Mesoscale variations in the assemblage structure and trophodynamics of mesozooplankton communities of the Adriatic basin (Mediterranean Sea)

Abstract

Abstract. Zooplankton are critical to the functioning of ocean food webs because of their utter abundance and vital ecosystem roles. Zooplankton communities are highly diverse and thus perform a variety of ecosystem functions, thus changes in their community or food web structure may provide evidence of ecosystem alteration. Assemblage structure and trophodynamics of mesozooplantkon communities were examined across the Adriatic basin, the northernmost and most productive basin of the Mediterranean Sea. Samples were collected in June–July 2019 along coast-offshore transects covering the whole western Adriatic side, consistently environmental variables were also recorded. Results showed a clear separation between samples from the northern-central Adriatic and the southern ones, with a further segregation, although less clear, of inshore vs. off-shore stations, the latter mostly dominated in the central and southern stations by gelatinous plankton. Such patterns were mainly driven by chlorophyll-a concentration (as a proxy of primary production) for northern-central stations, i.e. closer to the Po river input, and by temperature and salinity, for southern ones, with the DistLM model explaining 46 % of total variance. The analysis of stable isotopes of nitrogen and carbon allowed to identify a complex food web characterized by 3 trophic levels from herbivores to carnivores, passing through the mixed feeding behavior of omnivores, shifting from phytoplankton/detritus ingestion to microzooplankton. Trophic structure also spatially varied according to sub-area, with the northern-central sub-areas differing from each other and from the southern stations. Our results highlighted the importance of environmental variables as drivers of zooplanktonic communities and the complex structure of their food webs. Disentangling and considering such complexity is crucial to generate realistic predictions on the functioning of aquatic ecosystems, especially in high productive and, at the same time, overexploited area such as the Adriatic Sea.

The pelagic food web of the Western Adriatic Sea: a focus on the role of small pelagics

“…All data were then standardized to the ltered volume of water recorded for each haul. More abundant/representative groups, as resulted after sorting and identifying each sample, were analyzed for stable isotopes 24 .…”

“…After the survey was completed, a set of shing hauls was selected to be used for this study. The whole Western Adriatic (GSA 17 and GSA 18) has been divided into three different sub-areas 24 , mainly based on oceanographic characteristics: 1. the Northern Adriatic (NA) encompassing the northern part of the GSA 17 characterized by shallow waters, including the Po river mouth, up to the Conero Promontory (hauls 8-24 in Figure 7); 2. the Central Adriatic (CA) encompassing the lower part of the GSA 17 up to the Gargano Promontory (hauls 27-39) and 3. the Southern Adriatic (SA) including the whole GSA 18, characterized by the presence of the South Adriatic Pit and the Otranto Channel (hauls 40-46).…”

“…To identify the biological (i.e., resource availability) and environmental drivers of the trophic ecology, as by SIA, of the small pelagics in the Adriatic basin, stable isotope data of the three species separately were correlated to zooplankton abundance (i.e., number of taxa recorded at each haul, as detailed in section 2.2) by trophic group, as by 24 , and to environmental variables, as described below. Environmental data, obtained by CTD casts carried out close to the sampling hauls 24 , were pressure (dbar, decibar), temperature (°C), uorescence (µg/l), turbidity (NTU), dissolved oxygen (expressed as ml/l and saturation percentage), salinity and density (kg/m 3 ). Biological and environmental data were rst tested for collinearity among variables by using a Draftsman plot, with uorescence, Dissolved O 2 concentration (DO, ml/l), % of O 2 saturation and turbidity data being Log (x+1)-transformed to t a linear distribution in the Draftsman plot.…”

“…Furthermore, the use of POM_NA is justi able because cascading phenomena of dense shelf waters from the Northern Adriatic occur periodically in the area and are found to affect zooplanktonic communities in the Southern basin 56 . The SI signatures of zooplanktonic species were taken from the dataset of 24 . Macroaggregates are the SI signatures of macroaggregates from the Northern Adriatic 73 , POM_NA is the SI of POM (Particulate Organic Matter) from the Northern Adriatic 74 , Phyto1 and Phyto2 are the SI values of phytoplankton from the Northern Adriatic 73 , Consistently with the best mixing polygons determined for the three species of shes collected in the different sub-areas (Figure S4), we used the selected sources to run SIMMR models, speci cally, for each of the three sub-areas.…”

Seasonal Trophic Ecology and Diet Shift in the Common Sole Solea solea in the Central Adriatic Sea

“…The main food items identified with SCA were considered as potential food sources. We used the mean isotopic contents of pelagic fishes ( Sardina pilchardus and Engraulis encrausicolus from Fanelli et al, 2022 [ 64 ]) and ichthyoplankton (hereafter, “Fish larvae”) taken from [ 65 ].…”