Are mesophotic seamounts reservoirs for potentially toxic
dinoflagellates associated with Ciguatera poisoning? A case
study from the SW Indian ocean (expédition La Pérouse,
2019)
Fig. 1. Location map of La Pérouse seamount off La Réunion.
In the western Indian Ocean, a Ciguatera
Fish Poisoning (CFP) hotspot is located
in the coastal waters of the Mascarene
Islands (Mauritius, Rodrigues, Réunion)
and the offshore fishing banks of the
Mauritius-Seychelles ridge, seamounts
near Réunion and Mauritius (Fig. 1).
The size of the La Pérouse seamount,
160 km northwest of Réunion Island on
the oceanic floor, is comparable to that
of Mont Blanc in the Alps. La Pérouse
is one of the rare shallow (-60m) seamounts located in the region. The plateau comprises mainly fossil limestone
plaques covered with macrophytes,
sponges, corals (few), and sand and
rubble zones (see back page photo).
In 2005, an expedition organized
by ARVAM at La Pérouse seamount
(also known by local fishermen as 90
miles bank) collected carnivorous fish
containing I-CTXs for analysis, as well
as samples of sediment and macroalgae which subsequently facilitated the
identification of Gambierdiscus spp in
the area.
During October-November 2019,
a diving and scientific expedition (La
Pérouse 2019) was organized to generate a first description of the habitats and associated fauna and flora on
the seamount based on a High Quality
(HQ) photographic inventory. Although
few samples for geological and biological analyses were taken, the focus on
HARMFUL ALGAE NEWS NO. 64 / 2020
macroalgal biodiversity and sediments
meant it was possible to isolate the microalgae assemblage from these samples.
A preliminary inventory from these
samples collected at depths between
-60 & -120m, revealed the presence of
the main genera observed in typical
CFP habitats: Gambierdiscus, Prorocentrum, Coolia but also athecate taxa such
as Amphidinium and gymnodinoid dinoflagellates (Fig. 2), and thecate taxa such
as Cabra, Sinophysis, Bysmatrum and
scrippsielloids. Interestingly, among
potentially toxic taxa, Gambierdiscus
spp were clearly predominant in the
samples (approx. 95% of isolated cells)
while Ostreopsis spp and Fukuyoa spp
were very rare. In order to give a precise identification and better evaluation
of the diversity, preserved cells from approx. 35-40 morphotaxa have been isolated individually in order to allow SEM
observations and molecular sequencing of LSU rDNA from single-cells in the
coming months.
This study will provide a significant
contribution for better knowledge of
habitat preferences and vertical distribution of CFP sources. While CFP is
traditionally associated with coral reefs
near the ocean surface where sunlight
conditions are optimal for growth and
toxin production, in this case only a low
concentration of light penetrates to the
depths encountered at La Pérouse seamount, considered in the mesophotic
zone. Only blue light reaches the benthic community here and literature
about the influence of these conditions
on toxin production by primary progenitors involved in seafood poisonings is
scarce.
This study will also inform results of
source & sink mechanisms that allow
harmful species to spread at regional
scales from these seamounts to coastal
ecosystems.
Acknowledgements
To Sophie Durville and Thierry Mulochau for their enthusiasm and to Laurent Ballesta, Florian Holon and Thibault Rauby for diving deep and bringing
samples to the surface.
Authors
Jean-Pascal Quod, Arvam-Pareto, Technopole
de la Réunion, 97438 Réunion (France).
Nicolas Chomérat & Gwenael Bilien, Ifremer,
LER BO, Station de Biologie Marine, Place de
la Croix, F-29900 Concarneau (France)
Patrick Durville, SAS Galaxea, Saline les
Bains, 97434 Réunion (France)
Email corresponding author:
jpascal.quod@arvam.com
Fig. 2. Benthic dinoflagellates from La Pérouse seamount. (A) Gambierdiscus sp. (B) Amphidinium sp. (C) Prorocentrum sp. (D) Prorocentrum sp. (E) Coolia sp. Scale bars, 10 μm.
13
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