Assessing the influence of sea surface temperature on productivity: implications for aquatic food systems and fisheries management

Our study explored the influence of temperature on chlorophyll – a proxy for productivity in Kenya’s marine waters. The climate system, particularly the interaction between the atmosphere and the Indian Ocean, influences physical processes along the Kenyan coast that impact the aquatic food systems. Recent global warming and climate variability have significantly impacted marine food web. However, limited observational campaigns and research pose challenges for climate change studies in the region.

To address these gaps, in-situ temperature data, satellite-based sea surface temperature (SST) observations, and Glory model data were analyzed. Sub-surface processes on Kenya’s shelf were characterized using in-situ measurements and model-based data. The mixed layer depth (MLD) was found to differ between the Northeast Monsoon (NEM) and Southeast Monsoon (SEM): 28.0 m and 60.7 m (in-situ) and 20.1 m and 44.1 m (model-based), respectively. Mixed layer temperatures were 27.5°C during NEM and 26.2°C during SEM. Chlorophyll-a (Chl-a) and SST distributions were analyzed and their respective trends assessed using the Theil-Sen estimator and Mann-Kendall Trend Test, revealing significant warming in the North Kenya Banks (NKB) with trends of +0.3721 over 2002–2022. Seasonal trends during NEM and SEM were +0.3865 and +0.3668, respectively. A negative correlation between SST and Chl-a was found across all regions. Findings indicated a ~1.1°C temperature difference between the NEM and SEM seasons, with warmer waters in the south. Ocean currents and sporadic upwelling events were observed to considerably influence SST distribution; low SSTs enhanced chlorophyll concentration implying elevated productivity. The study highlighted a significant warming trend, particularly in southern waters, and decreasing Chl-a concentrations, especially in the north. This research enhances understanding of temperature and ecological dynamics in Kenyan waters, informs sustainable blue economy practices, and supports identification of potential fishing zones for coastal fishers and investment areas for blue foods.