Nocturnal relocation of adult and juvenile coral reef fishes in response to reef noise

Juvenile and adult reef fishes often undergo migration, ontogenic habitat shifts, and nocturnal foraging movements. The orientation cues used for these behaviours are largely unknown. In this study, the use of sound as an orientation cue guiding the nocturnal movements of adult and juvenile reef fishes at Lizard Island, Great Barrier Reef was examined. The first experiment compared the movements of fishes to small patch reefs where reef noise was broadcast, with those to silent reefs. No significant responses were found in the 79 adults that were collected, but the 166 juveniles collected showed an increased diversity each morning on the reefs with broadcast noise, and significantly greater numbers of juveniles from three taxa (Apogonidae, Gobiidae and Pinguipedidae) were collected from reefs with broadcast noise. The second experiment compared the movement of adult and juvenile fishes to reefs broadcasting high (>570 Hz), or low (<570 Hz) frequency reef noise, or to silent reefs. Of the 122 adults collected, the highest diversity was seen at the low frequency reefs; and adults from two families (Gobiidae and Blenniidae) preferred these reefs. A similar trend was observed in the 372 juveniles collected, with higher diversity at the reefs with low frequency noises. This preference was seen in the juvenile apogonids; however, juvenile gobiids were attracted to both high and low sound treatments equally, and juvenile stage Acanthuridae preferred the high frequency noises. This evidence that juvenile and adult reef fishes orientate with respect to the soundscape raises important issues for management, conservation and the protection of sound cues used in natural behaviour.     

Juvenile coral reef fish use sound to locate habitats

There is limited knowledge of the orientation cues used by reef fish in their movement among different habitats, especially those cues used during darkness. Although acoustic cues have been found to be important for settlement-stage fish as they seek settlement habitats, only a small number of studies support the possible role of acoustic cues in the orientation of post-settled and adult reef fish. Therefore, the aim of this study was to determine whether habitat-specific acoustic cues were involved in the nocturnal movements of juvenile reef fish to small experimental patch reefs that were broadcasting sound previously recorded from different habitats (Fringing Reef, Lagoon, Silent). Juvenile fish arriving at each patch reef were caught the next morning by divers and were identified. There were a greater number of occasions when juvenile fish (from all species together) moved onto the patch reefs broadcasting Fringing Reef and Lagoon sound (43 and 38%, respectively) compared to Silent reefs (19%) (χ² = 33.5; P < 0.05). There were significantly more occasions when juvenile fish from the family Nemipteridae were attracted to the patch reefs broadcasting Lagoon sound (63%) versus those reefs broadcasting either Fringing Reef sound (31%) or Silent (6%). In contrast, there were more occasions when juveniles from the family Pomacentridae were attracted to the patch reefs broadcasting Fringing Reef sound (56%) than either Lagoon (24%) or Silent patch reefs (20%) (χ² = 19.5; P < 0.05). These results indicate that some juvenile fish use specific habitat sounds to guide their nocturnal movements. Therefore, the fish are able to not only use the directional information contained in acoustic cues, but can also interpret the content of the acoustic signals for relevant habitat information which is then used in their decision-making for orientation.     

Terrestrial chemical cues help coral reef fish larvae locate settlement habitat surrounding islands

Understanding the degree of connectivity between coastal and island landscapes and nearby coral reefs is vital to the integrated management of terrestrial and marine environments in the tropics. Coral reef fish are capable of navigating appropriate settlement habitats following their pelagic larval phase, but the mechanisms by which they do this are unclear. The importance of olfactory cues in settlement site selection has been demonstrated, and there is increasing evidence that chemical cues from terrestrial sources may be important for some species. Here, we test the olfactory preferences of eight island-associated coral reef fish recruits and one generalist species to discern the capacity for terrestrial cue recognition that may aid in settlement site selection. A series of pairwise choice experiments were used to evaluate the potential role that terrestrial, water-borne olfactory cues play in island-reef recognition. Olfactory stimuli tested included near-shore water, terrestrial rainforest leaf litter, and olfactory cues collected from different reef types (reefs surrounding vegetated islands, and reefs with no islands present). All eight island-associated species demonstrated high levels of olfactory discrimination and responded positively toward olfactory cues indicating the presence of a vegetated island. We hypothesize that although these fish use a suite of cues for settlement site recognition, one mechanism in locating their island/reef habitat is through the olfactory cues produced by vegetated islands. This research highlights the role terrestrial olfactory cues play in large-scale settlement site selection and suggests a high degree of ecosystem connectivity.     

Assessing the accuracy of acoustic seabed classification for mapping coral reef environments in South Florida (Broward County, USA)

The Atlantic coast of Broward County, Florida (USA) is paralleled by a series of progressively deeper, shore-parallel coral reef communities. Two of these reef systems are drowned early Holocene coral reefs of 5 ky and 7 ky uncorrected radiocarbon age. Despite the case of access to these reefs, and their major contribution to the local economy, accurate benthic habitat maps of the area are not available. Ecological studies have shown that different benthic communities (i.e. communities composed of different biological taxa) exist along several spatial gradients on all reefs. Since these studies are limited by time and spatial extent, acoustic surveys with the QTCView V bottom classification system based on a 50 kHz transducer were used as an alternative method of producing habitat maps. From the acoustic data of a 3.1 km(2) survey area, spatial prediction maps were created for the area. These were compared with habitat maps interpreted from in situ data and Laser Airborne Depth Sounder (LADS) bathymetry, in order to ground-truth the remotely sensed data. An error matrix was used to quantitatively determine the accuracy of the acoustically derived spatial prediction model against the maps derived from the in situ and LADS data sets. Confusion analysis of 100 random points showed that the system was able to distinguish areas of reef from areas of rubble and sand with an overall accuracy of 61%. When asked to detect more subtle spatial differences, for example, those between distinct reef communities, the classification was only about 40% accurate. We discuss to what degree a synthesis of acoustic and in situ techniques can provide accurate habitat maps in coral reef environments, and conclude that acoustic methods were able to reflect the spatial extent and composition of at least three different biological communities.     

Behavioural response thresholds in New Zealand crab megalopae to ambient underwater sound

A small number of studies have demonstrated that settlement stage decapod crustaceans are able to detect and exhibit swimming, settlement and metamorphosis responses to ambient underwater sound emanating from coastal reefs. However, the intensity of the acoustic cue required to initiate the settlement and metamorphosis response, and therefore the potential range over which this acoustic cue may operate, is not known. The current study determined the behavioural response thresholds of four species of New Zealand brachyuran crab megalopae by exposing them to different intensity levels of broadcast reef sound recorded from their preferred settlement habitat and from an unfavourable settlement habitat. Megalopae of the rocky-reef crab, Leptograpsus variegatus, exhibited the lowest behavioural response threshold (highest sensitivity), with a significant reduction in time to metamorphosis (TTM) when exposed to underwater reef sound with an intensity of 90 dB re 1 μPa and greater (100, 126 and 135 dB re 1 μPa). Megalopae of the mud crab, Austrohelice crassa, which settle in soft sediment habitats, exhibited no response to any of the underwater reef sound levels. All reef associated species exposed to sound levels from an unfavourable settlement habitat showed no significant change in TTM, even at intensities that were similar to their preferred reef sound for which reductions in TTM were observed. These results indicated that megalopae were able to discern and respond selectively to habitat-specific acoustic cues. The settlement and metamorphosis behavioural response thresholds to levels of underwater reef sound determined in the current study of four species of crabs, enables preliminary estimation of the spatial range at which an acoustic settlement cue may be operating, from 5 m to 40 km depending on the species. Overall, these results indicate that underwater sound is likely to play a major role in influencing the spatial patterns of settlement of coastal crab species.     

Fish with Chips: Tracking Reef Fish Movements to Evaluate Size and Connectivity of Caribbean Marine Protected Areas

Coral reefs and associated fish populations have experienced rapid decline in the Caribbean region and marine protected areas (MPAs) have been widely implemented to address this decline. The performance of no-take MPAs (i.e., marine reserves) for protecting and rebuilding fish populations is influenced by the movement of animals within and across their boundaries. Very little is known about Caribbean reef fish movements creating a critical knowledge gap that can impede effective MPA design, performance and evaluation. Using miniature implanted acoustic transmitters and a fixed acoustic receiver array, we address three key questions: How far can reef fish move? Does connectivity exist between adjacent MPAs? Does existing MPA size match the spatial scale of reef fish movements? We show that many reef fishes are capable of traveling far greater distances and in shorter duration than was previously known. Across the Puerto Rican Shelf, more than half of our 163 tagged fish (18 species of 10 families) moved distances greater than 1 km with three fish moving more than 10 km in a single day and a quarter spending time outside of MPAs. We provide direct evidence of ecological connectivity across a network of MPAs, including estimated movements of more than 40 km connecting a nearshore MPA with a shelf-edge spawning aggregation. Most tagged fish showed high fidelity to MPAs, but also spent time outside MPAs, potentially contributing to spillover. Three-quarters of our fish were capable of traveling distances that would take them beyond the protection offered by at least 40–64% of the existing eastern Caribbean MPAs. We recommend that key species movement patterns be used to inform and evaluate MPA functionality and design, particularly size and shape. A re-scaling of our perception of Caribbean reef fish mobility and habitat use is imperative, with important implications for ecology and management effectiveness.     

Application of Acoustic Telemetry to Assess Residency and Movements of Rockfish and Lingcod at Created and Natural Habitats in Prince William Sound

Loss and/or degradation of nearshore habitats have led to increased efforts to restore or enhance many of these habitats, particularly those that are deemed essential for marine fishes. Copper rockfish (Sebastes caurinus) and lingcod (Ophiodon enlongatus) are dominant members of the typical reef fish community that inhabit rocky and high-relief substrates along the Pacific Northwest. We used acoustic telemetry to document their residency and movements in the nearshore waters of Prince William Sound, Alaska in order to assess use of created reef habitat in an individual-based manner. A total of 57 fish were surgically implanted with acoustic transmitters. Forty-five fish were captured and monitored in three habitats: artificial reef, low-relief natural reef, and patchy high-relief natural reef. Within each habitat, both rockfish and lingcod exhibited long periods of residency with limited movements. Twelve rockfish were captured at the natural reefs and displaced a distance of 4.0 km to the artificial reef. Five of the 12 rockfish returned within 10 d of their release to their initial capture site. Another five of the 12 displaced fish established residency at the artificial reef through the duration of our study. Our results suggest the potential for artificial reefs to provide rockfish habitat in the event of disturbances to natural habitat.     

Artificial reef design affects benthic secondary productivity and provision of functional habitat

1. Novel hard substratum, introduced through offshore developments, can provide habitat for marine species and thereby function as an artificial reef. To predict the ecological consequences of deploying offshore infrastructure, and sustainably manage the installation of new structures, interactions between artificial reefs and marine ecosystem functions and services must be understood. This requires quantitative data on the relationships between secondary productivity and artificial reef design, across all trophic levels. Benthic secondary productivity is, however, one of the least studied processes on artificial reefs.
2. In this study, we show that productivity rates of a common suspension feeder, Flustra foliacea (Linnaeus 1758), were 2.4 times higher on artificial reefs constructed from “complex” blocks than on reefs constructed from “simple” blocks, which had a smaller surface area.
3. Productivity rates were highest on external areas of reefs. Productivity rates decreased by 1.56%, per cm distance into the reef on complex reefs and 2.93% per cm into the reef on simple block reefs. The differences in productivity rates between reefs constructed from simple and complex blocks are assumed to reflect different current regimes and food supply between the external and internal reef areas, according to reef type.
4. Synthesis and applications. Our results show that artificial reef design can affect secondary productivity at low trophic levels. We demonstrate that the incorporation of voids into reef blocks can lead to a greater proportion of the structure serving as functional habitat for benthic species. By including such modifications into the design of artificial reefs, it may be possible to increase the overall productivity capacity of artificial structures.

     

Habitat associations of juvenile fish at Ningaloo Reef, Western Australia: the importance of coral and algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority.     

Fish assemblages on artificial and natural reefs in the Flower Garden Banks National Marine Sanctuary, USA

 Visual censusing was used to characterize fish assemblages on artificial and natural reefs located within the boundaries of the Flower Garden Banks National Marine Sanctuary (FGBNMS) in the northwestern Gulf of Mexico. Emphasis was placed on determining spatial and temporal patterns in habitat utilization by fishes on an offshore artificial reef (Mobil Platform HI-A389A). Overall, 43 species were observed during diurnal surveys in the upper 24 m of the artificial reef. Midwater pelagic fishes (i.e., carangids and scombrids) accounted for over 50% of all taxa enumerated on the artificial reef; however, these taxa were transient members of the assemblage and were observed infrequently. Labrids, pomacentrids, and serranids were the dominant reef-dependent taxa. Distinct trends in vertical, diel, and seasonal abundances were observed for juvenile and adult fishes. Of the three designated depth zones (upper 1.5–9.0, middle 9.0–16.5; lower 16.5–24.0 m), abundance and species diversity were lowest in the upper zone. Nocturnal counts were characterized by a marked reduction or complete absence of most species, due in part to twilight cover-seeking and movement activities. Seasonal variation in community composition and species abundance (May versus September) was primarily due to recruitment of juveniles (0-age fishes) to the artificial reef in late summer. Increases in total fish abundance (all taxa combined) coincided with both increasing habitat rugosity and degree of fouling. Species richness on natural coral reefs in the FGBNMS was higher than on the artificial reef. Unlike the artificial reef, fish assemblages on the natural reefs were dominated by a single family (Pomacentridae) which accounted for over 50% of all individuals observed. Accepted: 1 August 1996     

Cryptic species of cardinalfish with evidence for old and new divergence

Larval dispersal and limited knowledge of physical boundaries challenge our understanding of the processes that drive genetic divergence and potential speciation in the marine environment. Divergence, both within and between populations of marine taxa, is not uncommon, but spatial and temporal stability of observed genetic structure is not well known. Previously, we detected large genetic differences among populations of the cardinalfish species Ostorhinchus doederleini inhabiting adjacent coral reefs. Here, we determined the spatial and temporal persistence of these genetic structures over the course of ten consecutive generations. Using microsatellite markers, we detected large changes (genetic population distance, D _est, ranged from 0.04 to 0.46) in the genetic structure in some years, but some reefs maintained the same populations for nearly all sampling years. As this species’ life span does not exceed 1 yr, persistence of distinct reef populations suggests natal homing. Mitochondrial identity based on two mtDNA markers corroborates the nuclear genetic evidence for genetic differences large enough to constitute different clades and even cryptic species in O. doederleini, which, based on gross morphology, was thought to be a single taxon. Habitat specialization was observed in one clade that exclusively inhabited reef lagoons, while all clades could be observed on reef slopes. We suggest that local habitat recognition combined with local population recognition and selection against hybrids can form barriers that maintain a cryptic species complex.     

Performance of remote acoustic receivers within a coral reef habitat: implications for array design

Remote monitoring technologies are increasingly being implemented in the marine environment to better understand the movement patterns of taxa. Coral reefs are no exception. However, there is a paucity of information relating to the performance of acoustic receivers on coral reefs. Our results suggest that the detection performance of acoustic receivers may be significantly impacted by the unique nature of the reef environment. This study assessed the performance of passive acoustic receivers on a typical inner-shelf fringing reef, Orpheus Island, on the Great Barrier Reef, Australia. The detection range and diel performance variability of acoustic receivers was assessed using two parallel lines of 5 VR2W receivers spanning 125?m, deployed on the reef base and reef crest. Two 9-mm acoustic transmitters were moored at opposite ends of each receiver line. The working detection range for receivers was found to be approximately 90?m for the transmitter moored on the reef base and just 60?m for the transmitter moored on the reef crest. However, the detection range on the reef crest increased to 90?m when just the reef crest receivers were considered, highlighting importance of optimal receiver deployment. No diel patterns in receiver performance or detection capacities were detected, suggesting that no corrections are required when interpreting nocturnal versus diurnal activity patterns. We suggest that studies aiming for complete coverage of a site within a reef environment will require receivers in close (<100?m) proximity, and that the placement depth of receivers must be a major consideration, with shallow receivers exhibiting a greater detection range than those on the reef slope. Our results highlight the challenges imposed by coral reefs for acoustic telemetry and the importance of receiver placement for studies conducted within these habitats.     

Quantifying movement patterns for shark conservation at remote coral atolls in the Indian Ocean

Grey reef sharks (Carcharhinus amblyrhynchos) are apex predators found on many Indo-Pacific coral reefs, but little is known about their movement patterns and habitat requirements. We used acoustic telemetry to determine movements and habitat use of these sharks at the isolated Rowley Shoals atolls, 250 km off the coast of north-western Australia. We equipped 12 male and 14 female sharks ranging from 0.79 to 1.69 m in total length with transmitters that were detected by an array of 11 strategically placed receivers on two atoll reefs. Over 26,000 detections were recorded over the 325 days of receiver deployment. No sharks were observed to move between reefs. Receivers on the outer slopes of reefs provided nearly all (99%) of the detections. We found no differences in general attendance parameters due to size, sex or reef, except for maximum period of detection where larger sharks were detected over a longer period than smaller sharks. Male and female sharks were often detected at separate receivers at the outer slope habitat of one reef, suggesting sexual segregation, but this pattern did not occur at the second reef where males and females were detected at similar frequencies. We identified two patterns of daily behaviour: (1) sharks were present at the reef both day and night or (2) sharks spent more time in attendance during day than at night. Fast Fourier transforms identified 24-h cycles of attendance at the reef and a secondary peak of attendance at 12 h for most sharks, although no individuals shared the same attendance patterns. Our study provides baseline data that can be used to optimise the minimum area and habitat requirements for conservation of these apex predators.     

Spatial separation without territoriality in shark communities

Spatial separation within predator communities can arise via territoriality but also from competitive interactions among and within species. However, linking competitive interactions to predator distribution patterns is difficult and theoretical models predict different habitat selection patterns dependent on habitat quality and how competition manifests itself. While models generally consider competitors to be either equal in ability, or for one phenotype to have a fixed advantage over the other, few studies consider that an animal may only have a competitive advantage in specific habitats. We used  10 years of telemetry data, habitat surveys and behavioral experiments, to show spatial partitioning between and within two species of reef shark (grey reef Carcharhinus amblyrhinchos and blacktip reef sharks C. melanopterus) at an unfished Pacific atoll. Within a species, sharks remained within small ‘sub‐habitats’ with very few movements of individuals between sub‐habitats, which previous models have suggested could be caused by intra‐specific competition. Blacktip reef sharks were more broadly distributed across habitat types but a greater proportion used lagoon and backreef habitats, while grey reef sharks preferred forereef habitats. Grey reef sharks at a nearby atoll where blacktip reef sharks are absent, were distributed more broadly between habitat types than when both species were present. A series of individual‐based models predict that habitat separation would only arise if there are competitive interactions between species that are habitat‐specific, with grey reefs having a competitive advantage on the forereefs and blacktips in the lagoons and backreef. We provide compelling evidence that competition helps drive distribution patterns and spatial separation of a marine predator community, and highlight that competitive advantages may not be constant but rather dependent on habitats.     

Integrating multiple species connectivity and habitat quality into conservation planning for coral reefs

Incorporating connectivity into the design of marine protected areas (MPAs) has met with conceptual, theoretical, and practical challenges, which include: 1) the need to consider connectivity for multiple species with different dispersal abilities, and 2) the role played by variable habitat quality in determining the spatial patterns of connectivity. We propose an innovative approach, combining biophysical modeling with a routinely‐used tool for marine‐reserve design (Marxan), to address both challenges by using ecologically‐informed connectivity parameters. We showed how functional demographic connectivity for four candidate reef‐associated species with varying dispersal abilities and a suite of connectivity metrics weighted by habitat quality can be used to set conservation objectives and inform MPA placement. Overall, the strength of dispersal barriers varied across modeled species and, also across species, we found a lack of spatial concordance of reefs that were high‐quality sources, self‐persistent, and stepping‐stones. Including spatially‐heterogeneous habitat quality made a considerable difference to connectivity patterns, significantly reducing the potential reproductive output from many reefs. We also found that caution is needed in combining connectivity data from modeled species into multi‐species matrices, which do not perform reliably as surrogates for all connectivity metrics of individual species. We then showed that restricting the habitat available for conservation has an inequitable impact on different connectivity objectives and species, with greatest impact on betweenness centrality and long‐distance dispersers. We used Brazilian coral reefs as a case study but our approach is applicable to both marine and terrestrial conservation planning, and offers a holistic way to design functionally‐connected reserves to tackle the complex issues relevant to planning for persistence.     

Herbivorous fishes,ecosystem function and mobile links on coral reefs

Understanding large-scale movement of ecologically important taxa is key to both species and ecosystem management. Those species responsible for maintaining functional connectivity between habitats are often called mobile links and are regarded as essential elements of resilience. By providing connectivity, they support resilience across spatial scales. Most marine organisms, including fishes, have long-term, biogeographic-scale connectivity through larval movement. Although most reef species are highly site attached after larval settlement, some taxa may also be able to provide rapid, reef-scale connectivity as adults. On coral reefs, the identity of such taxa and the extent of their mobility are not yet known. We use acoustic telemetry to monitor the movements of Kyphosus vaigiensis, one of the few reef fishes that feeds on adult brown macroalgae. Unlike other benthic herbivorous fish species, it also exhibits large-scale (>2 km) movements. Individual K. vaigiensis cover, on average, a 2.5 km length of reef (11 km maximum) each day. These large-scale movements suggest that this species may act as a mobile link, providing functional connectivity, should the need arise, and helping to support functional processes across habitats and spatial scales. An analysis of published studies of home ranges in reef fishes found a consistent relationship between home range size and body length. K. vaigiensis is the sole herbivore to depart significantly from the expected home range–body size relationship, with home range sizes more comparable to exceptionally mobile large pelagic predators rather than other reef herbivores. While the large-scale movements of K. vaigiensis reveal its potential capacity to enhance resilience over large areas, it also emphasizes the potential limitations of small marine reserves to protect some herbivore populations.     

Recruitment of coral reef fishes along a cross-shelf gradient in the Red Sea peaks outside the hottest season

Knowledge on the early life history, ecology, and biology of marine species is crucial for future projections of the resilience of coral reef ecosystems and for adequate management strategies. A fundamental component of population dynamics is the recruitment of new individuals, and in some marine populations, this may be a limiting factor. Recruitment peaks of coral reef fishes commonly occur during the warmer months of the year in many subtropical and temperate locations worldwide. In the Red Sea, very little is known about the influence of temperature on reproductive patterns of coral reef fishes and studies on recruitment are missing. The Red Sea is one of the hottest and most isolated tropical seas in the world. We hypothesized that sea surface temperatures (SSTs) during the Red Sea’s hottest season may exceed the optimum for successful recruitment of some coral reef fishes, which therefore has to occur during other, cooler seasons, unlike recruitment among coral reef ecosystems around the world. We identified taxa among fish recruits by matching mitochondrial DNA sequences (using COI, commonly known as “barcoding”) and assessed potential biological and environmental drivers of recruitment. We studied three reefs located along a cross-shelf gradient for 12 consecutive months in the central Red Sea to capture seasonal changes in biotic and abiotic parameters along this gradient. Our results indicated that recruitment peaks did not occur during the hottest SSTs for most taxa, especially at the hottest inshore and mid-shelf reefs, and identified fish recruitment to be mainly and strongly correlated with the biomass of planktonic invertebrates. Moreover, temporal patterns of fish recruitment differed within and among taxonomic families among the reefs.

     

Predatory fish sounds can alter crab foraging behaviour and influence bivalve abundance

The risk of predation can have large effects on ecological communities via changes in prey behaviour, morphology and reproduction. Although prey can use a variety of sensory signals to detect predation risk, relatively little is known regarding the effects of predator acoustic cues on prey foraging behaviour. Here we show that an ecologically important marine crab species can detect sound across a range of frequencies, probably in response to particle acceleration. Further, crabs suppress their resource consumption in the presence of experimental acoustic stimuli from multiple predatory fish species, and the sign and strength of this response is similar to that elicited by water-borne chemical cues. When acoustic and chemical cues were combined, consumption differed from expectations based on independent cue effects, suggesting redundancies among cue types. These results highlight that predator acoustic cues may influence prey behaviour across a range of vertebrate and invertebrate taxa, with the potential for cascading effects on resource abundance.     

Comparative spatial ecology of fished spiny lobsters <Emphasis Type="Italic">Panulirus argus</Emphasis> and an unfished congener <Emphasis Type="Italic">P. guttatus</Emphasis> in an isolated marine reserve at Glover's Reef atoll,Belize

Palinurid lobsters are being exploited with increasing intensity in coral reef ecosystems, but marine protected areas may play a key role in preventing overfishing and local extinctions. In order to define the spatial requirements for protection, we compared the spatial and temporal patterns in distribution, density, biomass, size structure, and reproductive seasonality of Caribbean spiny lobsters Panulirus argus and the congeneric spotted lobsters P. guttatus on coral patch reef, forereef, and deep reef habitat at Glover's Reef, Belize. The relative impact of fishing on P. argus was also examined in an isolated marine reserve and adjacent fished habitats, in comparison with the relatively unfished distribution of P. guttatus. Over a 5-year period, both species co-occurred in all major reef habitats, but aspects of their population dynamics differed markedly due to both habitat and fishing effects. All size classes of spiny lobsters P. argus occupied shallow patch reefs, but large adults were predominant on the deep wall reef. Panulirus guttatus also occupied patch reefs in the lagoon, but spur-and-groove forereef appeared to be the primary habitat of this species. Density and exploitable (adult) biomass of P. argus increased significantly over time in the protected patch reef habitat of the lagoon but remained stable on deep reef habitat. The biomass of spotted lobsters P. guttatus in all habitats was at least an order of magnitude less than that of exploitable P. argus. Reproductive activity by both species was evident most of the year in all habitats, but breeding P. argus females were concentrated on the deep reef. Commercial fisheries for spotted lobsters P. guttatus are currently being considered for development, but data from this and other studies suggest that such a fishery may be relatively unproductive and may lead to rapid localized extinctions. Spiny lobsters P. argus used a variety of coral reef habitats, but spotted lobsters P. guttatus were habitat specialists restricted to shallow reef habitat. The protection needs of both species are similar in one aspect: large protected areas. However, P. argus required large areas with heterogeneous habitats including coral reefs and seagrass beds, whereas P. guttatus required large areas of coral reef habitat.     

Maximal species richness in Conus: diversity, diet and habitat on reefs of northeast Papua New Guinea

The gastropod genus Conus is shown to be among many marine taxa that attain maximal known diversity along the northeast coast of Papua New Guinea. Thirty-six species co-occurred on the reef platform fringing Laing Island in Hansa Bay, 33% more than previously documented on any single reef. Near Madang, 32 species occurred on four small reefs. Maximal density at both sites was 3/m², with overall density 0.1-0.2/m². Species richness, diversity, and general patterns of microhabitat use were similar at both, but composition differed markedly. Only 23 species were found at both sites, and proportional similarity was 44%. The most common species at each site were uncommon at the other. The diets of 34 species were determined; 26, including the most abundant, preyed exclusively on polychaetes. As on other Indo-Pacific reefs, species partitioned prey types more finely than substrate types. Among vermivores, a different polychaete dominated the diet of each predator. Other species specialized on an enteropneust, other gastropods, and fishes. Most prey were herbivores or deposit feeders, indicating that the major trophic role of Conus species in the reef community is as primary carnivores. The results suggest that species are not more specialized than where fewer congeners co-occur, but rather overlap somewhat more in resource use.