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Prey naivete, or the failure of prey to recognize non-native predators due to a lack of co-evolutionary history, is thought to underpin the large impact of invasive Indo-Pacific lionfish (Pterois sp.) on coral reef fish populations in the western Atlantic. Most previous studies of lionfish recognition have taken place in experimental tanks that did not mimic natural conditions or used bottle or cage field designs that constrained natural behaviour. To alleviate these issues, we compared the homing patterns of experimentally translocated Caribbean bicolor damselfish (Stegastes partitus) in the presence and absence of standardized models of a lionfish, of an ecologically similar native piscivore (black grouper; Mycteroperca bonaci), and of a native non-piscivore (French grunt, Haemulon flavolineatum) in the field. The native grouper model elicited a strong predator avoidance response: translocated damselfish became unlikely to home when released beyond ~ 2 m from their territory and took longer to do so. In contrast, damselfish facing a lionfish model exhibited similar homing behaviours to those of damselfish in the presence of a non-piscivorous grunt and in the absence of any model. Fish length and translocation distance also influenced homing: damselfish stopped homing when released more than 5.6 m away from their territory and larger individuals crossed wider sand gaps. Overall, our findings are consistent with the idea that bicolor damselfish are naive to the threat of predation presented by lionfish, but also with the notion that damselfish might be assessing, but deeming to be low, the threat of a stalking predator hunting over open sand. Both mechanisms point to inaccurate risk perception in relation to invasive lionfish. More broadly, we highlight a novel experimental translocation approach to evaluate behavioural responses of native prey species to novel predators under realistic field conditions.

Background Because the French grunt, Haemulon flavolineatum, is an ecologically important reef fish prized by both recreational anglers and public aquariums, the wild population requires limits on harvests. Yet, the environmental conditions conducive for French grunt spawning in aquarium settings is not well understood. Therefore, the goal of this study was to document the conditions leading to voluntary spawning and the number of eggs produced by French grunts without the use of hormones or artificial insemination. Methods We hypothesized and verified that it is possible for French grunts to spontaneously spawn in human care. Forty individuals were collected around the Florida Keys and haphazardly stocked in five recirculating seawater systems each containing two 250-L circular tanks. Over the course of 87 days, eggs were collected daily from each system and environmental parameters were monitored. Results Total daily number of eggs released ranged from 0 to 207,644 eggs. Of the observed environmental parameters, temperature and alkalinity had the greatest impact on number of eggs released. This study demonstrates that it is possible for French grunts to reproduce in captivity with little environmental manipulation, thus an ideal candidate to culture for the zoo/aquarium industry.

Genetic structure of the French grunt Haemulon flavolineatum, population was determined in four localities, two located in the Campeche Bank (Cayo Arcas and Alacranes) and two in the Mexican Caribbean (Puerto Morelos and Banco Chinchorro) using microsatellite loci. Intra- and inter-population genetic variabilities, and genetic distances were evaluated. The Monmonier’s maximum-difference algorithm was used to identify population structure and the putative genetic barriers across the oceanographic landscape. Overall expected heterozygosity (He) was lower (0.81) than the observed heterozygosity (Ho = 0.85). Inbreeding index indicated an excess of heterozygotes occur within the whole study area (F IS = -0.039); while fixation index denoted genetic significant differences between localities (F ST = 0.033). Nei’s genetic distances were wider between Puerto Morelos and Alacranes (0.232), while the narrower were observed between Alacranes and Cayo Arcas (0.106). Monmonier’s algorithm revealed three putative barriers: the first one separated the Campeche Bank from the Caribbean, the second one separated Puerto Morelos from Chinchorro, and finally the third one separated Cayo Arcas from Alacranes. Regional currents allow dispersion of H. flavolineatum between distant populations of the Mesoamerican Barrier Reef and the Gulf of Mexico, but they are not enough to homogenize the populations to form a panmictic population.

Organisms often utilise different habitats for different reasons, whether it be for acquiring resources, avoiding predation or for reproduction. In coastal tropical ecosystems, coral reefs, seagrass beds and mangrove forests frequently occur in a complex mosaic of intermixed habitats. One of the most commonly identified links between these habitats is the nursery function; that some fish species utilise mangroves and seagrass as juveniles before moving onto reefs as adults. We investigated whether this potential link between habitats is reflected in the similarity of their fish assemblages and if this similarity differs between major biogeographic realms. Visual surveys in the three focal habitats in the Caribbean and on the Great Barrier Reef (GBR) provided assemblage composition data. We found a near ten-fold increase in the percentage of species that occupy all three habitats in the Caribbean when compared to the GBR. When only assessing species that occurred in multiple habitats, the Caribbean displayed strong shifts linked to ontogeny and greater abundances of multihabitat species, supporting the proposed nursery function. GBR assemblages remained more distinct regardless of ontogeny, offering little support for the nursery function. Most multihabitat species in the Caribbean reach larger adult body sizes (≥30 cm, e.g. Haemulon flavolineatum) vs. smaller bodied (

The transition from a planktonic larval stage to a benthic or demersal juvenile stage, “recruitment”, is a crucial event in the life history of coral reef fishes, and has a strong influence on population size. Predation by piscivorous fishes is thought to be the main determinant of recruitment success, and has received the most attention. However, recent studies suggest that recently settled reef fishes are also an important target of micropredation from blood-feeding ectoparasites which may have significant lethal and sublethal effects. In this study, we quantified the relationship between levels of infestation by gnathiid isopods and mortality rates among juveniles of three species of reef fishes as a function of body mass both within and among species. We found that a single gnathiid isopod larva could kill fish of all three species shortly after settlement, up to 0.116 g [18 mm fork length (FL)] in French grunt (Haemulon flavolineatum), 0.027 g (15 mm FL) in masked goby (Coryphopterus personatus) and 0.01 g (9 mm FL) in beaugregory damselfish (Stegastes leucostictus). For juvenile S. leucostictus, we also compared the ability of fish to defend a territory when infested with a sublethal number of gnathiids versus uninfected individuals. Uninfected fish were significantly more likely to win-pairwise contests versus infected fish. These findings suggest that gnathiids can significantly impact juvenile coral reef fish survival, and affect population dynamics well past the settlement stage.

Stable isotope (δ(13)C and δ(15)N) and gut content analyses were used to investigate size-related feeding habits of four reef fishes (the beaugregory Stegastes leucostictus, the french grunt Haemulon flavolineatum, the schoolmaster snapper Lutjanus apodus and the yellowtail snapper Ocyurus chrysurus) inhabiting an offshore (non-estuarine) mangrove islet off Belize, Central America. Comparisons of isotopic niche space and Schoener diet similarity index suggested a low to moderate degree of niche overlap between fish size groups. The δ(13)C gradient between mangrove and seagrass prey as well as results of Bayesian mixing models revealed that sampled fishes relied mostly on seagrass prey items. Only small and large juveniles of the carnivorous species L. apodus derived a part of their diet from mangroves by targeting mangrove-associated Grapsidae crabs and fish prey, respectively. Isotopic niche shifts were particularly obvious for carnivorous fishes that ingested larger prey items (Xanthidae crabs and fishes) during their ontogeny. The utilization of mangrove food resources is less than expected and depends on the ecology and life history of the fish species considered. This research highlights that mangrove-derived carbon contributed relatively little to the diets of four fish taxa from an offshore mangrove islet.

The role of parasites in trophic ecology is poorly understood in marine ecosystems. Stable isotope analyses (SIA) have been widely used in studies of trophic ecology, but have rarely been applied to study the role of parasites. Considering that some parasites are associated with altered host foraging patterns, SIA can help elucidate whether parasitism influences host trophic interactions. French grunt (Haemulon flavolineatum), an abundant Caribbean coral reef fish, contributes greatly to trophic connectivity. They typically depart the reef at dusk, feed overnight in seagrass beds, and return to the reef at dawn. The large parasitic isopod Anilocra haemuli commonly infects French grunt, and infected fish are less likely to complete their diel migration, and are in poorer condition than uninfected conspecifics. Brown chromis (Chromis multilineata) are diurnally feeding planktivores and infection by Anilocra chromis does not influence host condition. To determine if Anilocra infection influences host diet and foraging locality, we conducted stable carbon and nitrogen isotope analyses on scale, muscle, heart and gill tissues of infected and uninfected French grunt and brown chromis. We determined that all French grunt had δ13C values representative of seagrass habitats, but infected French grunt were significantly enriched in 13C and 15N compared to uninfected conspecifics. This suggests that compared to uninfected conspecifics, infected French grunt forage in seagrass, but on isotopically enriched prey, and/or are in poorer condition, which can elevate δ13C and δ15N values. For brown chromis, infection did not significantly influence any δ13C and δ15N values; hence they all foraged in the same environment and on similar prey. This is the first study to use SIA to examine differences in resource use by Caribbean coral reef fishes associated with parasitism and to evaluate how closely related parasites might have host-dependent effects on host trophic ecology.

A morphological review and molecular characterization of Anilocra haemuli Bunkley Williams & Williams, 1981, were completed using specimens collected from Haemulon flavolineatum Desmarest, 1823 (French grunt) and Epinephelus guttatus Linnaeus, 1758 (red hind). Molecular and morphological data suggest that the isopods parasitizing H. flavolineatum and E. guttatus are different species. The specimens collected from E. guttatus are recognized as a new species, Anilocra brillae sp. n. Differences between Anilocra brillae sp. n. and A. haemuli include but are not limited to the pleonites 1–3 of A. brillae sp. n. being wider than 4–5 and 4–5 subequal, whereas the pleonites 1–2 of A. haemuli are wider than 3–5, and 3–5 are subequal. The seventh pereopod of A. brillae sp. n. is proportionally larger, has more robust setae, and the setae are distributed more extensively over the articles when compared to A. haemuli. Additionally, this study provides the first genetic characterization of three Anilocra spp. from the Caribbean, and is based on mitochondrial cytochrome c oxidase subunit gene (COI) for A. haemuli from H. flavolineatum, A. brillae sp. n. from E. guttatus, and A. chromis Bunkley Williams & Williams, 1981 from Chromis multilineata Guichenot, 1853.

Caribbean seagrass habitats provide food and protection for reef-associated juvenile fish. The invasive seagrass Halophila stipulacea is rapidly altering these seascapes. Since its arrival in the Caribbean in 2002, H. stipulacea has colonized and displaced native seagrasses, but the function of this invasive seagrass as a juvenile fish habitat remains unknown. To compare diversity, community structure, and abundance of juvenile fish between H. stipulacea and native seagrass beds, fish traps were deployed in four nearshore bays around St. Thomas, U.S. Virgin Islands. Traps were deployed in Frenchman, Lindbergh, and Sprat Bays for 24 h intervals in patches of bare sand, patches of H. stipulacea and patches of the native Caribbean seagrasses Thalassia testudinum and Syringodium filiforme. Traps were then deployed in Brewers Bay for 12 h intervals in stands of H. stipulacea and S. filiforme. Relative and total abundances of juvenile fish, identified at least to family, were compared across treatment habitats for each trap deployment period. The catch from H. stipulacea, compared to native seagrasses, comprised a greater abundance of nocturnal carnivores Lutjanus synagris (family Lutjanidae) and Haemulon flavolineatum (family Haemulidae). Additionally, the herbivore species Sparisoma aurofrenatum (family Labridae) and Acanthurus bahianus (family Acanthuridae) and the diurnal carnivore species Pseudopeneus maculatus (family Mullidae) were relatively scarce in H. stipulacea. The catch from sand was much smaller, compared to vegetated habitats, and comprised only L. synagris, H. flavolineatum, and H. aurolineatum. These results provide evidence of reduced family diversity and altered juvenile fish assemblages in H. stipulacea, driven by an abundance of some nocturnal carnivores and scarcity of herbivores and diurnal carnivores. The findings from the present work underpin the need for further investigation and mitigation of this invasion, particularly where H. stipulacea is driving seascape-alterations of key juvenile fish habitats.

Tropical Atlantic reef fishes in the family Haemulidae (grunts) remain quiescent on reefs during the day and migrate to seagrass beds or sand flats at night. Hypothesized advantages of such nocturnal migrations are increased food availability and/or decreased predation risk. Here, we tested predictions of an alternative hypothesis that nocturnal migrations of French grunt, Haemulon flavolineatum (Desmarest, 1823), reduce exposure to blood-feeding gnathiid isopods. The departure of grunts from the reef coincides with increasing gnathiid activity. In field experiments, subadult fish placed in cages and deployed on the reef at night harbored significantly more gnathiids than those placed in the seagrass habitat. However, this was not the case during the day when gnathiid activity in all habitats is low. In another experiment, the timing of return to the reef was determined to coincide with the postdawn decrease in gnathiid activity. Estimates of cumulative gnathiid exposure at two sites revealed that grunts remaining in reef habitat at night would experience an average of 3 and 44 times more gnathiids than if they spent the night in the seagrass bed, and could reach more than 300 gnathiids on a single fish. In a final field experiment, even recently-settled (

Francisella noatunensis is an emerging pathogen of fish that has been isolated from several cultured species worldwide. Here presented is a case involving several hundred marine grunts that were caught near the Florida Keys for display in public aquaria. These fish were maintained in a recirculating system where they began to experience mortalities approximately two weeks post-stocking. Postmortem examination revealed disseminated systemic granulomatous disease most severely affecting spleen and kidney. Splenic and renal tissue homogenates inoculated in modified Thayer Martin agar media yielded colonies consistent with F. noatunensis 4 days post inoculation. Bacterial colonies and tissues were confirmed positive after real-time PCR amplification of the intracellular growth loci gene (iglC) specific for F. noatunensis subspecies orientalis. Consequently, multiple novel host species for this pathogen were identified, including the French grunt (Haemulon flavolineatum) and the Caesar grunt (Haemulon carbonarium).

The objective of this study was to investigate the role of nutrient concentration by reef-resident fish on adjacent seagrass and macroalgal communities. One hypothesis is that the zone of enhanced plant productivity surrounding small patch reefs is initiated and maintained through nutrient enrichment from excretory products released by the localized fish aggregations that shelter by day in the immediate vicinity of these reefs. A manipulative field experiment demonstrated that the presence of dense assemblages of fish significantly enhanced nitrogen availability to the benthic plant community. In addition, this nitrogen availability led to significant increases in benthic primary production. Herbivore feeding quantified on the seagrass shoots demonstrated that the nitrogen enrichment of the primary producers lead to enhanced grazing intensity. This study addressed fundamental questions regarding habitat modification and facilitation of adjacent seagrass beds by reef-resident fish. The results have raised the possibility of a reciprocal, “positive feedback” relationship between seagrass communities and fish assemblages found at reefs, with each enhancing the growth and development of the other.

We aimed to identify biotic and abiotic factors underlying genetic structure and diversity of reef fish around Cuba. For three species, Stegastes partitus, Haemulon flavolineatum and Acanthurus tractus, we investigated the effects of shared environmental factors, such as the geography of the Cuban Archipelago, and specific characteristics, such as life history traits, on genetic structure and diversity. Samples were collected at five locations around Cuba. For S. partitus and H. flavolineatum, mitochondrial DNA and microsatellite loci were examined, whereas only mitochondrial DNA polymorphism was analyzed for A. tractus. All three species showed high genetic diversity. Mismatch distribution analyses suggest past population expansion in all species, but at different times in each species. Haplotype network and population genetic analyses suggest that: (1) S. partitus went through a recent population bottleneck in the late Pleistocene, (2) H. flavolineatum went through a population bottleneck but earlier, in the mid-Pleistocene, and (3) A. tractus has had a large and stable population size with coalescence times that go back to the late Pliocene. Genetic polymorphism in H. flavolineatum and A. tractus is homogeneous throughout the archipelago, whereas there is significant genetic structure in S. partitus. Genetic differentiation among S. partitus populations is most likely the result of the combined effects of egg type and oceanic current patterns along the Cuban coast.

Habitat selection by coral reef fish is influenced by a variety of biological and abiotic factors, but the relative importance of these factors is expected to change throughout ontogeny, espe- cially for species that utilize different habitats during their life cycle. In this study, 2 in situ choice ex- periments were designed to test the individual as well as the interactive effects of habitat structure and schooling (with conspecifics or heterospecifics) on refuge-seeking behavior of a coral reef fish. The experiments were conducted for 3 size-classes of the common reef fish Haemulon flavolineatum, a species that shows multiple habitat shifts throughout its ontogeny. We tested the hypothesis that, due to the additive effects of schooling and structure in providing suitable refuge, fish would be more attracted to a microhabitat with conspecifics or heterospecifics than to a microhabitat or conspecifics alone. In the habitat-only experiment, early juveniles (

Growth, survival, and abundance of young, and their connectivity to adult populations are four primary factors used to define nursery habitats. In the present study, we examined the relative quality of mangrove and seagrass habitats for juvenile French grunt, Haemulon flavolineatum (Desmarest, 1823), and schoolmaster, Lutjanus apodus (Walbaum, 1792), reef fish populations in St. Croix and Puerto Rico by using otolith microstructure to compare growth in these habitats. Mean daily otolith increment widths during the post-settlement period (30-60 d) of surviving late juvenile French grunts and schoolmaster collected in 2007 were compared between mangrove and seagrass habitats within each island. Increments widths were significantly wider during the post-settlement period in mangrove habitats at both study locations for both species. Our inferred growth interpretations indicate that mangroves may support faster growing fishes than seagrass habitats. However, due to the fact that the observed growth rates reflect the traits of the surviving cohorts among habitats, other factors, such as size-selective mortality/emigration and previous larval growth history, should also be considered in the interpretation of the observed growth patterns.

Ecosystems are intricately linked by the flow of organisms across their boundaries, and such connectivity can be essential to the structure and function of the linked ecosystems. For example, many coral reef fish populations are maintained by the movement of individuals from spatially segregated juvenile habitats (i.e., nurseries, such as mangroves and seagrass beds) to areas preferred by adults. It is presumed that nursery habitats provide for faster growth (higher food availability) and/or low predation risk for juveniles, but empirical data supporting this hypothesis is surprisingly lacking for coral reef fishes. Here, we investigate potential mechanisms (growth, predation risk, and reproductive investment) that give rise to the distribution patterns of a common Caribbean reef fish species, Haemulon flavolineatum (French grunt). Adults were primarily found on coral reefs, whereas juvenile fish only occurred in non-reef habitats. Contrary to our initial expectations, analysis of length-at-age revealed that growth rates were highest on coral reefs and not within nursery habitats. Survival rates in tethering trials were 0% for small juvenile fish transplanted to coral reefs and 24-47% in the nurseries. As fish grew, survival rates on coral reefs approached those in non-reef habitats (56 vs. 77-100%, respectively). As such, predation seems to be the primary factor driving across-ecosystem distributions of this fish, and thus the primary reason why mangrove and seagrass habitats function as nursery habitat. Identifying the mechanisms that lead to such distributions is critical to develop appropriate conservation initiatives, identify essential fish habitat, and predict impacts associated with environmental change.

Many animals release secretions in defense against predators. Some marine molluscs, including cephalopods (squid, octopus, cuttlefish) and gastropods (sea hares), release a colored ink secretion. Observational evidence supports the idea that inking is a defensive behavior that protects cephalopods from predators by forming a visual smokescreen or visual mimic (pseudomorph). Another possible function of cephalopod ink is to act against the chemical senses of predators either as a deterrent or distracting food mimic (phagomimic). Experimental tests of both hypotheses are lacking for cephalopods. In our study, we tested the hypothesis that squid use ink as a defense against attacks by predatory fish by performing three sets of experiments to examine the behavior of juvenile French grunts, Haemulon flavolineatum, toward ink from Caribbean reef squid, Sepioteuthis sepioidea. In the first set of experiments, a pseudomorph assay, in which ink was presented between a fish and a piece of food, assessed effects of ink on the approach and capture phase of a predator's attack. This showed that a pseudomorph of squid ink hindered the attack by significantly delaying food capture as well as evoking significantly more avoidance of or biting at the pseudomorph compared to a control pseudomorph of carboxymethylcellulose. A pseudomorph of carboxymethylcellulose plus food color to simulate the color of squid ink had a similar effect to the squid ink pseudomorph. In a second set of experiments, a disc assay, in which ink was added to meat-flavored paper discs, examined ink's effect on the consumption of food, simulating ink's protective effect if a squid and its ink are taken into a predator's mouth. This showed that squid ink added to meat-flavored discs significantly changed handling of the discs and increased, though non-significantly, their rejection. The same food color as used in the pseudomorph assay, when added to meat-flavored discs, significantly affected handling and rejection of the discs, showing that the food color itself, intended as a control, is unpalatable. In the third set of experiments, the disc assay was used to show that ink did not increase the acceptance of unflavored (i.e. without meat) discs, a result suggesting that ink is not a phagomimic. Our study presents the first experimental results supporting the hypothesis that inking protects squid against predatory fish, and that it acts during both the capture and consummatory phases of attacks: during the capture phase through visual and/or chemical effects against predators, and during the consummatory phase through unpalatable chemicals.

Juvenile French grunt Haemulon flavolineatum and schoolmaster Lutjanus apodus were captured in mangrove and seagrass stations in St. Croix, and Puerto Rico in 2006 and 2007 to deter- mine whether areas for juvenile fish can be discriminated by means of otolith chemistry. Concentra- tions of 16 elements were determined in 0-group fish otoliths using laser ablation-inductively coupled plasma mass spectrometry. Two stable isotopes, δ 18 O and δ 13 C, in French grunt and schoolmaster otoliths were also analyzed. Multi-elemental signatures for both species differed significantly (p < 0.001) among mangrove and seagrass stations within both islands. Furthermore, concentrations of 6 el- ements (Sr, Ba, Cu, Mg, Co, Na) as well as δ 18 O and δ 13 C for both species within each year differed sig- nificantly among mangrove and seagrass stations within islands (p < 0.001). Classification success for French grunt and schoolmaster juvenile areas within St. Croix across years ranged from 87 to 92% and from 76 to 77%, respectively, whereas in Puerto Rico, classification success for French grunt and schoolmaster for the 2 years ranged from 80 to 84% and 84 to 87%, respectively. Classification success between mangrove and seagrass habitats (stations combined) in Puerto Rico for French grunt ranged from 84 to 91%, and for schoolmaster ranged from 94 to 99%. In St. Croix, classification success for French grunt was 95 to 96%, and for schoolmaster was 86 to 89%. The percentages of French grunt subadults collected from forereef stations in St. Croix, identified as having resided as juveniles in man- grove habitats in 2006 and 2007, were 40 and 68%, respectively, while for Puerto Rico, these percent- ages were 70 and 74%. By contrast, for schoolmaster almost 100% of all fish in both islands resided as juveniles in mangrove habitats in both years. This study contains the first direct evidence of postsettle- ment fish movement connecting mangrove habitats to the reef using otolith chemistry.

Rockpools on Loggerhead Key in the Dry Tortugas National Park experience cyclic tidal changes in water quality and physical dimension resulting in ichthyofaunal assemblages that differ markedly from the adjacent coral reef. Within the beach rock formations and areas transitioning to the nearby reef, we observed 45 fish species; however, only four species – schoolmaster, Lutjanus apodus, French grunt, Haemulon flavolineatum, cocoa damsel, Pomacentrus variabilis, and frillfin goby, Bathygobius soporator – were found in all rockpools. All fishes were transient juveniles except for frillfin goby, which was a pool resident. High temperature tolerance, (Critical Thermal Maxima), and low oxygen tolerance, (Critical Oxygen Minima) for schoolmaster, French grunt, cocoa damsel, and frillfin goby were 40.9, 36.2, 37.6, 40.9 °C and 0.56, 0.77, 0.50, and 0.27 mg/L, respectively. All four species demonstrated thermal and hypoxia tolerance values similar to those published for species traditionally noted as abiotic specialists. Although fish distribution patterns in rockpools were likely influenced by structural complexity and spatial limitations, the relationship between pool morphology and species richness was weak, suggesting that physiological tolerance to high temperature and low oxygen among reef fishes may be more influential in determining which species inhabit the rockpools. Harsh thermal and oxic conditions that cannot be exploited by less tolerant species may be beneficial for some Loggerhead Key reef fishes in providing refuge from predators, foraging grounds, or potential nursery areas.

Tropical marine habitats are often energetically linked through feeding migrations by fish. A widely accepted assumption is that species of Haemulidae (grunts) undertake nocturnal feed- ing migrations from coral reefs to seagrass beds. This has been based on studies investigating migra- tions between small patch reefs and surrounding seagrass beds located in lagoons. Due to the size and location of these patch reefs, we argue that this does not represent migration from coral reef to seagrass ecosystems, and a literature search shows limited proof for such migration. We hypothesised that the spatial arrangement of these habitats in the seascape may have profound effects on the degree to which such migrations occur. Haemulon flavolineatum caught from seagrass beds located in semi-enclosed embayments, and thus isolated to a high degree from adjacent reefs, showed a diet and stable isotope signature of muscle tissue that differed from those collected from the coral reef. In contrast, fishes from open seagrass systems without restricted access from the reef showed the same stable isotope signature as those collected from the coral reef, suggesting feeding from the same habitat, viz. the seagrass beds. Additional visual census data showed that semi-enclosed seagrass beds did not have elevated densities of large-sized fish at night, which would be expected if large individuals from the reef migrated to the seagrass beds to feed. The data thus show that interlinkages between coastal ecosystems, such as coral reefs and seagrass beds, by fishes may strongly depend on the spatial arrangement of habitats within the seascape.

Many of the most abundant fish species using mangroves in the Caribbean also use other habitat types through daily home range movements and ontogenetic habitat shifts. Few studies, however, have considered the structure of the surrounding seascape when explaining the spatial distribution of fish within mangroves. This study develops an exploratory seascape approach using the geographical location of mangroves and the structure of the surrounding seascape at multiple spatial scales to explain the spatial patterns in fish density and number of species observed within mangroves of SW Puerto Rico. Seascape structure immediately surrounding mangroves was most influential in determining assemblage attributes and the density of juvenile Haemulon flavolineatum, which were significantly higher in mangroves with high seagrass cover (>40%) in close proximity ( 40 and >15%, respectively) in close proximity ( 40%) of seagrass within 600 m of the mangrove edge. We argue that there is an urgent need to incorporate information on the influence of seascape structure into a wide range of marine resource management activities, such as the identification and evaluation of critical or essential fish habitat, the placement of marine protected areas and the design of habitat restoration projects.

Item does not contain fulltext Studies showing that tagged reef fish connect different habitat types are crucial for effective ecosystem management on a seascape-level, but are rare. Therefore we analysed movement of juvenile Haemulon flavolineatum and Haemulon sciurus among seagrass beds, mangroves and fossilised eroded coral shoreline. Fishes were tagged individually with external, short-term bead-tags (both species) or with internal, long-term coded wire tags (H. flavolineatum only). We also tested the hypothesis that in spatially continuous habitat types with many seemingly suitable resting sites, these fishes show high fidelity to only a small number of sites. The linear distribution range of daytime sites was 4–171 m for H. flavolineatum and 4–152 m for H. sciurus, but in agreement with our hypothesis, externally tagged fishes showed high fidelity to small spatial areas within this range: the percentage of resightings within a 10 m radius of the core area of presence (i.e. the site used most intensively) was 69% for bead-tagged H. flavolineatum, and 62% for H. sciurus during the 47-day study-period. Site fidelity was also present over a longer time span: of the 1114 coded wire tagged H. flavolineatum 51 were recaptured and 49 of them were still present at the tagging location after 163–425 days at liberty. Median linear movement within a day was small (5 m for H. flavolineatum and 8 m for H. sciurus), nonetheless, part of the bead-tagged Haemulidae moved from shoreline shelter habitats (mangroves and rocky shoreline) to adjacent seagrass beds (mean ± SD distance moved 23 ± 10 m) in the afternoon, likely to start feeding there during daylight. When comparing the habitat type occupied during the late afternoon (15:30–17:30 h) and morning (8:00–10:30 h) on two subsequent days, most movement occurred from seagrass beds back to shoreline habitats (mean distance moved 23 ± 10 m), indicating that in the morning these fishes had returned to shelter sites at the shoreline. The current study thus shows existence of connectivity between back-reef habitats through fish movement on a relatively small spatial scale.

The transition from a planktonic larval stage to a benthic or demersal juvenile stage is a crucial event in the life history of coral reef fishes, and recruitment success has a strong influence on reef-fish population size. Post-settlement predation is thought to limit recruitment success. Most studies on post-settlement predation have focused on piscivorous reef fishes. However, recent studies in the tropical Pacific Ocean suggest that blood-feeding ectoparasites may also be an important source of predation. Here we provide further evidence that a gnathiid ectoparasite is capable of such "micropredation" on settlement-stage fish in the eastern Caribbean Sea. On 12 occasions in May-August, 2014 and 2015, during plankton light-trap recovery, we observed post-settlement fishes from the families Apogonidae, Bothidae, Gobiidae, Labrisomidae, and Tripterygiidae with attached ectoparasitic juvenile gnathiid isopods. In one laboratory experiment in which 10 settlement-stage French grunt, Haemulon flavolineatum (Desmarest, 1823), were fed upon by an average of one gnathiid per fish, all fish died compared to none in the control group. In a subsequent experiment in which individual settlement-stage French grunt were exposed to 0–3 gnathiids each, all 50 fish that were fed upon by at least one gnathiid died, compared with only one of 78 that were not fed on by any gnathiids. Combined with observations on damselfishes from the Pacific Ocean, these findings suggest that gnathiids are capable of micropredation on larval fish at time of reef settlement and that micropredation should be further evaluated as a factor affecting success of settlement and thus recruitment success of coral reef fishes.

Item does not contain fulltext Abstract Caribbean seagrass beds are important feeding habitats for so-called nocturnally active zoobenthivorous fish, but the extent to which these fishes use mangroves and seagrass beds as feeding habitats during daytime remains unclear. We hypothesised three feeding strategies: (1) fishes feed opportunistically in mangroves or seagrass beds throughout the day and feed predominantly in seagrass beds during night-time; (2) fishes start feeding in mangroves or seagrass beds during daytime just prior to nocturnal feeding in seagrass beds; (3) after nocturnal feeding in seagrass beds, fishes complete feeding in mangroves or seagrass beds during the morning. We studied the effect of habitat type, fish size, social mode and time of day on resting and feeding behaviour of large juvenile (5�10 cm) and sub-adult (10�15 cm) Haemulon flavolineatum in mangroves and seagrass beds during daytime. Sub-adults occurred in mangroves only, spent most time on resting, and showed rare opportunistic feeding events (concordant with strategy 1), regardless of their social mode (solitary or schooling). In contrast, large juveniles were present in both habitat types and solitary fishes mainly foraged, while schooling fishes mainly rested. Exceptions were small juveniles (�5 cm) in seagrass beds which foraged intensively while schooling. Large juveniles showed more feeding activity in seagrass beds than in mangroves. In both habitat types, they showed benthic feeding, whereas pelagic feeding was observed almost exclusively in the seagrass beds. In both habitat types, their feeding activity was highest during 8:00�10:30 hours (concordant with strategy 3), and for seagrass fishes, it was also high during 17:30�18:30 hours (concordant with strategy 2). The study shows that both mangroves and seagrass beds provide daytime feeding habitats for some life-stages of H. flavolineatum, which is generally considered a nocturnal feeder

Lutjanus apodus (Schoolmaster) were collected from several mangroves and coral reefs at Turneffe Atoll, Belize, in order to investigate whether elemental concentrations from the otolith edge could be used as a means to identify the habitat (mangrove or coral reef) and site (9 mangrove sites and 6 reef sites) from which they were collected. Results of a two factor nested MANOVA (sites nested within habitat) indicated significant differences in elemental concentrations between habitats (i.e., mangrove versus reef) as well as among sites. When separate Linear Discriminant Function Analyses (LDFA) were used to assess whether the spatial variability in otolith chemistry was sufficient to differentiate individuals to their respective habitats or sites, the results indicated that fish were classified (jackknife procedure) with a moderate to poor degree of accuracy (i.e., on average, 67% and 40% of the individuals were correctly classified to the habitat and site from which they were collected, respectively). Using a partial Mantel test we did not find a significant correlation between the differences in otolith elemental concentrations between sites and the distance between sites, while controlling the effect of habitat type (mangrove or reef). This suggests that for mangrove and reef sites at Turneffe Atoll, Belize, the overlap in terms of L. apodus otolith elemental concentrations is too high for investigations of fish movement. Finally, by comparing previously published Haemulon flavolineatum otolith chemistry to that of L. apodus we assessed whether these species showed similar habitat and/or site specific patterns in their otolith chemistry. Although both species were collected from the same sites our results indicated little similarity in their elemental concentrations, thus suggesting that habitat and site elemental signatures are species specific.

The extent of dispersal by pelagic larvae in marine environments, including coral reefs, is central for understanding local population dynamics and designing sustainable marine reserves. We present here the first example of a clear stepping-stone genetic structure throughout the Caribbean basin for a common coral reef species, the French grunt (Haemulon flavolineatum). Analysis of microsatellite DNA markers indicated that French grunt population structure may be characterized by overlapping populations throughout the Caribbean, influenced by independent population dynamics but with no fixed geographical boundaries. In addition, different spatial genetic patterns were found in different oceanographic regions. A second species, the bluehead wrasse (Thalassoma bifasciatum), has a much longer pelagic larval duration than French grunts and showed no explicit spatial pattern of genetic variation. This finding is concordant with the hypothesis of a positive relationship between larval dispersal and duration in the plankton. While the magnitude of the genetic signal of population structure in French grunts was very low (FST≈0.003), the pattern of isolation-by-distance throughout the Caribbean indicated considerable population structure with important ecological and conservation significance.

Contains fulltext : 35368.pdf (Publisher’s version ) (Open Access) Mangroves and seagrass beds are considered nurseries for juvenile fish, but little experimental evidence exists to elucidate which factors make them attractive habitats. A multifactorial field experiment on the use of these habitats by juvenile reef fish and their behaviour was performed during daytime with experimental units (EUs: 1 �1 �0.8 m), each representing a unique combination of the factors structure, shade, and food, using artificial seagrass leaves (AS) and artificial mangrove roots (AM). Diurnally active herbivores were most abundant in EUs containing food, and grazed on algae growing on the structures, but were not attracted to structures in the absence of food. The most abundant diurnally active zoobenthivores (Eucinostomus spp.) were present in highest numbers in any EU with food, where they fed on zoobenthos or rested on the bottom. The nocturnally active zoobenthivore/zooplanktivore Ocyurus chrysurus and the diurnally active piscivore Sphyraena barracuda were primarily attracted to structure, in which they rested and were not observed to feed. Haemulon flavolineatum was mainly attracted to AS, Lutjanus mahogoni was attracted to AS or shade, whereas L. apodus, O. chrysurus and S. barracuda were found in AM as well as in AS. The data suggest that during daytime, herbivores and diurnally active zoobenthivores are probably attracted to mangroves and seagrass beds primarily by food, and nocturnally active zoobenthivores by structure (in interaction with shade) that offers shelter from predation. S. barracuda is also attracted primarily to structure, but the larger individuals probably use this for ambush predation rather than for protection. In conclusion, our experiment clarifies that presence of structure, food and shade significantly contribute to the attractiveness of mangroves and seagrass beds to juvenile reef fish.

We tested the hypothesis for several Caribbean reef fish species that there is no difference in nursery function among mangrove, seagrass and shallow reef habitat as measured by: (a) patterns of juvenile and adult density, (b) assemblage composition, and (c) relative predation rates. Results indicated that although some mangrove and seagrass sites showed characteristics of nursery habitats, this pattern was weak. While almost half of our mangrove and seagrass sites appeared to hold higher proportions of juvenile fish (all species pooled) than did reef sites, this pattern was significant in only two cases. In addition, only four of the six most abundant and commercially important species (Haemulon flavolineatum, Haemulon sciurus, Lutjanus apodus, Lutjanus mahogoni, Scarus iserti, and Sparisoma aurofrenatum) showed patterns of higher proportions of juvenile fish in mangrove and/or seagrass habitat(s) relative to coral reefs, and were limited to four of nine sites. Faunal similarity between reef and either mangrove or seagrass habitats was low, suggesting little, if any exchange between them. Finally, although relative risk of predation was lower in mangrove/seagrass than in reef habitats, variance in rates was substantial suggesting that not all mangrove/seagrass habitats function equivalently. Specifically, relative risk varied between morning and afternoon, and between sites of similar habitat, yet varied little, in some cases, between habitats (mangrove/seagrass vs. coral reefs). Consequently, our results caution against generalizations that all mangrove and seagrass habitats have nursery function.

Using French Grunts (Haemulon flavolineatum) held captive within mangrove and reef sites, we determined (a) whether otolith microchemical differences existed between mangroves and reefs separated at a biologically relevant spatial scale (0.25–7.1 km), (b) whether patterns in elemental concentrations were consistent across years, and (c) whether it was possible to identify whether a given fish occupied a mangrove as a juvenile. Three sites were established at Great Exuma, Bahamas (two reefs and one mangrove, May 2001) and at Turneffe Atoll, Belize (one reef and two mangroves, August 2001 and 2002). Using concentrations of Sr and Ba, discriminant function analysis (DFA) indicated unique spatial microchemical signatures of fish from each of the three Bahamas sites allowing an average correct classification of 77%. Using concentrations of Sr, Ba, Sn and Pb (2001), and in addition Li, Mg, Cu and Rb (2002), DFA of the three Belize sites indicated an average correct classification of 68% and 85% in 2001 and 2002, respectively. To assess temporal variability in otolith microchemistry, we compared microchemical signatures of Belize fish from 2001 to those from 2002. On average, 42% of fish from 2002 were correctly classified to their captive sites using chemical information from 2001, thus suggesting considerable temporal variability in otolith microchemistry. Finally, to identify whether a given fish occupied a mangrove during its juvenile stage, we ablated the juvenile portion of the otolith taken from reefs in Belize 2002. Results of this analysis indicated that 36% of 39 individuals taken from the reef had a signature more representative of one of the mangrove sites. Although otolith microchemistry varied temporally and our analysis was restricted to the grouping of individuals to only one of three sites, mangroves appeared to contribute to reef populations.

There is an increasing interest in the relationship between adult coral reef fishes and their parasites; however, there is almost no information concerning post larvae (i.e. newly recruited) fish and their parasites. Newly recruited and juvenile fish are highly sensitive to their environment and they have a very low survival rate. Fish grouping behavior has been studied in several ways and many studies have shown that increasing group size might be a way to share a cost linked to parasitism, via a dilution effect. To my knowledge, this hypothesis has never been tested for juveniles of fish. The potential influence of school size and density of a juvenile coral reef fish, Haemulon flavolineatum (Haemulidae), on the success of a monogenean fish parasite, Haliotrema sp., was studied. First, the fish acquired their monogeneans when they were more than 40 mm long, size corresponding also to a change in their foraging behavior. Second, there was a positive effect of fish density on the success of the establishment of the parasite on the host population. Finally, although the parasite success was not directly related to fish group size, the parasite abundance was higher for intermediate shoal size. These results are discussed in terms of the consequence parasitism may have on a fish's shoaling and to a larger extent on the fish population.

The spatial size distribution of grunts and snappers have previously indicated the separation of juveniles in nursery habitats from the adults on the coral reef. This implies life cycle migrations from nursery habitats (such as seagrass beds and mangroves) to the coral reef. If diet shifts are related to such migrations, then the diets of these fish must change before or around the fish size at which such migrations take place. A wide size range of juveniles of two grunt species ( Haemulon sciurus and Haemulon flavolineatum ) and of two snapper species ( Lutjanus apodus and Ocyurus chrysurus ) were caught in seagrass beds and mangroves, and their gut contents identified and quantified. Regression analysis between fish size and dietary importance of small crustaceans showed a negative relationship in all four species. Positive relations were found for H. sciurus , L. apodus and O. chrysurus between fish length and the dietary importance of decapods, and for L. apodus and O. chrysurus between fish length and prey fish importance. Critical changes in the fish diets with fish size were examined by application of a Canonical Correspondence Analysis (CCA). The CCA yielded three clusters of size-classes of fishes with similar diets, and application of a Mantel test showed that each of these clusters had significantly different diets, and that each cluster diet was significantly specialised. The size at which a fish species ‘switched’ from one cluster to another was compared with size-at-maturity data and with the typical size at which these species migrate from the nursery habitats to the coral reef. H. sciurus and H. flavolineatum may be prompted to migrate from the nursery habitats to coral reef habitats because of dietary changes, or because of the development of the gonads. For L. apodus and O. chrysurus , a dietary changeover forms a more likely explanation for nursery-to-reef migrations than does sexual maturation because these species reach maturity at sizes much larger than the maximum size of individuals found in nursery habitats. Although other factors may theoretically initiate or promote the migration patterns, the results of this study indicate that ontogenetic dietary changes may crucially influence the nursery-to-coral reef migrations of these reef fish species.

We evaluated the day-time distribution of juvenile and adult French grunts, Haemulon flavolineatum, relative to the spatial configuration of hard and soft bottom areas in a benthic landscape. Probability of juvenile presence on hard bottom sites was inversely correlated with distance to soft bottom. Adults presence at hard bottom sites showed no significant relationship with distance to soft bottom. A significant and positive relationship was found between presence of juveniles on hard bottom sites and area of soft bottom within 100 m, but no significant relationship was found for area of soft bottom within 500 m. Adults exhibited no significant relationship with area of soft bottom for either distance tested. These distributions are suspected to be the result of the combined influence of larval settlement patterns and foraging behaviors associated with hard and soft bottom. This study indicates that data collected at very fine scales can be analyzed in the context of the broad-scale mosaic of habitats in the benthic landscape to predict patterns of fish distribution. Such spatially explicit conclusions are not possible through analysis of fine-scale or broad-scale data alone.

Grunts are fish that are well known to vocalize, but how they produce their grunting sounds has not been clearly identified. In addition to characterizing acoustic signals and hearing in the French grunt Haemulon flavolineatum, the present study investigates the sound-production mechanism of this species by means of high-speed X-ray videos and scanning electron microscopy of the pharyngeal jaw apparatus. Vocalizations consist of a series of stridulatory sounds: grunts lasting ~47 ms with a mean period of 155 ms and a dominant frequency of ~700 Hz. Auditory capacity was determined to range from 100 to 600 Hz, with greatest sensitivity at 300 Hz (105.0±11.8 dB re. 1 μPa). This suggests that hearing is not tuned exclusively to detect the sounds of conspecifics. High-speed X-ray videos revealed how pharyngeal jaws move during sound production. Traces of erosion on teeth in the fourth ceratobranchial arch suggest that they are also involved in sound production. The similarity of motor patterns of the upper and lower pharyngeal jaws between food processing and sound production indicates that calling is an exaptation of the food-processing mechanism.

Various species of aquatic animals have complex life cycles and utilize differenthabitats during consecutive phases of their life cycles. For example, many marine fish speciesoccupy different habitat types during juvenile and adult life stages. Juveniles of some speciesrecruit to inshore nursery habitats such as mangroves and seagrass beds, whereas large adultstend to dominate coral reefs. The mechanisms underlying apparent cross-habitat distribution pat-terns by life stage remain uncertain for many species. Here, we investigated potential mecha-nisms that produce a 5-phase, and possibly even a 6-phase life cycle pattern in a common Carib-bean coral reef fish species Haemulon flavolineatum (French grunt) across multiple coastalhabitats. At each discrete life stage, individuals were faced with important and stage-specific eco-logical trade-offs that could significantly augment fitness. Pelagic larvae settled on rubble habitatsnear bay entrances where they reached an optimum between predation risk (survival) and foodabundance (growth). Individuals subsequently shifted to seagrass beds, likely as a result of in -creased food resources, followed by a shift to mangroves as predation refugia. Before the uni-directional movement between bays and coral reefs, some fishes shifted from mangroves to boul-der/notch habitats. Likely, this habitat serves as an intermediate stop before their final shift to thecoral reef, where they reach maturity and reproduce. This study reveals ecological linkages andflows among habitat types that are of direct conservation importance to these ecosystems. Further-more, the identification of mechanisms that give rise to cross-habitat distribution patterns of mar-ine fishes in general might lead to enhanced conservation management solutions to declines infisheries at larger scales.KEY WORDS: Ontogenetic habitat shifts · Life cycle · Nursery · Food abundance · Condition ·Maturation · Trade-offs

The nursery function of various biotopes for coral reef fishes was investigated on Bonaire, Netherlands Antilles. Length and abundance of 16 commercially important reef fish species were determined by means of visual censuses during the day in six different biotopes: mangrove prop-roots ( Rhizophora mangle ) and seagrass beds ( Thalassia testudinum ) in Lac Bay, and four depth zones on the coral reef (0 to 3 m, 3 to 5 m, 10 to 15 m and 15 to 20 m). The mangroves, seagrass beds and shallow coral reef (0 to 3 m) appeared to be the main nursery biotopes for the juveniles of the selected species. Mutual comparison between biotopes showed that the seagrass beds were the most important nursery biotope for juvenile Haemulon flavolineatum , H. sciurus , Ocyurus chrysurus , Acanthurus chirurgus and Sparisoma viride , the mangroves for juvenile Lutjanus apodus , L. griseus , Sphyraena barracuda and Chaetodon capistratus , and the shallow coral reef for juvenile H. chrysargyreum , L. mahogoni , A. bahianus and Abudefduf saxatilis . Juvenile Acanthurus coeruleus utilized all six biotopes, while juvenile H. carbonarium and Anisotremus surinamensis were not observed in any of the six biotopes. Although fishes showed a clear preference for a specific nursery biotope, most fish species utilized multiple nursery biotopes simultaneously. The almost complete absence of juveniles on the deeper reef zones indicates the high dependence of juveniles on the shallow water biotopes as a nursery. For most fish species an (partial) ontogenetic shift was observed at a particular life stage from their (shallow) nursery biotopes to the (deeper) coral reef. Cluster analyses showed that closely related species within the families Haemulidae, Lutjanidae and Acanthuridae, and the different size classes within species in most cases had a spatial separation in biotope utilization.

Established hypotheses state that the rate of predation on coral reef fish should be highest during crepuscular periods (dawn and dusk) intermediate diurnally, and lowest nocturnally. We examined the relative risk of predation on juvenile French grunts (Haemulon flavolineatum Desmarest) during diurnal, dusk, and nocturnal periods on the fore- and back-reef at Teague Bay, U.S. Virgin Islands in July and August 1996. Tethering-devices recorded the exact amount of time between attaching a prey fish to its tether and subsequent predation on the prey fish. As tethering of prey usually inflates the actual rate of predation, times from our tethering devices were used to establish only the relative predation risk among treatments. During 3-h diurnal and nocturnal tethering experiments, relative predation was significantly higher during the nocturnal period, and differences between side of reef were not significant. In 30-min tethering experiments, which included all three time periods, the relative predation risk was significantly higher during dusk and nocturnal periods than during the diurnal period. Relative predation was not significantly different between the dusk and nocturnal periods, or between side of reef during any time period. The unexpected finding that the diurnal period had the lowest relative risk of predation indicates that the timing of predation events on reefs, as well as the adaptive reasons for nocturnal larval settlement, may need to be re-examined.

Eight species of prospective cleaners, four fishes (sharknosed goby Gobiosoma evelynae, and juveniles of bluehead (wrasse) Thalassoma bifasciatum, Spanish hogfish Bodianus rufus and gray angelfish Pomaccanthus arcuatus) and four shrimps (cleaner shrimp Lysmata grabhami, Pederson cleaner shrimp Periclimenes pedersoni, banded coral shrimp Stenopus hispidus and golden coral shrimp Stenopus scutellatus) were evaluated in aquaria for their ability to remove newly settled juveniles of the fish-parasitic cymothoid isopod Anilocra haemuli from French grunts Haemulon flavolineatum. Periclimenes pedersoni removed all isopods almost immediately. No other cleaners removed any isopods over a 24 hr challenge period. This study is the first evidence that cleaner shrimps can remove juvenile cymothoid isopods.

SUMMARYSusceptibility to infestation by a gnathiid isopod (Gnathia marleyi:Crustacea: Isopoda) was examined among 16 species from 9 families and 3 orders of common Caribbean reef fishes off St. John, United States Virgin Islands. Fish were placed in cages during times of peak gnathiid activity. Individuals from most (n=14) species were compared against a single species (French Grunt,Haemulon flavolineatum) that served as a standard and effectively controlled for the effects of habitat and variation in gnathiid abundance on exposure to and the likelihood and intensity of host infestation by gnathiids. All species were susceptible to infestation by gnathiids, with individual hosts harbouring up to 368 gnathiids. However, there was significant variation in levels of infestation among the 14 comparison species. Controlling for body size, nocturnal species from the families Haemulidae and Lutjanidae had the highest gnathiid infestation. Our finding that haemulids and lutjanids are particularly susceptible has important implications for the role of gnathiids in Caribbean reef food webs, given the role members of these families play in trophic connectivity between reefs and associated habitats. To our knowledge this is the first manipulative field study to examine variation among potential hosts in susceptibility to an ectoparasite in any terrestrial or aquatic system and is the greatest number of teleost hosts documented for any gnathiid species.

Retinomotor movements of three size classes of juvenile French grunts, Haemulon flavolineatum, are characterized during the periods of their daily evening and dawn migration. Differences in the extension and withdrawal of the cones correlate with the earlier departure and later return to the daytime schooling sites of the smallest juveniles as compared to the larger juveniles. For each size class changes in the dimensions and retinal distribution of the cone cells and optical properties of the eye are used to estimate differences in photosensitivity under conditions of equal radiant intensities. For a target subtending any given angle, calculation indicates that the largest juveniles should be capable of discrimination at one-thousandth the light intensity of the smallest juveniles. The differences in potential photosensitivity correlate with the different intensities at which they migrate. The likely trigger to initiate their daily migrations probably involves circadian factors at dawn and extension of the single cones from the focal region of the retina prior to the evening migration.

An unusual testicular structure in the white grunt, Haemulon plumieri, and the French grunt, H. flavolineatum, and a urinary exocrine gland in H. flavolineatum are described. The testes of both species are comprised predominantly of efferent ducts, with spermatogenetic tissue restricted to the gonadal periphery. The epithelial cells of the efferent ducts produce glycogen which may serve a role in the storage and nutrition of sperm. The urinary gland is a male accessory gland thought to be associated with reproduction. The gland is mesonephric in origin and the epithelial cells of the gland produce mucins which may be involved in intraspecific chemical communication.

Nocturnal foraging habitats of Haemulon flavolineatum and H. sciurus were investigated in the backreef habitat around Tobacco Caye, Belize. Grunts leave the reef at dusk to forage in the grass beds and sand flats surrounding the reef. The hypothesis that French and bluestriped grunts use separate foraging habitats was examined by following tagged fishes from their diurnal territories or schooling sites to nocturnal foraging grounds. The tag consisted of a small, glowing Cyalume light stick sutured to the dorsal musculature of the fish, next to the first dorsal fin. Surveys of foraging habitats were done to support the tracking study. Large quadrats (225 m2) were set out over the sand flats and grass beds during the day. The numbers of French and bluestriped grunts feeding in each habitat were counted one hour after dark. Foraging French grunts used sand flats, whereas bluestriped grunts usually fed in grass beds. Repeated sightings of two French grunts and one bluestriped grunt in the same individual night-time locations support the hypothesis that nocturnal foraging sites may be used repeatedly by the same individuals.