Fish Appear to Be Losing Their Color as Coral Reefs Decline, Scientists Warn

The Great Barrier Reef may become less colorful as oceans warm and corals bleach, according to a new Australian study that looked at changes in reef health, coral types, and resident fish over three decades.

Chris Hemingson and his James Cook University colleagues wrote in their paper that future reefs may not be as colorful as they are today.

Our findings suggest that reefs may be at a critical transition point and could become less colorful in the future.

The Great Barrier Reef was struck by another widespread bleaching event fueled by rising carbon emissions, which is why the study was focused on the reefs surrounding the mid-section of the largest coral reef system on Earth.

The study found that the coral reefs in the area have changed greatly due to previous coral bleaching events, with the loss of soft and branching corals a likely factor in the disappearance of brightly-colored fish.

As these complex corals become rarer, on future reefs impacted by climate change, fish communities may become duller, according to the trio of researchers.

Hemingson and colleagues looked at the diversity of colors found in communities of reef fishes and related that to the habitats where those fishes live.

Bright colors to stand out and attract a mate or neutral tones to blend in and avoid predators are all linked to coral reefs.

Fish communities in healthy parts of the reef with plentiful complex corals were compared to other areas where massive, encrusted corals dominate in the wake of major disturbances.

Hemingson found that the diversity and range of colors present on fishes living in and around the reef increases as the coral cover increases.

As the cover of turf algae and dead coral rubble increases, the diversity of colors declines to a more generalized, uniform appearance.

Hemingson et al. are part of the Global Change Biology.

There are healthy fish communities and damaged parts of the reef.

Hemingson and colleagues looked back at the data collected annually for the past 27 years to see if the trends held up over time.

According to previous studies, only 2% of the Great Barrier Reef remains untouched by the five mass coral bleaching events of the past 30 years.

Hemingson and colleagues found that the first mass bleaching event of 1998 caused a complete shift in fish communities.

The lemon damselfish and green coral goby are two of the most eye-catching yellow and green fishes.

Hemingson said that ongoing declines are likely to lead to a complete loss of these brightly colored species, which would effectively drain the color out of fish communities.

Although the boulder corals that replaced soft, branching corals are more resistant to heat impacts, they probably don't provide as much protection to brightly colored fishes.

The researchers write that the corals that are most capable of surviving the immediate impacts of climate change are unlikely to maintain the diversity of colors currently supported by coral reefs.

Even if coral cover remains high, fish communities on future reefs are likely to be a duller version of their previous configurations.

Hemingson acknowledges the grief that people may feel as fish species and corals are lost, an ecological grief that scientists studying coral reefs first-hand know all too well.

Scientists have shown that gusto can be a powerful motivational force that spurs people to take action.

Emma Camp, a coral biologist at the University of Technology Sydney told Nature in 2019: "I can either give up when I feel upset, or use those emotions to motivate me and find better solutions."

Fighting words to live by.

The study was published in a journal.