The coral reef ecosystem is a natural habitat for many marine organisms that has high economic and tourist significance. Nonetheless, this ecosystem has very low tolerance to the effects of changes brought about by increasing sea surface temperatures and ocean acidification. This study sought to investigate the combined effect of rising sea surface temperatures and ocean acidification on the Kenyan coral reef ecosystem. This was achieved by determining the spatial-temporal variability of ocean acidification over the Kenyan coastline; and simulating the combined effect of sea surface temperature increases and ocean acidification on the coral reef ecosystem.
Historical (2000-2021) data on sea surface temperature (SSTs) was obtained from the National Oceanic and Atmospheric Administration (NOAA) and data on dissolved total carbon dioxide (TCO2) and pH from Global Ocean Data Analysis Project (GLODAP). Future (2022-2081) sea surface temperature and dissolved carbon dioxide data was downloaded from Coupled Model Intercomparison Project (CMIP6) experiment for two Shared Socioeconomic Pathways (SSPs) namely SSP2-4.5 and SSP5-8.5. Statistical, graphical and model simulations analyses were applied in the study to investigate the combined effect of increasing SST and ocean acidification on coral reef ecosystem over the Kenyan coastline.
Results indicate that mean sea surface temperature and dissolved carbon dioxide along the Kenyan coastline varied with seasons and had increased between the years 2000-2021. Trend tests of SSTs and TCO2 revealed a significant upward trend at 5% level of significance. Rising SSTs led to bleaching in coral reefs along this coastline whereas TCO2 led to reduced amount of carbonate ion concentration and reduced pH in the sea surface waters which affected the rates of calcification and survival of the coral reefs. The results of the Combined Mortality and Bleaching Output model simulation revealed that bleaching and ocean acidification had negatively affected the coral reef cover resulting in a decline of more than 30% of cover between 2000 and 2021. The results of the simulation also projected that the coral reef cover will continue to decline in the long-term by 52% under SSP2-4.5 and 63% under SSP5-8.5 if the trends in SSTs and TCO2 are maintained.
This study recommends collaborative implementation of climate change policies and practices by national and regional governments, communities and policy makers; enhanced efforts by coastal county governments in Kenya and research organisations to expound on scientific knowledge base while simultaneously implementing sustainable targeted solutions to ensure that the socio-economic benefits of the coral reef ecosystem are sustained.
Ogali S. C., 2022. Effects of climate change on the Kenyan coral reef eco-system. MSc thesis, University of Nairobi, 64 p. Thesis.
