Life in a cold environment - Antarctica: Global Science from a Frozen Continent - page 179

place to attempt to avoid the mistakes of the past (see Chapter 10 ). The harvesting of
the animals of the region has also had unintended consequences. For example, many
tens of thousands of seabirds have been accidentally killed during long-line fishing

operations in the Southern Ocean and this has reduced

several species of albatrosses and petrels to extremely low levels, including the
very real threat of extinction. Contrast this effect with the anecdotal accounts of the
vast numbers of seabirds that must have been supported by the offal discards from
the industrial whaling operations of the past and it becomes evident that human
interference in the ecosystems of the Antarctic has a long history and that the
effects of this interference are not always predictable.

' incidental mortality '

Marine benthic ecosystems

Estimations of the biodiversity of the Antarctic continental shelf are still
inadequate as many geographic areas are still to be sampled representatively
(e.g. those of Wilkes Land and the Bellingshausen and Amundsen Seas),
although the outcomes of the recent Census of Antarctic Marine Life are leading
to considerable increases in coverage. The benthic groups with the most species
are the poriferans, polychaetes, gastropods, bryozoans, amphipods, isopods and
ascidians and, in some speci c locations, also bivalves and gastropods. Sessile taxa

are favoured on the continental shelf in the Southern Ocean, possibly because of the
preponderance of substrata provided by glacial-marine sediments and dropstones.
Epifaunal taxa appear to have adapted well to the coarse-grained glacial substrates,
with sessile filter and particle feeders being especially prominent. Dense

communities of sponges, ascidians, anemones, hydroids, gorgonians, corals,
bryozoans, and crinoids are characteristic of the modern Antarctic shelf fauna at
depths below the zone of the in uence of ice

scour and anchor ice formation. This fauna often
forms strati ed three-dimensional communities

(analogous with tropical rain forests). Associated
with this sessile biota are mobile and wandering
or even swimming taxa such as echinoderms
(ophiuroids, asteroids, echinoids, holothurians),
pycnogonids, isopods, amphipods, nemerteans
and gastropods. There are two major types of
shelf communities. One is dominated by sessile

Figure 6.14 Sponge community on the Southern Ocean

shelf. (Credit: Julian Gutt, AWI)