Page 67

Factors that affect coral reef resilience The average values for the Reef Health Index (RHI) and Simplified Reef Health Index (SRHI) were fairly similar between sites, ranging from a low of 2 (poor) to a high of 3.25 (fair). Individual parameters that make up these measures showed more variation. The Coral Index (cover, recruitment and disease prevalence) ranged from 1.33 at PB-14 to 3.33 at PB-03, 11, 16, while the Reef Biota Index ranged from a low of 1.75 at PB-02 to a high of 3.75 at PB-18. The overall Health Index ranged from 2 (PB-17, 19) to 3 (PB-03, 15, 18). The Simplified Reef Health Index, which relies on fewer measures, results in somewhat different indices: the highest measure was recorded at PB-06 (3.5), followed by PB-03, 18 (3.25), while the lowest was at PB01. It is apparent that changes in the number of variables used and the weighting can result in different grades of health. Seven of the 19 sites increased by one grade, from poor to fair, when using the SRHI instead of the RHI. It is important to understand that the values represent "a compromise position between grading for the ideal “pristine” reef conditions and what we can realistically hope to achieve in modern times and conditions." For instance, coral cover observed on Pedro Bank is relatively low compared to historical cover estimates (e.g. 30-50%) which resulted in ranked data that was fairly uniform at all sites. Coral cover did show considerable variation among sites, however, ranging from a low value of 4% (PB-01) to a high of 19%. A. Coral diseases and other biotic stressors A number of biological factors affected the health of corals including bleaching, coral disease, overgrowth by clionid sponges, predation by C. abbreviata, Stegastes planifrons algal lawns, and fish bites (Fig. 55-57). Of all these factors, the mean prevalence of disease was fairly high (>5%) which translated to a low rank (1 or 2) in the Reef Health Index for more than half of the sites. In fact, six of the sites had a large number of corals showing signs of disease (PB-06, 07, 08, 10, 14 and 20) with a prevalence of over 7%. This must be placed in context of the type of disease and the species affected, however. The most virulent diseases affecting Caribbean reefs today are white plague and yellow band disease, especially among Montastraea annularis complex (Fig. 55). While these diseases were observed on Pedro Bank, they affected a very small proportion of colonies (20 colonies of M. annularis complex were identified with YBD and 8 with white plague, most of which were in two locations). In contrast, the most widespread condition affecting corals was dark spots disease (DSD), but very few colonies showed any partial mortality attributed to this syndrome. DSD was observed on eight species (122 corals), with most cases (75%) observed on Agaricia agaricites. In general, corals exhibited very low levels of tissue loss. Most corals were almost completely live (mean % partial mortality was 10%) and there was very little recent mortality. The overall partial mortality, when compared to the rest of the Caribbean, was considerably less.

 

60 

Profile for Khaled bin Sultan Living Oceans Foundation

Global Reef Expedition Final Report: Jamaica  

In March of 2012, scientists on the Global Reef Expedition set out to assess the community structure, health, and resilience of corals and c...

Global Reef Expedition Final Report: Jamaica  

In March of 2012, scientists on the Global Reef Expedition set out to assess the community structure, health, and resilience of corals and c...

Advertisement