Eric Lecuyer

Environmental Control on Fish and Macrocrustacean Spring Community-Structure, on an Intertidal Sandy Beach

The inter-annual variability of the fish and macrocrustacean spring community on an intertidal sandy beach near the Canche estuary (North of France) was studied from 2000 to 2013 based on weekly spring sampling over an 11-year period. Twenty-eight species representing 21 families were collected during the course of the study. The community was dominated by a few abundant species accounting for > 99% of the total species densities. Most individuals caught were young-of-the-year indicating the importance of this ecosystem for juvenile fishes and macrocrustaceans. Although standard qualitative community ecology metrics (species composition, richness, diversity, evenness and similarity) indicated notable stability over the study period, community structure showed a clear change since 2009. Densities of P. platessa, P. microps and A. tobianus decreased significantly since 2009, whereas over the period 2010-2013, the contribution of S. sprattus to total species density increased 4-fold. Co-inertia and generalised linear model analyses identified winter NAO index, water temperature, salinity and suspended particular matter as the major environmental factors explaining these changes. Although the recurrent and dense spring blooms of the Prymnesiophyte Phaeocystis globosa is one of the main potential threats in shallow waters of the eastern English Channel, no negative impact of its temporal change was detected on the fish and macrocrustacean spring community structure.

Bio-optics and primary production model in case-2 waters: example of the eastern English Channel

Remote sensing represent a powerful tool to estimate chla concentrations and to predict primary production in coastal waters. However, in order to use this tool efficiently in such variable ecosystems we need to increase our knowledge concerning bio-optical properties, phytoplankton community and photosynthetic parameters variability in order to develop adapted regional algorithms. Spatial and temporal variations of these key parameters were investigated during spring 2000 in the English Channel across five mesoscale cruises (BIOPTEL) realised between February and October 2000. From this in situ data set (phytoplankton pigments obtained by HPLC, nutrients concentration, phytoplankton productivity estimated by variable fluorescence technique (Phyto-Pam), yellow substance absorption, particulate matter absorption), we assessed the scales of variation of primary production model inputs in the several identified biological provinces and throughout spring. These in situ observations were used to proceed to sensitivity analyses of a local primary production model. Further, from this local modelisation we discussed on (i) the biases induced by the using of existing algorithms developed to obtain primary production directly from satellite data in such ecosystems and (ii) of the improvements which should be done concerning such general models.

Mesoscale and seasonal bio-optical properties variability in coastal waters using the example of the eastern English Channel during Spring, 2000

Remote sensed chlorophyll α (chlα) maps are useful to proceed to phytoplankton dynamics study and primary production modelization in coastal waters. However, chlα remote sensing depend on the bio-optical characteristics of waters masses which are site-specific and highly variable according to space and time in coastal waters. In order to study the seasonal variability of phytoplankton and bio-optic parameters as well as the factors controlling their spatio-temporal distributions, five mesoscale cruises (BIOPTEL) were carried out in the eastern English Channel during the spring 2000 (between February and October). Phytoplankton absorption spectrum showed a high variability according to space and time due to the algal community composition and the physiological state. Considering these scales of variation, a local model was defined. The variability of the two other components of marine absorption: yellow substances and non algal particles are also presented and related to exogenous parameters such as river flow, temperature and hydrodynamism. Furthermore, in order to appreciate how important are the local IOPs (Inherent Optical Properties) variability on AOPs (Apparent Optical Properties) restitution a sensitivity analysis was realized. In the frame of biomass estimation, marine reflectance were simulated considering the local absorption coefficients rather than the standard ones.