Zooplankton community response to the winter 2013 deep convection process in the NWMediterranean Sea

Abstract

The Gulf of Lion is an important area of deep convection, where intense winter vertical mixing brings nutrients up from deeper layers, promoting the largest bloom in the Mediterranean at the end of winter/early spring. The DEWEX program conducted cruises in February and April 2013 to investigate the ecosystem level impacts of deep water convection. Zooplankton data were collected through net sampling and imaging with an Underwater Vision Profiler. In winter, low zooplankton abundance and biomass were observed in the Deep Convection Zone (DCZ) and higher values on its periphery. In spring, this pattern reversed with high biomass in the DCZ and lower values on the periphery. On average for the whole area, the potential grazing impact was estimated to increase by one order of magnitude from winter to spring. In April, all areas except the DCZ incurred top‐down control by zooplankton on the phytoplankton stock. In the DCZ, the chlorophyll‐a values remained high despite the high zooplankton biomass and carbon demand, indicating a sustained bottom‐up control. The zooplankton community composition was comparable for both periods, typified by high copepod dominance, but with some differences between the DCZ and peripheral regions. In spring the DCZ was characterized by a strong increase in herbivorous species such as Centropages typicus and Calanus helgolandicus, and an increase in the number of large zooplankton individuals. Our study indicates that the DCZ is likely an area of both enhanced energy transfer to higher trophic levels and organic matter export in the North Western Mediterranean Sea.

Trophic pathways of phytoplankton size classes through the zooplankton food web over the spring transition period in the north‐west Mediterranean Sea

“…The zooplankton community taxonomic composition is discussed in detail in Donoso et al [2017]. That study found that copepods contributed 95% to total zooplankton abundance.…”

Combining laser diffraction, flow cytometry and optical microscopy to characterize a nanophytoplankton bloom in the Northwestern Mediterranean

“…For cytometry, the effective upper size limit is smaller than the theoretical one given. Method horizontal distribution of these three profile types, it is useful to consider the preceding winter period when deep convection was occurring over a large region centered on station 99 (See Donoso et al, 2017;Mayot et al, 2017 andSeverin et al, 2017). This intense process created two well defined zones: the Deep Convection Zone (DCZ) with homogeneous vertical profiles, low phytoplankton and high nutrient concentrations, and the peripheral zone with various degrees of stratification and phytoplankton abundance.…”

Challenges for Sustained Observing and Forecasting Systems in the Mediterranean Sea

“…Regular and long-term monitoring in the MOOSE network has provided significant results that can be used to interpret the temporal variability of nutrients and the zooplankton community, which are sensitive to deep vertical mixing events (Donoso et al, 2017). Coastal observations showed that the long-term evolution of nutrient inputs here is driven by Rhône River water discharges, which respond differently depending on whether a climatic or an anthropogenic forcing occurs (Cozzi et al, 2018).…”