Temporal fluctuations in zooplankton size, abundance, and taxonomic composition since 1995 in the North Western Mediterranean Sea

Abstract

In the Gulf of Lions, small pelagic fish have shown reduced body size and body condition after 2007 that would result from changes in zooplankton community. We therefore examined zooplankton density, body size, and taxonomic composition at the closest long-term monitoring station (1995–2019): the coastal Point-B. To cover a broader spectrum of zooplankton community, samples obtained from two nets, the WP2 (200 µm mesh size) and the Regent (690 µm), were analysed with the imaging Zooscan method. One important result was the high stability through time of the zooplankton community. No long-term monotonous trends in density, size, and taxonomic composition were detected. Interannual variations in zooplankton size and density were not significantly correlated to any environmental variable, suggesting the possible importance of biotic interactions. Still, an increase in temperature was followed by a sharp decrease of zooplankton density in 2015, after which only gelatinous groups recovered. No change in the zooplankton community was detected around 2007 to support bottom-up control on small pelagic fish. Whether this derives from different local processes between the Gulf of Lions and the Ligurian Sea cannot be excluded, highlighting the need for simultaneous monitoring of different ecosystem compartments to fully understand the impact of climate change.

The role of oceanographic conditions and colony size in shaping the spatial structure ofPyrosoma atlanticumin the NW Mediterranean Sea

“…Although our results show a strong difference in the abundance of P. atlanticum in the two years studied, longer time series would be necessary to confirm the high interannual variability that has been described for gelatinous zooplankton in the Mediterranean ( García-Comas et al ., 2011 ; Fullgrabe et al ., 2020 ; Feuilloley et al ., 2021 ). This high variability has been related to the winter environmental conditions, which cause mixing of the water column and the input of nutrients to the surface waters, ultimately modulating the phytoplankton bloom ( García-Comas et al ., 2011 ; Fullgrabe et al ., 2020 ).…”

“…Previous studies carried out on gelatinous zooplankton in the NW Mediterranean have shown high spatial variability closely linked to oceanographic dynamics and water mass structure ( Guerrero et al ., 2016 ; Sabatés et al ., 2018 ). At a temporal scale, high interannual variability has been reported in abundance and species composition ( Licandro and Ibanez, 2000 ; Guerrero et al ., 2018b ; Feuilloley et al ., 2021 ), but there is no clear consensus on long-term trends ( Molinero et al ., 2005 ; García-Comas et al ., 2011 ; Licandro et al ., 2012 ; Guerrero et al ., 2018a ). Studies on P. atlanticum in the Mediterranean are scarce.…”

Applications of Machine Learning in Chemical and Biological Oceanography

“…The model also improved the accuracy of detecting rare taxa by an average of 4.02% and has the potential to be included in autonomous underwater vehicles for real-time identification and plankton ecosystem observation . The model proposed by Gorsky et al ZooScan with ZooProcess was successfully implemented in the identification and estimation of ZP abundance in the bay of Villefranche-sur-Mer, France . This shows that ML algorithms are a potential tool not only for the identification of ZP but also used to solving ecological problems.…”

“… 119 The model proposed by Gorsky et al 104 ZooScan with ZooProcess was successfully implemented in the identification and estimation of ZP abundance in the bay of Villefranche-sur-Mer, France. 120 This shows that ML algorithms are a potential tool not only for the identification of ZP but also used to solving ecological problems. Still, few improvements are required in this field to achieve full automation to detect rare taxa and morphologically similar species.…”

Mistaking plastic for zooplankton: Risk assessment of plastic ingestion in the Mediterranean sea

“…Zooplankton communities and their quality as food supply for predators were not assessed. Feuilloley et al (2022), using a long time series of zooplankton observations in the northwestern Mediterranean, showed that changes in zooplankton composition, size, and density may impact higher trophic levels, such as the fitness of small pelagic fish. Results should be considered cautiously as both plastic and zooplankton were averaged over 6 months in the same year (June-November 2014).…”