Mesozooplankton variability in the Bay of Marseille (NW Mediterranean): towards understanding the trophic context of small pelagics - Archive ouverte HAL Access content directly
Conference Papers Year : 2022

Mesozooplankton variability in the Bay of Marseille (NW Mediterranean): towards understanding the trophic context of small pelagics

Abstract

In the Gulf of Lion, biomass, size and body condition of some small pelagic fish diminished since 2007. Bottom-up control by a modification of mesozooplankton is the main hypothesis which could explain such observation (Saraux et al. 2019, Chen et al. 2019, 2021). Since 2004, mesozooplankton has been monitored bimensually at the SOLEMIO station of RNO SOMLIT program, east of the Gulf of Lion. This work aimed at highlighting mode of changes in the environment which could explain variations in the zooplankton community in the Bay of Marseille on the 2005-2021 period. Time series of climatic indexes, meteorological data, physico-chemical data, microphytoplankton data, pico-nanoplankton and zooplankton data has been compiled. Dynamic Factor Analysis (DFA) allowed to describe 2 interannual trends in the biotic and abiotic environment of zooplankton. Those trends highlighted: a fast diminution (2005-2009) in nutrients concentrations, suspended particulate matters, carbon and nitrogen organic particulate, an offshore signal between 2005- 2008, and an increase since 2011 of abundance and a diminution of size indexes of most of planktonic groups. Mesozooplankton has been characterized by three trends. The first, highlighted the diminution of biomass of all size class. The second linked biomass variations of the bigger size class (1000 - 2000 μm) with modifications of size structure and diversity community structure. The second environmental trend explained variations of biomass diminution by size class (200-300 and 500-200 μm) after 2011. Seasonal patterns of the mesozooplankton groups have been described and are typical of coastal sites in the NW-Mediterranean Sea, with a spring peak production for biomass, calanoids and oithonoids and a summer peak for chaetognaths, crustaceans, cnidarians, salp and pteropods. The diversity community shift in 2011, seemed to have affected the seasonal pattern of some mesozooplankton variable. Lower peak values were observable in the second half of the series for size-class biomasses, calanoids and oithonoids abundances, while stronger signal was detected for summer peak-like groups. To discuss on the implication of those change for the higher trophic level, the date from which cumulative annually production (biomasses and abundances) overpassed the 0.3-percentile cumulative production of the series (DCAP) were derived for mesozooplankton groups. The year-to-year variations showed a delay of DCAP for size class biomass and for total zooplankton, calanoids and oithonoids abundances after 2011. Finally, the relation between winter environmental context and zooplankton DCAP has been investigated. We highlighted that winter temperature and winter abundance of nano-eukaryotes were among the variable the most correlated with zooplankton DCAP. The results described a shift, 2011, in the pelagic ecosystem of the Bay of Marseille and allow to discuss on the bottom- up control of plankton on small pelagic fish.
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Dates and versions

hal-04276431 , version 1 (09-11-2023)

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  • HAL Id : hal-04276431 , version 1

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Théo Garcia, Daniela Bănaru, Loïc Guilloux, Véronique Cornet, Gérald Gregori, et al.. Mesozooplankton variability in the Bay of Marseille (NW Mediterranean): towards understanding the trophic context of small pelagics. SIBECOL-AIL Meeting 2ndMeeting of the Iberian Ecological Society (SIBECOL) XXI conference of the Iberian Association of Limnology (AIL) 21stNational Congress of the Portuguese Ecological Society (SPECO), Center for Environmental and Marine stusies at University of Aveiro, Portugal., Jul 2022, Aveiro, Portugal. ⟨hal-04276431⟩
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