Assessing the buffering effect of algae Gongolaria barbata against anthropogenic pressures in associated invertebrates.

Marine ecosystems face increasing pressure from global and local anthropogenic stressors. Marine heatwaves (MHW) have grown in frequency and intensity, impacting flora and fauna in the Venice Lagoon. Habitat-forming macroalgae may buffer warming stress by producing additional oxygen during the day, though this has only been observed with single-species studies. This thesis aims to evaluate whether local macroalgae Gongolaria barbata provides a buffer effect at the community-level with associated invertebrates under MHW conditions and exposure to local contaminants, glyphosate and mercury. Mesocosms with only algae, only fauna, and both were exposed to control (~16℃) and an artificial MHW (16-24℃) conditions for nine days. Oxygen saturation was monitored during day and night to estimate algal photosynthesis and organism respiration. Photosynthetic efficiency and pigment content were also measured. Associated invertebrates Ophiothrix fragilis and Carcinus aestuarii were acclimatized for a week with and without G. barbata, after which they were exposed to 0.5 mg/L of glyphosate or mercuric chloride for 24 hours. In O. fragilis respiration was measured while in C. aestuarii hemocyte parameters were measured. Results showed a limited buffer effect during MHWs, but nighttime respiration rates were similar across treatments with both algae and fauna. This suggests that G. barbata may reduce metabolic stress in invertebrates under stress at night when oxygen is low. Contaminants experiment yielded mixed results. Glyphosate and mercury did not significantly affect O. fragilis respiration rates. In C. aestuarii, mercury exposure increased hemocyte cell counts regardless of prior algal acclimation. These findings suggest a limited but potentially supportive role of G. barbata, and warrants further experimentation at varying conditions.