The mucus feeding structures or "houses" of the giant larvacean Bathochordaeus provide abundant material for the study of deep-sea detrital communities, particularly their poorly known zooplankton associates. We sampled houses between 100 and 500 m in Monterey Bay with a submersible ROV (remotely operated vehicle) and surveyed houses for metazoans by database search of video footage taken from the ROV. Up to an order of magnitude more metazoans were found on houses than in surrounding waters. On average, copepods constituted as much as 96% of the assemblage on houses, and many of the species possess benthiclike morphology and feeding strategies. Poecilostomatoid copepods (genus Oncaea) averaged as many as 64.6 house-', and scarcely known calanoid copepods (genus Scopalatum) occurred in 56% of the samples. Higher numbers of metazoans occurred on shallower houses (lo&300 m), likely due to a difference in the species of larvacean present and (or) to reduce oxygen levels at greater depths.At least one copepod species, Scopalatum vorax, occurred on houses more frequently during the nonupwelling season, possibly due to the lack of other food. Our results suggest that midwater detritus contains a unique invertebrate community that has been largely undetected, mostly due to sampling difficulties. The houses also provide benthiclike habitats for midwater zooplankton and serve as feeding centers. These particle-associated zooplankton may therefore contribute to remineralization of particulate organic carbon at depth.Marine snow, aggregates of organic detritus typically consists of a detrital or mucus matrix > 0.5 mm in diameter, harbors rich commuwith associated dinoflagellates, ciliates, other nities of associated organisms. Marine snow protozoa, and bacteria, which are often enriched orders of magnitude over those in the surrounding water (reviewed by Alldredge and

The composition of sea ice communities in the Ross Sea region was examined during the autumn to winter transition and during the summer. The biomass of autotrophs and heterotrophs in autumn reached maximum values of 709 and 167 mg C m , respectively. During the autumn-winter cruise, most of the biomass was found within ice floes as interior and bottom layer communities. During summer, surface-layer slush communities occurred throughout the ice-covered regions. The biomass was highly variable throughout the study regions during both cruises. Diatoms dominated the autotrophic biomass; however, autotrophic dinoflagellates and autotrophic flagellates contributed significantly to the community make-up. Among heterotrophs, ciliates predominated during both cruises, followed by heterotrophic flagellates and heterotrophic dinoflagellates. Similarity analysis, based on the biomass composition of major groups, showed consistency between and within cruises, with most samples > 70% similar. The autumn to winter samples (all from within floes) showed higher similarity clusters that could be related to changing compositions of diatoms, ciliates, and autotrophic dinoflagellates. Most variable were some summer surface slush samples, where samples dominated by Phaeocystis, Pyramimonas, Gymnodinium, and the ciliate Gymnozoum formed outlying clusters. The dynamics of ice biota may be determined by relatively few taxa that are persistently found within the ice floes. Surface blooms may develop either from a biota within the ice or from opportunistic forms from the water column that are introduced during flooding events. Thus, these assemblages may show considerably more variability in composition than those that develop within the underlying ice. KEY WORDS: Sea ice community · Antarctic · ProtistsResale or republication not permitted without written consent of the publisher

No 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 65³ to 74³ S in the western Ross Sea along135³,150³ and 165³ 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.

Over the past decade, blooms of the domoic acid (DA) producing diatom Pseudonitzschia have been responsible for numerous deaths of marine mammals and birds in Monterey Bay, California. Euphausiids (krill) are important members of the local zooplankton grazer community and comprise the primary diet of squid, baleen whales, and many seabirds. Krill are thus a key potential vector for the transfer of DA to higher trophic level organisms in Monterey Bay. A better understanding of the quantitative trophic interactions and body burden of DA in krill is required to predict whether they can act as an effective vector for this neurotoxin. Here we report results of toxin analyses and gut content examinations of krill Euphausia pacifica collected from Monterey Bay in 2000. Corresponding counts of toxic Pseudo-nitzschia species in the water and their cellular DA concentrations were also obtained at the collection sites. Toxin analysis by receptor binding assay demonstrated that DA in krill tissue varied between 0.1 to 44 µg DA equiv. g -1 tissue (confirmed by tandem mass spectrometry), with levels corresponding to the abundance of toxic Pseudo-nitzschia species present in the water. The occurrence of Pseudo-nitzschia australis frustules in the digestive tract of E. pacifica verified that a toxic species of this diatom was an important part of their diet and thus implicated this phytoplankter as the source of DA. These findings provide compelling evidence for the role of krill as a potential transfer agent of the phycotoxin DA to higher trophic levels in marine food web. 237: 209-216, 2002 toxigenic species of the diatom Pseudo-nitzschia to sea lions and seabirds. The first major event occurred in 1991, when more than 200 brown pelicans and Brandt's cormorants were found dead on the beaches of Monterey Bay (Fritz et al. 1992, Work et al. 1993. Similarly, Monterey Bay was the site of another major DA poisoning incident in 1998, when sea lions were observed dying on the beaches suffering from neurological symptoms (Lefebvre et al. 1999, Scholin et al. 2000. In all DA poisoning events in this region, Pseudo-nitzschia australis was determined to be the primary source of the toxin, and filter-feeding anchovies Engraulis mordax the apparent vector. Anchovies are not the only potential filter-feeding vectors of DA in the Monterey Bay system. For example, zooplankton are generally key consumers of phytoplankton. Nonetheless, while the link between zooplankton and toxic dinoflagellates has been confirmed (e.g. White 1981, Huntley et al. 1986, Ives 1987, McClatchie 1988, Uye & Takamatsu 1990, Turriff et al. 1995, Bagoien et al. 1996, Teegarden & Cembella 1996, Shaw et al. 1997, Turner & Tester 1997, Tester et al. 2000, there has been less attention focused on toxin transfer between toxic diatoms and zooplankton grazers (Windust 1992, Tester et al. 2001, Lincoln et al. 2001. KEY WORDS: Krill · Pseudo-nitzschia · Domoic acid · Harmful algal blooms · Toxic algae · Trophic transfer · Food webs Resale or republication not p...

By using a remotely operated vehicle (ROV), we studied large mucous aggregates produced by the larvacean Bathochordaeus in Monterey Bay, California. These fragile structures or "houses," cannot be sampled by typical water or net collecting devices, and likely represent a class of cosmopolitan, widely spaced aggregates in subsurface waters. ROV samples allowed us to determine the contribution of the aggregate-associated communities to populations of microorganisms at depths of 100-500 m. Because the giant houses only average -1 per 100 m', they harbor

Sea ice communities were sampled across the Ross Sea in the austral autumn. The biota in first-year pack ice was assessed by measuring chlorophyll a (chl a), phaeopigments, total particulate carbon and nitrogen (POC and PON, respectively) and collecting samples for identification by microscopy. Physical and chemical parameters were also measured to characterize the environment. Chl a concentrations in ice ranged from 0 to 96.9 µg l -1 in discrete samples and from 0.02 to 20.9 mg m -2 for values integrated throughout floes. Maximum values were similar to those observed in first-year pack ice at other Antarctic locations. Chl a concentrations varied with ice structure and with latitude. POC:chl a and C:N ratios (molar) were high, possibly indicating detritus accumulations. The higher chl a levels north of approximately 72°S were apparently a result of ice forming in the south early in the season with subsequent advection to the north. These dynamics would result in older ice in the mid-or northern pack ice zone that was maintained in a favorable light and temperature regime during the seasonal progression of formation and drift. Chlorophyll levels were low in surface-layer communities. High chlorophyll concentrations were associated with internal communities. Bottom-layer algal populations, while present, did not reach the levels of high biomass reported for autumn blooms in some land-fast ice regions. Apparent nutrient and CO 2 depletion were correlated with biomass parameters but accounted qualitatively for only a fraction of the biomass accumulation measured. Overall, autumn ice-associated production in the Ross Sea may be lower than expected because of the ice drift dynamics, apparently low production in the near-surface layers of first year ice flows, and the absence of rich bottom-layer assemblages.

A central question addressed by the VERTIGO (VERtical Transport In the Global Ocean) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m).Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size-partitioning of Net Primary Production (NPP) and subsequent transformations prior to export; estimates of the ratio of algal-to faecal- This decrease in predicted export at K2 matches the observed trend for E 150 . Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 to 500 m. This strong surface-subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic 3 particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone. IntroductionThe biological pump is one of several (such as the solubility pump) that sequester