Reproductive isolation in temperate reef fishes

Opportunity and recognition isolation can lead directly to reproductive isolation, the former via divergence in the location and timing of breeding, and the latter via differential mate preferences. We describe the potential significance of these factors in the maintenance of reproductive isolation in a clade of triplefin fishes that occur sympatrically around coastal New Zealand. Specifically, we investigate the roles of spawning time and nesting habitat in promoting opportunity isolation, and of interspecific variation in male body length and breeding colouration in promoting recognition isolation. The triplefin species investigated are reproductively active over several months and show high overlap in breeding times, thus rejecting temporal isolation as a mechanism. Differences in nesting habitats resulted in a reduced probability of encounter between some species, especially between sister-species pairs. Interspecific colour differences generally decreased during the reproductive period, and males of sister-species pairs showed no interspecific colour differences in the ultraviolet light spectrum, thus mate selection based on male colour patterns is unlikely to lead to premating isolation. Finally, males of closely related triplefin species differed in body length, a secondary sexual trait often involved in assortative mating. Thus, spatial differences in nesting habitats reduce the chances of encountering allospecific mates, which may facilitate opportunity isolation and differences in male length, possibly related to species-specific female selection on male body size, may lead to recognition isolation. The combination of limited spatial overlap in nesting habitat and differences in male body size may facilitate species assortative mating in sympatry or parapatry.     

Demographic plasticity in tropical reef fishes

We use age-based analyses to demonstrate consistent differences in growth, mortality, and longevity of coral reef fishes from similar habitats (exposed reef crests) 20 km apart. On outer-shelf reef crests of the northern Great Barrier Reef (GBR), size in four taxa of reef fishes (Chlorurus sordidus, Scarus frenatus, and S. niger and the acanthurid Acanthurus lineatus) was systematically and significantly smaller when compared with the same taxa on adjacent mid-shelf reef crests. Differences in size could be attributed to differences in growth between habitats (shelf positions). On outer reef crests the species examined had consistently lower size at age profiles and also reduced life spans compared with populations from mid-shelf reefs. To confirm this relationship, two of the most abundant species (C. sordidus and S. frenatus) were selected for more detailed spatial analysis of demographic patterns. Sampling adults of both taxa from reef crests on three mid- and three outer-shelf reefs revealed that most of the variation in growth was explained by shelf position, although C. sordidus also displayed differences in growth among mid-shelf reefs. We conclude that differences in body sizes across the continental shelf of the northern GBR are primarily determined by these trends in growth. Strong spatial patterns also existed in the mean ages of populations and longevity estimates for C. sordidus and S. frenatus between shelf positions. Both species on outer-shelf reefs displayed less variable cohort sizes, significantly reduced mean ages, and foreshortened longevity compared with populations on mid-shelf reefs. Furthermore, differences in these parameters were rare among replicate reefs within mid- and outer-continental-shelf positions. Age-based catch curves suggested that rates of S. frenatus natural mortality on the outer shelf were nearly twice as high as on the mid shelf. Visual surveys indicated that total scarid densities on outer-shelf reef crests are on average fourfold higher than for equivalent mid-shelf habitats. This fact, coupled with significantly reduced growth rates, reduced mean ages, and increased mortality rates, suggests that density-dependent processes may be responsible for observed differences among localities.     

Diel patterns of abundance of presettlement reef fishes and pelagic larvae on a coral reef

Most presettlement reef fish settled at night at One Tree Island, Great Barrier Reef. Fish were sampled day and night using channel nets located on the reef crest, and a plankton-mesh purse-seine net in the lagoon (1992–1994). Catches of fish at night were generally tens to hundreds of times greater than those taken during the day. Preflexion fish, as well as postflexion and pelagic juveniles, were taken in greater numbers at night. Preflexion forms were a combination of those that had hatched from demersal eggs and later stages that had been transported over the reef crest. Highest numbers of postflexion and pelagic juvenile forms of Apogonidae, Blenniidae, Gobiesocidae, Gobiidae, Labridae, Lutjanidae, Mugiloididae, Mullidae, Pomacentridae, Scaridae, Serranidae and Tripterygiidae were found at night. Observations, while SCUBA diving, and purse-seine samples in the lagoon indicated that the only resident larvae were of the genera Spratelloides and Hypoatherina; most of the fishes caught in nets, therefore, were immigrants. Patch reefs, sampled for new settlers early in the morning and late in the day, indicated that the majority of apogonids (Apogon doederleini, >95%) settled at night. Although greater numbers of pomacentrids were found in morning counts (e.g. Pomacentrus wardi), if data were converted to an hourly rate, many pomacentrids showed a similar hourly rate of settlement day and night. Depth-stratified sampling in waters near One Tree Island (to 20 m) indicated that some taxa rise to the surface at night. This behaviour, perhaps combined with avoidance of diurnal predators may explain on-reef movement of potential settlers soon after dark. Studies on settlement cues, therefore, need to focus on night-related phenomena. Received: 3 March 2000 / Accepted: 20 June 2000     

Comparative study of metamorphosis in tropical reef fishes

This study explores the types of changes in pigmentation and morphology that occur immediately after settlement in 13 families of tropical reef fishes encompassing 34 species. The morphology of individual fishes was recorded daily from when they were first caught at night as they came into the vicinity of a reef to settle. Changes in pigmentation and morphology were species specific and often varied greatly among species within a family or genus. Pigmentation changes were typically rapid (<36 h) and dramatic. Morphological changes involved the elongation and regression of fin spines and changes in head shape and body depth. Eighteen percent of species experienced changes in snout shape and dorsal spine length of greater than 5%. Similarly, 15% experienced changes in pectoral fin length and head length of greater than 5%. Changes typically occurred gradually over 6 or more days, although in about 44% of the species the major change in one of the measured body dimensions occurred rapidly (within 36 h). Moderately strong positive relationships were found between both growth and developmental rates and the extent of metamorphosis in the damselfishes (Pomacentridae) (r=0.48 and 0.63, respectively). This suggests there may be a minimum level of development necessary to be a fully functional demersal juvenile. Although many of the changes that occur are subtle compared to the preceding development, these changes occur at an important ecological transition. Published online: 16 August 2002     

The use of clear-water non-estuarine mangroves by reef fishes on the Great Barrier Reef

Within the tropics, mangroves and coral reefs represent highly productive biomes. Although these habitats are often within close proximity, the role and importance of mangrove habitats for reef fish species remains unclear. Throughout the Indo-Pacific, reef fish species appear to have few links with estuarine mangrove habitats. In contrast, clear-water non-estuarine mangrove habitats throughout the Caribbean support many reef fish species and may be fundamental for sustaining reef fish populations. But how important are clear-water non-estuarine mangroves for reef fishes within the Indo-Pacific? Using visual surveys during diurnal high tide, the fish assemblages inhabiting clear-water mangrove and adjacent reef habitats of Orpheus Island, Great Barrier Reef, were recorded. Of the 188 species of fishes that were recorded, only 38 were observed to inhabit both habitats. Of these, only eight were observed more than five times within each habitat. These observations provide little indication that the clear-water mangroves are an important habitat for reef fish species. In addition, although based on just a 3-month survey period, we found little evidence to suggest that these areas are important nurseries for reef fish species. The clear-water mangroves of Orpheus Island may, however, provide an additional foraging area for the few reef fish species that were observed to utilize these habitats during high tide. The difference in the importance of clear-water mangroves for reef fishes within this study compared with clear-water mangrove counterparts within the Caribbean is surprising. Although only preliminary, our observations would support suggestions that the patterns reflect the different hydrological characteristics and evolutionary histories of these two biogeographic regions.     

Behavioural flexibility in reef fishes responding to a rapidly changing wave environment

Flexible traits can be crucial in helping animals meet the challenges of a highly variable environment. We examined whether coral reef fishes systematically alter their swimming behaviour in response to temporal changes in hydrodynamic conditions. Exploiting site-based differences in wave energy impinging on reef habitats over calm and rough weather, we found many reef fishes changed their swimming behaviour alongside increases in wave-driven water motion. Most fishes tended to orient their bodies parallel to oncoming wave-driven flow and recruited additional stabilising fins during rough weather; such changes in swimming behaviour aid stability and minimise drag. However, not all species displayed such flexibility, with fishes possessing highly tapered pectoral fins and high levels of swimming performance continuing to successfully navigate reef habitats without significantly altering their swimming behaviour. We highlight how labile behaviours augment the morphology and performance of species to underpin their occupation of habitats subject to variable environmental conditions.     

Video-monitored predation by Caribbean reef fishes on an array of mangrove and reef sponges

Although predation by fishes is thought to structure benthic invertebrate communities on coral reefs, evidence to support this claim has been difficult to obtain. We deployed an array of eight sponge species on Conch Reef (16 m depth) off Key Largo, Florida, USA, and used a remote video-camera to record fish activity near the array continuously during five daylight periods (6 h for 1 d, at least 11.5 h for 4 d) and one night period (11 h). Of the eight sponge species, four were from adjacent reefs (Agelas wiedenmayeri, Geodia neptuni, Aplysina fistularis, and Pseudaxinella lunaecharta), and four were from a nearby mangrove habitat (Chondrosia collectrix, Geodia gibberosa, Halichondria sp., andTedania ignis). Each species of reef sponge was chosen to match the corresponding mangrove species in form and color (black, brown, yellow, and red, respectively). Predation events only occurred during daylight hours. Tallies of the number of times fishes bit sponges revealed intense feeding by the expected species of sponge-eating fishes, such as the angelfishHolacanthus bermudensis, H. tricolor, andPomacanthus arcuatus, the cowfishLactophrys quadricornis, and the filefishCantherhines pullus, but surprisingly also by the parrotfishSparisoma aurofrenatum andS. chrysopterum. Of 35 301 bites recorded, 50.8% were taken by angelfish, 34.8% by parrotfish, and 13.7% by trunkfish and filefish. Mangrove sponges were preferred by all reef fishes; 96% of bites were taken from mangrove species, with angelfish preferringChondrosia collectrix and parrotfish preferringGeodia gibberosa. Fishes often bit the same sponge repetitively, and frequently consumed entire samples within 30 min of their deployment. Sponge color did not influence fish feeding. Two of the four mangrove sponge-species deployed on the array were also found living in cryptic habitats on adjacent reefs and were rapidly consumed by fishes when exposed. Our results demonstrate the importance of fish predation in controlling the distribution of sponges on Caribbean reefs.     

Interactions during feeding among certain coral reef fishes in Elat

From July 1983 to March 1984 coral reef fishes in Elat (Red Sea) were fed in novel feeding situations. Thalassoma rüppelli had the shortest latency to first feed, Chaetodon paucifasciatus had the longest latency, while Sufflamen albicaudatus, Coris aygula and Lethrinus sp. had intermediate latencies. The mean number of T. rüppelli feeding at the beginning of experiments was higher than that of the other species. The difference decreased rapidly and disappeared within 90 s of the beginning. Latencies to first feed, and the number of fish feeding, were not correlated with the number of fish of each species in the study area. Aggression was directed predominantly by S. albicaudatus and by C. aygula towards Lethrinus sp. and T. rüppelli. It is suggested that these species which suffer more disturbances during their feeding and which receive more aggression are more likely to approach and feed more quickly in novel feeding situations.     

Spatial repartition and ontogenetic shifts in habitat use by coral reef fishes (Moorea,French Polynesia)

This study explores the extent to which ontogenetic habitat shifts modify spatial patterns of fish established at settlement in the Moorea Island lagoon (French Polynesia). The lagoon of Moorea Island was divided into 12 habitat zones (i.e. coral seascapes), which were distinct in terms of depth, wave exposure, and substratum composition. Eighty-two species of recently settled juveniles were recorded from March to June 2001. Visual censuses documented changes in the distribution of juveniles of each species over time among the 12 habitats. Two patterns of juvenile habitat use were found among species. Firstly, some species settled and remained in the same habitat until the adoption of the adult habitats (i.e. recruitment; e.g. Chaetodon citrinellus, Halichoeres hortulanus, Rhinecanthus aculeatus). Secondly, others settled to several habitats and then disappeared from some habitats through differential mortality and/or post-settlement movement (e.g. 65–70 mm size class for Ctenochaetus striatus, 40–45 mm size class for Epinephelus merra, 50–55 mm size class for Scarus sordidus). A comparison of the spatial distribution of juveniles to that of adults (61 species recorded at both stages) illustrated four patterns of subsequent recruitment in habitat use: (1) an increase in the number of habitats used during the adult stage (e.g. H. hortulanus, Mulloidichthys flavolineatus); (2) a decrease in the number of habitats adults used compared to recently settled juveniles (e.g. Chrysiptera leucopoma, Stethojulis bandanensis); (3) the use of different habitat types (e.g. Acanthurus triostegus, Caranx melampygus); and (4) no change in habitat use (e.g. Naso litturatus, Stegastes nigricans). Of the 20 most abundant species recorded in Moorea lagoon, 12 species modified the spatial patterns established at settlement by an ontogenetic habitat shift.Communicated by T. Ikeda, Hakodate     

Diurnal space utilization in coral reef fish communities

The diurnal use of space by 25 resident species of coral reef fishes was investigated along three depth (10 to 40 m) transects over an 18 month period. Emphasis was placed on the small, cryptic members of the communities. Three aspects of the use of space — temporal utilization, occupancy and time span — are defined and quantified for each of the species. In addition, an estimate of the diurnal home range volume of each species is provided. The territorial pomacentrids showed the highest level of temporal utilization, holding the same territories throughout the study. The consistent presence of the holocentrid species within the reef infrastructure had the potential to influence the space available to other species. Some species residing in tube-worm holes and sponges also exhibited constant use of space.     

Association of color and feeding deterrence by tropical reef fishes

Summary. While many marine molluscs have been suggested to use aposematic coloration to avoid predation, few studies have tested the ability of marine predators to learn to associate colors with distasteful prey. In field experiments, we tested the ability of two populations of reef fishes to discriminate among red, yellow, and black artificial nudibranch models when one color was paired with a feeding deterrent. We offered fishes (1) the models without any feeding deterrents, (2) the models with a feeding deterrent coated onto one color, and (3) the models without deterrents again. If reef fishes learn to associate colors with noxious prey, we expected the color paired with the feeding deterrent to be eaten less frequently in the final assay than the initial assay. In both populations, fishes formed clear associations between color and feeding deterrence. However, when the experiment was repeated in one population, changing the color paired with the feeding deterrent, fishes did not form an association between color and feeding deterrence. In this case, prior learning may have affected subsequent trials. Our study indicates that common colors of nudibranchs are recognizable by fishes and can be associated with noxious prey. Received 24 September 1998; accepted 18 December 1998.     

Marker technique for investigating gut throughput rates in coral reef fishes

Artemia sp. shells were evaluated to determine their accuracy for tracing the passage of algal filaments through the gut of the damselfish Pomacentrus amboinensis Bleeker, 1868 (family Pomacentridae), an omnivorous coral reef fish. An automatic faeces-collection apparatus enabled the quantitative collection of markers and faeces in the laboratory. Defecation rates were similar for light and heavy doses of Artemia sp. shells and controls, indicating no detrimental effects of Artemia sp. shells on the gut throughput rate of P. amboinensis. In addition, similar rates and patterns of the passage of Artemia sp. shells and the algal markers Enteromorpha sp. and Lyngbya sp. indicated that Artemia sp. shells provide a reliable representation of the throughput rate of algal filaments. The mean throughput time of P. amboinensis was 4.6 h ±0.3 SE, with a modal recovery time of 4 h. Laboratory throughput estimates were validated by comparing the distribution patterns of Artemia sp. shells in the dissected gut of specimens administered markers in the laboratory and field. In addition, the retention of markers in the stomach of P. amboinensis suggested a likely site of prolonged processing. Received: 24 October 1996 / Accepted: 18 March 1997     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Consequences of patch reef spacing for density-dependent mortality of coral-reef fishes

The spatial configuration of habitat patches can profoundly affect a number of ecological interactions, including those between predators and prey. I examined the effects of reef spacing on predator-prey interactions within coral-reef fish assemblages in the Bahamas. Using manipulative field experiments, I determined that reef spacing influences whether and how density-dependent predation occurs. Mortality rates of juveniles of two ecologically dissimilar species (beaugregory damselfish and yellowhead wrasse) were similarly affected by reef spacing; for both species, mortality was density dependent on reef patches that were spatially isolated (separated by 50 m), and density independent on reef patches that were aggregated (separated by 5 m). A subsequent experiment with the damselfish demonstrated that a common resident predator (coney) caused a substantial proportion of the observed mortality, independent of reef spacing. Compared to isolated reefs, aggregated reefs were much more likely to be visited by transient predators (mostly yellowtail snappers), regardless of prey density, and on these reefs, mortality rates approached 100% for both prey species. Transient predators exhibited neither an aggregative response nor a type 3 functional response, and consequently were not the source of density dependence observed on the isolated reefs. These patterns suggest that resident predators caused density-dependent mortality in their prey through type 3 functional responses on all reefs, but on aggregated reefs, this density dependence was overwhelmed by high, density-independent mortality caused by transient predators. Thus, the spatial configuration of reef habitat affected both the magnitude of total predation and the existence of density-dependent mortality. The combined effects of the increasing fragmentation of coral reef habitats at numerous scales and global declines in predatory fish may have important consequences for the regulation of resident fish populations.