Experimental Assessment of Vulnerability to Warming in Tropical Shallow-Water Marine Organisms

Abstract

Tropical shallow-water habitats represent the marine environments with the greatest biodiversity; however, these habitats are the most vulnerable to climate warming. Corals, seagrasses, and macroalgae play a crucial role in the structure, functions, and processes of the coastal ecosystems. Understanding their growth and physiological responses to elevated temperature and interspecific sensitivity is a necessary step to predict the fate of future coastal community. Six species representatives, including Pocillopora acuta, Porites lutea, Halophila ovalis, Thalassia hemprichii, Padina boryana, and Ulva intestinalis, collected from Phuket, Thailand, were subjected to stress manipulation for 5 days. Corals were tested at 27, 29.5, 32, and 34.5°C, while seagrasses and macroalgae were tested at 27, 32, 37, and 42°C. After the stress period, the species were allowed to recover for 5 days at 27°C for corals and 32°C for seagrasses and macroalgae. Non-destructive evaluation of photosynthetic parameters (Fv/Fm, Fv/F0, ϕPSII and rapid light curves) was carried out on days 0, 3, 5, 6, 8, and 10. Chlorophyll contents and growth rates were quantified at the end of stress, and recovery periods. An integrated biomarker response (IBR) approach was adopted to integrate the candidate responses (Fv/Fm, chlorophyll content, and growth rate) and quantify the overall temperature effects. Elevated temperatures were found to affect photosynthesis, chlorophyll content, and growth rates of all species. Lethal effects were detected at 34.5°C in corals, whereas adverse but recoverable effects were detected at 32°C. Seagrasses and macroalgae displayed a rapid decline in photosynthesis and lethal effects at 42°C. In some species, sublethal stress manifested as slower growth and lower chlorophyll content at 37°C, while photosynthesis remained unaffected. Among all, T. hemprichii displayed the highest thermotolerance. IBR provided evidence that elevated temperature affected the overall performance of all tested species, depending on temperature level. Our findings show a sensitivity that differs among important groups of tropical marine organisms inhabiting the same shallow-water environments and highlights the importance of integrating biomarkers across biological levels to assess their vulnerability to climate warming.

Comparative study on anatomical traits and gas exchange responses due to belowground hypoxic stress and thermal stress in three tropical seagrasses

“…Inhibition of photosynthesis by warming was also detected in C. rotundata measured as lower ETR and T. hemprichii measured as lower ETR, oxygen release and DIC uptake. These results agree with previous reports in C. rotundata , T. hemprichii and other tropical seagrasses ( Collier & Waycott, 2014 ; Pedersen et al, 2016 ; George et al, 2020 ; Rasmusson et al, 2020 ; Rasmusson et al, 2021 ; Yucharoen et al, 2021 ). Nevertheless, in the present study, such photoinhibition did not affect gas exchange in the BG tissues of C. rotundata and T. hemprichii , pointing to the significance of efficient regulation of internal oxygen levels in these two seagrasses.…”

“…Halophila are colonizing species, characterized by relatively high growth and turnover rates ( Kilminster et al, 2015 ; O’Brien et al, 2018 ; Lamit & Tanaka, 2021 ), while Cymodocea and Thalassia are considered opportunistic and persistent seagrasses, respectively ( Kilminster et al, 2015 ; O’Brien et al, 2018 ). Previous observations reported similar aboveground productivity between C. rotundata and T. hemprichii ( Cebrián et al, 1998 ; Yamamuro & Chirapart, 2005 ; Collier & Waycott, 2014 ) and higher aboveground productivity in H. ovalis ( Yamamuro & Chirapart, 2005 ; Yucharoen et al, 2021 ). In the present study, H. ovalis also displayed unique responses among the three tested species seen as significant modulation of gas exchange under changing conditions.…”

Calcification in Three Common Calcified Algae from Phuket, Thailand: Potential Relevance on Seawater Carbonate Chemistry and Link to Photosynthetic Process

“…Since the mid-18th century, atmospheric CO 2 has risen from 280 to 400 ppm, and is predicted to increase to 730-1200 ppm by 2100 as a result of human activities, such as the burning of fossil fuel, deforestation, agriculture and industrialization [1,2]. This has led to an increase in sea-surface temperature (ocean warming) and a decrease in ocean pH (ocean acidification), which have affected a range of marine floras and faunas [3][4][5]. Macroalgae play important roles as primary producers in the marine food chain and serve as habitat for various animals, which directly contribute to the livelihood and food security of the coastal community [6,7].…”