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A high-resolution 3D biophysical model was used to investigate the patterns of larval transport for an important commercial and recreational temperate fish, snapper Pagrus auratus, from a well-established marine reserve (Cape Rodney to Okakari Point marine reserve, CROP), and spawning ground. Our focus was to study the effects of local hydrodynamics, contrasting larval vertical behaviours and changing El Nino-Southern Oscillation (ENSO) cycles (via their effect on wind forcing) on the potential larval supply to adjacent non-protected areas. The model suggests the CROP marine reserve provides significant larval subsidies within a relatively small scale (≤40 km), the details of which depend on larval behaviour and ENSO patterns. Changing ENSO patterns mostly affected the dispersal direction of larvae, while larval behaviour was a strong driver only under La Nina conditions. Modelling suggests that under El Nino conditions, snapper larvae are more likely to settle successfully and hence make a strong contribution to surrounding fished stocks. Understanding the contribution of MPAs to fisheries management will require multiple approaches. Modelling will help identify the strength of contributing physical and biological factors, and in due course enable site- and time-specific examples of larval subsidy to be generalised.

Underwater sound emanating from reefs has been shown to be attractive to pre-set- tlement larval stages of fish and crustaceans, but its ecological importance depends on the range at which this cue can be detected by these larvae. Here we show, through field measurement and modelling, that the spatially extended sound source of a reef creates a surrounding zone, which extends for a distance offshore equal to the length of the reef, within which there is almost no loss in the sound level. Beyond this zone, the sound level decreases with cylindrical spreading plus any seafloor attenuation. This 'reef effect' means that the sound from a reef would be detectable at a much greater distance from the reef than would be estimated from a spot measurement near the reef or by using theoretical models of sound spreading from a point source. The greater reach for sound emanating from a reef means that reef noise could play a greater role in directing larval reef fishes and crabs to suitable settlement habitats than previously estimated.

There is evidence that ambient underwater sound is used by some pelagic larval reef fishes and decapods as a guide to direct them toward coastal areas. It would be advantageous to these organisms if they were also able to use sound to remotely identify suitable settlement habitats. However, it is unknown whether different coastal habitats produce different sounds that would be capable of providing distinctive cues for larvae. This study identified marked differences in the char- acteristics of ambient underwater sound at 3 distinct types of coastal habitat: a macroalgal-dominated reef, a sea urchin-dominated reef, and a sandy beach. The sea urchin-dominated reef habitat pro- duced sound that was significantly more intense overall in a biologically important frequency band (800 to 2500 Hz), compared with that from macroalgal-dominated reefs and beach habitats. The sound produced by snapping shrimp also exhibited marked differences among habitat types, with the sea urchin-dominated reef having significantly more snaps than the macroalgal-dominated reef or beach habitat. Many of the differences in the sound produced by the 2 reef habitats became more apparent at dusk compared with noon. This study provides evidence that there are significant differ- ences in the spectral and temporal composition of ambient sound associated with different coastal habitat types over relatively short spatial scales. An acoustic cue that conveys both directional and habitat quality information that is transmitted considerable distances offshore would have the poten- tial to be of immense value to the pelagic larval stage of a coastal organism attempting to remotely locate a suitable habitat in which to settle.

The marine environment imposes severe constraints on the means by which location information can be obtained from submerged, freely swimming animals. Standard methods of tracking marine organisms are often labour intensive, expensive, or of low spatial and temporal resolution. Here, we describe a new method by which larger species of fish that live in shallow or surface waters can be tracked using an inexpensive telemetry device based on the global positioning system (GPS). We fixed small GPS data-logger units configured to record position fixes at 90 to 150 s intervals to low-drag tow-bodies and then attached these units by means of a tether to New Zealand eagle rays Myliobatis tenuicaudatus. After deployment periods lasting up to 29 h we recovered the tracking gear and downloaded the location data, which were stored onboard. The GPS units worked well, with mean fix-success rates >90%, and allowed accurate reconstruction of the movements of the rays throughout an estuary in Northland, New Zealand. Although our method is restricted to animals that swim on or near the surface of the water, it does provide a means of cheaply describing the movement patterns of suitable species for substantial periods of time at heretofore unprecedented spatial and temporal scales.

Ambient sound intensity in coastal waters typically increases by as much as 2 to 3 orders of magnitude (20 to 30 dB) immediately after sunset and before sunrise in what is known as a dawn and evening chorus. The dominant feature of the chorus is most often a dramatic increase in spec- trum level usually in a narrow frequency range of around 400 to 4000 Hz. While the sources of some choruses have been identified, the sources of many choruses remain unidentified. Here we confirm that in New Zealand, the sound is the feeding noises of sea urchins for which frequencies in the range of 800 to 2800 Hz are amplified by the ovoid calcareous skeleton, or 'test', of urchins acting as a Helmholtz resonator. Furthermore, the timing of the dawn and dusk choruses is related to the crepus- cular feeding activity of sea urchins. Underwater sound recordings from individual sea urchins of a range of sizes confirm earlier speculation that the urchin test acts as a Helmholtz resonance chamber capable of generating sufficient acoustic power to create these choruses. These results indicate the potential importance of coastal urchin populations as a major contributor to the underwater choruses, which appear to be important in assisting the larvae of key reef species, such as fishes, crabs, and lobsters, to locate suitable settlement sites.