It’s been a rough few years for coral reefs. Rising sea surface temperatures have bleached and killed many tropical corals around the world. Those that survive this warming have to deal with the large algal blooms that result from humans overfishing herbivorous reef fish. And now word is coming in from Australia of another threat to coral reefs, the crown-of-thorns starfish.
The crown-of-thorns starfish (Acanthaster planci) is an echinoderm found among coral reefs throughout much of the Indo-Pacific. And not only does it sound like the newest character to hit Game of Thrones, it can be just as deadly. These starfish prey primarily on Scleractinia, or reef-building, corals. In reefs with just a small number of crown-of-thorns starfish, these echinoderms feed on the larger corals and open up space for younger corals to grow. The problem comes when you have larger than expected populations of the starfish. In areas of the Pilbara coral reef off the coast of Australia, CSIRO (Commonwealth Scientific and Industrial Research Organization) researchers observed over 180 individuals per hectare. To get an understanding of how large a number that is, an “outbreak” of crown-of-thorns starfish is defined as more than 15 per hectare.
Researchers are still debating the cause of this species’ population increase, but many of the leading hypotheses (predator removal, predator migration due to habitat destruction, increased phytoplankton abundance due to nutrient loading) are direct results of anthropogenic impacts to marine ecosystems. This ecological shift in coral reef habitats just goes to show how complex and connected ocean conservation issues are. It’s easy to associate oil spills and pollution with declining reef health, but higher toxicity levels aren’t the only detrimental result of marine pollution.
Coral reefs are the source of an incredible amount of biological diversity and economic benefits. Corals’ symbiotic relationship with photosynthetic zooxanthellae provide the base of productive temperate and tropical marine ecosystems. Healthy reefs protect coastal communities from hurricane and storm damage by reducing wave energy close to shore. They’re a hotspot for medical research and the aquaculture industry, and are vital for many ecotourism ventures. And we’re destroying them at an alarming rate.
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