The role of acoustics within the sensory landscape of coral larval settlement

Abstract

Recruitment of coral larvae on reefs is crucial for individual survival and ecosystem integrity alike. Coral larvae can detect and respond to a wide range of biotic and abiotic cues, including acoustic cues, to locate suitable sites for settlement and metamorphosis. However, the acoustic ecology of coral larvae, including how they perceive auditory cues, remains poorly understood. In this mini-review we consider both ex situ physiology and behavior, and in situ ecological and behavioral studies, to first provide an updated overview of the abiotic and biotic cues used by coral larvae to guide settlement. We then explore in detail the use of acoustic cues and the current literature on behavioral responses to acoustic stimuli. Finally, we discuss gaps in our understanding of the mechanisms by which coral larvae detect acoustic cues, highlighting a novel application of technology to explore these sensory capabilities. We also address how larval phonotaxis, i.e., the ability to orient to a sound cue, can be applied to coral reef conservation. Current research suggests that acoustic cues are likely used at small spatial scales, and that coral larvae may have directional acoustic sensitivity enabling phonotactic behavior. Recruitment of coral larvae on reefs is significantly influenced by habitat-specific soundscape variation and likely affected by anthropogenic disturbance. We propose a novel application of the remote sensing technology, micro-scanning laser Doppler vibrometry (LDV), to quantify the micromechanical responses of putative acoustically sensitive epidermal microstructures. We then highlight the potential for incorporation of acoustic enrichment techniques in coral reef conservation and restoration interventions.

Unlocking the soundscape of coral reefs with artificial intelligence: pretrained networks and unsupervised learning win out

“…We present only a limited set of problem tasks, further experimentation with ML will help disentangle the relationship between soundscapes and the attributes of reefs which drive these. These experiments could be performed across ecological gradients, used to track temporal cycles, reveal patterns in functions reliant on soundscapes (46–48), or explore other novel applications. To train models that can identify relationships with raw biodiversity measures, ground-truth ecological survey data from a representative selection of sites will be essential.…”

Soundscape enrichment increases larval settlement rates for the brooding coral Porites astreoides

“…Sound detection is in turn a sensory mode broadly used by adult and larval stages of many marine organisms, including mammals, fishes and various marine invertebrates, to navigate and communicate underwater [ 31 , 32 ]. Given the central sensory importance of soundscapes to coral reefs, consideration has begun to be directed towards the integration of acoustic cues into reef restoration practises [ 33 ].…”

Coral larval settlement induction using tissue-associated and exuded coralline algae metabolites and the identification of putative chemical cues

“…Coral larvae are known to actively select their settlement location [1][2][3][4][5] in response to biochemical cues [6,7], microbial biofilm composition and density [8,9], and abiotic chemical and physical cues such as salinity [10], light [11], turbulence [12] and external sounds [13,14]. Crustose coralline algae (CCA) are commonly described as beneficial members of reef ecosystems, producing chemical cues that coral larvae sense and use for both navigation [15] and metamorphosis [16,17].…”

“…The role of CCA on the induction of coral larval settlement and metamorphosis has been widely studied [15,[23][24][25] (further reviewed within [3,14]), with a large proportion of these studies targeting metabolites that putatively act as metamorphosis facilitators. Such molecules can be found within the extracellular matrix of CCA (tissueassociated), either produced by the organism itself or by its associated biofilm communities [6,7,16,26].…”