RISKY: A view of the sea and a staircase leading up to Cave 13B at Pinnacle Point in Mossel Bay. The decline in plants could impact food security in the Indian Ocean rim countries and the global fisheries market. Picture: REUTERS
RISKY: A view of the sea and a staircase leading up to Cave 13B at Pinnacle Point in Mossel Bay. The decline in plants could impact food security in the Indian Ocean rim countries and the global fisheries market. Picture: REUTERS
TAKING HUGE TOLL: A large construction ship is seen off the coast at Sea Point. The availability of organic compounds through photosynthesis by microscopic plants is the basis of the marine food web. Picture: David Ritchie
TAKING HUGE TOLL: A large construction ship is seen off the coast at Sea Point. The availability of organic compounds through photosynthesis by microscopic plants is the basis of the marine food web. Picture: David Ritchie

Staff Reporter

A STUDY by a UCT researcher and international colleagues has found that there has been a 20 percent decline in the number of microscopic plants in the Indian Ocean over the past decade.

This is due to the surface of the ocean warming and having a great impact on fish, the study, published in the journal Geophysical Research Letters by the Indian Institute of Tropical Meteorology (IITM), has found.

UCT researcher Marcello Vichi, with other researchers from across the globe, contributed to the study.

According to the study, the decline in microscopic plants can potentially impact food security in the Indian Ocean rim countries and the global fisheries market in Japan, US and several EU countries. Vichi found that this decline in microscopic plants might affect the food chain, turning the biologically productive region into an ecological desert.

Ocean primary production, the availability of organic compounds through photosynthesis by microscopic plants, is the basis of the marine food web.

The Indian Ocean, especially the western region, hosts one of the largest microscopic plants blooms in summer due to the availability of nutrient-rich waters driven by the Monsoons, found Vichi. He said he found the large-scale distribution of tuna and other fish was associated with the abundance of these microscopic plants.

“The ocean has absorbed the largest portion of the extra heat caused by increased atmospheric greenhouse gases,” said Vichi.

Among the tropical oceans, the warming is most prominent in the western Indian Ocean, possibly taking a huge toll on the marine ecosystem, he said.

The summer warming during the past century is up to 1.2ºC, which is very large compared to a global surface warming of up to 0.8ºC during the same period, added Vichi.

He said rising ocean surface temperature resulted in less dense water on the surface and dense water in the subsurface, adding that such a condition inhibited the vertical upwelling of nutrient-rich subsurface waters to the surface.

“This vertical exchange is a critical process for introducing nutrients into the upper zones, where sufficient light is available for photosynthesis,” Vichi said.

“Future simulations project a further decline in marine primary productivity due to surface warming in the coming decades and the western Indian Ocean may act as an early indicator that needs to be constantly monitored.”