Natural or anthropogenic variability? A long-term pattern of the zooplankton communities in an ever-changing transitional ecosystem

Abstract

The Venice Lagoon is an important site belonging to the Italian Long-Term Ecological Research Network (LTER). Alongside with the increasing trend of water temperature and the relevant morphological changes, in recent years, the resident zooplankton populations have also continued to cope with the colonization by alien species, particularly the strong competitor Mnemiopsis leidyi. In this work, we compared the dynamics of the lagoon zooplankton over a period of 20 years. The physical and biological signals are analyzed and compared to evaluate the hypothesis that a slow shift in the environmental balance of the site, such as temperature increase, sea level rise (hereafter called “marinization”), and competition between species, is contributing to trigger a drift in the internal equilibrium of the resident core zooplankton. Though the copepod community does not seem to have changed its state, some important modifications of structure and assembly mechanisms have already been observed. The extension of the marine influence within the lagoon has compressed the spatial gradients of the habitat and created a greater segregation of the niches available to some typically estuarine taxa and broadened and strengthened the interactions between marine species.

Sea level and temperature extremes in a regulated Lagoon of Venice

“…On the contrary, the sea surface salinities recorded by satellite manifested an increasing trend of 0.08 pss from 2010 to 2020, highlighting the Northern Adriatic Sea salinification in the last decade (Sammartino et al, 2022). Camatti et al (2023) detected an increasing trend in salinity in the inner part of the Venice Lagoon and not near the inlet. This is explained by the fact that the relative sea level rise (RSLR) produces an increase in the lagoon volume that, even considering no significant reduction in the freshwater runoff, induces the long-term salinization of the lagoon.…”

“…The first, in addition to determining an increase in flood frequency, induces the long-term salinization of the lagoon. Indeed, Camatti et al (2023) detected a significant increase of salinity in the 25-year in the inner part of the lagoons, while no clear drift is observed near the inlets. Ferrarin et al (2013) also underlined that the sea level rise increases both the salinity and the renewal time in the lagoon.…”

Planktonic Copepoda along the Confinement Gradient of the Taranto Sea System (Southern Italy) after Lockdown of Human Activities Due to the COVID-19 Pandemic

“…The increasing instability in annual environmental conditions from the Gulf to Mar Piccolo II inlet, however, was a constant feature of the growing confinement verifiable from Gulf to Mar Piccolo in the Taranto sea system. The biotic fraction considered was formed by the planktonic Copepoda, which are the main zooplankton components in this system [1], similar to many other coastal marine areas of the Mediterranean sea [21][22][23][24][25][26]. Zooplankton in confined areas are generally different from those in the open sea due to a simplification in the community composition, and a reduction in the body sizes of adults [2] of select species highly tolerant and/or able to rest in unfavorable conditions without abandoning the site [27].…”

“…In the Mar Piccolo I inlet, we detected an unusual richness in species in the samples collected in the Summer of 2020, a situation typical of less confined sites, and which was not registered in corresponding seasons in T1 and T2, 15 and 30 years before. Recently, a study [26] established an increase in temperature and marinization in the lagoon of Venice, which seems to have driven the new organization in the lagoon zooplankton, including the arrival of new species. The ongoing climate change appears, in that study, to parallel the human disturbance/pressure in the final results (smaller species and lower species richness).…”