Auditory and olfactory abilities of pre-settlement larvae and post-settlement juveniles of a coral reef damselfish (Pisces: Pomacentridae)

The propagules of most species of reef fish are advected from the reef, necessitating a return to reef habitats at the end of the pelagic stage. There is increasing evidence of active attraction to the reef but the sensory abilities of reef fish larvae have not been characterized well enough to fully identify cues. The electrophysiological methods of auditory brainstem response (ABR) and electroolfactogram (EOG) were used to investigate auditory and olfactory abilities of pre- and post-settlement stages of a damselfish, Pomacentrus nagasakiensis (Pisces, Pomacentridae). Audiograms of the two ontogenetic stages were similar. Pre-settlement larvae heard as well as their post-settlement counterparts at all but two of the tested frequencies between 100 Hz and 2,000 Hz. At 100 and 600 Hz, pre-settlement larvae had ABR thresholds 8 dB higher than those of post-settlement juveniles. Both stages were able to detect locally recorded reef sounds. Similarly, no difference in olfactory ability was found between the two ontogenetic stages. Both stages showed olfactory responses to conspecifics as well as L-alanine. Therefore, the auditory and olfactory senses have similar capabilities in both ontogenetic stages. Settlement stage larvae of P. nagasakiensis can hear and smell reef cues but it is unclear as to what extent larvae use these sounds or smells, or both, as cues for locating settlement sites. An erratum to this article can be found at     

The impact of exploiting grazers (Scaridae) on the dynamics of Caribbean coral reefs.

Coral reefs provide a number of ecosystem services including coastal defense from storms, the generation of building materials, and fisheries. It is increasingly clear that the management of reef resources requires an ecosystem approach in which extractive activities are weighed against the needs of the ecosystem and its functions rather than solely those of the fishery. Here, I use a spatially explicit simulation model of a Caribbean coral reef to examine the ecosystem requirements for grazing which is primarily conducted by parrotfishes (Scaridae). The model allows the impact of fishing grazers to be assessed in the wider context of other ecosystem processes including coral-algal competition, hurricanes, and mass extinction of the herbivorous urchin Diadema antillarum. Using a new analytical model of scarid grazing, it is estimated that parrotfishes can only maintain between 10% and 30% of a structurally complex forereef in a grazed state. Predictions from this grazing model were then incorporated into a broader simulation model of the ecosystem. Simulations predict that scarid grazing is unable to maintain high levels of coral cover (> or = 30%) when severe hurricanes occur on a decadal basis, such as occurs in parts of the northern Caribbean. However, reefs can withstand such intense disturbance when grazing is undertaken by both scarids and the urchin Diadema. Scarid grazing is predicted to allow recovery from hurricanes when their incidence falls to 20 years or less (e.g., most of Central and South America). Sensitivity analyses revealed that scarid grazing had the most acute impact on model behavior, and depletion led to the emergence of a stable, algal-dominated community state. Under conditions of heavy grazer depletion, coral cover was predicted to decline rapidly from an initial level of 30% to less than 1% within 40 years, even when hurricane frequency was low at 60 years. Depleted grazers caused a population bottleneck in juvenile corals in which algal overgrowth caused elevated levels of postsettlement mortality and resulted in a bimodal distribution of coral sizes. Several new hypotheses were generated including a region-wide change in the spatial heterogeneity of coral reefs following extinction of Diadema. The management of parrotfishes on Caribbean reefs is usually approached implicitly through no-take marine reserves. The model predicts that depletion of grazers in nonreserve areas can severely limit coral accretion. Other studies have shown that low coral accretion can reduce the structural complexity and therefore quality of the reef habitat for many organisms. A speculative yet rational inference from the model is that failure to manage scarid populations outside reserves will have a profoundly negative impact on the functioning of the reserve system and status of non-reserve reefs.     

Biochemical systematics of fishes of the genus Stegastes (Pomacentridae) from the Southern Marianas

The biochemical systematics of the subset of species of Stegastes (Pisces: Pomacentridae) available from coral reefs surrounding Guam, USA, was studied using three species of Pomacentrus as the outgroup. Analyses of allozymic variation at 14 presumptive loci (10 of which were polymorphic) using various evolutionary tree-construction techniques identified S. fasciolatus as the sister species of an assemblage comprised of S. albifasciatus, S. nigricans, and S. lividus: within this assemblage, S. lividus is the sister species of S. albifasciatus and S. nigricans, the pair of species which shared the most synapomorphic alleles and consistently exhibited the lowest degree of genetic distance relative to estimates for the other pairs of species studied. The consistency of ingroup topologies produced by parsimony analyses using Manhattan rectilinear distances computed from allele frequencies with those produced using the distance Wagner procedure and UPGMA (unweighted pair-group method of arithmetic averages) clustering, substantiates strongly the proposed phylogeny. The systematic scheme inferred from molecular data is concordant with predictions based on morphologic differences, i.e., differences in numbers of dorsal spines, that have been used as evidence in support of the proposal to partition Stegastes into at least two subgenera.     

Variability in larval development of the tropical reef fish Pomacentrus amboinensis (Pomacentridae): the parental legacy

The effects of food availability, female size, and social interactions on the quality of Pomacentrus amboinensis larvae at hatching were examined using two field-based experiments. In Experiment 1, food availability and female size significantly influenced size, eye diameter and levels of yolk reserves of larvae at hatching. Small females (47 to 52 mm standard length, SL) whose diets were not supplemented, produced the longest larvae (3.0 ± 0.01 mm total length, TL) with the least yolk reserves (50.1 ± 1.04 μm²). Irrespective of female size, those that received additional food produced larvae with the largest yolk-sacs (large females: 87.60 ± 1.53 μm²; small females: 80.14 ± 1.24 μm²). In Experiment 2, interactions with conspecifics had a greater affect on the somatic development of larvae at hatching than food availability. Increased social interactions resulted in larvae that were ⋍3% longer, with 2% greater head depth, than larvae from females that spawned in isolation on the experimental reefs. Fed females produced larvae with ⋍20% more yolk than larvae from females whose diets were not supplemented. All three factors (food availability, female size, and intensity of social interactions) tested within these experiments vary spatially and temporally among reefs. There is the potential, therefore, for larvae at the onset of the planktonic stage to vary in quality, level of development, and probability of survival. Received: 12 August 1996 / Accepted: 26 August 1996     

Swimming ability and its rapid decrease at settlement in wrasse larvae (Teleostei: Labridae)

Wrasses are abundant reef fishes and the second most speciose marine fish family, yet little is known of their larval swimming abilities. In August 2010 at Moorea, Society Islands, we measured swimming ability (critical speed, Ucrit) of 80 settlement-stage larvae (11–17 mm) of 5 labrid species (Thalassoma quinquevittatum [n = 67], Novaculichthys taeniourus [n = 6], Coris aygula [n = 5], Halichoeres trimaculatus [n = 1] and H. hortulanus [n = 1]) and 33 new recruits of T. quinquevittatum. Median (mdn) larval Ucrit was 7.6–12.5 cm s⁻¹. In T. quinquevittatum (n = 67), larvae of 12.5–14.5 mm swam faster (mdn 16.9 cm s⁻¹) than smaller or larger larvae (mdn 3.9 and 3.2 cm s⁻¹, respectively). Labrid larvae Ucrit is similar to that of other similar-sized tropical larvae, so labrids and species with comparable settlement sizes should have similar abilities to influence dispersal. Ucrit of T. quinquevittatum recruits decreased to 47–56% of larval Ucrit in 2 days, implying rapid physiological changes at settlement.     

Predator biomass,prey density,and species composition effects on group size in recruit coral reef fishes

Group incidence and size are described for recruit parrotfishes, wrasses, and damselfishes on Hawaiian reefs over 3 years (2006–2008) at sites spanning the archipelago (20–28°N, 155–177°W). Coral-poor and coral-rich areas were surveyed at sites with both low (Hawaii Island) and high (Midway Atoll) predator densities, facilitating examination of relations among predator and recruit densities, habitat, and group metrics. Predator and recruit densities varied spatially and temporally, with a sixfold range in total recruit densities among years. Group (≥2 recruits) metrics varied with time and tracked predator and recruit densities and the proportion of schooling species. Groups often included heterospecifics whose proportion increased with group size. A non-saturating relationship between group size and recruit density suggests that the anti-predator benefits of aggregation exceeded competitive costs. Grouping behavior may have overarching importance for recruit survival–even at high recruit densities–and merits further study on Hawaiian reefs and elsewhere.     

Quantitative distribution of herbivorous reef fishes in the Gulf of Aqaba (Red Sea)

The distribution of the main herbivorous fishes (Acanthuridae, Scaridae, Siganidae) was studied across a coral reef of the Jordanian coast in the Gulf of Aqaba (Red Sea). Visual counts were realized by diving along transects (200 m long and 5 m wide), parallel to the shore, at 10 stations located from the lagoon to 40 m deep on the outer reef slope. Herbivorous reef fishes reach their highest abundance on the reef front, where 234 fishes were counted per 1,000 m². Their density decreases on the reef flat, with an average of 150 fish 1,000 m^-2, and is lowest on the outer reef slope (69 fish 1,000 m^-2). Surgeonfishes form 63% of the herbivorous ichthyofauna, parrotfishes 35%, and rabbitfishes 2%. Families and species display different distributions according to biota. The Acanthuridae dominate on the reef flat, whereas the Scaridae are more numerous on the outer reef slope. The evolution of the social structure of the main species was observed: the adults generally school in the lagoon and on the reef flat, but are mainly solitary on the reef slope. The distribution of juvenile individuals is more restricted: they are concentrated on the reef front and on the upper part of the reef slope.This study is part of a cooperation programme between the University of Nice (France) and the University of Jordan, to study the ecology of the coral reefs and the surrounding waters of the Jordanian coast (Gulf of Aqaba, Red Sea)     

Pleistocene diversification of the Pomacentrus coelestis species complex (Pisces: Pomacentridae): historical biogeography and species boundaries

Pleistocene eustatic changes in sea level are often invoked to explain genetic divergence among marine organisms. However, molecular phylogenies have revealed relatively few examples of speciation events dating to the Pleistocene. We present a species-level hypothesis of the timing of evolution for the Pomacentrus coelestis species complex (Pomacentridae), based on the nuclear S7 intron and the mitochondrial Cytb gene, and reconstruct ancestral range distributions across the timetree. Ancestral range reconstruction suggests the complex originated in the Coral Triangle and East Indian Ocean, with subsequent range expansion outward from this region. We suggest that land barriers to dispersal (e.g., Indo-Pacific barrier) may be responsible for the divergence between Indian (P. alleni, P. similis, P. caeruleopunctatus, and P. caeruleus) and Pacific (P. micronesicus, P. auriventris, and P. coelestis) species groups, and subsequent isolation by Pleistocene sea-level fluctuations in certain areas of the Coral Triangle (glacial refugia) may play an important role in the diversification of this species complex. Additionally, our analyses show cryptic lineages within P. micronesicus and highlight the need for comprehensive sampling within and among species to reveal recent speciation events.     

Preliminary observations on the circulatory system in eggs and early larvae of some teleostean fishes

Observations on the pattern of blood circulation in eggs and early larvae of Ambassis, Mugil, Dorosoma and Thrissocles species have been made. In the initial stages, the tubular heart lies on the left side, near the cephalic region. The anterior end of the heart lies near the snout. The posterior end is attached to a point mid-way between the orbits and auditory vesicles; the position of the anterior end is greatly influenced by the size of yolk. Initially, the tubular heart and dorsal aorta lie in a line. As a result of yolk absorption, the anterior end of the tubular heart gradually sinks to a position posterior to the attached end. Liquified yolk is circulated through the heart in early stages; blood corpuscles become apparent only in larvae. The heart-beat, which is initially irregular, gradually becomes regular as development progresses. In the initial stages the blood flows to the caudal and not to the cephalic region. The blood vessels are narrow, and the oval-shaped blood corpuscles must therefore pass through individually, with their long axes parallel to the passage. A definite capillary system is not evident. The blood vessels can dilate and contract when required.     

Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations

The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators, obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean. Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition factor of these same larvae. Among species U-crit ranged from 5.5 cm s⁻¹ to 100.8 cm s⁻¹ (mean=37.3 cm s⁻¹), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat use following settlement.     

Planktonic larval duration of one hundred species of Pacific and Atlantic damselfishes (Pomacentridae)

The plankton larval duration for 100 species of Pacific and Atlantic damselfishes was estimated from daily growth increments on the otolith of juvenile fish collected at various localities between July 1987 and September 1988. For newly-settled fishes, larval duration was determined by counting the entire number of increments present on the otolith, while for older juveniles estimates were made by counting the number of increments between the center of the otolith and a mark corresponding to settlement. We document the development of otolith formation during the period when eggs are incubated on the reef and show that daily increments are only accreted after larvae hatch and enter the planktonic phase. The planktonic larval duration for damselfish is shorter and less variable, both between and within species, compared to other groups of reef fishes such as wrasses and surgeonfishes. Larval duration ranged from 12 to 39 d. Average duration between species ranged from 13.1 to 35.2 d. The time spent in the plankton was not significantly correlated with geographic distribution when evaluated among species, however, genera with confined regional distribution have a shorter mean larval life than do widely distributed genera. Size at settlement was positively correlated with time spent in the plankton among species, but a significant correlation between these variables was only evident within one of ten species. The low variance in planktonic larval duration within species indicates that most damselfish are unable to delay metamorphosis following competency. This inability to postpone settlement limits the potential for dispersal, especially when dispersal time between suitable habitats is greater than about 30 d.     

Influence of some coral reef communities on the calcium carbonate budget of Tiahura reef (Moorea,French Polynesia)

The calcium carbonate budget of coral reefs is the result of the interaction of the processes of calcification and biological degradation, and is reflected in the chemical properties of the seawater overlying the reefs. A series of experiments at Moorea Island (French Polynesia) in 1988 monitored the diurnal and nocturnal variations in the chemical properties of seawater under field and laboratory conditions. Our results revealed that in the study area (Tiahura barrier reef flat), the calcium carbonate budget varied over space and time as a function of location in the water current. Two in-situ sites were investigated; one was situated 100 m from the algal crest of the barrier reef, the other 300 m further downstream. As a result of cumulative upstream events, the daily net calcification was ten times higher at the downstream (5.22 gm^-2 d^-1) than at the upstream (0.45 gm^-2 d^-1) site. The carbonate uptake by in situ Porites lobata in enclosures (8 kgm^-2 yr^-1) was ten times higher than the uptake by the whole community in the surrounding water (0.8 kgm^-2 yr^-1) and five times higher than that recorded for P. lobata in laboratory experiments (1.4 kgm^-2 yr^-1), where illumination levels were 10% of in situ levels. In laboratory experiments, the planktonic fraction of the seawater had no perceptible influence on the calcium carbonate budget. In the absence of bioeroders, living coral totally depleted the carbonate content of the seawater (3.7 gm^-2d^-1). Bioerosive organisms played an important role in restoring this calcium carbonate; e.g. sea urchins grazing on algal turf covering dead coral ingested CaCO₃ and released this as a carbonate powder (1.26 gm^-2d^-1); a form of carbonate which is extremely accessible to chemical dissolution.     

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     

Seasonal abundance, philopatry and demographic structure of Caribbean reef shark (Carcharhinus perezi) assemblages in the north-east Exuma Sound, The Bahamas

The Caribbean reef shark (Carcharhinus perezi), an abundant coral-reef-associated apex predator, is one of the most economically and ecologically important, yet least studied species of large shark in the greater Caribbean region. The relative abundance and population structure of C. perezi off Cape Eleuthera, The Bahamas, was surveyed by standardised longline surveys from May 2008 to October 2011, which resulted in the capture of 331 sharks. Abundance peaked in the summer and was lowest during the winter. Females were 1.6 times more abundant than males and the assemblage was dominated by immature female sharks (45.5 %). The abundance of mature male and female sharks peaked a month apart in June and August, respectively. All 331 sharks were tagged and released with 15.4 % being recaptured after periods at liberty between 5 and 1,159 days (Mean = 333.4 ± 42.7 SE). The mean distance between tagging and recapture was 1.77 km for recaptures in excess of 6 months, indicating seasonally stratified philopatry in this species. C. perezi inhabiting Bahamian waters have developed complex habitat use patterns that are both spatiotemporally and demographically segregated, most probably in response to the large and diverse habitat mosaic available on the Bahamas Banks compared to contemporary study sites. This study represents an important step in understanding the spatiotemporal population structure of C. perezi and illustrates the potential for studies examining behavioural plasticity in response to environmental variation and anthropogenic disturbance.     

Sexual reproduction of the reef coral Montastreacavernosa (Scleractinia: Faviidae) in the Santa Marta area, Caribbean coast of Colombia

Sexual reproduction of the reef-building coral Montastreacavernosa was studied in the Santa Marta area, Caribbean coast of Colombia, from October 1990 to October 1991. The area is subjected to a seasonal upwelling–outwelling regime. From microscopical analysis of tissue sections sampled each lunar month around the full moon, it was confirmed that this is a gonochoric, broadcasting species, with a single gametogenic cycle per year, and a 1:1 sex ratio. Oogenesis began a few weeks after spawning, and extended for 11 mo. The onset of spermatogenesis occurred just before the full moon of June, later than at other localities where sea-water temperatures during the first half of the year are not as low. The amount of reproductive tissue strongly increased in both sexes after July, in association with an increase in sea-water temperature and a decrease in photoperiod. The gonad index of fully mature female colonies was about four times lower than at other localities, perhaps due to the stressful seasonal regime. The male gonad index was lower than that of the female, indicating sex-related differences in the rates of biomass allocation to reproduction. As in other Caribbean localities, spawning occurred after the full moons of August and September. However, there was some evidence of a third spawning episode after the full moon of October, possibly associated with a delay in the occurrence of maximum sea-water temperatures in near-equatorial localities compared to higher latitudes. The probability of cross-fertilization in this species with a gonochoric breeding system and a broadcasting mode of reproduction is favored by its balanced sex ratio, its usually high within-reef zone abundance, and by localized and repeated spawning episodes, synchronized by lunar phase. Received: 19 April 1996 / Accepted: 24 September 1996     

Comparative species richness,composition, and abundance of invertebrates in Caribbean seagrass (Thalassia testudinum) meadows (Panamá)

The results of a year-long study in which epibenthic invertebrates were collected monthly from seagrass (Thalassia testudinum) meadows along the Caribbean coast of Panamá and the Panamá Canal Zone are described in this paper. Differences in species composition and abundance among sites were primarily due to the proximity of surrounding habitats, especially coral reefs, which contain a number of species that utilize the seagrass meadows. In contrast to many previous characterizations of tropical marine habitats, important seasonal fluctuations in both species number and abundance took place at each of the sites. Data on breeding activity among several species of decapod crustaceans indicate year-round reproduction, although considerable seasonal differences occur in the percentage of ovigerous females. These interspecific differences in observed reproductive output may be explained by differences in life-cycle length, a factor not often considered in discussions of seasonal breeding patterns in tropical marine invertebrates. Overall species composition was qualitatively similar to that reported in comparable studies of tropical and subtropical seagrass meadows elsewhere, although caridean shrimp and xanthid orab species were reduced in number and total abundance were much lower than in previous studies.     

Evidence of limited gene flow in three species of coral reef fishes in the lagoon of New Caledonia

Allozyme variation was used to investigate the genetic structure of the coral reef fishes Stegastes nigricans, Epinephelus merra and Acanthurus triostegus around New Caledonia. Each species was sampled from each of three sites in the ≃1000 km circumference of the lagoon of New Caledonia. Allelic variation was recorded for each species at 14, 13 and 17 loci, respectively, and heterozygosity diversity (H s) was 0.082, 0.065 and 0.116, respectively. Analysis of genetic differentiation between sites produced inconsistent results between species, with spatial heterogeneity in two species (S. nigricans, F st  = 0.038; A. triostegus, F st = 0.049) and homogeneity in one species (E. merra, F st = 0.000). Hydrological and climatic data from the lagoon suggest that the eastern and western sides of the lagoon are isolated, since they lie in water masses of different origin. This may explain the genetic differentiation and restricted gene flow found at a local scale for S. nigricans and A. triostegus. Homogeneity in populations of E. merra is discussed in relation to its low genetic diversity and its reproductive behaviour. Received: 23 April 1997 / Accepted: 25 September 1997