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Hard corals have a symbiotic relationship with tiny algae that live inside them. This means that the two organisms live together as one. In this case, the relationship is useful for both the coral and the algae. The algae use the waste products (nutrients and carbon dioxide) from the coral. The algae are photosynthetic which means they use light to produce sugar and protein. This process also produces oxygen. The coral uses these products to grow and build its skeleton. There are three types of hard coral: branching, massive/encrusting, plate;
Branching coral looks similar to branches in plants. It can sometimes have a small base attachment to rock or the sea floor, but sometimes it does not. Cauliflower Coral (Pocillopora damicornis) is an example of a branching coral. Massive/encrusting coral lives in dome shaped or rounded colonies. The widest part of the colony is firmly attached to rock or the sea floor. Encrusting coral colonies are more flattened than the usual massive dome shape. Flowerpot coral (Alveopora fenestrate) is an example of a massive/encrusting coral. Foliose/plate coral are colonies with plate-like horizontal or vertical folds. Yellow Scroll Coral (Turbinaria reniformis) is an example of a foliose/plate coral.
Threats include; human activity (inappropriate boating, anchoring, fishing and diving practices), pollution and climate changing causing increased water temperature and low salinity