x Abu Dhabi, UAETuesday 25 July 2017

'Algal bloom threat will rise with heavy increase of ship traffic'

The deadly impact of red tide on fish species is also detailed in a new study.

Red tide comes close to Jumeirah Beach in April last year.
Red tide comes close to Jumeirah Beach in April last year.

ABU DHABI // Harmful algal blooms are expected to increase in frequency and intensity as the invasive species are brought from other parts of the world in ship ballast water, according to a study.

The research is also the first to catalogue the impact of the 2008 red tide in Fujairah on fish species. Recent studies have shown the marine algae that turned the water rusty brown in the Gulf of Oman two years ago, and ate away at its coral reefs, is closely related to strains in the US and Malaysia.

John Burt, a professor of practice of biology at New York University Abu Dhabi, and one of the authors of the study, said: "These invasive species are likely to be an up-and-coming threat to coral reefs due to a heavy increase in ship traffic and climate change.

"We cannot control this without some sort of regulation of the maritime industry. The problem is that there are so many jurisdictions on the state and national levels that oversee the volume of ship traffic in these waters."

To help tackle algal blooms, Prof Burt said the region could use the same filtering technology used in the North American Great Lakes to prevent the further spread of zebra mussels, which have had detrimental effects on ecosystems there.

Before the red tide hit, just over half of the sea floor had been covered with living hard coral, compared with less than three per cent during the bloom, according to the study. Dead coral jumped from eight per cent to about 60 per cent.

The abundance of fish communities on the Dibba coast, the hardest hit by the algal bloom, dropped by more than two-thirds. The overall biomass of fish of different sizes slid to about a thirteenth of what it was.

"We're hopeful that over the span of a decade or more, the ecosystem will recover to pre-red tide levels of coral and fish, but at this point the levels still remain depressed," Prof Burt said.

Populations of commercial fish in Dibba and nearby East Musandam plummeted, according to the study. About one-third of blackspot snappers survived, as did about 10 per cent of hammour.

Moon wrasse, bluetail trunkfish and pearly goatfish, among others, disappeared.

Other fish benefited as competition in the ecosystem died off. The population of Indo-Pacific sergeant more than tripled in Dibba, while the amount of three-spot dascyllus, or domino damsels, surged in East Musandam.

There was a strong change in the composition of species functions. Only about a 10th of invertivores, or fish that feed on invertebrates, and less than a third of planktivores that eat phytoplankton, survived.

Grazers and excavators showed little change in East Musandam, where the supply of normally occurring live sea floor algae resources, which fish feed on, was stable.

Though there was some movement of fish away from the bloom, the changes in species were the result of increased mortality rather than emigration, the study said.

The effects were similar to those of severe bleaching events, which happen when brightly coloured coral reefs turn white due to pollution or other stresses, the report said.

Climate change will cause shifts in the water's temperature, acidification and nutrients that "may contribute to the permanent alteration of the structure and function of coral reef communities," the study said.

econroy@thenational.ae