Influence of seasonal ice formation on life cycle strategies of Antarctic copepods

• Main Author: Swadling, KM
• Format: Thesis
• Language: English
• Published: 1998
• Subjects: Ice sheets; Zooplankton; Marine ecology; Copepoda; Antarctic; East Antarctica; Vestfold; Vestfold Hills; Antarc*; Antarctica; ice algae; Sea ice; Copepods
• Online Access: https://eprints.utas.edu.au/22306/; https://eprints.utas.edu.au/22306/1/whole_SwadlingKerrieMarguerite1998_thesis_.pdf

Zooplankton from inshore marine and marine-derived lacustrine Antarctic habitats were studied over two summers and the intervening winter from December 1993 to March 1995 at two sites in the Vestfold Hills region, East Antarctica. Particular emphasis was placed on the interaction between fast ice and the underlying water column, and the effect of this on the ecology of dominant copepod species. The overwintering strategies of commonly found copepods were investigated. The sea ice habitat was characterised by high abundance and low diversity of metazoans. Paralabidocera antarctica dominated the metazoan assemblage, reaching densities of up to 500,000 individuals `m^(-2)`.Other taxa present included Drescheriella glacialis, unidentified harpacticoids, Stephos longipes and Ctenocalanus citer. Horizontal patchiness of the sympagic biota varied as much on scales of less than one metre as it did at scales of several kilometres. Metazoan density was not clearly correlated with chlorophyll concentration, salinity or particulate organic carbon. The zooplankton assemblage at the inshore marine site was numerically dominated by Oncaea curvata and Oithona similis throughout the sampling period. Diversity was highest in the summer when the break-out of the fast ice, coupled with the phytoplankton bloom, encouraged the development of meroplanktonic larvae of benthic species. Other copepod species present included Paralabidocera antarctica, Calanoides acutus, Ctenocalanus citer, Stephos longipes, and unidentified harpacticoids. Grazing impact by the copepod assemblage on primary productivity during the 1994-5 summer was consistently low, ranging between 1 and 5%. The life cycle of Paralabidocera antarctica was strongly associated with the growth and development of ice algae. Lipid storage by this species was predominantly in the form of triacylglycerols, indicating that copepods were feeding throughout the year. In contrast, Oithona similis and Oncaea curvata predominantly stored wax esters, and their life cycles were not linked strongly to the summer phytoplankton bloom. A lacustrine population of Paralabidocera antarctica was also found to store triacylglycerols, suggesting that the copepods were able to graze throughout the year. This species, the only planktonic metazoan consumer present in the lake, reached abundances of up to 35,000 `m^(-3)`. The life cycle of this population had become much less tightly regulated than at the coastal site, and specimens were rarely found living within the lake ice. The lack of predators and competitors, along with measurable quantities of phytoplankton present in the lake throughout the year, has resulted in the decoupling of the life cycle of this population from the growth cycle of the ice algae.