Gabriel Grimsditch

The Effects of Habitat on Coral Bleaching Responses in Kenya

This study examines the bleaching responses of scleractinian corals at four sites in Kenya (Kanamai, Vipingo, Mombasa and Nyali) representing two distinct lagoon habitats (relatively shallow and relatively deep). Bleaching incidence was monitored for the whole coral community, while zooxanthellae densities and chlorophyll levels were monitored for target species (Pocillopora damicornis, Porites lutea, and Porites cylindrica) during a non-bleaching year (2006) and a year of mild-bleaching (2007). Differences in bleaching responses between habitats were observed, with shallower sites Kanamai and Vipingo exhibiting lower bleaching incidence than deeper sites Nyali and Mombasa. These shallower lagoons display more fluctuating thermal and light environments than the deeper sites, suggesting that corals in the shallower lagoons have acclimatized and/or adapted to the fluctuating environmental conditions they endure on a daily basis and have become more resistant to bleaching stress. In deeper sites that did exhibit higher bleaching (Mombasa and Nyali), it was found that coral recovery occurred more quickly in the protected area than in the non-protected area.

Extreme white colouration of frogfish Antennarius maculatus due to coral bleaching event

An individual of thewarty frogfish speciesAntennariusmaculatus was observed camouflaging itself against fully bleached corals at 10 m depth at the Velidhoo Island resort reef (4 11¢41.35†N, 72 49¢20.55†E) in North Ari Atoll, Maldives, on 19 May 2016. The frogfish was approximately 20 cm long, and being completely white, matching the bleached coral background, it displayed several camouflage flaps and appendages on its body that resembled the turf algae growing on dead parts of a Goniastrea coral skeleton. The individual was first spotted resting at the bottom of the reef slope, amongst Didemnum molle sea squirts, bleached corymboseAcropora and bleachedGoniastrea colonies (Fig. 1a). Within a 5-min period, the individual had moved to the other side of the coral blockwhere it was surrounded entirely by a bleached and dead skeleton of a Goniastrea colony, as well as patches of turf algae (Fig. 1a, b). BecauseAntennariusmaculatus is a sedentary species that rarelymoves location, it is probable that this individual changed its colouration to match the bleached coral. Coral bleachingmostly likely occurred in lateApril or early May 2016 given that the sea surface temperature anomalies were above the 31 C coral bleaching threshold in the Maldives at that time (NOAA Coral Reef Watch 2016). Individuals from the Antennarius genus have been known to change colour in both experimental aquaria and in field observations (Pietsch 1984). However, it would be interesting to observe whether the frogfish would change colour tomatch the coral as the coral either regained its pigmentation after bleaching or died and was covered in turf algae or other benthic organisms. This sighting is an interesting example of the extreme changes in colouration that frogfish are capable of, and of how frogfishmay react to increasingly frequent coral bleaching events around the world.

Mapping Factors That Contribute to Coral Reef Resilience Using In situ and Satellite Data in East Africa

Understanding factors that promote coral reef resilience to climatic and anthropogenic stressors is required in order to develop methods and decision support systems to establish resilient Marine Protected Areas (MPAs) and other marine managed areas. This study presents an analysis of coral reef resilience factors obtained from a rapid assessment of coral reefs in 5 locations along the East African coast. The sites span more than 600Km along the coastline of Kenya and Tanzania and are subjected to varying environmental conditions. The study also attempts to present an approach to mapping reef resilience factors and their integration into planning or decision support tools that inform management actions. The analysis revealed that coral reef resilience is highly influenced by biological and anthropogenic factors. Highly resilient reefs were found in areas with high scores for biological factors and low anthropogenic activities. It also revealed that areas with higher cumulative thermal stress and lower levels of pollution from terrestrial sources had higher overall resilience; whilst terrestrial pollution was a major limiting factor on coral reef resilience in the region. Interestingly, the results reveal that reefs with higher resilience are also found in more populated areas compared to reefs in marginal areas that were found to have relatively lower resilience scores. Although this correlation is the weakest compared to other correlations, it could imply that coral reefs found in these highly populated areas are at risk of degradation in the future. However, it is noteworthy that these reefs were those that are within already established MPAs. In order to anticipate and plan for future likelihood of degradation of these reefs, results from this study are proposed to assist in identifying and prioritizing alternative reefs for conservation and management away from such high population density areas. We conclude that incorporating coral reef resilience factors into decision support tools such as GIS can inform management actions aimed at conserving reef ecosystems.

Coral Recruitment and Coral Reef Resilience on Pemba Island, Tanzania

This study explores the patterns of coral recruitment, survivorship and resilience on the coral reefs of the west coast of Pemba Island, Tanzania. The results show that recovery from the 1998 mass coral bleaching event has been patchy, with great variation in coral cover among sites, and a generally high macroalgal cover. Sites with low coral recovery were found to exhibit higher numbers of coral recruits but lower survivorship, implying that larval supply is not impeding recovery but rather that local stressors are reducing coral reef resilience. The main stressors observed were predation by Acanthaster plancii, overfishing and use of destructive fishing methods (including dynamite fishing). A. plancii predation was shown to negatively correlate with coral recruit survivorship, implying that it is a potential cause of failure of corals to reach adult sizes. Fish surveys showed that Pemba is being overfished, with the vast majority of fish observed less than 10 cm in length, and only 4 individuals larger than 40 cm recorded throughout the whole survey. It is recommended that the two major, and potentially synergistic, stressors of A. plancii predation and overfishing/destructive fishing are addressed in order to avoid loss of Pemba’s coral reefs. Land-ocean connections are also explored in this context.