| Summary: | open Anthropic effects of industrialization and greenhouse gas emissions affect ocean ecosystems by gradually decreasing seawater pH in a phenomenon called Ocean Acidification (OA). This effect has a negative impact on most marine animals, especially calcifying organisms. Sea urchins can provide valuable insights on the impact of OA on an ecosystemic level, due to their importance as benthic grazers and the lack of many predatory species. Most of the experiments on AO have been conducted on indoor aquaria, but natural volcanic oases can simulate near-future acidified conditions. In this experiment, behavioural and physiological responses of the sea urchin Arbacia lixula were examined alongside natural volcanic vents in Ischia, Italy. Adult sea urchins were collected from three sites, two of which were located in Castello Aragonese (S1, ~pH 8.1 and S2, ~pH 7.7) and the third one (SP, ~pH 8.1) was alongside San Pietro bay. Experimental design consists in exposing to two to different pH conditions (pH 8.1, pH 7.7) the individual collected from each site. Experiments were replicated at 5 selected times (October 2023, January, April, June and August 2024) over the course of two years (October 2022, August 2024). Two physiological (Excretion rate, Respiration rate) and two behavioural (Righting time, Sheltering time) response variables were selected; furthermore, supplementary data of benthic cover was provided to possibly link any variations to the surrounding environment or vice-versa. Hypothesis consists in different responses of urchins collected from experimental sites, possibly demonstrating physiological or behavioural adaptations to chronic exposure to reduced pH. Our results provide significant effects of pH, sites and/or their interaction for at least some of the selected times across all the response variables. These results indicate that effects of pH inevitably have effect on adults of Arbacia lixula, but also that environmental complexity and the interactions with other factors could mitigate, enhance ...
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