Sea sponges vulnerable to global warming

August 22nd, 2008 - 3:45 pm ICT by IANS  

Sydney, Aug 22 (IANS) Sea sponges are at risk from global warming because the symbiotic relationship they share with a complex community of microbes would come unstuck at 33 degrees Celsius. This is identical to the threshold at which corals experience bleaching, also a breakdown in the symbiotic relationship between the host and its microbes.

Work by Australian Institute of Marine Science’s Nicole Webster has shown that the elevated sea temperatures expected as climate change progresses would threaten the survival of sponges.

These remarkable living creatures are an essential part of many marine ecosystems, including the Great Barrier Reef (GBR). Nearly 40 percent of the weight of some sponges is made up of microscopic symbiotic bacteria, contributing a range of benefits including chemical defence systems and the processing of nutrition and waste.

In a series of experiments in which Webster and her colleagues exposed a common GBR sponge (Rhopaloeides odorabile) to water temperatures ranging from 27 degrees to 33 degrees, the clear line of demarcation between a continued healthy symbiotic microbial community in the sponge and a switch to harmful microbes that cause disease consistently emerged at 33 degrees.

By 2100, the 33 degree sea surface temperature threshold would be crossed regularly on the waters of the GBR, based on current climate change projections.

As microbes have symbiotic relationships with nearly all marine invertebrates, profound changes to the marine world are likely to flow from these higher sea temperatures.

Webster’s work points to the need for greater emphasis on the unseen world of microbes in understanding threats from climate change.

She presented her findings Thursday at the 12th conference of the International Society for Microbial Ecology paper at Cairns.

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