Climate Change and its Impact on Occurrence of Sargassum Natans and Sargassum Fluitans on Coastline of Lagos and its Environ

Abstract

Climate change is an important emerging threat to every kind of life on earth, especially in the areas where populations are economically poor. West Africa is part of them and vulnerable to the effects of climate change. Among those effects are the shifts of algae species from their native place to new areas more suitable. As a result of warming oceans, aquatic species shifted their distribution. This is the case for two algae species identified as Sargassum natans and Sargassum fluitans which shifted from the Brazilian coast to West African coast. The occurrence of these algae along the Nigerian coast was the subject of this study. The species affect mostly food security and coastal population economy. The aim of this study is to examine the impacts of climate change on spatial distribution of Sargassum natans and Sargassum fluitans along the coast of Nigeria through the analysing of the relationship between climate change variables and their spatial distribution; analysing remote sensing images to map Sargassum distribution from 2011-2016; evaluation of the perception of coastal residents on the presence of Sargassum on the banks and their notion of climate change; and evaluation of the past trend of the major variables that drive Sargassum phenomena along the Nigerian shores. To achieve these objectives, a combined quantitative and qualitative approach was performed to study coastal communities perceptions among household heads in Lagos State where a total of 206 household heads were interviewed. The outputs were analysed using R software. The monthly images from Modis Aqua GIOVANNI on normalized Fluorescence Line Height (nFLH) between 2011 to 2016 were displayed in Seadas software to highlight spatial algae blooms along the Nigerian coast. Through a Principal Component Analysis (PCA) method performed in R software on six (6) oceanic parameters listed as sea surface salinity, precipitation, sea surface temperature, wind and ocean current component from 2011 to 2016. The relationship between these parameters and Sargassum species distribution were analysed also, the trends of these oceanic parameters were analysed. The results show that the knowledge about climate change and the reason of the occurrence of Sargassum is limited (69.9%) due to low level of education and limitation of information access. Also, the climate change and the presence of Sargassum species have several consequences on the respondents’ livelihood and activities (77.7%). Moreover, the analysis of Modis Aqua image reveals the past spatio-temporal patterns of Sargassum species along the Nigerian coast. The species fluorescence does not fit with the monthly range trends reported by previous studies. Indeed, that would correspond to an undetected Sargassum species patterns or another algae specie with almost the same fluorescence characteristics. Furthermore, The principal variables involved in their motions are the wind patterns associated with the horizontal current velocity. The parameters such as v-velocity, salinity, precipitation, sea surface temperature, play important but indirect roles in the shift and the distribution of Sargassum species. Finally, there is temporal trend in the oceanic parameters which evolve together and lead to Sargassum species new distribution. Sargassum events in Nigerian coast could be mostly explained by and how long the oceanic parameters have reacted to the climatic changes which affect the species. As recommendations, coastal population must be educated about climate change, winds and currents motions must be monitored to predict Sargassum events, fishermen must be assisted in their activities.