For the countries bordering the tropical Western Indian Ocean (TWIO), living marine resources are vital for food security. However, this region has largely escaped the attention of studies investigating potential impacts of future climate change on the marine environment. Understanding how marine ecosystems in coastal East Africa may respond to various climatic stressors is vital for the development of conservation and other ocean management policies that can help to adapt to climate change impacts on natural and associated human systems. Here, we use a high-resolution (1/4 degrees) ocean model, run under a high emission scenario (RCP 8.5) until the end of the 21st century, to identify key regionally important climate change stressors over the East African Coastal Current (EACC) that flows along the coasts of Kenya and Tanzania. We also discuss these stressors in the context of projections from lower resolution CMIP5 models. Our results indicate that the main drivers of dynamics and the associated ecosystem response in the TWIO are different between the two monsoon seasons. Our high resolution model projects weakening of the Northeast monsoon (December-February) winds and slight strengthening of the Southeast monsoon (May-September) winds throughout the course of the 21st century, consistent with CMIP5 models. The projected shallower mixed layers and weaker upwelling during the Northeast Monsoon considerably reduce the availability of surface nutrients and primary production. Meanwhile, primary production during the Southeast monsoon is projected to be relatively stable until the end of the century. In parallel, a widespread warming of up to 5 degrees C is projected year-round with extreme events such as marine heatwaves becoming more intense and prolonged, with the first year-long event projected to occur as early as the 2030s. This extreme warming will have significant consequences for both marine ecosystems and the coastal populations dependent on these marine resources. These region-specific stressors highlight the importance of dynamic ocean features such as the upwelling systems associated with key ocean currents. This indicates the need to develop and implement a regional system that monitors the anomalous behaviour of such regionally important features. Additionally, this study draws attention to the importance of investment in decadal prediction methods, including high resolution modelling, that can provide information at time and space scales that are more directly relevant to regional management and policy making.

Although it is well established that microalgae take up metals and other contaminants from water and it has been suggested that algae may play a significant role in mobilizing sediment bound contaminants, there has been little research on the uptake of sediment-associated contaminants by microalgae. This may be important for microphytobenthos, which is closely associated with sediments. We report on laboratory experiments investigating the uptake of cadmium (Cd) from sediment and water by Cylindrotheca closterium over 96 h. The role of microalgae in the partitioning of Cd between sediment and water was also investigated. While concentrations do not typically represent those in the natural environment, we showed C. closterium takes up Cd from sediment, and concentration in microalgae is affected by sediment organic matter content. Cylindrotheca closterium influenced Cd movement between sediment and water: transfer from water to sediment was slowed, while transfer from sediment to overlying water (all treatments) and interstitial water (unprocessed sediment treatments) was increased. This is the first article to describe Cd uptake by diatoms from intertidal sediment in relation to sediment properties and mobilization of Cd from sediment in the presence of diatoms. Microalgae may serve as a pathway for sediment-associated metals to enter into aquatic food webs, and their presence appears to increase metal concentrations in water potentially making any mobilized metals available for uptake by other species. Given this and their importance as the basis of the food chain, there may be implications for environmental and human health and potential impacts for the biological stability of the sediment.