Coral Reef Indicators

Corals are anthozoans, the largest class of organisms within the phylum Cnidaria. Comprising over 6,000 known species, anthozoans also include sea fans, sea pansies and anemones. Stony corals (scleractinians) make up the largest order of anthozoans, and are the group primarily responsible for laying the foundations of, and building up, reef structures. For the most part, scleractinians are colonial organisms composed of hundreds to hundreds of thousands of individuals, called polyps (from NOAA - What are corals and coral reefs? The basic taxonomic classification of corals is below (from Reef Relief).

Phylum:
Cnidaria - All organisms belonging to this phylum are characterized by the presence of: tentacles, nematocysts (stinging cells), central digestive cavity, radial symmetry
Class:
Hydrozoa - Portuguese-man-of-war, Fire Coral, Hydroids, Siphonophores
Schvphozoa - Jelly fish (medusea)
Anthozoa - Sea anemones and corals
Subclass:
Octocorallia - Sea whips, Sea feathers, Sea plumes, Other gorgonians
Zooantharia
Order:
Actinaria - anemones
Zooanthiniaria - carpet anemones
Scleractina - true stony corals

For more on indicators, please visit Coral Reef Biocriteria.

Scleractinian Coral Bioindicators (true stony corals)

• Percentage hard coral cover, diversity indices, and vitality indices
• Growth rate (measurement of coral growth rates as an indication of water quality)
• Productivity and calcification profiles (measurement of productivity and calcification profiles as an indication of water quality)
• Coral fecundity and recruitment
• Zooxanthellae loss (quantifying the occurence and extent of coral bleaching as a general bioassay of environmental stress on corals)
• Coral diseases and cyanobacterial blooms (frequency and severity of occurances of coral diseases and cyanobacterial blooms)
• Bioaccumulation of metals, phosphorus in coral skeletons
• Physical damage

Non-Coral Bioindicators

• Butterflyfish (for those species of butterflyfish which are obligate corallivores, a decline in the health of a reef, manifested by decreasing food quality of the stressed coral polyps, will result in a decrease in the abundance and diversity of these species and an increase in territory size, feeding rate and agonistic encounters as mated pairs attempt to maintain their nutritional intake by expanding their territories to include more coral colonies)
• Ectoparasites on coral reef fishes (incidence of ectoparasitism on reef fishes should increase with deteriorating water quality)
• Larval assemblages of fish and other reef taxa (sensitivity of larval fishes, along with their position in the pelagic food web, make them excellent indicators of environmental perturbations)
• Indicators of Fishing/Shell Collecting
• Organic contaminants and the development of fishes (occurrence of developmental defects in a demersal spawning fish as a bioindicator of pollution effects)
• Bioaccumulation in molluscs and macrophytes
• Sessile reef organisms (sponges, gorgonians)
• Heterotrophic macroinvertebrates (stressed reefs undergo an "ecosystem shift" from those dominated by coral-algal symbionts towards those dominated by heterotrophic macroinvertebrates, especially scavengers, filter feeders, and internal bioeroders. )
• Internal bioeroders (rubble, or live coral colonies, invaded by bioeroding sponges and bivalves)
• Coelobites (reef cavity-dwellers)
• Foraminifers (used as community response to gradually increasing nutrient flux, whether natural or anthropogenic)
• Stomatopod crustaceans (stomatopod abundance, diversity, and recruitment are strongly negatively correlated with various pollution measures.)
• Amphipods (are more sensitive than other species of invertebrates (decapods, polychaetes, molluscs, and asteroids) to a variety of contaminants.)
• Gastropod imposex (imposition of male sexual characters on females is extremely sensitive indicator of exposure to tributyl tin)
• Corallivores (specifically abundance of corallivores such as crown-of-thorns starfish (Acanthaster planci) and Drupella gastropods)