Climate Change and Coral Reefs

by Sue Taggart

The warming of the world’s oceans is a prime factor in the global loss of reef building corals, which are home to thousands of species of fish. When the corals die, the fish have nowhere else to go. Coral reef fish populations are in danger of being devastated—these fish are an essential part of the ecosystem, which supports commercial and recreational fisheries and tourism. The 4,000 fish species living in or around coral reefs are a major source of sustenance to an estimated 200 million people worldwide.

When coral fish breed, their eggs are swept out to sea and the baby fish then swam back to resettle on the reefs. If reefs have been extensively damaged or the composition of their corals altered due to global warming impacts, this process of re-stocking the reefs with fish can be disrupted. Baby fish are going to be affected by the changes in water temperature and the acidification of the oceans too. Some fish may migrate to cooler waters if the temperatures around the reefs heat up too much.

When summertime temperatures are warmer than usual, corals can die from “bleaching” and disease outbreaks. This in turn is devastating for the countless organisms that inhabit coral reefs.

In the long-term, ocean acidification is likely to be the most significant impact of a changing climate on the Great Barrier Reef ecosystem.

Ocean acidification, which is a change in ocean chemistry is also likely to impact fish reproductive processes. Fish eggs are more sensitive to pH changes than fish adults, and thus the population numbers may dwindle if this impact is significant. Lots of species of fish live in and around coral reefs, and most feed on the microbes in the water, which provide fish with their carbon requirements. In general, the overarching affects of ocean acidification on coral formation and the abundance of carbon in the food chain will impact fish species through habitat and food availability.

Sea surface temperature also plays a part. Fish body temperature is moderated by water temperature. Increasing sea temperatures can affect important biological processes of fish including growth, reproduction, swimming ability and behavior. Reproduction is only possible in a narrow temperature range, and therefore could be affected by the forecast temperature rises associated with climate change.

A broad estimate indicates that more than a third of coral reef fish species are in jeopardy of local extinction from the impacts of climate change.

So, not only are hundreds of species of fish at risk of extinction, ocean ecosystems will collapse and million of people who make their living from the coral reefs will lose their livelihood. Not to mention the loss of such amazing natural beauty.

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