Experimental evidence of the synergistic effects of warming and invasive algae on a temperate reef-builder coral

Abstract

In the current global climate change scenario, stressors overlap in space and time, and knowledge on the effects of their interaction is highly needed to understand and predict the response and resilience of organisms. Corals, among many other benthic organisms, are affected by an increasing number of global change-related stressors including warming and invasive species. In this study, the cumulative effects between warming and invasive algae were experimentally assessed on the temperate reef-builder coral Cladocora caespitosa. We first investigated the potential local adaptation to thermal stress in two distant populations subjected to contrasting thermal and necrosis histories. No significant differences were found between populations. Colonies from both populations suffered no necrosis after long-term exposure to temperatures up to 29 °C. Second, we tested the effects of the interaction of both warming and the presence of invasive algae. The combined exposure triggered critical synergistic effects on photosynthetic efficiency and tissue necrosis. At the end of the experiment, over 90% of the colonies subjected to warming and invasive algae showed signs of necrosis. The results are of particular concern when considering the predicted increase of extreme climatic events and the spread of invasive species in the Mediterranean and other seas in the future.

Response diversity in Mediterranean coralligenous assemblages facing climate change: Insights from a multispecific thermotolerance experiment

“…Exploring species-specific thermal sensitivities among different components of benthic communities is, therefore, a key step toward forecasting the future composition and functionality of these communities in the face of climate change. However, while important efforts in this direction have been taken in shallow tropical reefs, thermotolerance analyses in temperate benthic communities largely lag behind (Kersting et al, 2015;Linares, Cebrian, Kipson, & Garrabou, 2013;Savva, Bennett, Roca, Jordà, & Marbà, 2018;Torrents, Tambuté, Caminiti, & Garrabou, 2008).…”

Heterotrophy mitigates the response of the temperate coral Oculina arbuscula to temperature stress

“…Recently, these results were contrasted by a study which demonstrated that long‐term exposure of C. caespitosa to thermal stress (29°C) resulted in no impact on tissue necrosis or photosynthetic efficiency (Kersting et al. ). However, exposure to temperature stress in addition to the presence of invasive algae negatively impacted photosynthetic efficiency and caused tissue necrosis in the coral (Kersting et al.…”

“…However, exposure to temperature stress in addition to the presence of invasive algae negatively impacted photosynthetic efficiency and caused tissue necrosis in the coral (Kersting et al. ). Another study found that for two temperate coral species ( C. caespitosa and Oculina patagonica ), short‐term thermal stress up to 5°C above the mean summer temperature resulted in no change in symbiont density (Rodolfo‐Metalpa et al.…”

Correlation between pollution and decline of Scleractinian Cladocora caespitosa (Linnaeus, 1758) in the Gulf of Gabes

“…Since 1999, this coral was exposed to several mass mortalities due to the warming events (Garrabou et al, 2009; Jiménez et al, 2014; Kersting et al, 2013a; Kružić et al, 2013; Perez et al, 2000; Rodolfo-Metalpa et al, 2005) and declined to 55% in some parts of the Mediterranean Sea (Casado-Amezúa et al, 2015). In addition to warming events, competition with invasive algae likely contributed to the mortality of this coral species (Kersting et al, 2015). Invasive algae were observed in different regions of Mediterranean Sea where living C. caespitosa are present (Kersting et al, 2014a; Kružić et al, 2012).…”

“…2) (Casado-Amezúa et al, 2011; Casado-Amezúa et al, 2014; Kersting, 2013; Kersting et al, 2013a; Kersting et al, 2013b; Kersting et al, 2014a; Kersting et al, 2014b; Kersting et al, 2015; Kersting et al, 2016; Kružić and Benkovic, 2008; Kružić and Požar-Domac, 2003; Kružić and Požar-Domac, 2007; Kružić et al, 2012; Kružić et al, 2013). Some colonies in the Eastern part of the Adriatic Sea are particularly threatened by anthropogenic activities such as e.g., tuna farming (Kružić and Požar-Domac, 2007).…”