Assessing the Threat of Coral Decline on Fish Diversity in Response to Temperature

Misali, a PECCA-protected island off the east coast of Pemba, Tanzania, is considered to be a marine biodiversity hotspot with a protected Non-Extractive Zone (NEZ) and remaining Extractive Zone (EZ). Upon protection, the island’s fringe reefs faced severe coral bleaching during the 1998 bleaching event, estimated to kill up to 70% of corals. Since the event, several others have occurred in addition to restructuring the management plan in 2006 to expand the region to 1000km. While the damage from the most recent coral bleaching event in 2020 has yet to be surveyed, this study investigates the current reef health in reflection of temperature differences caused by the western NEZ zone’s proximity to the cold upwelling of the Pemba Channel. In doing so, reef health was defined as high levels of rugosity, low levels of bleaching, and high levels of fish diversity and abundance. These variables were examined independently and concurrently to understand their interdependency and relationships. Once established, reef health was further analyzed in two different temperature zones to understand how reef health in a higher temperature range in the EZ would differ from the reef health in the colder temperature range in the NEZ. Over a 22-day period, 2,799 fish from 24 different families were surveyed along 30 transects split evenly between the NEZ and EZ. For each transect, environmental data were collected, reef rugosity and coral bleaching percent cover estimated, and fish counted according to the pre-established family guide. Statistical significance was found between temperature measurements in the NEZ and EZ, effectively confirming the hypothesis that reefs in the NEZ would inhabit cooler temperatures. Additionally, several families exhibited statistical significance between the two zones, with more inhabiting NEZ reefs. While coral bleaching percent cover was found to have no significant difference between the two zones, the trends expressed graphically identify a relationship between rugosity, bleaching, and fish abundance. The results not only supported the assertion that the three variables shared a correlation with one another but further indicated that reef health as identified above, was stronger in the NEZ cooler waters than in the EZ warmer waters. Thus, this study identifies anthropogenic threats to coral reef ecosystem resiliency on Misali Island in hopes of informing future conservation efforts of Zanzibar’s reefs and beyond