Hawaiian Coral Reef Research Articles

Habitat use and movements of parrotfishes in a Hawaiian coral reef seascape

Habitat use and movements of parrotfishes in a Hawaiian coral reef seascape

Moonlight-driven biological choruses in Hawaiian coral reefs.

Sounds from fish and invertebrates in coral reefs can create persistent cacophonies that can be recorded for ecosystem monitoring, including during nighttime hours where visual surveys are typically not feasible. Here we use soundscape measurements in Hawaii to demonstrate that multiple coral reef communities are rapidly responsive to shifts in nighttime ambient light, with sustained changes in biological sound between moonrise and moonset. High frequency pulse train sounds from fish (0.5-1.5 kHz) are found to increase during moonlight hours, while low frequency fish vocalizations (0.1-0.3 kHz) and invertebrate sounds (2-20 kHz) are found to decrease during moonlight hours. These discoveries suggest that the rising and setting of the moon triggers regular shifts in coral reef ecosystem interactions. Future acoustic monitoring of reef health may be improved by comparing soundscapes during moonlight and non-moonlight hours, which may provide early indicators of shifts in the relative abundance of separate reef communities.

Acoustic enrichment trials using autonomous cameras on a Hawaiian coral reef

Playbacks of ambient sound from healthy shallow coral reefs, known as acoustic enrichment (AE), can attract fish larvae and potentially coral larvae to degraded or artificial reefs. Large-scale studies face power supply challenges and require less intensive in-person surveys of recruited larvae (≤500 μm) and fish. Here, we present a preliminary assessment of artificial structure deployments with AE, conducted between July and September 2023 in Kane’ohe Bay (Oahu, Hawai’i). The artificial structures were designed to attract herbivorous juvenile reef fish and subsequently suppress algal growth. The work is part of a future artificial reef construction project in Hawai’i where in-person surveys and frequent battery replacements are logistically challenging. The deployments consisted of one control and one treatment site 65 m apart, in 5 m water depth and 10 m from the natural reef. To document ecosystem responses, both sites use open-source burst-mode autonomous cameras, a directional vector sensor seafloor acoustic recorder, and hydrophones. A 3.8 kW-h NiMh battery supply powers sound output for three weeks during evening hours. We discuss preliminary evaluations of AE and the validity of using autonomous cameras in evaluating performance in terms of fish recruitment and algal growth. [Work sponsored by DARPA.]

Long-term ecological monitoring of reefs on Hawai’i Island (2003-2020): Characterization of a common cryptic crust, Ramicrusta hawaiiensis (Peyssonneliales, Rhodophyta)

The recently described crustose calcifying red algal species Ramicrusta hawaiiensis, known only from mesophotic depths off Lehua Island, west of Kaua’i Island, was found in shallow benthic reef habitats (3-18 m deep) along the western coast of Hawai’i Island. Molecular and microscopy techniques were used for genetic confirmation and for detailed morphological and anatomical examination. Two independent benthic cover survey datasets collected from west Hawai’i Island were used to investigate temporal and geographic distribution of Ramicrusta. In both datasets, we report Ramicrusta at approximately 60% of the sites surveyed. Benthic cover for this alga varies among sites and among years and its presence in west Hawai’i is evident since at least 2003. These findings help to document Hawaiian coral reef ecosystem change and benthic community composition reshuffling. This study also emphasizes the critical importance of taxonomy and proper identification of macroalgal species to understand the potential for phase-shifts of dominant taxa in coral reef ecosystems after environmental disturbances and fluctuations in abiotic factors. In the last decade, members of the red algal order Peyssonneliales have increased in abundance and overgrown other benthic species in reef ecosystems in the Caribbean and tropical Pacific. The novel aspect of finding abundant Ramicrusta in much shallower water than originally described, the decadal presence of Ramicrusta, and its potential for competition with other benthic organisms make this research valuable to coral reef ecology and justify further investigation of Ramicrusta ecology and biology in the Hawaiian Islands and globally.

Low-level nutrient enrichment during thermal stress delays bleaching and ameliorates calcification in three Hawaiian reef coral species.

Terrestrial-based nutrient pollution has emerged as one of the most detrimental factors to coral health in many reef habitats. Recent studies have shown that excessive dissolved inorganic nutrients can reduce coral thermal tolerance thresholds and even exacerbate bleaching during thermal stress, yet the effects of minor nutrient enrichment under heat stress have not been extensively studied. In this study, Lobactis scutaria, Montipora capitata, and Pocillopora acuta colonies under heated conditions (~30.5 °C) were exposed to low and balanced nitrogen and phosphorous concentrations over a 31-day heating period. Coral colonies were collected from Kāne‘ohe Bay, O‘ahu, which has a unique history of nutrient pollution, and held in mesocosms that allowed for environmental manipulation yet are also influenced by local field conditions. Principal findings included delays in the bleaching of nutrient-enriched heated colonies as compared to heated-only colonies, in addition to relatively greater calcification rates and lower proportions of early-stage paling. Species-specific outcomes were prevalent, with L. scutaria demonstrating no difference in calcification with enrichment under heat stress. By the end of the heating stage, however, many heated colonies were at least partially impacted by bleaching or mortality. Despite this, our findings suggest that low levels of balanced nutrient enrichment may serve as a mitigative force during thermal events. Further field-based studies will be required to assess these results in different reef habitats.

Influencing Hotel Patrons to Use Reef-Safe Sunscreen

The health of Hawaiian coral reefs is threatened by sunscreen ingredients (e.g., oxybenzone). This study sought to determine factors leading to the pro-environmental behavior of using reef-safe sunscreen (RSS) and identify practices hoteliers could implement to influence patrons to engage in this behavior. The study applied a framework to model pro-environmental behavior in the hospitality industry. It proposed that attitudes, personal capabilities, and habits are causal variables that influence pro-environmental intention, the predictor of pro-environmental behavior. Contextual factors were proposed as moderating variables for the relationship between pro-environmental intention and pro-environmental behavior. Past Hawaiian hotel patrons (n = 400) were the subjects for this survey. Intention to use RSS and the factors that influenced intention were investigated. Responses were analyzed using multiple linear regression and ANOVA. Results suggested that hotel patrons’ intention to use RSS was primarily influenced by three determinants: attitudes, personal capabilities, and contextual factors. Targeting the development of personal capabilities and employing contextual factors that facilitate the behavior were shown as effective methods to influence RSS use. Findings supported educational campaigns and complimentary RSS programs as practices that Hawaii hotel operators could use to influence patrons’ intention to use RSS.

Identifying the drivers of structural complexity on Hawaiian coral reefs

Habitat structural complexity is created by biotic and abiotic processes that operate over a range of scales. This can be seen clearly on coral reefs, where corals and reef geomorphology create structure from mm to km scales. Here, we quantified the relative contribution of biotic and abiotic structures to habitat complexity using ‘Structure from Motion’, a technology that allows accurate 3D models of environments to be reconstructed from overlapping photographs. We calculated the linear fractal dimension of these models using a virtual analogue of a profile gauge. By adjusting the spacing between profile gauge rods, we partitioned structural complexity into a series of scale intervals. We identified scales that were most indicative of coral cover (0.5-16 cm) and reef geomorphology (16-256 cm). We found that reefs in the Main Hawaiian Islands have more complexity at finer scales than reefs in the Northwest Hawaiian Islands, which we attribute to the latitudinal gradient in coral cover along the archipelago. At coarser scales, islands at each end of the archipelago have sites with high structural complexity, with less complexity in the center of the archipelago. These differences are consistent with geologic factors shaping island uplift, subsidence, and reef formation. In addition, we found that different coral genera and morphologies display unique patterns of fractal dimension, with branchingPoritescorals creating the greatest amount of habitat structure at nearly all scales. This study demonstrates how multi-scale approaches can be used to identify the processes responsible for reef structural complexity and changes in structure over time.

Understanding the determinants of biodiversity non-use values in the context of climate change: Stated preferences for the Hawaiian coral reefs

Global climate change is leading to rapid deteriorations of the health and productivity of coral reefs. There is limited research on the associated human welfare implications, particularly in terms of the non-use values that people hold for coral reefs. We examine climate related changes in non-use values of coral health, coral cover, water clarity, fish numbers, fish species diversity and presence of turtles. Using a discrete choice experiment conducted among 1,369 Hawaiian and US mainland residents, we find that climate change induced declines in coral cover and fish numbers result in large welfare losses; whereas, declines in coral health and fish species diversity lead to moderate welfare losses. Deterioration in water clarity results in large welfare losses for US mainland residents but relatively smaller losses for Hawaiian residents. On aggregate, differences in welfare estimates for the US mainland and Hawaii sample are minor. However, we find significant differences in the underlying determinants of willingness-to-pay for partial climate change mitigation including income and beliefs in the need to mitigate climate change. The paper concludes with some recommendations for policy on the basis of these findings.

Metabarcoding as a tool to examine cryptic algae in the diets of two common grazing surgeonfishes, Acanthurustriostegus and A. nigrofuscus

AbstractSurgeonfishes (Acanthuridae) are an important group of herbivores that are abundant on reefs globally. Acanthurids consume macroalgae that can compete with corals for space, turf algae that can proliferate on degraded reefs, and detritus that may smother adult corals or inhibit settlement. For these reasons, they are of particular interest at present to resource managers seeking to restore and conserve reefs that are facing a myriad of stressors. To contribute to our understanding of the diet breadth and potential vulnerability of these important fishes, we employed metabarcoding to identify and compare the algal diets of two common Hawaiian surgeonfishes, the convict tang or manini (Acanthurus triostegus) and the brown surgeonfish or maʻiʻiʻi (A. nigrofuscus). These species serve important biological and cultural roles in Hawaiian coral reef ecosystems, and manini, in particular, constitute an essential component of traditional Hawaiian diets. Although diet richness was not significantly different between the species, with 64 unique taxa identified from the gut contents of 89 A. triostegus and 57 taxa from 73 A. nigrofuscus, A. nigrofuscus exhibited greater diet diversity as measured by the Simpson's Diversity Index. A. nigrofuscus had a greater relative read abundance of brown algae, cyanobacteria, and material from the epilithic algal matrix. A. triostegus had a taxonomically more specialized diet, consuming primarily red algae. A. triostegus showed greater variability between sites in diet composition than A. nigrofuscus, and when grouped at the site, shore, or species level, A. triostegus tended to have greater diet overlap among individuals. Conversely, A. nigrofuscus exhibited greater variation in diet among individuals, with less diet variability between sites. Grazing surgeonfishes such as these are critical components of existing and future herbivore management plans, making their diet breadth and consequent vulnerability to habitat loss or disturbance of great interest to resource managers.

Physiological and molecular responses of lobe coral indicate nearshore adaptations to anthropogenic stressors

Corals in nearshore marine environments are increasingly exposed to reduced water quality, which is the primary local threat to Hawaiian coral reefs. It is unclear if corals surviving in such conditions have adapted to withstand sedimentation, pollutants, and other environmental stressors. Lobe coral populations from Maunalua Bay, Hawaii showed clear genetic differentiation between the 'polluted, high-stress' nearshore site and the 'less polluted, lower-stress' offshore site. To understand the driving force of the observed genetic partitioning, reciprocal transplant and common-garden experiments were conducted to assess phenotypic differences between these two populations. Physiological responses differed significantly between the populations, revealing more stress-resilient traits in the nearshore corals. Changes in protein profiles highlighted the inherent differences in the cellular metabolic processes and activities between the two; nearshore corals did not significantly alter their proteome between the sites, while offshore corals responded to nearshore transplantation with increased abundances of proteins associated with detoxification, antioxidant defense, and regulation of cellular metabolic processes. The response differences across multiple phenotypes between the populations suggest local adaptation of nearshore corals to reduced water quality. Our results provide insight into coral’s adaptive potential and its underlying processes, and reveal potential protein biomarkers that could be used to predict resiliency.

Characterization of acoustic attenuation in a coral reef environment

Coral reefs are complicated and understudied acoustic propagation environments. In addition to geometric spreading, there are propagation losses due to bottom attenuation, volumetric scattering, and boundary scattering from bathymetric variability and sea surface roughness. On a Hawaiian coral reef, a field test was performed in shallow water during which low-level tones were projected from an underwater speaker and received by a single hydrophone at various ranges up to 500 m from the source. Acoustic data gathered during the field test were analyzed to characterize the sound propagation environment. Conventional geometric spreading assumptions were challenged for the sloping bathymetry characteristic of the Hawaiian coral reef environment. Geoacoustic parameters of the coral reef environment were extracted from transmission loss measurements using a nonlinear least-squares inversion. Losses were estimated for frequencies of 500 Hz, 2 kHz, 5 kHz, 10 kHz, and 15 kHz.Coral reefs are complicated and understudied acoustic propagation environments. In addition to geometric spreading, there are propagation losses due to bottom attenuation, volumetric scattering, and boundary scattering from bathymetric variability and sea surface roughness. On a Hawaiian coral reef, a field test was performed in shallow water during which low-level tones were projected from an underwater speaker and received by a single hydrophone at various ranges up to 500 m from the source. Acoustic data gathered during the field test were analyzed to characterize the sound propagation environment. Conventional geometric spreading assumptions were challenged for the sloping bathymetry characteristic of the Hawaiian coral reef environment. Geoacoustic parameters of the coral reef environment were extracted from transmission loss measurements using a nonlinear least-squares inversion. Losses were estimated for frequencies of 500 Hz, 2 kHz, 5 kHz, 10 kHz, and 15 kHz.

Photosynthesis by marine algae produces sound, contributing to the daytime soundscape on coral reefs.

We have observed that marine macroalgae produce sound during photosynthesis. The resultant soundscapes correlate with benthic macroalgal cover across shallow Hawaiian coral reefs during the day, despite the presence of other biological noise. Likely ubiquitous but previously overlooked, this source of ambient biological noise in the coastal ocean is driven by local supersaturation of oxygen near the surface of macroalgal filaments, and the resultant formation and release of oxygen-containing bubbles into the water column. During release, relaxation of the bubble to a spherical shape creates a monopole sound source that ‘rings’ at the Minnaert frequency. Many such bubbles create a large, distributed sound source over the sea floor. Reef soundscapes contain vast quantities of biological information, making passive acoustic ecosystem evaluation a tantalizing prospect if the sources are known. Our observations introduce the possibility of a general, volumetrically integrative, noninvasive, rapid and remote technique for evaluating algal abundance and rates of primary productivity in littoral aquatic communities. Increased algal cover is one of the strongest indicators for coral reef ecosystem stress. Visually determining variations in algal abundance is a time-consuming and expensive process. This technique could therefore provide a valuable tool for ecosystem management but also for industrial monitoring of primary production, such as in algae-based biofuel synthesis.

Modeled larval connectivity of a multi-species reef fish and invertebrate assemblage off the coast of Moloka'i, Hawai'i.

We use a novel individual-based model (IBM) to simulate larval dispersal around the island of Moloka‘i in the Hawaiian Archipelago. Our model uses ocean current output from the Massachusetts Institute of Technology general circulation model (MITgcm) as well as biological data on four invertebrate and seven fish species of management relevance to produce connectivity maps among sites around the island of Moloka‘i. These 11 species span the range of life history characteristics of Hawaiian coral reef species and show different spatial and temporal patterns of connectivity as a result. As expected, the longer the pelagic larval duration (PLD), the greater the proportion of larvae that disperse longer distances, but regardless of PLD (3–270 d) most successful dispersal occurs either over short distances within an island (<30 km) or to adjacent islands (50–125 km). Again, regardless of PLD, around the island of Moloka‘i, connectivity tends to be greatest among sites along the same coastline and exchange between northward, southward, eastward and westward-facing shores is limited. Using a graph-theoretic approach to visualize the data, we highlight that the eastern side of the island tends to show the greatest out-degree and betweenness centrality, which indicate important larval sources and connectivity pathways for the rest of the island. The marine protected area surrounding Kalaupapa National Historical Park emerges as a potential source for between-island larval connections, and the west coast of the Park is one of the few regions on Moloka‘i that acts as a net larval source across all species. Using this IBM and visualization approach reveals patterns of exchange between habitat regions and highlights critical larval sources and multi-generational pathways to indicate priority areas for marine resource managers.

Local Biomass Baselines and the Recovery Potential for Hawaiian Coral Reef Fish Communities

Understanding the influence of multiple ecosystem drivers, both natural and anthropogenic, and how they vary across space is critical to the spatial management of coral reef fisheries. In Hawaii, as elsewhere, there is uncertainty with regards to how areas should be selected for protection, and management efforts prioritized. One strategy is to prioritize efforts based on an area’s biomass baseline, or natural capacity to support reef fish populations. Another strategy is to prioritize areas based on their recovery potential, or in other words, the potential increase in fish biomass from present-day state, should management be effective at restoring assemblages to something more like their baseline state. We used data from 717 fisheries-independent reef fish monitoring surveys from 2012-2015 around the main Hawaiian Islands as well as site-level data on benthic habitat, oceanographic conditions, and human population density, to develop a hierarchical, linear Bayesian model that explains spatial variation in: (1) herbivorous and (2) total reef fish biomass. We found that while human population density negatively affected fish assemblages at all surveyed areas, there was considerable variation in the natural capacity of different areas to support reef fish biomass. For example, some areas were predicted to have the capacity to support ten times as much herbivorous fish biomass as other areas. Overall, the model found human population density to have negatively impacted fish biomass throughout Hawaii, however the magnitude and uncertainty of these impacts varied locally. Results provide part of the basis for marine spatial planning and/or MPA-network design within Hawaii.

Spatial distribution of sewage pollution on a Hawaiian coral reef

While sewage pollution is contributing to the global decline of coral reefs, its offshore extent and direct reef impacts from water column mixing and benthic seeps are poorly documented. We addressed this knowledge gap on a Hawaiian coral reef using sewage indicator and benthic cover measurements, macroalgal bioassays, and a pollution scoring tool. Fecal indicator bacteria (FIB) and nutrient concentrations were spatially variable in surface and benthic waters, with shoreline values being highest. Shoreline macroalgae δ15N and %N indicated high nitrogen loads containing sewage, while offshore surface and benthic values suggested lower nitrogen loads from environmental sources. Coral cover was negatively correlated with FIB, macroalgal δ15N, and nutrient concentrations. Benthic salinity and temperature measurements detected daily tidal groundwater pulses which may explain these associations. While pollution scores revealed that sewage was largely concentrated along the shoreline, results showed some reached the reef and may be contributing to its declining condition.

Trade-offs in disease and bleaching susceptibility among two color morphs of the Hawaiian reef coral, Montipora capitata

Two threats impacting coral reefs are bleaching and disease, and differential susceptibility to both exists among and within coral taxa. Bleaching resistance is commonly linked to the clade of endosymbiotic Symbiodinium, but may come at a cost to other biological traits. Montipora capitata is an Indo-Pacific reef-building coral with two color morphs, red and orange, which harbor different clades of Symbiodinium. We explored whether these color morphs displayed differences in bleaching/disease susceptibility and other biological traits (growth rate, reproductive output, and lipid content). We found a trade-off between disease and bleaching susceptibility. The orange morph had significantly higher disease prevalence, whereas the red morph had significantly higher bleaching prevalence. Thermal stress experiments found that bleaching and loss of photochemical efficiency occurred significantly faster in the red morph, but at normal temperatures, the red morph had a significantly higher growth rate. Higher abundance of the red morph in the field suggests that disease resistance is a more successful strategy in the absence of thermal stress events. The orange morph may better tolerate increases in sea temperatures, but may not persist due to decreased growth rate and increased disease susceptibility. Trade-offs in response to stressors highlight the need to consider local and global threats to coral reefs.

New evidence of Hawaiian coral reef drowning in response to meltwater pulse-1A

Fossil coral reefs are valuable recorders of glacio-eustatic sea-level changes, as they provide key temporal information on deglacial meltwater pulses (MWPs). The timing, rate, magnitude, and meltwater source of these sea-level episodes remain controversial, despite their importance for understanding ocean-ice sheet dynamics during periods of abrupt climatic change. This study revisits the west coast of the Big Island of Hawaii to investigate the timing of the −150 m H1d terrace drowning off Kawaihae in response to MWP-1A. We present eight new calibrated 14C-AMS ages, which constrain the timing of terrace drowning to at or after 14.75 + 0.33/-0.42 kyr BP, coeval with the age of reef drowning at Kealakekua Bay (U-Th age 14.72 ± 0.10 kyr BP), 70 kms south along the west coast. Integrating the chronology with high-resolution bathymetry and backscatter data, detailed sedimentological analysis, and paleoenvironmental interpretation, we conclude the H1d terrace drowned at the same time along the west coast of Hawaii in response to MWP-1A. The timing of H1d reef drowning is within the reported uncertainty of the timing of MWP-1A interpreted from the IODP Expedition 310 Tahitian reef record.

Follow that fish: Uncovering the hidden blue economy in coral reef fisheries.

Despite their importance for human well-being, nearshore fisheries are often data poor, undervalued, and underappreciated in policy and development programs. We assess the value chain for nearshore Hawaiian coral reef fisheries, mapping post-catch distribution and disposition, and quantifying associated monetary, food security, and cultural values. We estimate that the total annual value of the nearshore fishery in Hawaiʻi is $10.3-$16.4 million, composed of non-commercial ($7.2-$12.9 million) and commercial ($2.97 million licensed + $148,500-$445,500 unlicensed) catch. Hawaii’s nearshore fisheries provide >7 million meals annually, with most (>5 million) from the non-commercial sector. Over a third (36%) of meals were planktivores, 26% piscivores, 21% primary consumers, and 18% secondary consumers. Only 62% of licensed commercial catch is accounted for in purchase reports, leaving 38% of landings unreported in sales. Value chains are complex, with major buyers for the commercial fishery including grocery stores (66%), retailers (19%), wholesalers (14%), and restaurants (<1%), who also trade and sell amongst themselves. The bulk of total nearshore catch (72–74%) follows a short value chain, with non-commercial fishers keeping catch for household consumption or community sharing. A small amount (~37,000kg) of reef fish—the equivalent of 1.8% of local catch—is imported annually into Hawaiʻi, 23,000kg of which arrives as passenger luggage on commercial flights from Micronesia. Evidence of exports to the US mainland exists, but is unquantifiable given existing data. Hawaiian nearshore fisheries support fundamental cultural values including subsistence, activity, traditional knowledge, and social cohesion. These small-scale coral reef fisheries provide large-scale benefits to the economy, food security, and cultural practices of Hawaiʻi, underscoring the need for sustainable management. This research highlights the value of information on the value chain for small-scale production systems, making the hidden economy of these fisheries visible and illuminating a range of conservation interventions applicable to Hawaiʻi and beyond.

A budget of algal production and consumption by herbivorous fish in an herbivore fisheries management area, Maui, Hawaii

AbstractThe relative rates of carbon fixed by primary producers vs. consumption by primary consumers shape the community of organisms in ecosystems. On coral reefs, it is important to understand the demography of algae, given known competitive dynamics with reef‐building corals. Numerous studies have shown that fleshy algal abundance is enhanced in the absence of top‐down control by herbivores on coral reefs. However, fewer studies have quantified and compared rates of production by the benthic fleshy algal community and consumption by herbivores. Here, we estimate a budget for fleshy algal growth and herbivorous fish consumption on a Hawaiian coral reef based upon integration of field‐measured and taxonomically specific variables. Data were collected at Kahekili Herbivore Fisheries Management Area, Maui, established in 2009, in which taking of herbivorous fish and urchins is prohibited. Daily algal production was determined by quantifying benthic community composition, standing stock of algal biomass, and growth rates of common algal components. Consumption was determined using distributions of biomass and size classes of herbivorous fish species, consumption rates of herbivores on different algal species, and herbivore bite sizes. Our results show that throughout the first five years of herbivore protection, algal production consistently exceeded the grazing capacity of the herbivorous fish assemblage, but by a diminishing margin since 2010 (consumption 20.8% of production) to the end of the study in 2014 (consumption 67.0% of production). Further, larger size classes of herbivorous fishes in the scraper/excavator herbivore guild contributed more to consumption in later years, which could have additional feedbacks that promote reef‐building taxa. Projecting the budget using data from a neighboring decades‐long protected herbivorous fish assemblage indicated that the production and consumption budget for Kahekili could become balanced in future with continued management.

Coral reef soundscapes may not be detectable far from the reef.

Biological sounds produced on coral reefs may provide settlement cues to marine larvae. Sound fields are composed of pressure and particle motion, which is the back and forth movement of acoustic particles. Particle motion (i.e., not pressure) is the relevant acoustic stimulus for many, if not most, marine animals. However, there have been no field measurements of reef particle motion. To address this deficiency, both pressure and particle motion were recorded at a range of distances from one Hawaiian coral reef at dawn and mid-morning on three separate days. Sound pressure attenuated with distance from the reef at dawn. Similar trends were apparent for particle velocity but with considerable variability. In general, average sound levels were low and perhaps too faint to be used as an orientation cue except very close to the reef. However, individual transient sounds that exceeded the mean values, sometimes by up to an order of magnitude, might be detectable far from the reef, depending on the hearing abilities of the larva. If sound is not being used as a long-range cue, it might still be useful for habitat selection or other biological activities within a reef.