Seagrass in decline

Seagrasses in Cairns have suffered unprecedented declines over the past three years and are at their smallest ever recorded distribution.

Staff from James Cook University’s Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER) have been surveying seagrass in Cairns Harbour and Trinity Inlet since 1984.

The Centre’s seagrass team, formerly based at Fisheries Queensland, has released its annual monitoring and updated baseline survey for seagrass in Cairns Harbour and Trinity Inlet.

“Seagrass coverage around Cairns peaked between 2007 and 2009, and has declined each year since then,“ Principal Research Scientist Dr Michael Rasheed said.

“Given the ecological and economic value of these seagrass beds, this is cause for serious concern.”

Dr Rasheed said regional, climate-related events were the major factors in the seagrass decline.

“A number of above-average wet seasons, combined with the La Niña events of 2010-11, and tropical cyclone Yasi, have all contributed,” he said.

“Cairns is not alone in this. Seagrasses along the coast and estuaries of both the wet and dry tropics regions have been particularly affected.

“We have recorded similarly large declines of coastal seagrasses over the same period in other monitored locations such as Mourilyan Harbour, Bowen and Townsville.

“The breadth of the decline points to regional, climate-related causes.”

Dr Rasheed said coastal and estuarine seagrass beds were highly productive nurseries for the region’s fisheries.

“Previous research estimates that the Cairns seagrass meadows are worth more than a million dollars a year to the tiger prawn fishery alone. They are also critical to other fisheries and, of course, to non-commercial species.”

In response to these latest findings TropWATER researchers are investigating the capacity for seagrass recovery.

“The early results are promising. The next stage is to assess the viability of those seeds, and to monitor for signs of recovery during the seagrass growing season in the second half of the year,” Dr Rasheed said.

“We’re looking at the seed bank – the reserves of seeds lying dormant in the sediment in areas where seagrasses used to occur.”

The researchers are also increasing the frequency of their surveys to quarterly, investigating what local factors might contribute to seagrass change, and assessing the light and temperature requirements for seagrass growth.

“The team’s work since 1984 has helped establish the natural variation for seagrass communities, and some of the links between seagrass change and climate,” Dr Rasheed said.

Since 2001 the seagrass monitoring program has been a joint initiative with Ports North.

“The results are used to assess the health of the port’s marine environment and to inform management plans by providing regular updates on the health and resilience of these key fisheries habitats,” Dr Rasheed said.

Issued May 27, 2013

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