The sound of recovery: Coral reef restoration success is detectable in the soundscape

Natural soundscapes of lowland river habitats and the potential threat of urban noise pollution to migratory fish

Migratory fish populations have experienced great declines, and considerable effort have been put into reducing stressors, such as chemical pollution and physical barriers. However, the importance of natural sounds as an information source and potential problems caused by noise pollution remain largely unexplored. The spatial distribution of sound sources and variation in propagation characteristics could provide migratory fish with acoustic cues about habitat suitability, predator presence, food availability and conspecific presence. We here investigated the relationship between natural soundscapes and local river conditions and we explored the presence of human-related sounds in these natural soundscapes. We found that 1a) natural river sound profiles vary with river scale and cross-sectional position, and that 1b) depth, width, water velocity, and distance from shore were all significant factors in explaining local soundscape variation. We also found 2a) audible human activities in almost all our underwater recordings and urban and suburban river parts had elevated sound levels relative to rural river parts. Furthermore, 2b) daytime levels were louder than night time sound levels, and bridges and nearby road traffic were much more prominent with diurnal and weekly patterns of anthropogenic noise in the river systems. We believe our data show high potential for natural soundscapes of low-land river habitat to serve as important environmental cues to migratory fish. However, anthropogenic noise may be particularly problematic due to the omnipresence, and relatively loud levels relative to the modest dynamic range of the natural sound sources, in these slow-flowing freshwater systems.

Characterizing offshore polar ocean soundscapes using ecoacoustic intensity and diversity metrics

Polar offshore environments are considered the last pristine soundscapes, but accelerating climate change and increasing human activity threaten their integrity. In order to assess the acoustic state of polar oceans, there is the need to investigate their soundscape characteristics more holistically. We apply a set of 14 ecoacoustic metrics (EAMs) to identify which metrics are best suited to reflect the characteristics of disturbed and naturally intact polar offshore soundscapes. We used two soundscape datasets: (i) the Arctic eastern Fram Strait (FS), which is already impacted by anthropogenic noise, and (ii) the quasi-pristine Antarctic Weddell Sea (WS). Our results show that EAMs when applied in concert can be used to quantitatively assess soundscape variability, enabling the appraisal of marine soundscapes over broad spatiotemporal scales. The tested set of EAMs was able to show that the eastern FS, which is virtually free from sea ice, lacks seasonal soundscape dynamics and exhibits low acoustic complexity owing to year-round wind-mediated sounds and anthropogenic noise. By contrast, the WS exhibits pronounced seasonal soundscape dynamics with greater soundscape heterogeneity driven in large part by the vocal activity of marine mammal communities, whose composition in turn varies with the prevailing seasonal sea ice conditions.

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.

Multidimensional comparison of underwater soundscapes using the soundscape codea)

The soundscape of a given habitat is a product of its physical environment, human activity, and presence of soniferous marine life, which can be used to understand ecosystem processes, habitat quality, and biodiversity. Shallow coral habitats are hotspots of biodiversity and marine life. Deep-sea coral environments, in comparison, are generally poorly understood. Four soundscapes along the U.S. Outer Continental Shelf (OCS) and one soundscape from the Great Barrier Reef were quantified to explore how differences in habitat, depth, and substrate manifest acoustically. Comparisons were made between (1) deep, cold-water and shallow, warm-water coral reefs and (2) deep-sea coral and sandy bottom habitats. Application of the soundscape code to recordings in each location seeded cluster analyses of soundscape metrics and an assessment of daily trends to quantitatively compare the soundscapes. The shallow, tropical reef soundscape differed from the deep-sea soundscapes in amplitude and impulsiveness. Differences in soundscape properties among the deep-sea soundscapes suggested cold-water coral sites produce different soundscapes than the deep sites without live hard bottom. This initial assessment of deep-sea soundscapes along the U.S. OCS provides baseline acoustic properties in a region likely to experience changes due to climate and human use.

Effects of anthropogenic noise and natural soundscape on larval fish behavior in four estuarine species

The larval and post-larval forms of many marine organisms, such as oysters, crabs, lobster, coral, and fish, utilize ambient acoustic cues to orient, settle, or metamorphose. In this study, the effect of anthropogenic and ambient sounds on the orientation behavior of four larval estuarine fishes was examined in a controlled, laboratory experiment. Pre-settlement size red drum Sciaenops ocellatus, southern flounder Paralichthys lethostigma, spotted seatrout Cynoscion nebulosus, and Florida blenny Chasmodes saburrae larvae were exposed to four sound treatments-control, estuarine soundscape, seismic airguns, and large-ship passage-in a linear acoustic chamber. Initial significant (p < 0.05) avoidance of airguns was observed in three of the four species (all but the Florida blenny), but habituation to this sound occurred as the experiment progressed. All species avoided ship passage sounds; however, the avoidance behavior was not significant. Interestingly, none of the species studied were significantly attracted to the acoustic cues alone of the estuarine soundscape; in fact, three of the four species spent less time near the speaker when it was broadcast. These results suggest that larval fish can potentially habituate to anthropogenic noise relatively quickly (<10 min). Understanding how sounds affect larval behavior is necessary because successful recruitment ultimately affects a population's success.

Toward a New Era of Coral Reef Monitoring

Coral reefs host some of the highest concentrations of biodiversity and economic value in the oceans, yet these ecosystems are under threat due to climate change and other human impacts. Reef monitoring is routinely used to help prioritize reefs for conservation and evaluate the success of intervention efforts. Reef status and health are most frequently characterized using diver-based surveys, but the inherent limitations of these methods mean there is a growing need for advanced, standardized, and automated reef techniques that capture the complex nature of the ecosystem. Here we draw on experiences from our own interdisciplinary research programs to describe advances in in situ diver-based and autonomous reef monitoring. We present our vision for integrating interdisciplinary measurements for select "case-study" reefs worldwide and for learning patterns within the biological, physical, and chemical reef components and their interactions. Ultimately, these efforts could support the development of a scalable and standardized suite of sensors that capture and relay key data to assist in categorizing reef health. This framework has the potential to provide stakeholders with the information necessary to assess reef health during an unprecedented time of reef change as well as restoration and intervention activities.

Coral micro-fragmentation assays for optimizing active reef restoration efforts

The global decline of coral reefs has driven considerable interest in active coral restoration. Despite their importance and dominance on mature reefs, relatively few coral restoration projects use slower growth forms like massive and encrusting coral species. Micro-fragmentation can increase coral cover by orders of magnitude faster than natural growth, which now allows cultivation of slow growing massive forms and shows promise and flexibility for active reef restoration. However, the major causes of variation in growth and survival of outplanted colonies remain poorly understood. Here, we report simple outplanting assays to aid in active reef restoration of slower growing species and increase the likelihood of restoration success. We used two different micro-fragmentation assays. Pyramid assays were used to examine variation associated with fragment size (ranging from ≈1-9 cm2), nursery residence time (for both in-situ and ex-situ nurseries), and 2D vs. 3D measurements of growth. Block assays were used to examine spatial variation among individual performance at outplanting sites in the field. We found 2D and 3D measurements correlated well, so measured survivorship and growth using top-down planar images for two of the main Hawaiian reef building corals, the plating Montipora capitata and the massive Porites compressa. Pyramid assays housed and outplanted from the in-situ nursery showed no effect of residence time or size on overall survivorship or growth for either species. Results from the ex-situ nursery, however, varied by species, with P. compressa again showing no effect of nursery residence time or size on survivorship or growth. In contrast, nursery culture resulted in improved survivorship of small M. capitata fragments, but net growth showed a weak positive effect of nursery time for medium fragments. Small fragments still suffered higher mortality than either medium or large fragments. Due to their lower mortality, medium fragments (≈3 cm2) appear to be the best compromise between growth and survivorship for outplanting. Likewise, given weak positive gains relative to the investment, our results suggest that it could be more cost-effective to simply outplant medium fragments as soon as possible, without intermediate culture in a nursery. Furthermore, the block assay revealed significant differences in survivorship and growth among sites for individuals of both species, emphasizing the importance of considering spatial variation in coral survival and growth following outplanting. These results highlight the value of using short-term micro-fragmentation assays prior to outplanting to assess size, and location specific performance, optimizing the efficiency of active reef restoration activities and maximizing the probability of success for active coral restoration projects.