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Relationship between habitat and recruitment of the Asian shore crab Hemigrapsus sanguineus (De Haan, 1835) and the indigenous shore crab Carcinus maenas (Linnaeus, 1758) on Normandy seashores

Pezy J.-P. & Raoux A.

On the French coast, Hemigrapsus sanguineus (H.s) was observed for the first time in 1999 in Le Havre. Since then, H. sanguineus adult population has been spreading along the French coast of the English Channel and have strong interaction with the indigenous crab Carcinus maenas (C.m). Juveniles populations of H. sanguineus and C. maenas are preferentially present in mussel beds (279 ± 108 ind·m−2 for H.s and 238 ± 77 ind·m−2 for C.m) and barnacles (63 ± 16 ind·m−2 for H.s and 28 ± 9 ind·m−2 for C.m). On the contrary, within macroalgae dominated habitats, only juveniles of C. maenas were observed (30 ± 11 ind·m−2).

Keywords: competition; English Channel; intertidal; Mytilus edulis; non-indigenous species

First online: 28th February 2023


New reports of Ammothea hilgendorfi (Pycnogonida, Ammotheidae) on the coast of Brittany

Le Roux A., Corbrion P., Gully F., Cochu M. & Picard C.

The presence of the pycnogonid
Ammothea hilgendorfi, an introduced species from the Pacific, is reported in 4 new places in Brittany: in the Rance maritime, the marina of Bas-Sablons at Saint-Malo, the Gulf of Morbihan and Pénestin seashore. An attempt to summarize the ecological characteristics of the occupied sites is proposed.

Ammothea hilgendorfi; gulf of Morbihan; Rance maritime

First online: 7th December 2022


An oomycotan disease, tentatively attributed to Lagenidium callinectes, is striking barnacles (Crustacea, Cirripedia) in the Morbihan gulf (South Brittany, France)

Le Roux A.

A disease due to an oomycota whose first symptoms were detected in 2016 in the barnacle
Chthamalus stellatus strikes four other species, Chthamalus montagui, Austrominius modestus, Perforatus perforatus and Amphibalanus eburneus in the Morbihan gulf. The hyphae develop inside the eggs or the embryos which they digest. Outside they form a very dense network especially on the outer layers of the egg masses and entrap the healthy embryos and nauplius larvae, generally leading to their death. The parasite, most probably introduced into the Morbihan gulf, presents characters compatible with those of Lagenidium callinectes, a species to which it is tentatively attached.
If this identification is confirmed, it would be the first record of
L. callinectes in European waters. It would be also a source of concern, not only for cirripedes, notably Pollicipes pollicipes, but also for commercially important decapods that the parasite may contaminate. Monitoring of the spawning of these species would be highly desirable.
The author proposes to call this pathology “the barnacle disease of Mor-Bihan” (with a hyphen, to indicate that it concerns the “little sea” and not the French department of Morbihan).

Amphibalanus; Austrominius; barnacles; Chthamalus; Lagenidium; Morbihan gulf; parasite; Perforatus

First online: 15th June 2022

First record of Lysmata seticaudata (Risso, 1816) from île de Ré (Pertuis Charentais Sea)

Sauriau P.-G. & Le Gall P.

The Monaco shrimp
Lysmata seticaudata (Risso, 1816) was first reported from île de Ré in the summer of 2018. First seen by divers in June, two others specimens were collected with shrimp push-nets by recreational fishers in August. This species is widely distributed in the Mediterranean Sea and is also present in warm-temperate waters of the eastern Atlantic. This new addition to the marine fauna of the Pertuis Charentais Sea underlines the potential of opportunistic citizen science data gathering combined with post-validation process. Together, they can produce reliable contribution to marine biodiversity inventories and refine biogeographic distribution of warm-temperate species in the context of climate changes. The historical record of the species at Jersey "about the year 1889" is discussed in light of a thorough literature review and is pushed back to the winter 1883-1884.

Keywords: biodiversity; citizen science; Decapoda; Lusitanian species; Lysmatidae; Monaco shrimp; Pertuis Charentais

First online: 21st June 2021


Description of a poorly known maerl bed off the island of Groix (southern Brittany)

Guyonnet B.

From 2010 to 2016, several cartographic and biological investigations located between the harbor of Lorient and the Groix island, have helped to increase the knowledge of the maerl bed so far poorly known. The distribution of the maerl bed, its edaphic characteristics as well as its associated biodiversity are here discussed.

Keywords: biodiversity; cartography; Groix; maerl

First online: 28th June 2019


Functional mapping as management tool of biogenic habitats: case study of the Belle-Île-en-Mer maerl bed (Southern Brittany, France)

Dubreuil J., Grall J. & Barillé A.-L.

In-depth knowledge of habitat functioning of is a prerequisite when trying to set up the best possible conservation measures that are required by marine habitats under anthropogenic stress. Within many Natura 2000 sites such knowledge appears to be mainly patchy and obviously incomplete, in particular when dealing with complex habitats such as biogenic habitats. In such context we have mapped maerl density and maerl vitality within the natural protected area of Belle-Île-en-Mer island (Southern Brittany, France). The results show coastal areas of living coralline algae densities, places of high maerl production. These contrast with off shore areas constituted of dead maerl fragments, probably drifting northward and to higher depth under the influence of dominating currents. Beyond the increase of knowledge regarding this complex habitat functioning, our results allow to better understand maerl beds dynamics at various scales: from the algae itself through the vitality measurement, to the geolocation of biogenic material export areas, and maerl production levels. We believe that specific conservation actions need to focus on areas where maerl beds show the highest liveliness, which will allow the sustainability of the maerl bed on the integrality of its surface. The methodology used here could be adapted (in terms of scale and/or frequency) to the management of other complex/biogenic habitats.

Keywords: maerl; Brittany; functionality; mapping; Natura 2000

First online: 7th November 2017