NMI corals at risk Rising sea temperature killing corals

Posted on Apr 19 2002

Rising sea temperature has resulted in the massive death of corals on the Saipan Lagoon, an indication that the Commonwealth is experiencing an El Niño-like phenomenon that is currently wreaking havoc in the mainland U.S. and in other parts of Asia.

If sea temperature continues to rise, a wider scale of coral death may impact on the fish communities that use the corals as their habitat. Corals also take carbon dioxide from the atmosphere and release oxygen instead, mitigating global warming of the earth.

“El Niño brings either the change in currents or the slowdown of the currents that normally run along CNMI, bringing in new fresh, cooler waters. So when the stagnant waters sit there, two thing happen: the water becomes warmer because it’s not moving and it’s not being refreshed by waters coming from Hawaii and along the equator and places like that; and another thing that happens is that sunlight—UV [ultraviolet] rays—are able to penetrate deeper into the water,” said Division of Environmental Quality marine biologist Peter Houk.

However, the phenomenon being experienced by the CNMI has not been officially classified yet as El Niño.

“We put up continuous temperature monitoring instruments about two months ago, and we’re going to leave them out there throughout the summer, and we’re going to document [the results],” said Houk, referring to the Saipan Lagoon.

The warming phenomenon has resulted in the death of corals not just on the Saipan Lagoon, but also on Tinian and Rota’s waters.

“An estimate that we have is that of this large Staghorn coral that’s in the area of the lighthouse—that would be about Fishing Base going south towards Sugar Dock—we’ve lost anywhere between 50 and 70 percent of our Staghorn coral beds ,” he said.

On Rota and on Tinian, estimates of coral death was at 10 percent each. Houk said surveys would also be conducted on the waters surrounding the Northern Islands.

Staghorn corals are considered one of the most dominant coral beds on Saipan Lagoon. Scientifically known as acropora, their pores contain thousands of algae that photosynthesize sunlight. The algae are known as zooxanthellae.

“Thousands and thousands of zooxanthellae – these are algae that live inside there and they photosynthesize the sunlight and they give the corals energy to grow – the high temperature makes the corals expel these zooxanthellae so they no longer get food from these tiny algae,” he said.

When this happens, the healthy, brownish color of the twig-looking corals – that adds to the beautiful scenery underwater – is lost, and the corals turn extremely white, according to Houk. When the corals die, they will break down, depriving fish of the habitat they should have provided.

“These corals function many things. They’re habitat for fish, octopus, lobsters, and things that we like to eat, things that tourists like to come and see. Also these corals photosynthesize and on a big scale, I’m pretty sure they dig up carbon dioxide out of the atmosphere and release oxygen just like trees,” the marine biologist said.

Currently, he said the impact on fish communities of the coral deaths may hardly be seen yet, since many Staghorn branches have yet to break down.

But he added: “The fish communities will change as the Staghorn breaks down because now it’s dead. When it was alive it will continue growing, but now that it’s dead, the branches will slowly break down and form rubble.”

So-called farmer fish would then dominate near the rubbles, the type of fish that is not preferred as food by fishermen, said Houk.

Unconfirmed information received by the DEQ also revealed that sea water temperature is expected to rise further, aggravating the situation in the coming months.

To mitigate this, Houk said a clean, healthy marine habitat should be in place. This will allow new corals to come in and grow.

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