Marine debris has become a global problem affecting coral health around the globe. However, the photophysiological responses of corals to marine debris stress remain unclear. Therefore, this study firstly investigated transparent and opaque plastic bag shading and fishing nets directly contacting the coral. Photosynthetic performance, pigment content, symbiont density, and calcification rate of a branching coral Pocillopora acuta and a massive coral Porites lutea were investigated after 4 weeks of exposure to marine debris. The results show that the maximum quantum yield of PSII significantly decreased in P. lutea with all treatments, while P. acuta showed no effect on the maximum quantum yield of PSII from any treatments. Transparent plastic bag shading does not affect P. acuta, but significantly affected the maximum photochemical efficiency of P. lutea. Photoacclimation of cellular pigment content was also observed under opaque plastic bag shading for both species at week 2. Fishing nets had the strongest effect and resulted in P. acuta bleaching and P. lutea partial mortality as well as a decline in zooxanthellae density. Calcification rate of P. acuta significantly decreased with treatments using opaque plastic bag and fishing net, but for P. lutea only the treatment with fishing net gave any observable effects. This study suggests that the sensitivities of corals to marine debris differ strongly by species and morphology of the coral.

No abstract

No abstract

Increasing levels of greenhouse gases lead to ocean warming, which affects a range of marine organisms. Corals live in a narrow temperature range and become stressed when the temperatures change. Bleaching occurs when the temperature exceeds the coral’s threshold, and can be severe when this is combined with other stressors such as light. In order to understand how temperature and light affect corals in their physiological responses and photosynthetic performance, Pocillopora acuta from Maiton Island (MT) and Panwa Cape (PW), representing different environments, were investigated. The results show that light and temperature had by regime different effects on Symbiodiniaceae photosynthesis and the coral growth rate. There was a synergistic effect of elevated temperature and light on photosynthesis, as observed in the photochemical efficiency and pigment contents, suggesting photo-damage. A higher growth rate in Panwa corals was observed in control, and while elevated temperature reduced coral growth. Elevated temperature affected the Panwa coral less, suggesting that corals from this regime might be able to recover when the temperature returns to normal. This information is important for predicting the coral responses to elevated temperature especially in the summer, as regards the possibility of coral bleaching.

Macrophytes play an important role in the freshwater ecosystem. However, human activities and climate change are currently affecting aquatic lakes and species in various ways. The heterogeneity of macrophyte ecophysiology might lead to different responses to changing environments. To understand the photosynthetic responses of freshwater macrophytes to changes in light, six freshwater macrophyte species from Songkhla Lagoon were investigated. The results showed that there was a diurnal response of photosynthetic activities in all species. The Fv/Fm and ∆F/Fm′ of all species decreased at midday (9 a.m.–3 p.m.) then recovered at 6 p.m. close to the 6 a.m. level. As well as alpha, the positive relation between alpha and light showed the adaptation of plants. The saturating irradiance (Ik) revealed that plants from different light regimes showed different responses to light and temperature changes. To maintain a positive carbon balance and cope with light and temperature conditions, macrophytes had strategies such as modifying light harvesting capacity and light use. This study provides a better understanding of the vulnerability of each species to environmental changes and photosynthetic responses that enable species from different light regime to adapt to changing light environments.