Boat noise alters behaviour of two coral 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 focused on fish & marine mammals, even though invertebrates represent over 92 % of all marine life. The few studies conducted on invertebrates have demonstrated clear negative effects of anthropogenic noise pollution. 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. T. maxima functions as prey for many fish species, contributes up to 9 % of the reef's calcium carbonate budget, and plays a role in nutrient cycling. The herbivorous strombid L. lambis can occur in large numbers on reef flats and is prey for other snails and several elasmobranchs. Using two case study reefs, we show that both boat noise and biotic sounds are prominent sound sources in Red Sea reef habitats. In-situ controlled exposure experiments were conducted on two shallow central Red Sea reefs, where Daily Diary smart tags were used to measure the reactions of T. maxima and L. lambis during underwater playback of boat noise and ambient reef sound. Both macroinvertebrates exhibited behavioral changes during the boat noise treatment. Our results suggest that L. lambis and T. maxima individuals may spend energy averting the invisible "threat" of boat noise, rather than feeding or staying open for symbiotic algae to perform photosynthesis, in the case of T. maxima. As boat noise is prevalent on Red Sea reefs, invertebrates may be affected on a large scale in the Red Sea.