Coral larvae move toward reef sounds

Free-swimming larvae of tropical corals go through a critical life-phase when they return from the open ocean to select a suitable settlement substrate. During the planktonic phase of their life cycle, the behaviours of small coral larvae (<1 mm) that influence settlement success are difficult to observe in situ and are therefore largely unknown. Here, we show that coral larvae respond to acoustic cues that may facilitate detection of habitat from large distances and from upcurrent of preferred settlement locations. Using in situ choice chambers, we found that settling coral larvae were attracted to reef sounds, produced mainly by fish and crustaceans, which we broadcast underwater using loudspeakers. Our discovery that coral larvae can detect and respond to sound is the first description of an auditory response in the invertebrate phylum Cnidaria, which includes jellyfish, anemones, and hydroids as well as corals. If, like settlement-stage reef fish and crustaceans, coral larvae use reef noise as a cue for orientation, the alleviation of noise pollution in the marine environment may gain further urgency.Mark J. A. Vermeij, Kristen L. Marhaver, Chantal M. Huijbers, Ivan Nagelkerken and Stephen D. Simpso

Urbanisation alters processing of marine carrion on sandy beaches

Sandy shores are highly attractive for urban development. Urbanisation of beaches is, however, not without environmental consequences, but metrics of ecological change along metropolitan coasts are poorly developed. This lack of metrics impedes environmentally effective coastal zone management. Here we test the effects of urbanisation on a pivotal ecological process on sandy shorelines: carrion removal by vertebrate scavengers. Scavenging is a key process linking ocean and land ecosystems via animal carcasses deposited on beaches and subsequently consumed by mostly terrestrial animals. In this study, experimentally placed fish carcasses were monitored with motion-triggered cameras on urban and rural beaches on the east coast of Australia. Urbanisation substantially influenced the structure of the scavenger guild and the frequency of carrion removal within 24 h. Large raptors were abundant on rural beaches where they rapidly detected and consumed carrion (98% of carcasses removed within 24 h). We detected no scavenging activity of raptors on urban beaches, where scavenging birds of prey were functionally replaced by nocturnally foraging, non-native mammals (red fox, Vulpes vulpes) or feral species (cats, dogs) known to threaten beach-dwelling wildlife. Our findings emphasise the value of non-urbanised coastal dunes and sandy beaches as important feeding sites and habitats for iconic and threatened raptors. We also show that human changes in coastal land-use profoundly alter ecological structures and processes on sandy shorelines, aspects that warrant explicit inclusion in landscape management and planning of the coastal strip

Appendix A. Description of the spatial simulation model.

Description of the spatial simulation model

Appendix E. Optimal fitted model for observed fish counts on Bermuda and Grand Cayman.

Optimal fitted model for observed fish counts on Bermuda and Grand Cayman

Map of the study area.

<p>Reef contours (approx. 17 m depth) are indicated by thick black lines. Hatched area indicates location of the mangrove forest. SGK  =  sampling site at the shoreline seagrass bed at Kunduchi. Nearshore reefs fringe the island of Mbudya, while offshore reefs are located at ‘Far Reef’ and ‘Gold Reef’.</p

Appendix D. Optimization of the size-dependent dispersal model.

Optimization of the size-dependent dispersal model

Appendix B. Multivariate analysis of δ13C and δ18O signatures of fish otoliths.

Multivariate analysis of δ13C and δ18O signatures of fish otoliths

Limited functional redundancy in vertebrate scavenger guilds fails to compensate for the loss of raptors from urbanized sandy beaches

Aim: Globally, urbanization is one of the most widespread, intense and ecologically destructive forms of landscape transformation, and it is often concentrated in coastal areas. Theoretically, species losses attributable to urbanization are predicted not to alter overall ecosystem function if functional redundancy (i.e. replacement of function by alternative species) compensates for such losses. Here, we test this expectation by measuring how coastal urbanization affects scavenger guilds on sandy beaches and whether changes in guild composition result either in an overall loss of scavenging efficiency, or in functional compensation under alternative guild structures, maintaining net ecosystem functioning. Location: Fourteen beaches along the east coast of Australia with variable levels of urbanization. Methods: Scavenging communities and rates of carrion removal were determined using motion-triggered cameras at the beach-dune interface. Results: A substantial shift in the community structure of vertebrate scavengers was associated with gradients in urbanization. Iconic and functionally important raptors declined precipitously in abundance on urban beaches. Importantly, other vertebrates usually associated with urban settings (e.g. dogs, foxes, corvids) did not functionally replace raptors. In areas where &lt; 15% of the abutting land had been developed into urban areas, carcass removal by scavengers was often complete, but always &gt; 70%. Conversely, on beaches bordering coastal cities with &lt; 40% of natural vegetation remaining, two-thirds of fish carcasses remained uneaten by scavengers. Raptors removed 70-100% of all deployed fish carcasses from beaches with &lt; 8% urban land cover, but this number dropped significantly with greater levels of urbanization and was not compensated by other scavenger species in urban settings. Main conclusions: There is limited functional redundancy in vertebrate scavenger communities of sandy beach ecosystems, which impacts the system\u27s capacity to mitigate the ecological consequences of detrimental landscape transformations

Appendix C. Combined results from the spatial simulation model and the visual census survey for the best fit of the observed fish size distributions in correspondence with a median dispersal distance of 10.7 km/yr.

Combined results from the spatial simulation model and the visual census survey for the best fit of the observed fish size distributions in correspondence with a median dispersal distance of 10.7 km/yr

Estimated contribution (% ± SD) from Maximum Likelihood Analysis of different potential juvenile habitats to adult nearshore and offshore reef populations of three reef fish species, and large juvenile (>15 cm TL) <i>L. harak</i> in seagrass beds.

<p>Classification success is based on a quadratic discriminant function analysis using jack-knife classification to examine the success of assigning individuals to their known origin. Both analyses are based on δ¹³C and δ¹⁸O values combined. Because seagrass and mangrove habitat signatures did not differ for <i>L. lentjan</i>, they had to be combined for this analysis. CR  =  coral reef; SG  =  seagrass bed; MG  =  mangroves.</p