There is a problem with the Great Barrier Reef, according to a new Australian study focusing on the health and types of corals, as well as resident fish. Indeed, the fish communities that live there could become less colorful as the oceans warm and the corals bleach.
According to marine ecologist Chris Hemingson and colleagues at James Cook University in an article published in the journal Global Change Biology, future reefs are unlikely to be the colorful ecosystems we know. It would appear that the reefs are currently at a critical transition point. The results of the study showed that coral bleaching events have profoundly changed the composition of coral reefs in the region. It has been observed that the loss of soft and branching corals could be a likely factor in the disappearance of brightly colored fish.
This depletion of complex corals at future reefs impacted by climate change could lead to lackluster fish populations.
The relationship between the color diversity of fish and their habitats
Hemingson and his colleagues looked at the diversity of colors found in reef fish communities and matched it to the types of habitats where these fish live. Some fish have developed bright colors to stand out and be able to attract a mate while others feature neutral tones to blend in with the environment and protect themselves from predators. But overall, the coloration of these fish is naturally tied to the coral reefs they inhabit.
Scientists have observed that as the cover of structurally complex corals increases on a reef, so does the diversity and color range of the fish that live there. In any case, this is what Hemingson observed by observing the small fish which rarely venture far from their homes.
Conversely, when the cover of algae and dead coral debris increases, the diversity of colors declines. This situation does not bode well for reef fish where the waters tend to warm up.
The effects of massive coral bleaching
Previous studies have shown that only 2% of the Great Barrier Reef has been spared from five mass coral bleaching events in the past 30 years. The first recorded event was in 1998, hitting the reefs hard around the island of Orpheus. The complex branching corals in this part were particularly affected, resulting in a complete change in fish communities. For example, there has been a nearly two-thirds decline in yellow and green fish such as damselfish and green coral gobies over the past three decades.
On the other hand, it would seem that the rocky corals that have replaced soft branching corals are more resistant to climate change, but they are less suited to protecting brightly colored fish from predators. So even if the coral cover remains high, the future population of fish that will inhabit it will be a rather lackluster version.
Scientists lament the situation but hope it will serve as a wake-up call to spur people to take drastic action.