KARACHI: The red algal bloom that occurred along the Sindh-Balochistan coast in the months of August and September killed a number of marine species, a World Wide Fund for Nature-Pakistan (WWF-P) expert said on Monday.

Apart from fish mortality reported from Pasni and Ormara in Balochistan, the phenomenon commonly referred to as red tide also severely affected the coral reefs of Churna Island in Karachi.

“The red tide (called mara pani in local language) started from Gwadar in early August and then moved towards the east and covered the entire Pakistan coast. It died down by the end of last month,” said Mohammad Moazzam Khan, working as technical advisor on marine fisheries with WWF-P. He added that the tide caused the death of benthic fishes and invertebrates.

He, however, didn’t link the presence of dead fish on the Sea View beach in early August with the red tide. “There must be some other reason for their death because the red tide had almost died down by the time it reached Karachi. I was in Gwadar where the phenomenon had developed and took photos of the discoloured seawater,” he added.

The information about the bleached coral reefs, he noted, was recently provided by some scuba divers who had gone to Churna Island.

“Since there has been no significant change in the marine ecology in that area in recent times, it appears that the red tide had turned the multi-coloured coral reefs white and green and killed the little organisms that make up their diverse ecosystem,” he said.

He also emphasised the need for a thorough investigation into the bleaching of coral reefs.

First reported red tide

A red tide, Mr Khan explained, was a ‘bloom’ of microscopic, single-celled plants called phytoplankton, that occur naturally in coastal waters.

“A ‘bloom’ occurs when a particular species of phytoplankton begins reproducing rapidly to the extent that the colour of the water changes from its bluish shade to hues of red, orange, green, yellow etc,” he said, adding that red tides in Pakistan was not a rare occurrence.

Every year during March-April, August-September and October-November, he pointed out, red tides might occur. Some of these red tides could be toxic (because of the toxins produced by the plants).

According to him, the first record of red tide in Pakistan was reported by Ibn Majid, an Omani who was considered as a great navigator of the Indian Ocean. He mentioned the discolouration of the sea resulting in the death of fishes near the Indus Delta back in the 14th century.

In 1907, the British government piloted a commission to investigate the cause beh­ind the decline of Karachi’s characteristic high quality oysters. Mr Hornell submitted a report in 1908 in which he attributed the decline to overfishing, and the red tide.

“Since the 1970s, many studies have been conducted about the plants responsible for causing the red tide and many such species have been identified,” he said. He added that 10 dolphins were reported dead following a red tide that hit Karachi in 1995; the phenomenon was also reported in the city in 2013.

He further said that in developed countries the practice was to close down the area where a red tide occurred and fishing was banned as catch from such waters could harm humans. In Pakistan, however, people lacked awareness on this issue.

According to a research published in the Marine Pollution Bulletin last year, algal blooms (red tide) may be either of natural origin (currents, high winds, dust deposition, etc) or the result of anthropogenic activities (coastal industries, maritime transportation, domestic and commercial actions).

“These blooms are detrimental in many aspects as they affect the environment (aquatic life and water quality), economy (fishing, fish farming and desalination industry), and tourism (closing down of beaches and coastal parks),” says the report.

The phenomenon can last for days and even months.

Published in Dawn, October 6th , 2015

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