Renewable energy sources such as the wind and oceanic tides are rapidly expanding as utilized resources. However, the growth of these industries brings along environmental side effects. Recently, the impact of underwater anthropogenic, ‘man-made,’ sound due to tidal and wind turbines on the settlement and metamorphosis of two estuarine brachyuran crabs species, the tunneling-mud crab and hairy-handed crab, was studied. Researchers of New Zealand found the crabs were rattled by the immense sound of the turbines to the point of disrupted metamorphosis.
These crabs use physical and chemical cues to first find a suitable settlement during their megalopae, post larvae, stage followed by metamorphosis into a juvenile initialized by similar environmental cues. This species of marine life was chosen because of its ubiquity in coastal environments. The time to metamorphosis (TTM) was tested in this study. When compared to silent controls (measured as decibels in reference to 1 micro pascal), the following results were gathered:
– TTM was shorter for crabs exposed to naturally occurring mudflat sounds. Median reductions of 31% and 21%, P < 0.001.
– TTM was longer for crabs exposed to 145dB re 1µPa tidal turbine sounds. Median increase of 26%, P=0.006.
– TTM was longer for crabs exposed to 145dB re 1µPa wind turbine sounds. Median increase of 15%, P=0.006.
– Finally, intensity of sound was found to have no significant effect on TTM. Given a source of 145dB versus 125dB re 1µPa the difference in TTM between the two was found to have a P value of 0.69 indicating statistical insignificance.
The culmination of results indicate that these renewable energy generating turbines, tidal and wind, do cause a disturbance of the settlement and metamorphosis time in the estuarine brachyuran crab species studied. This delay in metamorphosis can result in the death or impaired post-settlement growth of these crabs. This study indicates a need to further research the environmental effects of renewable energy generation.
To prevent harming crabs such as this or other coastal critters, a means of sound mitigation would be the next necessary step for successful energy generation innovation.
Matthew K. Pine, Andrew G. Jeffs, Craig A. Radford. 2012. Turbine Sound May Influence the Metamorphosis Behaviour of Estuarine Crab Megalopae. PLoS ONE.