Exploring overlooked components of remote South‐east Pacific oceanic islands: Larval and macrobenthic assemblages in reef habitats with distinct underwater soundscapes

Abstract

1. Identifying the diverse assemblage of species inhabiting rocky and coral reef habitats in isolated oceanic environments, and the important sound cues emitted from the reef, are crucial components to understand how species locate suitable habitats for the completion of their life-cycle and, thus, the functioning of these vulnerable ecosystems. 2. Recent field information suggests that the majority of reef biodiversity comprises small cryptic invertebrates; however, knowledge on these small components is extremely scarce. 3. The present study used light attraction methods to explore the diversity of larval, post-larval and macrobenthic cryptic fauna, and hydrophones to characterize the natural soundscape of rocky and coral reef habitats at the Robinson Crusoe island (Juan Fernandez Archipelago; 33 38 0 S, 78 50 0 W), and Rapa Nui (Easter Island; 27 7 0 S, 109 21 0 W), respectively. 4. Pelagic collections found important site-specific patterns and identified two main species assemblages: early-life stages (e.g. eggs, larval and juvenile stages of crustaceans, molluscs, and fishes) and emerging macrobenthos (e.g. demersal zooplankton such as peracarid crustaceans, ostracods, copepods, and polychaetes), with the latter contributing between 73 and 98% to the total catches. 5. The soundscape records showed marked differences among sites and seasons at Robinson Crusoe island, with variable differences found between day and night. However, at Rapa Nui, there were no differences between sites, but the ambient sound was higher at night possibly due to higher snapping shrimp activity. 6. This information highlights the importance of considering small-scale (site-to-site) patterns when evaluating overlooked components of diversity (i.e. biological or acoustic) in oceanic habitats, and provides the basis for understanding the importance of natural noise in the settlement of most reef-associated species, crucial features for the conservation of these remote and vulnerable ecosystems.

Tracing trophic pathways through the marine ecosystem of Rapa Nui (Easter Island)

“…Recent studies using metabarcoding of reef fish stomach contents have revealed elevated contributions of crustaceans (brachyuran and caridea), annellids, and fish larvae in their diets (Casey et al, 2019). In this study, brachyuran, caridean larvae, and nereid polychaetes, were important components of the emergent zooplankton assemblage (see Carrasco et al, 2020), with mixing models indicating distinct contributions from different sources of organic matter (macroalgae and coral mainly; Figure 5), emphasizing the potential trophic role of cryptofaunal adults and larval stages transferring OM through coral reefs (Kramer et al, 2013).…”

“…mainly early life stages of benthic reef fauna) were sampled by deploying two light traps between 15 and 20 m depth and moored at 1-2 m from the reef bottom (Table 1). In all cases, traps were positioned to sample during one night and estimated to attract specimens from approximately 21:00 to 09:00 h; see Carrasco, Vandecasteele, Rivadeneira, Fernández, & Pérez-Matus, 2017;Carrasco et al, 2020).…”

“…Moreover, different ontogenetic stages of cryptic fauna that constitute the larval and emergent zooplankton from Rapa Nui coral reefs (e.g. brachyuran zoea and caridean; see Carrasco et al, 2020), could be a main pathway of OM transference between pelagic and benthic ecosystem (Casey et al, 2019).…”

Combining Passive Acoustics and Environmental Data for Scaling Up Ecosystem Monitoring: A Test on Coral Reef Fishes

“…Beyond fish sounds, PAM captures the whole soundscape (i.e., ambient sound). As such, it can also be used to monitor the cryptobiome [27,28] or to measure noise pollution [29]. In comparison with diver-based methods, PAM is cost-effective and can be deployed in a wide variety of situations.…”