Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Marine Biodiversity
Specific Objective 6: To identify and measure diversity, distribution and densities of
mesozooplankton, macrozooplankton and meroplankton.
This objective addressed the samples taken by Multiple Opening/Closing Net and Environmental
Sampling System (MOCNESS) from the sea surface to the sea floor. The samples were
quantitatively divided at sea to allow several complementary analyses to be performed. In terms of
the mesozooplankton community in the Ross Sea, copepods were the dominant zooplankton
collected in most samples, and this was primarily calanoids and cyclopoids (i.e., Oithona spp.).
However, in certain cases pteropods (Limacina helacina antarctica) and salps (Salpa thompsoni)
made important contributions to mesozooplankton abundance. Total water column
mesozooplankton biomass ranged between 0.6-9.1 g C m -2 and was usually highest close to the
surface. Mesozooplankton biomass in the Ross Sea was generally higher than expected, and can
rival that of productive subantarctic regions (e.g., South Georgia). Salps were the main
macrozooplankton species recorded in the MOCNESS samples and a paper describing the
population ecology and distribution of Salpa thompsoni on the continental slope and around the
seamounts to the north of the Ross Sea has been published by Pakhamov et al. (2011).
Samples were also preserved in ethanol for the analysis of meroplankton species composition and
DNA sequencing. Larvae from at least eight phyla were found, with a remarkable dominance of
annelids in both abundance and diversity. Overall, larval abundances observed were lower than
other Antarctic studies, likely attributable to the late summer sampling, months after Ross Sea’s
phytoplankton bloom and the main trigger of spawning in many benthic invertebrates. Analysis of
variation in meroplankton community composition showed significant differences among
geographic regions (Shelf, Slope and waters of the Antarctic Circumpolar Current - ACC), among
water masses (Shelf Water, Antarctic Surface Water, and Circumpolar Deep Water), and among
depth strata (upper, midwater and bottom). Overall, near surface waters showed greater larval
abundances, and these values decreased from the continental shelf to the slope, declining further in
the deeper waters of the ACC. Differences between these locations were due not only to the
presence or absence of certain taxa, but also a result of changes in OTU abundance.
Specific Objective 7: To determine diversity, distribution and densities of viral, bacterial,
phytoplankton and microzooplankton species in the water column.
The full data sets have been completed and loaded into an MPI database and to the South western
Pacific OBIS node (Gordon 2000). Phytoplankton and nanoplankton cell counts have revealed that
there is a significant difference between shelf and abyssal site water column assemblages, both in
terms of cell numbers, diversity and density. These data now have to be integrated with the water
column data to help understand what may be driving the changes in these compositions.
Specific Objective 8: To determine the spatial distribution, abundance (biomass), diversity, and size
structure of shelf and slope demersal fish species and associated invertebrate species using a
demersal survey.
This objective had three key tasks; (i) to identify specimens, update the Ross Sea species list and
determine biodiversity, (ii) to identify fish assemblages and relate them to environmental data, and
(iii) to compare estimates of fish density and abundance between trawls, visual (video & still
images) and acoustic sampling techniques. A fourth key task, to determine density and abundance
of demersal fish using a bottom trawl survey, was funded under MPI project ANT2007-02. Results
have been published as three scientific journal papers with an additional paper in review, and have
been submitted to several CCAMLR working group meetings.
A paper on the distribution and diversity of demersal and pelagic fish species in the Ross Sea
region including results from both the BioRoss and IPY surveys and collections from the toothfish
fishery will soon be published (Hanchet et al. in press). A diverse collection of over 2,500 fish
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