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Twenty-five participants from Spain and Germany gathered in Ferrol to discuss results based on material collected during the first two DIVA expeditions to the southeastern Atlantic Ocean in 2000 and 2005, and to make plans for the expeditions DIVA-3 to the Argentine Basin (southeastern Atlantic Ocean) and DIVA-4 to a basin in the northern Atlantic. Seventeen oral presentations and eleven posters gave an overview of the achievements of the last seven years and provided a base for future plans. Several themes emerged from the presentations which are summarised below.
The
project name DIVA stands for “Latitudinal gradients of deep-sea
biodiversity in the Atlantic Ocean”, and while biodiversity data were
astonishing for many taxa, the concept of latitudinal gradients in
biodiversity- greater diversity toward the equator than toward the
poles- could not generally be verified for the deep sea, based on the
comprehensive data set assembled from DIVA 1 & 2 material.
Distributional patterns of deep-sea animals are still not well
understood.
Generally, it seems that distance is not a factor regulating
biogeographic distribution in the deep sea. For example, the bacterial diversity of the
basins was found to be the highest ever detected in oligotrophic
deep-sea sediments, and different abyssal basins harbour different
communities which are, however, difficult to define by statistics.
Moreover, the communities did not become more different from each other
with increasing distance, which means that a factor other than distance
influences community structure- sedimentary characteristics may be more
important. Interestingly, this phenomenon has also been described from
macrofaunal communities in the Southern Ocean. Among the meiofaunal
organisms, harpacticoid copepods proved to be highly diverse- during
DIVA 1 alone, nearly 700 species of harpacticoids were identified from
little more than 2000 specimens!
For Harpacticoida, results from both DIVA expeditions
suggest that geographic structures, such as ridges between two basins,
does not influence the distribution or occurrence of species. A
particular complex of harpacticoid genera (Ceratonotus-Dendropsyllus)
was investigated in terms of distribution, which is apparently
worldwide. As for macrofaunal crustaceans, it appears that many isopod
species in the Southeast Atlantic deep sea have a wider distribution
than hitherto assumed, and that the species turnover in the deep sea is
much lower than expected. Some species of isopods seem to be more
restricted in their distribution than others in the same genus
(Haploniscus). On the other hand, the tanaidaceans seem to be highly
endemic to one abyssal basin, but since nearly all species discovered
in DIVA material are new to science, this finding may change with more
material being analysed.
While samples taken during a single expedition are necessarily just one
frame out of a movie, long-term investigations at the Porcupine Abyssal
Plain add a time axis and allow to investigate the dynamics of a
deep-sea site. It could be shown that sea cucmbers (genus Amperima)
affect meiofaunal distribution in the sediment. A downward movement
deeper in the sediment was evident, in response probably both to the
impoverishment and reworking of the surface layer and the downward
mixing of organic matter in the sediment by larger macro- and
megabenthic organisms.
Data from the Southern Ocean proved interesting in another context as
well, the postulated gradient in deep-sea diversity from the equator to
the poles. Even molluscs, the organisms providing the original evidence
for this paradigm in the northern hemisphere, seem to behave
differently in the southern hemisphere, as comparison of data from DIVA
and ANDEEP (Weddell Sea) has proven. Several new species of
Solenogastres, worm-like molluscs, were presented from abyssal depths
and from upper slope depths (project DIVA-Artabria I) in areas adjacent
to the abyssal plains sampled during DIVA.
Deep-sea organisms are also analysed with molecular genetic methods.
During the DIVA-2 expedition DNA of over 300 specimens assigned to
about 38 species of Desmosomatidae and other related isopod families
was extracted.
Deep-sea taxonomists are used to a high percentage of new species in
every sample they analyse, but each program provides its special
highlights. For DIVA, one of these highlights is the very large number
of new species of Loricifera, a group of meiofaunal animals described
in the 1980’s. They may be the third most abundant meiofaunal taxon
after harpacticoid copepods and nematodes, and the DIVA-2 material
yielded over 1200 specimens of Loricifera representing probably about
120 new species. Stunning details of their intricate and beautiful
morphology can be made visible with the
confocal-laser-scanning-microscope.The discovery of new families is
another very special result of a taxonomic analysis. A new harpacticoid
family has been described with more than 30 new species from DIVA 1
& 2 and NODINAUT samples collected in the southeast Atlantic and
central Pacific Oceans, respectively. New families may also have to be
established for several amphipods.
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