Thierry Comtet

Station Biologique de Roscoff · Adaptation et Diversité en Milieu Marin - UMR 7144 CNRS UPMC

Deep-sea hydrothermal vent systems are under investigation for metal and rare earth element exploitations. The negative impacts on natural and endemic populations in these areas are still unclear. Larval dispersal is critical for colonization and settlements of populations in marine environments, and assessing connectivity is challenging, especiall...

Marinas are high-priority targets for marine non-indigenous species (NIS), where they compose a large portion of the biofouling communities. The practicality of water samples collection makes environmental DNA (eDNA) metabarcoding an interesting tool for routine NIS surveys. Here the effectiveness of water-eDNA-metabarcoding to identify biofouling...

The coastal oceans can be highly variable, especially near ocean fronts. The Ushant Front is the dominant oceanographic feature in the Iroise Sea (NE Atlantic) during summer, separating warm stratified offshore waters from cool vertically-mixed nearshore waters. Mesozooplankton community structure was investigated over an annual cycle to examine re...

• High‐throughput sequencing of amplicons (HTSA) has been proposed as an effective approach to evaluate taxonomic and genetic diversity at the same time. However, there are still uncertainties as to how the results produced by different bioinformatics treatments impact the conclusions drawn on biodiversity and population genetics indices. • We eval...

Marine hard-bottom communities are undergoing severe change under the influence of multiple drivers, notably climate change, extraction of natural resources, pollution and eutrophication, habitat degradation, and invasive species. Monitoring marine biodiversity in such habitats is, however, challenging as it typically involves expensive, non-standa...

The ability of marine invertebrate larvae to control their vertical position shapes their dispersal pattern. In species characterized by large variations in population density, like many echinoderm species, larval dispersal may contribute to outbreak and die-off phenomena. A proliferation of the ophiuroid Ophiocomina nigra was observed for several...

High-throughput sequencing (HTS) technologies offer new promise to support surveillance programs targeting marine non-indigenous species (NIS). Metabarcoding might surpass traditional monitoring methods, for example through its ability to detect rare species, a key feature in early detection of NIS. Another interest of this approach is the identifi...

This study described the occurrence of abnormalities in bivalve larvae from the Puck Bay. Analyses of plankton samples collected in 2012–2013 showed that larval Mytilus trossulus, Mya arenaria, and Cerastoderma glaucum exhibited abnormalities that could indicate adverse environmental impacts. The deformities were mainly in shells, but missing soft...

In many marine invertebrates, long-distance dispersal is achieved during an extended pelagic larval phase. Although such dispersal should result in high gene flow over broad spatial scales, fine-scale genetic structure has often been reported, a pattern attributed to interfamilial variance in reproductive success and limited homogenization during d...

Biological invasions are a major threat to the world’s biodiversity with consequences on ecosystem structure and functioning, species evolution, and human well-being (through ecosystem services). Conservation of biological diversity and management of biological resources require multi-level management strategies on non-native species, in order to (...

Early life history stages of marine organisms are generally thought to be more sensitive to environmental stress than adults. Although most marine invertebrates are broadcast spawners, some species are brooders and/or protect their embryos in egg or capsules. Brooding and encapsulation strategies are typically assumed to confer greater safety and p...

Recruitment success of marine invertebrate populations not only depends on the number of recruits but also on their quality which affects their survival. In species characterized by a mixed development (encapsulated embryonic development and release of planktotrophic larvae), the offspring quality depends on both maternal provisioning and larval fe...

Reproductive cycles of marine invertebrates with complex life histories are considered to be synchronized by water temperature and feeding conditions, which vary with season and latitude. This study analyses seasonal variation in the occurrence of oyster (Crassostrea gigas) and mussel (Mytilus edulis/ galloprovincialis) larvae across European coast...

In Europe, the gastropod Crepidula fornicata is an invasive species characterized by a long reproductive period (from February to November). Thus, its larvae are exposed to variations in available food sources (in terms of quantity and quality). We aimed to investigate if bacteria could contribute to larval food both in presence or absence of phyto...

Many marine gastropod species brood their embryos in thin-walled capsules to protect them during development. Despite its beneficial effects, encapsulation has two major constraints, nutrition and oxygen supply, which affect embryo development and larval survival. Developing embryos usually rely on intracapsular food sources provided by the mother,...

The relationship between meroplankton distribution and spatio-temporal variability of coastal mesoscale hydrological structure was investigated in the northern Bay of Biscay, North-East Atlantic. For the three coastal polychaetes studied, i.e. Pectinaria koreni, Owenia fusiformis and Sabellaria alveolata, the highest larval abundances were sampled...

In many marine benthic invertebrates, the larval stage is the main vector of dispersal. Selective metamorphosis of larvae into an appropriate habitat is then essential to the survival of the benthic adult, with profound implications for population dynamics. Within this context, the identification of causal external factors triggering larval metamor...

Human-mediated transport and aquaculture have promoted the establishment of non-indigenous species in many estuaries around the world over the last century. This phenomenon has been demonstrated as a major cause of biodiversity alterations, which has prompted scientists to provide explanations for the success or failure of biological invasions. Cre...

In diverse invertebrate species characterized by a biphasic life cycle, metamorphosis represents a fundamental biological transition which determines the fate of benthic population dynamics through settlement and recruitment. Within this context, nitric oxide (NO) is thought to act as an endogenous inhibitor of metamorphosis. While attention has be...

Marine invertebrate larvae represent a transitory, but nonetheless important component of planktonic communities. Assessing their contribution to plankton diversity has been hindered by numerous methodological difficulties, notably at the identification step. For many sessile invertebrates, planktonic larvae also play a crucial role, as they are th...

The gregarious polychaete Sabellaria alveolata is an important foundation species whose reef structures add topographic complexity and high levels of biodiversity in sandflats. In the Bay of Mont-Saint-Michel, France, S. alveolata reefs are considered the largest reef formations in Europe and are increasingly endangered by anthropogenic pressure. I...

Accurate and efficient identification to the species level of early larval stages has long been a problematic step in the study of marine invertebrates, due to the extremely small size of the larvae and their lack of diagnostic morphological characters. It is nonetheless, a prerequisite for any ecological study. As a consequence, a number of molecu...

δ13C and δ15N measurements are still poorly conducted in benthic invertebrate larvae. To assess the δ13C and δ15N changes occurring after a dietary shift, experiments were conducted on veliger larvae of Crepidula fornicata fed with two cultured microalgae (Isochrysis galbana and Pavlova lutheri) of known isotopic composition, 13C-enriched and 15N-d...

Viral gametocytic hypertrophy was reported for the first time in 2001 in Pacific oyster Crassostrea gigas in France. Since this date, the number of reported cases and the distribution area have increased every year; however, the cases are not associated with macroscopic signs or increased mortality rates. Both male and female gametes were hypertrop...

Steinhausia mytilovum is a globally distributed microsporidian parasite which infects the oocytes of the blue mussels Mytilus edulis and M. galloprovincialis. Despite the intensive monitoring effort made on mussel populations, the parasite has not previously been reported in France. We report herein on the occurrence of S. mytilovum in Mytilus sp....

We report the occurrence of the microsporidian parasite Steinhausia sp. in the oocytes of the common cockle Cerastoderma edule in a natural population in France, where high mortalities occurred. Steinhausia sp. appeared primarily as sporocysts containing many small spores, and putative earlier developmental stages were also observed. Both its preva...

Near the Azores Triple Junction as the Azores Plateau is approached, the ridge axis becomes shallower; its depth decreases from ca. 2400 m in the Rainbow vent field (36°13′N) to ca. 850 m in the Menez Gwen vent field (37°35′N). In this area, extensive mussel beds of the mytilid Bathymodiolus azoricus dominate the hydrothermal vent fauna, along with...

Until 1985, seven vent fields were described from the Mid-Atlantic Ridge (MAR). An eighth field, Mount Saldanha (36° N), discovered in 1998, showed unusual geological and biological settings. Vent sites on the MAR exhibit varied environmental conditions, resulting from depth variation of the axis and associated physical parameters, and different so...

This paper describes the first successful attempt to trap and identify the larvae of a deep-sea vent organism using a combination of sediment traps and molecular analysis. During the European Union-funded MARVEL cruise in August and September 1997, sediment traps containing a high-salt DNA preservative were deployed around active black smoker chimn...

To provide information about the export and the distribution of hydrothermal material to the deep ocean, two sediment traps with current-meters were moored on the Lucky Strike segment of the Azores Triple Junction (Mid-Atlantic Ridge). The results of a 25-day experiment with a single trap deployed 1.5 m from a chimney (2 m above the bottom) are use...

The polychaete family Polynoidae (scale-worms) is well-represented at deep sea hydrothermal vents. Most species are free-living in a wide range of habitats: from high-temperature hydrothermal `chimney' walls to diffuse venting areas. Conversely, species of the genus Branchipolynoe live inside the mantle cavity of vent and seep mytilids. Specimens,...

Histological sections of the gonad of Bathymodiolusazoricus from the Lucky Strike and Menez Gwen hydrothermal vent fields (Mid-Atlantic Ridge) demonstrated a spawning event in this species in May 1994, synchronous between the two vent fields located 60 km apart, and a sexual pause in gametogenesis. As reported for other vent mytilid species, B.azor...

Bathymodiolus azoricus n. sp. is described from the Lucky Strike (31°17′N) and the Menez Gwen (37°50′N) hydrothermal fields on the Azores Triple Junction, Mid-Atlantic Ridge, and another species, Bathymodiolus sp. aff. B. puteoserpentis from Logatchev (14°45′N) hydrothermal field is treated but not named. Both species are compared with B. puteoserp...

Population structure and recruitment pattern of undescribed mytilid bivalves that dominate the animal communities associated with vents of the Lucky Strike and Menez Gwen hydrothermal vent fields (37 degrees 17' N and 37 degrees 50' N on the Mid-Atlantic Ridge) were studied from size-frequency analyses. Intra-site comparisons reveal that length-fre...

The Menez Gwen fauna which is thriving within the vent field is mostly composed of patchy mussel beds (Bathymodiolus sp., also occurring at Lucky Strike), some little swarms of Bresiliid shrimps [Mirocaris fortunata and Chorocaris chacei (Williams and Rona, 1986)] and a few Bythograeid crabs (Segonzacia mesatlantica). The commensal worm Branchipoly...

A significant number of marine invertebrate species inhabiting the deep-sea hydrothermal vent environment produce planktonic larvae with varying life-spans in the water column. An obvious benefit derived from long-term dispersal abilities is that species may colonize new areas over a wide geographical range, and therefore maintain gene flow between...

Biological communities associated with hydrothermal activity reflect the peculiarities of the sea water composition around the vents. They are functionally dependent on the association between the macro-organisms, their symbiotic chemoautotrophic bacteria, the reduced chemicals present in the fluid (sulphide, methane...) and the oxygen of sea water...

Newly discovered hydrothermal vent communities at Lucky Strike on the Mid-Atlantic Ridge (37°18′N, 32°16′W) are comprised of an invertebrate fauna sufficiently different from known vent faunas of TAG and Snake Pit to consider Lucky Strike part of a new biogeographic province. The dominant component of the fauna is a new species of mussel, and the m...