Heterogeneous distribution in sediments and dispersal in waters of Alexandrium minutum in a semi-enclosed coastal ecosystem

Abstract

Within the framework of research aimed at using genetic methods to evaluate harmful species distribution and their impact on coastal ecosystems, a portion of the ITS1rDNA of Alexandrium minutum was amplified by real-time PCR from DNA extracts of superficial (1-3cm) sediments of 30 subtidal and intertidal stations of the Bay of Brest (Brittany, France), during the winters of 2013 and 2015. Cell germinations and rDNA amplifications of A. minutum were obtained for sediments of all sampled stations, demonstrating that the whole bay is currently contaminated by this toxic species. Coherent estimations of ITS1rDNA copy numbers were obtained for the two sampling cruises, supporting the hypothesis of regular accumulation of A. minutum resting stages in the south-eastern, more confined embayments of the study area, where fine-muddy sediments are also more abundant. Higher ITS1rDNA copy numbers were detected in sediments of areas where blooms have been seasonally detected since 2012. This result suggests that specific genetic material estimations in superficial sediments of the bay may be a proxy of the cyst banks of A. minutum. The simulation of particle trajectory analyses by a Lagrangian physical model showed that blooms occurring in the south-eastern part of the bay are disconnected from those of the north-eastern zone. The heterogeneous distribution of A. minutum inferred from both water and sediment suggests the existence of potential barriers for the dispersal of this species in the Bay of Brest and encourages finer analyses at the population level for this species within semi-enclosed coastal ecosystems.

Human-induced river runoff overlapping natural climate variability over the last 150 years: Palynological evidence (Bay of Brest, NW France)

“…where the maximum occurrences of toxic algal blooms are observed today within the Bay of Brest (Klouch et al, 2016a), also corresponds to the site where maximal percentages of agriculture-type pollen markers are observed in Bay of Brest modern sediments (Lambert et al, 2017), confirming the link between increased runoff on agricultural soils and the disturbance of the phytoplankton community. This may be related to the small size of the watershed and the isolation of the Daoulas estuary from main tidal currents.…”

“…In this study, a core from the outlet of the Daoulas Estuary in the Bay of Brest has provided a very high-resolution palynological record from 1870 AD to present. The Daoulas Bay records today the most intense toxic bloom of dinoflagellates Alexandrium minutum within the Bay of Brest (Klouch et al 2016a). Furthermore, the palaeobiodiversity of dinoflagellate communities has been recently reported on the same sampled Daoulas core with molecular data (Klouch et al, 2016b), suggesting a great increase in bloom frequency of this toxic species A. minutum over the past decades.…”

Influence of environmental and anthropogenic factors on the composition, concentration and spatial distribution of microplastics: A case study of the Bay of Brest (Brittany, France)

“…The MARS 3D model of the Bay of Brest (limits: 48.20°N -48.44°N and 4.09°W -4.72°W) has a horizontal resolution of 50 m, with 20 sigma layers for vertical coordinates (equidistant layers throughout the domain that change with sea surface elevation). The model has already been validated on temperature and salinity datasets (Petton S. et al, unpublished) and previously used for trajectories of toxic algal cells released from estuarine zones (Klouch et al, 2016 mesh of the whole hydrodynamic model inside the bay, which led to a total of 1,437,500 passive particles for each run. Coastline behaviour was set as beaching, as the MARS 3D model is implemented with a wetting-drying numerical method in intertidal areas.…”

“…Indeed, it would be of great interest to further refine details on outputs and sources. Klouch et al (2016) studied the trajectories of Alexandrium minutum cells in the surface water of the Bay of Brest, considering only the mouth of the main rivers where the blooms of A. minutum occur. Considering estuaries as starting points for A. minutum cell release, the retention of the particles appeared higher, from 56 to 81%, compared to our study.…”

Fossil maerl beds as coastal indicators of late Holocene palaeo-environmental evolution in the Bay of Brest (Western France)

“…Most of the sedimentation takes place in the inner zone of estuaries because tidal energy is stronger than river flow (Dyer, 1997;Moskalski et al, 2018). Klouch et al (2016a) demonstrated that the south-east of the bay is disconnected from the Elorn estuary, which is the area exporting the highest proportion of particles outside the BB.…”