Susan L. Coale

Toxic diatoms and domoic acid in natural and iron enriched waters of the oceanic Pacific

Near-surface waters ranging from the Pacific subarctic (58°N) to the Southern Ocean (66°S) contain the neurotoxin domoic acid (DA), associated with the diatom Pseudo-nitzschia. Of the 35 stations sampled, including ones from historic iron fertilization experiments (SOFeX, IronEx II), we found Pseudo-nitzschia at 34 stations and DA measurable at 14 of the 26 stations analyzed for DA. Toxin ranged from 0.3 fg·cell−1 to 2 pg·cell−1, comparable with levels found in similar-sized cells from coastal waters. In the western subarctic, descent of intact Pseudo-nitzschia likely delivered significant amounts of toxin (up to 4 μg of DA·m−2·d−1) to underlying mesopelagic waters (150–500 m). By reexamining phytoplankton samples from SOFeX and IronEx II, we found substantial amounts of DA associated with Pseudo-nitzschia. Indeed, at SOFeX in the Antarctic Pacific, DA reached 220 ng·L−1, levels at which animal mortalities have occurred on continental shelves. Iron ocean fertilization also occurs naturally and may have promoted blooms of these ubiquitous algae over previous glacial cycles during deposition of iron-rich aerosols. Thus, the neurotoxin DA occurs both in coastal and oceanic waters, and its concentration, associated with changes in Pseudo-nitzschia abundance, likely varies naturally with climate cycles, as well as with artificial iron fertilization. Given that iron fertilization in iron-depleted regions of the sea has been proposed to enhance phytoplankton growth and, thereby, both reduce atmospheric CO2 and moderate ocean acidification in surface waters, consideration of the potentially serious ecosystem impacts associated with DA is prudent.

Fluxes of living radiolarians and their skeletons along a northeast Pacific transect from coastal upwelling to open ocean waters

Abstract Sinking fluxes of living polycystine and phaeodarian radiolarians and their intact empty skeletons were measured from surface waters to 2000 m using free-floating particle interceptor traps at three sites ranging from highly productive coastal upwelling to oligotrophic central gyre waters in the northeast Pacific Ocean. Total radiolarian fluxes and living pheodarian fluxes were generally highest at the coastal site throughout the water column. There was no consistent site-specific pattern for fluxes of living polycystines, polycystine empty skeletons, and phaeodarian empty skeletons. Living phaeodarians were the only group that showed the same rank order of sites with respect to flux at both the base of the euphotic zone and at 2000 m. Thus different short-term processes occurring in the water column (e.g. destructive and non-destructive predation and midwater addition of living radiolarians) altered radiolarian fluxes. Neither radiolarian fluxes at the base of the euphotic zone nor fluxes at 2000 m showed a simple correspondence with primary production, indicating that short-term measurements did not reveal long-term patterns. At most depths at all sites, fluxes of living, skeleton-bearing phaeodarians outnumbered fluxes of empty phaeodarian skeletons. In contrast, at most depths at all sites, fluxes of empty polycystine skeletons outnumbered fluxes of living, skeleton-bearing polycystines. Relatively large, living skeleton-less phaeodarians were the numerically dominant radiolarian in the uppermost traps at the oceanic and coastal sites. These phaeodarians agglutinate siliceous skeletons of other plankton and contributed 5% of the silicoflagellate flux, 16% of the polycystine flux, and 2% of the centric diatom flux at these depths. The resemblance of skeleton-less phaeodarians to fecal pellets may cause them to be misidentified as fecal material when trap contents are dried for processing.

Loricate choanoflagellates (Acanthoecidae, Choanoflagellida) from the Weddell Sea, Antarctica

A study of the choanoflagellate species composition of an Antarctic ice edge zone (northern Weddeil Sea, March 1986) has resulted in the finding of 16 taxa of which one, Cosmoeca takahashii Thomsen sp.n., is described here. An emended description is given of Parvicorbicula circularis. Morphological, numerical and dimensional aspects of other species have been analysed in an attempt to improve the circumscription of certain taxa, and to increase our understanding of the nature of intraspecific variability. Data on the relative abundance of choanoflagellate species along seaward transects perpendicular to the ice edge showed that seven species account for more than 95% of all choanoflagellates identified. The two most abundant species were Parvicorbicula socialis and Diaphanoeca pedicellata.

Biomass, production and microhabitat characteristics near the freeboard of ice floes in the Ross Sea, Antarctica, during the austral summer

Abstract The physical, chemical and biological characteristics of surface and freeboard habitats in the summer pack ice in the eastern Ross Sea, Antarctica, were documented in a continuing effort to determine the factors controlling the distribution, production and succession of sea-ice biota. Three longitudinal transects from approximately 65° to 74° S in the western Ross Sea along 135°, 150° and 165° W were visited where samples of slush and slush interstitial water from surface and freeboard habitats as well as sea water were collected at every degree of latitude. Freeboard and surface habitats, found at all stations in the pack ice, contained a large range (five orders of magnitude) of microalgal biomass (measured as chlorophyll a concentrations) and nutrients ranging from below levels of detection to those of the surrounding sea water. The geophysical attributes of the freeboard habitat (i.e. a layer of semi-consolidated ice overlying a layer containing unconsolidated ice crystals and sea water) are consistent with previous descriptions of this environment. However, additional information is presented on the range of biomass concentrations as well as the small-scale distributions of the habitat and biota.