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Seagrasses response to climate change
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Context: Increasing sea surface temperatures endangers coastal and marine communities around the globe. One of the communities expected to be greatly influenced by rising sea water surface temperature is seagrasses community. Seagrasses are marine macrophytes inhabiting’s subtidal and intertidal coastlines in temperate to tropical bioregions around the world. Seagrasses are angiosperms (flowering plants) consisting of approximately fifty species belonging to ten genera. There are several threats to seagrasses populations and ecosystems worldwide today such as pathogens and parasites, climate change and rise in sea water temperatures. As sea surface temperatures are expected to increase and the tendency of heat waves expected to become more frequent with greater magnitude, seagrasses populations and particularly edge populations are predicted to be negatively influenced. In addition seagrasses population’s ability to resist pathogens and parasites might be reduced due to the negative effects of heat waves, effecting their survival.
Objective: The study aims to evaluate ability of seagrasses to endure future heat waves reflected as increase in sea water temperature, and examine the effects of such sudden temperature increase on growth, quantum yield and survivability of seagrass species Cymodocea nodosa from: Mauritania and southern coast of Portugal, which represents the Atlantic southern and northern distribution edges respectively. It is expected that Mauritania population will be better adapted to higher constant temperature than Ria Formosa population due to their natural environment (Mediterranean vs temperate). In addition, to examine the diversity of oomycete infections, their proliferation and effects on the seagrass populations being subjected to heat wave in terms of percentage of infection and the variety of infections with the expectation that as the temperatures increase the resistance to pathogens will decrease in both populations.
Materials and Methods: In each experiment 45 specimens were divided randomly and equally into 3 treatment groups in three independent tanks: control, 28°C, 31°C. 28°C and 31°C groups were experiencing a gradual ascent in temperatures from 17°C to 28°C and 31°C respectively followed by a gradual decrease in temperature to 17°C. Each heatwave treatment consisted of five independent experimental units containing three shoots each. One shoot was sampled from each treatment at three different periods: Acclimation (T6), End of heatwave (T14) and Recovery (T25) when each number represents days from the beginning of the experiments. PAM (pulse-amplitude modulated) fluorometry method was used to calculate photosynthetic quantum yield. The leaf puncturing technique was used to estimate leaf growth and software Image J was used to evaluate percentage of infection and growth from photographs. Isolation techniques were used to estimate the oomycete diversity of both seagrass populations.
Results: Our study results suggest that Mauritania population has a higher thermal tolerance than Ria Formosa population based on the results in Fig.2 at day 26 in recovery period. In addition results regarding quantum yield suggest that at day 6 in acclimation phase Mauritania population had a higher quantum yield values compared with Ria Formosa population in all treatment groups. In terms of diversity of infections the results imply that Mauritania population has a greater variety of infections compared with Ria Formosa population based on control and 28°C groups at the end of heatwave phase (T14) in Fig.6.
Conclusion: Our study results suggest that as anticipated Mauritania population may have a better response to future heatwaves than Ria Formosa population in terms of survivability and quantum yield. In addition the results imply that Mauritania population have greater variety of infections compared with Ria Formosa population and that Mauritania pathogens may have a better thermal tolerance compared with Ria Formosa pathogens. However no significant difference were observed regarding growth, percentage of infection and weight.
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Keywords
Seagrasses Cymodocea nodosa Temperature Pathogen Heatwave Eco physiology