Coral reefs are facing extinction

A diving buddy pair taking Reef Check Australia substrate data on the Great Barrier Reef.

In this last of four posts, I will discuss some unknown causes of coral reef mortality. In the first post, I looked at the dismal situation of coral reefs and their lack of official protection from trade, plus the incredible importance of these species for the survival of marine life and, in turn, human life. In the second post, I explored how climate change is jeopardizing the existence of coral reefs across the world’s oceans. And in the third post, I wrote about the overexploitation of pink and red corals in particular.

Unknown causes of seaweed overgrowth

Australia’s 345,000-square-km Great Barrier Reef has been found partly choked by seaweed, according to surveys conducted in 2009. Over 40% of the coral reef areas closest to shore were found clogged with the weed.

“We are concerned about it because it does look like a lot of weed and in other places in the world, weed is an indication of decline,” said marine biologist Professor David Bellwood from James Cook University.

Bellwood suspects the overgrowth has been caused by the depletion of algae-eating fish around the coral reef. Without the presence of fish to feed on algae, of course, the plant is allowed to flourish unfettered and smother coral polyps.

“The question is, does this mean the Barrier Reef is in real trouble? That the reef is rotting from the inside out? Or does it mean to say that that amount of weed is natural? And the answer is: it’s hard to say,” he said.

Yet, alarmingly, he assured that

“The Great Barrier Reef is in the best condition of any reef in the world.”

Yowza. Sounds like dire news to me. It’s like saying that guy who suffers from asthma still breathes better than everyone else. He’s still got asthma, so how well can he really be doing?
As well, algae growth is caused by elevated nutrient levels in the water due to fertilizer runoff (from golf courses, farms, and so on) and untreated sewage.
It has also been suggested that sedimentation—possibly caused by heavy rainfall—can spark algal overgrowth. Other ways sedimentation promotes coral death is by smothering or burial (reef-building corals depend on high light, high oxygen, low turbidity, low nutrients, and open ocean salinity to remain healthy); decreasing growth through coral abrasion and shading; increasing the production of respiration and mucus; and by reducing coral reproduction, coral larval settlement, and early survival.

Unknown causes of coral malformations

White warts and tumors that show up on coral reefs are irregular shaped skeletal abnormalities. Because these malformations display fewer protective mucous cells than regular corals, and a porous skeleton, they are especially vulnerable to predation and erosion from algae and other organisms. In turn, damaged coral abnormalities cause local coral mortality and can thwart colony fitness and fecundity.
The causes of coral malformations are speculated to “range from biological pathogens transmitted by corralivore fishes, genetic mutations and external environmental conditions such as excessive UV radiation exposure,” according to APEX Environmental.

Yellow-band disease on a stony coral