Gunnar Gad
40th European Marine Biology Symposium
AG Zoosystematik und Morphologie
Carl von Ossietzky University
26111 Oldenburg, Germany
e-mail: gunnar.gad @mail.uni-oldenburg.de
Vienna, 21-25 August 2005
Special thematic session on Seamounts
and abrupt deep Topographies
The Draconematidae (Nematoda) fauna of the
plateau of the Great Meteor Seamount
The examination of the Draconematidae revealed information on:
(1) distribution and abundance of Draconematidae on the seamount and the surrounding
deep sea
(2) important clues regarding their taxonomy and phylogeny
(3) zoogeography and possible origin of the species colonizing the plateau
The occurrence of a diverse fauna of Draconematidae on the Great Meteor Seamount
indicates that their distribution in oceanic habitats is more widespread than previously
assumed.
Example 1: A new species of the genus
Tenuidraconema have been found. This is the first
species of this genus reported from the Atlantic.
Around the same time a Belgium colleague (Marten
Raes, in press) discovered another congener living
on North Atlantic cold-water corals. These deepsea coral reefs are assumed to be one of the
locations in the North Atlantic from which the
elongate, surface-dwelling Draconematidae may
have managed to colonize the plateau.
50 μm
Example 3: The four new Dracograllus-species as
interstitial species inhabit the coarse calcareous
sand of the plateau. The examination of them
indicates the way in which this genus urgently needs
to be revised, because within Dracograllus there are
three species-groups which can clearly be delineated
whereas one species-group remains heterogeneous.
Furthermore, the next congeners of this species are
known from the Mediterranean Sea. In the case of
the stout interstitial Draconematidae, this is the most
likely location from which a faunal exchange with the
plateau may have taken place a slight fauna
exchange between both localities.
The Great Meteor Seamount is one of the largest of the 810 known seamounts of the North
Atlantic and rises from a depth of 4,500 m up to 287 m below the surface of the sea. Its summit
is a flat oval plateau of roughly 1,465 km2 size. The GMS is an old volcano with an age of 40-50
Mio. years and part of the Atlantis-Meteor-Seamount-Complex in the Iberian Basin. The
distance to the nearest coast is about 1,600 km. The sediment covering the plateau of the GMS
is biogenic coarse calcareous sand which has been proven to harbour an astonishingly diverse
interstitial meiofauna. The inventory of the meiofauna was done during the SEMEC (Seamount
Ecology) expedition to the GMS in 1998. Twenty major taxa of meiofauna were discovered
including Draconematidae (Nematoda).
The Draconematidae were chosen among others for this study because of their complex and
specialised external morphology related to their mode of locomotion and the habitat they
inhabit. At present, there are 80 known species of Draconematidae. The majority of species has
been reported form the Indo-Pacific region, but distribution data of single species are still rare.
The examined samples yielded 14 species of Draconematidae, 12 of them presumably new to
science and representing nine genera. Four monotypic genera, known so far only from their
type localities, are represented by new species on the plateau. The most abundant group on the
plateau is constituted by the 4 interstitial species, followed by 8 surface-dwelling species. Only a
few specimens of the 2 demersally dwelling species have been found on the plateau and the
surrounding deep-sea bottom as well. There are four possible areas from which the
Draconematidae may have managed to colonized the plateau of the GMS:
(1) Deep-sea reefs of cold-water corals (see example 1)
(2) Shallow water habitats of the North Atlantic (see example 2)
(3) Coast of the Mediterranean Sea (see example 3)
(4) Soft bottoms of the surrounding deep sea (see example 4)
Example 2: Three new Prochaetosoma-species
have been discovered inhabiting the plateau,
probably as an endemic group. Remarkably, these
species are easily distinguished by female features.
They were found separately in different areas on the
plateau with minor overlaps in their distribution. The
next congeners of these species are found in shallow
water habitats of the North Atlantic.
Example 4: A new Cephalochaetosoma-species and
another new species which, among others, is
currently being described as a characteristic representative of a genus of deep-sea Draconematidae.
These demersally dwelling species live on soft
bottoms and have been found recently in several
other deep-sea localities across the Atlantic.
Cephalochaetosoma-species and representatives of
this new genus have so far only been reported from
the deep sea of the Pacific. Both species were found
in low abundances on the plateau as well as in the
surrounding deep sea, which indicates a slight fauna
exchange between both localities.