Effect of Anthropogenic Noise on Reef Macroinvertebrates (Lambis lambis and Tridacna maxima)

Boat noise has been shown to distract and cause harm to many marine organisms. Most of the study effort has been focused on fish & marine mammals, even though invertebrates represent 99% of all living organisms, both terrestrial and aquatic. The small amount of studies conducted on invertebrates have demonstrated a clear negative correlation between anthropogenic noise pollution and invertebrate well-being. The small giant clam Tridacna maxima and the spider conch Lambis lambis are two invertebrate species which play key roles in coral reef ecosystems, and are little studied for the effects of noise disturbance. If their behaviour is significantly affected by boat noise, this could cause a knock on effect on the rest of the reef ecosystem. T. maxima functions as prey to many fish species, contributing up to 9% of the reef’s calcium carbonate budget, as well as playing a role in nutrient cycling. L. lambis is essential prey for molluscivore snails and certain elasmobranchs, and through its herbivorous feeding, helps to keep filamentous algae levels low. Moreover, coral reefs are reliant on the biological sound primarily created by invertebrates, such as snapping shrimp, to attract larvae from the pelagic environment for settlement. During experiments conducted in February 2020 in the Red Sea, Daily Diary Monitoring (DDMT) smart tags were used to measure the reactions of T. maxima and L. lambis respectively during underwater playback of boat noise compared with ambient reef sound. It was found that both T. maxima and L. lambis exhibited behavioral changes during the boat noise treatment. The implications of this study is that individuals of L. lambis and T. maxima may spend energy averting the invisible "threat" of boat noise, rather than feeding and/or photosynthesizing, in the case of T. maxima. If this hinders the acquisition of food/production, the whole reef ecosystem may be compromised in a knock-on effect from these producers and primary consumers. As boat noise is prevalent on inshore Red Sea reefs, shown by a 24-hour acoustic analysis of a patch reef sound pressure levels (SPL), invertebrates might be affected on a large scale in the Red Sea.