Abstract
Climate change threatens the structure and function of marine ecosystems, highlighting the importance of understanding the response of species to changing environmental conditions. However, thermal tolerance determining the vulnerability to warming of many abundant marine species is still poorly understood. In this study, we quantified in the field the effects of a temperature anomaly recorded in the Mediterranean Sea during the summer of 2015 on populations of two common sympatric bryozoans, Myriapora truncata and Pentapora fascialis. Then, we experimentally assessed their thermal tolerances in aquaria as well as different sublethal responses to warming. Differences between species were found in survival patterns in natural populations, P. fascialis showing significantly lower survival rates than M. truncata. The thermotolerance experiments supported field observations: P. fascialis started to show signs of necrosis when the temperature was raised to 25–26 °C and completely died between 28–29 °C, coinciding with the temperature when we observed first signs of necrosis in M. truncata. The results from this study reflect different responses to warming between these two co-occurring species, highlighting the importance of combining multiple approaches to assess the vulnerability of benthic species in a changing climate world.
Highlights
Marine ecosystems are highly affected by climate change, with impacts predicted to increase in the coming years[1,2,3]
Our results revealed a thermal anomaly in Medes islands during the summer of 2015 when the sea water temperature was higher than the average of the previous years (2005–2014) (19.32 ± 0.22 °C versus 18.99 ± 0.24 °C)
This result agrees with data from previous mass mortality events in the Mediterranean, which revealed P. fascialis to be among the affected species together with gorgonians, corals or sponges[5,6,32]
Summary
Marine ecosystems are highly affected by climate change, with impacts predicted to increase in the coming years[1,2,3]. To understand the response of Mediterranean marine species to global warming, several studies have performed thermotolerance experiments in multiple co-occurring Mediterranean benthic species, such as anthozoans, revealing highly divergent levels of sensitivity[20,21,22] In some cases, these divergences occur at population level, as in shallow populations of the red coral Corallium rubrum (Linnaeus, 1758), where some populations can be more tolerant to an increase www.nature.com/scientificreports/. We selected two model co-occurring species of common and abundant Mediterranean bryozoans, Myriapora truncata (Pallas, 1766) and Pentapora fascialis (Pallas, 1766), with different distribution patterns at local and regional scales Despite these two erect calcified species inhabiting similar hard rocky habitats across the Mediterranean, M. truncata populations are found from 1 m depth in marine caves to 60 m in coralligenous bottoms, reaching 130 m in Tunisian area. We combined field data of two erect heavily calcified species during a temperature anomaly in the Mediterranean in the summer of 2015, and the experimental study of the lethal and sublethal effects of thermal stress on both species in aquaria under controlled conditions
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