Peringia ulvae

Abstract: Maritime transport, in particular of ballast water, is considered to be one of the most important pathways of marine biological invasions worldwide. Here we provide the first molecular evidence of potential survival of the European mudsnail, Peringia ulvae, in ballast water on cross-latitudinal voyages. Ballast water from the RV Polarstern was sampled at its departure from the North Sea and again in tropical latitudes; DNA was extracted and amplicon-sequenced employing high-throughput sequencing methodology. Mollusc species were detected by cytochrome oxidase subunit I DNA barcode sequences. The increasing proportion of operational taxonomic units that were identified as P. ulvae after 2 weeks of navigation suggests that this species withstands the harsh conditions in the ballast tank. As such, P. ulvae has the potential to reach very distant, new marine areas where it eventually might establish itself as a nonindigenous species. We also discuss the potential of environmental DNA analysis for en-route biodiversity screening and species-specific risk assessments, as well as some current limitations of the approach.

Abstract: Microphytobenthos (MPB) from intertidal mudflats are key primary producers at the land-ocean interface. MPB can be more productive than phytoplankton and sustain both benthic and pelagic higher trophic levels. The objective of this study is to assess the contribution of light, mud temperature, and gastropod Peringia ulvae grazing pressure in shaping the seasonal MPB dynamics on the Brouage mudflat (NW France). We use a physical-biological coupled model applied to the sediment first centimeter for the year 2008. The simulated data compare to observations including time-coincident remotely sensed and in situ data. The model suggests a MPB annual cycle characterised by a main spring bloom, a biomass depression in summer, and a moderate fall bloom. In early spring, high simulated photosynthetic rates due to mud surface temperature (MST) values close to the MPB temperature optimum for photosynthesis and to increasing solar irradiance trigger the onset of the MPB spring bloom. Simulated peaks of high P. ulvae grazing (11 days during which ingestion rates exceed primary production rate) mostly contribute to the decline of the MPB bloom along with the temperature limitation for MPB growth. In late spring-summer, the MPB biomass depression is due to the combined effect of thermo-inhibition and a moderate but sustained grazing pressure. The model ability to infer on biotic and abiotic mechanisms driving the seasonal MPB dynamics could open the door to a new assessment of the export flux of biogenic matter from the coast to the open ocean and, more generally, of the contribution of productive intertidal biofilms to the coastal carbon cycle.