Inorganic nutrient input effects and severity of disturbance in zooplankton community structure

Abstract

Abstract Mediterranean coastal lagoons are increasingly affected by nutrient enrichment from both natural and anthropogenic sources. While most studies focus on total nutrient loads, little is known about how the mode of nutrient delivery, pulsed or continuous, affects plankton community dynamics. This study aimed to experimentally test how different nutrient input regimes influence zooplankton community structure and plankton biomass under microcosm conditions using natural lagoon water. Three nutrient regimes were applied: Pulse (P), Continuous (C), and Pulse–Continuous (PC), along with a Control (no addition), with total nutrient concentrations standardized across regimes. Biomass of bacterioplankton, phytoplankton, and zooplankton, as well as hydrochemical variables and species composition, were monitored over 28 days. P regimes led to reduced zooplankton biomass and impaired reproduction, while C and PC regimes maintained higher productivity and favored shifts in rotifer and copepod composition. To evaluate community response, we used the Z 2 index, a disturbance metric developed for Mediterranean lagoons that quantifies the severity of environmental disturbance based on zooplankton assemblages. Z 2 scores revealed a gradient aligned with nutrient delivery mode, with small but consistent increases in C and PC regimes. These findings highlight the potential long-term impacts of continuous low-level nutrient inputs in restructuring aquatic communities.