Abstract
It is now widely accepted that a shift towards renewable energy production is needed in order to avoid further anthropogenically induced climate change. The ocean provides a largely untapped source of renewable energy. As a result, harvesting electrical power from the wind and tides has sparked immense government and commercial interest but with relatively little detailed understanding of the potential environmental impacts. This study investigated how the sound emitted from an underwater tidal turbine and an offshore wind turbine would influence the settlement and metamorphosis of the pelagic larvae of estuarine brachyuran crabs which are ubiquitous in most coastal habitats. In a laboratory experiment the median time to metamorphosis (TTM) for the megalopae of the crabs Austrohelice crassa and Hemigrapsus crenulatus was significantly increased by at least 18 h when exposed to either tidal turbine or sea-based wind turbine sound, compared to silent control treatments. Contrastingly, when either species were subjected to natural habitat sound, observed median TTM decreased by approximately 21–31% compared to silent control treatments, 38–47% compared to tidal turbine sound treatments, and 46–60% compared to wind turbine sound treatments. A lack of difference in median TTM in A. crassa between two different source levels of tidal turbine sound suggests the frequency composition of turbine sound is more relevant in explaining such responses rather than sound intensity. These results show that estuarine mudflat sound mediates natural metamorphosis behaviour in two common species of estuarine crabs, and that exposure to continuous turbine sound interferes with this natural process. These results raise concerns about the potential ecological impacts of sound generated by renewable energy generation systems placed in the nearshore environment.
Highlights
Underwater tidal turbine technology has advanced at a rapid rate due to increasing commercial interest across many countries
Pooling of replicates There was no significant difference in the median to metamorphosis (TTM) among individual replicates within both the sound and the silent treatments for all seven metamorphosis experiments (KruskalWallis test) (Table 1)
The results of the current study indicate that underwater sound produced by wind and tidal turbines have the potential to interfere with natural acoustic settlement cues in coastal crab species, most likely delaying or discouraging metamorphosis of megalopae whilst in the vicinity of the turbine
Summary
Underwater tidal turbine technology has advanced at a rapid rate due to increasing commercial interest across many countries. This is the result of a widely recognised need to shift energy production from fossil fuels to renewable sources in order to limit further anthropogenically induced climate change [1,2,3]. Tidal power generation is an emerging renewable energy technology, and many wind turbines are already in place within coastal waters of numerous countries [4] and a few pilot projects on underwater tidal turbines [1,5,6]. The addition of these anthropogenic sound sources are likely to result in the masking of underwater ambient sound for organisms that rely on acoustic communication or natural acoustic cues within this frequency range [7]
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