Systematics and Biogeography of Antarctic Deep-Sea Gromiids


Rothe, Nina (2009) Systematics and Biogeography of Antarctic Deep-Sea Gromiids. University of Southampton, Faculty of Engineering Science and Mathematics, School of Ocean and Earth Science, Doctoral Thesis , 256pp.

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Description/Abstract

Gromiids are large amoeboid protozoans with an organic test and filose pseudopodia, which
protrude through a shell aperture that is surrounded by an oral capsule. The first shallow-water
gromiid, Gromia oviformis, was described by Dujardin in 1835 and is found worldwide. It was
only in 1994, however, that gromiids were found for the first time at bathyal depths in a nonfjord
setting, when the first deep-sea gromiid, G. sphaerica, was recovered from below the
oxygen minimum zone on the continental slope off Oman in the Arabian Sea. The present study
is based on the largest sample set of undescribed deep-sea gromiids thus far. The core of this
thesis is the description of twelve new morphospecies from bathyal and abyssal depths (1180 m
– 4800 m) in the Weddell Sea, Antarctica, using a combination of morphological and molecular
criteria. All species possess a distinct oral capsule and a layer of “honeycomb membranes”,
which form the inner part of the organic test wall. Both these features are characteristic of
gromiids. Their identification as gromiids is confirmed by analyses of partial small subunit
ribosomal DNA (SSU rDNA) gene sequences for three of the twelve new species: Gromia
marmorea sp. nov., Gromia melinus sp. nov., and Gromia winnetoui sp. nov. Phylogenetic
analysis using the maximum likelihood method revealed that G. marmorea and G. melinus form
two distinct clades reflecting the morphological differences amongst the Weddell Sea species,
and between deep-water Southern Ocean Gromia and previously described shallow-water
gromiid G. oviformis, as well as gromiids from the deep Arabian Sea. Gromia winnetoui forms a
third clade which branches with one of the Arabian Sea species. Both these species are
morphologically very distinct and therefore the molecular results are inconsistent with the
morphological characteristics. Based solely on morphological criteria, another sixteen
morphospecies from the Northeast Atlantic are described, including specimens from the
Northwest African margin (1320 m), the Porcupine Seabight and the Rockall Trough (1028-
3000 m), the Skagerrak (664 m), and the fjords of Møre along the western coast of Norway (65-
667 m). Most deep-sea gromiids appear to range in size between 0.1 and 4.0 mm, except for
morphospecies B2 from the Skagerrak as well as most of the Arabian Sea species, which display
a wider size range. The different morphospecies exhibit a variety of shapes, including spherical,
droplet, conical, grape, elongate oval, sausage, bowling pin, vermiform, and irregular. The
results of this thesis support the hypothesis that gromiids occur at depths >200 m in all major
oceans. They are predominantly found along continental margins between 1000 and 3000 m.
This thesis presents the only two records of Gromia (G. melinus and Species 154) from depths
>4000 m in the Weddell Sea. It is hypothesized that further sampling will increase the number of
species and novel morphotypes. Gromiids appear to be found in highest abundances in areas
with elevated fluxes of organic matter. They are likely to play an important role in carbon and
nitrogen cycling, as well as increasing local biodiversity.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QH Natural history > QH301 Biology
G Geography. Anthropology. Recreation > GC Oceanography
Divisions: University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
ePrint ID: 69035
Date Deposited: 15 Oct 2009
Last Modified: 27 Mar 2014 18:48
URI: http://eprints.soton.ac.uk/id/eprint/69035

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