Mangoni¹, Olga, Vincenzo Saggiomo², Adriana Zingone², Diana Sarno², Maria Saggiomo^1,2, Mario De Stefano² and Gian Carlo Carrada¹

¹University of Naples “Federico II”, via Mezzoccanone, 8 – 80134 Naples, Italy, Tel: +39(081)2535149, Fax: +39(081)2535134, E-mail: olga.mangoni@unina.it and ²Zoological Station “A. Dohrn”, Naples, Italy

The role of sympagic microalgae in seeding phytoplankton blooms in Terra Nova Bay (Ross Sea, Antarctica)

Sea ice microalgal communities in Terra Nova Bay are dominated by diatoms and attain biomass values up to 280 mgChla m^-2. During the XV Italian Antarctic Expedition (October-December 1999), a study was carried out on the role of bottom and platelet sea ice flora in seeding pelagic blooms. Samples of consolidated pack ice, platelet ice and interface waters were collected every three days. Photosynthetic experiments, HPLC pigment analyses and light and electron microscopy observations were performed on ice samples and on water samples from experimental mesocosm. The bottom ice community was dominated up to 90% cryobenthic species (e.g., Entomoneis kjelmanni, Nitzschia stellata), while the platelet ice community included both cryobenthic and cryopelagic diatoms (e.g., Fragilariopsis spp., Stellarima microtrias, Chaetoceros spp., Nitzschia spp., Pseudo-nitzschia subcurvata), and microflagellates. The bottom ice biomass markedly increased over the sampling period (from 4.7 to 542 mg m ^-3). A very low P^B_max (AVG 0.12 mgC g chl a^-1) and low photoadaptation index (<18 µE m^-2 sec^-1) were measured, which suggest that the observed increase was due to accumulation processes. In mesocosms experiments the platelet ice communities adapted to 85% and 10% of incident irradiance within a few days, giving rise to an exponential growth lasting until total disappearance of macronutrients. By contrast, the bottom ice communities were photo-damaged at irradiance levels commonly recorded in the photic zone of an ice-free water column. These results suggest that platelet ice communities are the major contributors to the development of phytoplankton blooms during the Austral spring.