Spatio-temporal amphipods diversity of the suprabenthic community from the western part of the Bay of Seine (English Channel)
Résumé
The suprabenthos corresponds to organisms that migrate at night in the lower water layers and
are in the sediment during the day. Among the suprabenthic peracarids, amphipods were
frequently the most diversified while mysids were the most abundant group. During two-years
of study of the prawn Palaemon serratus larvae, to state of the complete cycle of this species
along the Normandy coast (English Channel), the suprabenthic fauna appeared particularly rich
in shallow waters (10 m) of the Bay of Veys. The suprabenthos was collected using a
suprabenthic sledge filtering the water at 0.10-0.40 m above the sea bottom. The sledge was
equipped with a WP2 plankton net (0.5 mm mesh size) with a flow meter at its centre to measure
the volume of water filtered, allowing the standardization of abundance for 100 m3. For all
surveys, three replicates were monthly collected for a sampling duration of 15 mn at a speed of
1.5 knots from February 2021 to January 2022 and seasonally from March 2022 to January
2023. A total of 53 species was recorded, among them eight species (Perioculodes longimanus,
Tryphosa nana, Megaluropus agilis, Nototropis guttatus, Apherusa bispinosa, Synchelidium
maculatum, Bathyporeia elegans and Phtisica marina) showed an occurrence ≥ 50 % of the
total samples. The amphipod diversity varied from 0 in September 2021 to 28 in June 2022.
The most abundant species were Apherusa bispinosa (67.7 % of the total abundance),
Perioculodes longimanus (7.5 %), Nototropis guttatus (4.3 %) and Synchelidium maculatum
(4.1 %). Moreover, the fauna showed very high monthly and pluriannual changes in relation
with reproductive pelagic phases with very high abundances during peaks such as Perioculodes
longimanus and Synchelidium maculatum in March 2021 and March 2022, Apherusa bispinosa
in June 2021, following by low abundances in the successive samples. Most of the Ampelisca
spinipes collected were pelagic males as in June 2021.