The Impact of Human Activities on Epibenthic Bivalve Communities

Abstract

A total of 17 bivalve species belonging to 13 families were collected and identified in Malindi and Mombasa Marine National Parks; and Kanamai from Oct.'97 to Mar.'98. Bivalve fauna showed low densities (2/m2), and low diversity. Modiolus auriculatus and Pinna muricata were the most represented. There was a significant difference in species diversity between Malindi and Mombasa reef flats at p>0.10. Shallow lagoons had very low-density and diversity as compared to sea grass and reef flat zones. This was attributed to the high deposits of shell, coral, and sand. Swimming, gogeling/scuba diving, walking/trampling and turning of rocks were identified as the main forms of human activities causing disturbance to the bivalves. Frequencies of occurrence of these activities varied in the three areas with Kanamai exhibiting the highest. Trampling had the most notable im- pact and was used to show the impact of human activities on the most vulnerable species. Results show that the distribution of bivalve fauna in the protected and unprotected areas is density independent and is not only influenced by human activities and management strategy but rather by other biological and environmental factors such as substrate type, tide range and wave activity. Human activities however affect those bivalves with fragile shells such as Pinna muri- cata, through trampling resulting in injury and/or death. Presence of man affects the routine activ- ities of the others such as Tellina flavum, Anadara antiquata, Tridacna squamosa and Codakia punctata. Therefore spreading out of human activities within the marine parks is rec- ommended to reduce their impacts. These activities should be spread out into the reserves and unprotected areas.