. A comparisonwith January/February 2000 revealed higher abundances of krill larvae throughout the ScotiaSea in 2000 as well as a more advanced generation of the copepod Calanoides acutus. Ice cover duringthe 2 years differed considerably; in 2000 the position of the summer ice edge broadly accordedwith the 25 yr average, whereas in 2003 the ice edge lay much further north than usual. We suggestthat the timing of ice retreat influenced the timing of reproduction with the late retreat in 2003causing delayed reproduction and reduced population sizes.last_img read more