Healthy Reefs
Indicators of Functional Integrity
Functional indicators include key ecological and evolutionary processes (e.g., mortality, recruitment, herbivory). They are the processes required to sustain biodiversity and they influence how structural components interact.
Reproduction & Recruitment
Reproduction and recruitment are among the most critical processes governing reef communities. If coral populations are not replenished through reproduction and recruitment, then the reef framework will eventually degenerate, having a cascading affect on the entire reef community. The major reef builders in the MAR (e.g., Montastraea spp. - star corals and Acropora spp. - elkhorn & staghorn corals) reproduce by broadcast spawning, which leaves successful fertilization to chance encounters in the water column during a few hours on a couple of nights each year.
The destruction of critical habitats - particularly mangroves and seagrasses - may be reducing the overall recruitment success of some fish and invertebrate species. In addition, fishing of spawning aggregations greatly reduces the overall reproductive success of these species. Protection of these spawning sites can help ensure reproductive success.
Coral Mortality
Corals are clonal organisms that experience either complete or partial mortality. Partial coral mortality - both recent and old dead - is a key indicator of coral fitness and allows the potential to hind cast when corals died based on their appearance. Many coral species, such as Elkhorn coral (Acropora palmata), retain a calcareous record of their colonial structure long after they die (up to 15-20 years). Thus, even standing dead colonies can provide a glimpse into past population history. Corals die from both natural and human factors and it is often difficult to discern between the two. The spatial extent, location, and severity of any increase in mortality are valuable in assisting this distinction.
Coral 'Condition'
In addition to coral mortality, indicators used to describe coral condition or fitness include disease, bleaching, and predation.
Coral Disease: Coral disease infections result in varying amounts of actual mortality, but generally indicate a reduction in the vitality of corals, which is directly relevant to the overall assessment of reef health. Following the 1998 bleaching event and damage from Hurricane Mitch, a strong linkage was observed between bleaching-related mortality and infectious diseases in the Mesoamerican region.Coral Bleaching: Natural or background coral bleaching is often transient in nature with corals regaining their pigmentation after several weeks or a few months, but the increase in frequency and severity of mass bleaching is of great concern for MAR coral reef health. Severe mass bleaching or prolonged bleaching may result in reduced skeletal growth, decline in reproduction, and inability to resist competition.
Predation: Certain fish, worms, barnacles, crabs, and snails feed on coral polyps. Some of those fish also destroy substrata in the process, thereby preventing coral recruits from settling. Under past natural conditions, these coral predators likely exerted minor effects, but with the additional stressors on corals today, predation may now have proportionally greater impacts.
Herbivory
Herbivory is probably the most important process influencing reef community structure. Sea urchins and fishes are the two most important groups of herbivores that control the abundance and species composition of both corals and algae, particularly the larger “macroalgae” that are in direct competition for space with corals. Thus, their decline can result in a rapid increase in macroalgae. Perhaps the most influential herbivore on Caribbean reefs is the long-spined sea urchin (Diadema antillarum). The mass mortality of long-spined sea urchins throughout the Caribbean in 1983 coincided with a dramatic and rapid increase in macroalgal cover on many reefs.
- Key Functional Indicators
- Table of Functional Indicators
- Ranking Results —Functional Indicators (pdf version - 60KB)
