Spatial changes in community composition and food web structure of mesozooplankton across 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 the community or food web structure may provide evidence of ecosystem alteration. Assemblage structure and trophodynamics of mesozooplankton communities were examined across the Adriatic basin, the northernmost and most productive basin of the Mediterranean Sea. Samples were collected in June–July 2019 within the framework of the MEDIAS (MEDiterranean International Acoustic Survey) project, along coastal–offshore transects and from the surface to ca. 200 m depth, 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. offshore stations, the latter being mostly dominated in the central and southern stations by gelatinous plankton. Such patterns were mainly driven, based on the outputs of the distance-based linear model, by fluorescence (as a proxy for primary production) for northern-central stations, i.e. closer to the Po River input, and by dissolved oxygen, together explaining 44 % of the total variance. Overall, at the basin level, the analysis of stable isotopes of nitrogen and carbon allowed for identifying a complex food web characterized by three trophic levels from filter feeders–herbivores to carnivores, passing through a general pattern of omnivory with varying preference towards herbivory or carnivory. Stable isotope signatures spatially varied between inshore vs. offshore communities and across sub-areas, with the northern Adriatic exhibiting greater δ15N and more variable δ13C than the other two sub-areas, likely attributable to the occurrence in the area of organic matter of both terrestrial and marine origin. Our results contribute to the knowledge of mesozooplankton community and trophic structure, at the basin scale across a coastal–offshore gradient, also providing a baseline for the future assessment of pelagic food webs within the European Council (EC) Marine Strategy Framework Directive.

Coastal Eukaryotic Plankton Diversity of the Southern Adriatic as Revealed by Metabarcoding

“…Seasonspecific genera were mostly recorded in lower read abundances. Pontella and Copilia were also recorded only sporadically and in lower abundances in previous Southern Adriatic zooplankton studies based on morphological identification [28,29]. Most of the copepod genera recorded by metabarcoding are known as common species of the Adriatic, living mainly in coastal and surface waters (Paracalanus, Clausocalanus, Calanus, Calocalanus, Acartia, Centropages, Oithona and Euterpina), but some were characterised as very rare copepods for the Adriatic (Pachos, Neocalanus) in previous studies [25][26][27].…”

“…Diversity 2024, 16,293 13 of 20 on morphological identification [28,29]. Most of the copepod genera recorded by metabarcoding are known as common species of the Adriatic, living mainly in coastal and surface waters (Paracalanus, Clausocalanus, Calanus, Calocalanus, Acartia, Centropages, Oithona and Euterpina), but some were characterised as very rare copepods for the Adriatic (Pachos, Neocalanus) in previous studies [25][26][27].…”

“…For the Southern Adriatic, previous plankton research in this area also included mainly zooplankton and phytoplankton studies on certain representative groups. Zooplankton studies focused on copepods [25][26][27][28][29], tintinnids [30][31][32] and gelatinous invertebrates [33][34][35][36][37], while phytoplankton studies mainly characterised diatoms [38][39][40]. Moreover, the studies were predominantly based on traditional methods of taxa identification.…”

Interannual Variation in the Zooplankton Community of the North Adriatic Sea under Short-Term Climatic Anomalies

“…Copepods faced a general increase in abundance in 2022, particularly in some herbivorous or mixtivorous species, like Centropages ponticus, Calanus helgolandicus, and Clauso-Paracalanidae [35,75,76]. The enhanced abundance of these primary consumers, despite the concurrent decrease in phytoplankton biomass, might be related to the decrease in competing herbivorous blooming species, i.e., Noctiluca in the northern sub-area and doliolids in the southern sub-area, which are known for easily monopolizing access to trophic resources [61,77].…”