Abstract

People’s impacts have had a significant impact on coral reefs and will likely continue to do so for the foreseeable future. These ecosystems are home to millions of species. Many of the same mechanisms that affect other ecosystems that are heavily influenced by humans also affect reefs, but a few unique characteristics stand out: (i) numerous powerful reef builders release eggs and sperm into the water column, where fertilisation takes place. They are consequently especially susceptible to Allee effects, including the risk of extinction brought on by persistent reproductive failure. (ii) Small, weedy corals with short lifespans and restricted larval dispersal ability are most likely to be resistant to the effects of habitat deterioration. Thus, the emergence of genetically separated groups of inbreeding corals will be caused by habitat deterioration combined with habitat fragmentation. (iii) Coral “bleaching,” or the breakdown of the coral-algal symbiosis, can result in changes in symbiont communities, coral death, and average sea temperature increases of as little as 1°C, which are most likely a result of global climate change. (iv) Human activity near reefs increases fertiliser inputs as well as fishing pressure. In general, these dynamics favour competitors that grow more quickly, which are frequently fleshy seaweeds, and may also cause booms in the populations of predators. (v) Stress-related combinations seem to be linked to ecological shocks like deadly disease outbreaks and threshold reactions. (vi) According to the fossil record, corals as a whole are more likely to go extinct than some of the other taxa that they connect with, whose habitat requirements might be less demanding.