Reproductive behavior of the sergeant major,Abudefduf saxatilis,within a closed system aquarium

Synopsis The reproductive and social biology of the sergeant major,Abudefduf saxatilis, was studied for six months in The Living Seas aquarium (the largest aquarium ever constructed). The purpose of the study was to discern possible behavioral differences between captive and wild breeding populations of this species. A total of 350 h of observation were obtained using closed circuit SCUBA, open circuit SCUBA, and remote operated vehicles. Slight differences were observed in the behavior of individuals in the sample population and those seen in wild populations. These differences may be due to the effects of a controlled closed system on the biology of these fishes.     

Sound production and associated behavior in a cichlid fish,Cichlasoma centrarchus. II. Breeding pairs

Synopsis Pairs of Cichlasoma centrarchus were observed daily in the laboratory. Both males and females made sounds during a breeding cycle but all sounds were aggressive in context; no sounds were heard to accompany courtship. Males made more sounds before spawning than afterwards and these were associated with territorial defense and with establishment of dominance over the female. Females produced more sounds after spawning than before, most in the context of brood defense but some toward the male during pre-spawning nest preparation. Prior to spawning, the number of sounds made by the males toward their mates increased but the aggressive actions accompanying them became less intense. No such inverse correlation of agonistic intensity with number of sounds made was found for the females. From this study and earlier ones by the author it was concluded that sound in this species is a threat display which 1) provides an expression for agonism alternative to the performance of actions which could injure the female or drive her away, and 2) lessens the risk of injury to male or female during territory or brood defense.     

Reef fish community structure on coastal islands of the southeastern Brazil: the influence of exposure and benthic cover

Patterns of community structure in the marine environment are strongly influenced by population relationships to biotic and physical gradients. The aim of this work is to explore the relationships of tropical rocky reef fish assemblages to wave exposure and benthic coverage in a gradient of distance from the coast. The study was conducted on the Guarapari Islands, southeastern Brazilian coast. Fish were sampled by underwater visual census (166 transects) and benthic cover was estimated with quadrats (223 replicates). Two main kinds of habitats were found to be derived from the close interrelation between exposure and benthic coverage: (1) exposed areas subjected to major hydrodynamic forcing, and (2) sheltered or moderately exposed areas. The first group is associated with mid-water schooling species like planktivorous labrids and Chromis, piscivorous Caranx, as well as gregarious omnivores like Abudefduf and Diplodus. In terms of benthic composition, macroalgae and encrusting calcareous algae prevail in this high-energy habitat. The second group is characterized by site-attached and reef associated species like territorial pomacentrids, invertebrate feeders such as Halichoeres poeyi and Chaetodon striatus, and small cryptobenthic fishes (e.g. blenniids and labrisomids). Turf algae, zoanthids and massive corals dominate this environment. Environmental plasticity is also common with some genera showing high abundances in all habitats (e.g. Holocentrus, Haemulon, Acanthurus). Examples of the coupling of food availability and fish abundance were found. Planktivores, territorial herbivores, macroalgae browsers and spongivores were positively related with the abundance of their preferred food items along the exposure gradient. Within-family analyses of Pomacentridae and Labridae showed that niche partitioning is likely occurring and seems to be mediated by swimming ‘ability’ and associated feeding performance.     

A forceful upper jaw facilitates picking-based prey capture: biomechanics of feeding in a butterflyfish,Chaetodon trichrous

Biomechanical models of feeding mechanisms elucidate how animals capture food in the wild, which, in turn, expands our understanding of their fundamental trophic niche. However, little attention has been given to modeling the protrusible upper jaw apparatus that characterizes many teleost species. We expanded existing biomechanical models to include upper jaw forces using a generalist butterflyfish, Chaetodon trichrous (Chaetodontidae) that produces substantial upper jaw protrusion when feeding on midwater and benthic prey. Laboratory feeding trials for C. trichrous were recorded using high-speed digital imaging; from these sequences we quantified feeding performance parameters to use as inputs for the biomechanical model. According to the model outputs, the upper jaw makes a substantial contribution to the overall forces produced during mouth closing in C. trichrous. Thus, biomechanical models that only consider lower jaw closing forces will underestimate total bite force for this and likely other teleost species. We also quantified and subsequently modeled feeding events for C. trichrous consuming prey from the water column versus picking attached prey from the substrate to investigate whether there is a functional trade-off between prey capture modes. We found that individuals of C. trichrous alter their feeding behavior when consuming different prey types by changing the timing and magnitude of upper and lower jaw movements and that this behavioral modification will affect the forces produced by the jaws during prey capture by dynamically altering the lever mechanics of the jaws. In fact, the slower, lower magnitude movements produced during picking-based prey capture should produce a more forceful bite, which will facilitate feeding on benthic attached prey items, such as corals. Similarities between butterflyfishes and other teleost lineages that also employ picking-based prey capture suggest that a suite of key behavioral and morphological innovations enhances feeding success for benthic attached prey items.     

The biology of the golden hammerhead,Sphyrna tudes,off Trinidad

Synopsis The golden hammerhead is a poorly known species of shark that inhabits the northeastern coast of South America from Venezuela to Uruguay. It is found in coastal waters at depths of 9–40 m over muddy bottoms. It is a small species which attains a maximum size of 122 cm and 9 kg. The most distinctive characteristic of this species is its striking bright orange or yellow color. Juveniles less than 80 cm TL are bright yellow or orange; adults are pale yellow. The color is apparently due to pigments present in their diets; juveniles feed primarily on shrimp, while adults feed on fish and catfish eggs. Two pigments have been isolated and their characterization is presently being ascertained. Males mature at about 80 cm TL; females mature at about 98 cm TL. Ovulation and mating occur in August. Gestation appears to last about ten months. Parturition occurs in shallow waters from late May to June. Broods consist of five to twelve young, which measure about 30 cm at birth. The ovarian cycle runs concurrently with the gestation cycle, so it is likely that females are fertilized shortly after parturition, and that the species reproduces yearly.     

Natural fishing experiments in marine reserves 1983–1993: community and trophic responses

 This study examined the effect of fishing on the density, biomass, species richness and overall structure of the reef fish community at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. A series of natural fishing experiments over this period involving marine reserves were monitored at each island, where estimates of fishing intensity and selectivity were available. Fishing intensity (15% and 25% of biomass removed per year at Sumilon and Apo, respectively) was high enough to affect total community biomass, but not density, significantly. Species richness was not affected significantly by fishing, except at Sumilon reserve. The fishery was relatively non-selective with most families/trophic groups caught roughly in proportion to their contribution to community biomass. Thus fishing did not alter the relative abundance of the major families/trophic groups significantly, except during a period of use of explosives and drive nets in the Sumilon reserve. At the level of family/trophic group the community displayed strong resilience of structure. There was little evidence of secondary effects e.g. declines in abundance of large predators resulting in measurable increases in abundance of their prey. This resilience of the community to the effects of fishing most likely results from three important community attributes (open nature of the component populations, likely maintenance of upstream recruitment supply and apparent lack of any obvious “keystone” species or families) and one important characteristic of the fishery (relatively non-selective with respect to the components of the community). Accepted: 30 June 1998     

The reproductive biology of closely related coral species: gametogenesis in<Emphasis Type="Italic"> Madracis</Emphasis> from the southern Caribbean

Reproductive patterns were studied in closely related coral species of the genus Madracis on Curaçao, Netherlands Antilles. Gonadal development of six sympatric species was examined over a 13-month period. Reproductive differences among Madracis species are small. All species are hermaphroditic brooders and show similar patterns in gamete development. Timing of gamete maturation is positively correlated with seawater temperature in all species. Oocyte development typically begins in June and precedes the development of spermaries. Mature gametes, male and female, are present from August to November when seawater temperatures reach their yearly maximum. Developmental pathways for male and female gametes are identical among species. Interspecific differences exist in the number and size of oocytes. Our data indicates that differences in gametogenic development between closely related, but ecologically different subspecies are small or absent and do not necessarily match with species separations based on morphological criteria.Communicated by Topic Editor D. Barnes     

Natural fishing experiments in marine reserves 1983 – 1993: roles of life history and fishing intensity in family responses

 This study examined the effect of fishing on the abundance and species richness of families of coral reef fish at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. Natural fishing experiments occurred in marine reserves at each island, where long term estimates of fishing intensity were available. Responses to fishing were interpreted in terms of life histories of fish. The intensity of fishing and fish life histories were generally good predictors of the differential rates of decline and recovery of abundance in response to fishing. Large predators had vulnerable life histories (low rates of natural mortality, growth and recruitment) and were subjected to high intensity fishing. They declined significantly in density when fished and increased significantly but slowly when protected from fishing. Caesionidae, a family with a life history resilient to fishing (high rates of natural mortality, growth and recruitment) but fished intensively also declined rapidly in abundance when fished. Thus, knowledge of life history alone was insufficient to predict response to fishing. Acanthuridae were fished relatively hard and had a life history of intermediate vulnerability but displayed weak responses to fishing. Thus level of fishing intensity alone was also not sufficient to predict response to fishing. For Chaetodontidae, effects of fishing conformed to expectations based on life history and fishing intensity at one island but not the other. Three families with intermediate vulnerability and subjected to intermediate to light fishing (F. Scaridae, Labridae and Mullidae) displayed predictably weak responses to fishing, or counter-intuitive responses (e.g., increasing in abundance following fishing). These counter-intuitive responses were unlikely to be secondary effects of increase in prey in response to declines of predators. Two lightly-fished families with resilient life histories (F. Pomacentridae, Sub F. Anthiinae) predictably displayed weak numerical responses to fishing except during a period of use of explosives and drive nets. Accepted: 30 June 1998     

Resilience of predators to fishing pressure on coral patch reefs

Numbers and biomass of piscivorous fish and their predation on other fish may often be high in undisturbed coral reef communities. The effects of such predation have sometimes been studied by removal of piscivores (either experimentally or by fishermen). Such perturbations have usually involved removal of large, highly vulnerable, mobile piscivores that are often actively sought in fisheries. The effects of fishing on smaller, demersal, semi-resident piscivores have been little studied. We studied such effects on the fish communities of patch reefs at Midway atoll by experimentally removing major resident, demersal, piscivorous fishes. First, four control reefs and four experimental reefs were selected, their dimensions and habitats mapped, and their visible fish communities censused repeatedly over 1 year. Census of all control and experimental reefs was continued for the following 39 months, during which known piscivores were collected repeatedly by hand spearing. Records were kept of catch and effort to calculate CPUE as an index of predator density. Spearfishing on the experimental reefs removed 2504 piscivorous fish from 12 families and 43 taxa (mostly species). The species richness of the catch did not show an overall change over the duration of the experiment. Spearman rank correlation analysis showed some unexpected positive correlations for density in numbers and biomass of major fished piscivorous groups (especially lizardfish) over the experiment. Only two relatively minor fished piscivorous taxa declined in abundance over the experiment, while the overall abundance of piscivores increased. Visual censuses of fish on the experimental reefs also failed to show reduction of total piscivores over the full experimental period. No significant trend in the abundance of lizardfish censused over the full period was apparent on any of the control reefs. The high resilience of piscivores on these experimental reefs to relatively intense fishing pressure could result from their protracted recruitment seasons, high immigration rates, cryptic habits, or naturally high abundances. A major factor was the high immigration rates of lizardfish, replacing lizardfish and other less mobile piscivores removed from the reefs by spearing. On the fished reefs, the removed lizardfish population replaced itself >20 times during the experiment; other piscivorous taxa replaced themselves only 5 times.     

Morphological structure in a reef fish assemblage

Two key morphological traits, horizontal gape and eye diameter, were measured in a large representative group of coral reef fishes. These morphological traits were used concurrently to assess their utility in exploring abilities of coral reef fishes at an assemblage level. A total of 1,218 specimens from 181 species found on the Great Barrier Reef were examined. Cryptobenthic fishes were included to provide a broader representation of reef fish groups. In the analyses, a clear morphological distinction was found between nocturnal and diurnal fishes. Nocturnal fishes had larger relative horizontal gapes and relative eye diameters by factors of 1.6 and 1.5, respectively. A bivariate plot separated into quadrants was used to assess the implications of morphological variation. The morphological measures reflected distinct ecological traits in each quadrant. Whilst nocturnal fishes had large relative gapes and eye diameters, diurnal predators and detritivores had the same wide gapes, but small relative eye diameters. Highly selective, visual feeders such as the Chaetodontidae and Pseudochromidae had large eyes and small gapes, whilst non-selective feeders with low visual dependence such as the grazing herbivores (Acanthuridae, Siganidae, etc.) had both small eye diameters and gape sizes. The analysis proved to be robust enough to apply to a wide assemblage, but with enough subtlety to distinguish morphological differences within individual families. The methods used in this study may have broad applications to other fish assemblages, both fossil and extant. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diurnal variation in the abundance of juvenile parasitic gnathiid isopods on coral reef fish: implications for parasite-cleaner fish interactions

 The dynamics of parasitic gnathiid isopod infestation on the fish Hemigymnus melapterus were examined at Heron Island, Great Barrier Reef, by measuring the abundance and feeding state of gnathiids on fish collected between dawn and sunset and by estimating the time required for gnathiids to become engorged on host fluids. A model was developed to estimate gnathiid abundance on fish for any given time of day and host size. Fish at dawn had 2.4 times as many gnathiids compared with fish at sunset, indicating that some gnathiids infest fish overnight. Most gnathiids had engorged guts (72–86%); the proportion of empty guts and engorged guts did not differ in three time periods of collection (<0800 h, 0800 to 1100 h, and >1100 h). In the laboratory, gnathiids fed quickly with 75% of gnathiids exposed to fish for 4 h having engorged guts. The short time required for gnathiids to become engorged and the presence of gnathiids with empty guts throughout the day suggests that gnathiids also infest fish during the day. Thus gnathiids eaten by cleaner fish during the day may be replaced by other gnathiids during the day or night suggesting that interactions between gnathiids and cleaner fish are highly dynamic. Accepted: 15 April 1999     

The courtship and spawning behaviors ofCanthigaster valentini (Tetraodontidae)

Synopsis The sharpnose puffer,Canthigaster valentini, occurs in male-dominated harems of territorial females at Lizard Island (Australia). Spawning occurs daily and year-round. Males only spawn with the females of their social group, inside the female's territory. Females signal their readiness to begin courtship with a display that exposes their egg swollen abdomen. Courtship is long and males do not develop specific courtship colors or perform unique displays. Eggs are fertilized in a demersal nest and there is no parental care.     

Experimental removal of piscivorous groupers of the genus Cephalopholis (Serranidae) from coral habitats in the Gulf of Aqaba (Red-Sea)

Synopsis Elimination of adult groupers (Cephalopholis spp.) from various reef formations in the Gulf of Aqaba (Red Sea) resulted in replenishment by other predatory fishes of different taxa and only partly (21.6%) by species of the same genus. Three years later, the initial population composition had not been restored. Recolonization by juvenile groupers presumably settling from the plankton was only 11.3%. Censuses of the typical piscine prey of groupers, before and 36 months after the removal of Cephalopholis, showed virtually no change in abundace and species composition.     

Fish communities of the upper Danube River (Germany,Austria) prior to the new Rhein-Main-Donau connection

Synopsis Ultrasonic telemetry was used to study the movement and behavior of nine adult muskellunge, 69 to 101 cm in total length. Intensive fish tracking conducted from June to August 1978 produced 1178 contacts, the basis for summer home range determinations. Eight fish established summer home ranges by the time surface water temperatures rose above 17°C in mid-June, and by early July all fish exhibited home range behavior. Individual summer home ranges were 39 to 443 ha (mean = 146 ha) in area as determined by the minimum convex polygon method, and 27 to 73 ha (mean = 63 ha) as estimated by the grid-square method. Six fish had home ranges comprised of two distinct activity centers, 2.0 to 3.5 km apart. Some home ranges spatially overlapped, but occurrences of two fish at a common location were rare. In autumn, six of eight surviving fish remained within or near their summer home ranges. Observations on these eight fish during spring and summer 1979 provided evidence of reproductive and nonreproductive homing behaviorJournal Paper No. J-11155 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2236     

Fish-habitat associations across multiple spatial scales

Important to the study of reef fish ecology is understanding the degree to which fish community structure varies across space, what factors can account for such variation, and whether these factors are scale dependent. This study examined the structure of reef fish communities across four spatial scales (1, 10 100, and 200 m²) visually censused from seven sites within Tague Bay, St. Croix, U.S. Virgin Islands. Relative differences in the number of individuals and species among sites indicated a pattern that was consistent across spatial scales. Spearmans rank correlation revealed significant positive correlation in site rankings, in terms of species richness, between 1 and 10 m², and 100 and 200 m²; and for the abundance of individuals between 100 and 200 m². In order to understand the degree to which quantified habitat variables account for patterns in the abundance of individuals and species, and whether these fish-habitat relationships were consistent regardless of spatial scale, separate canonical correlation analyses were conducted at each scale. Independent of scale, the total number of individuals and species were correlated with specific habitat variables, either negatively (with areas of pavement, sand, no algae, and low structural complexity) or positively (with areas of Amphiroa rigida, Halimeda incrassata, high structural complexity, and diverse algae/seagrass communities). These habitat variables explained 31–81% (at scales of 1–200 m²) of the variation in the number of individuals and species. Similar analyses were also performed on the abundances of the nine most common species, and whether their specific habitat associations were independent of scale. Results indicated that habitat variables explained 19–73% (at scales of 1–200 m²) of the variation in abundances of each species. Unique fish-habitat relationships were observed for each species, and most such relationships were consistent across spatial scales. The structure of reef fish communities of Tague Bay was explained in large part by the composition of coral and algae communities present. Both the spatial variation in community structure and the fish-habitat relationships, at the community and population level, appeared to be largely independent of the spatial scale examined. This suggests that generalizations across Tague Bay are possible. Similar habitat associations reported in the literature are discussed with regard to the possibility for generalizations across regions.     

Courtship and spawning behavior of the pygmy grouper,Cephalopholis spiloparaea (Serranidae: Epinephelinae), with notes on C. argus and C. urodeta

Synopsis Courtship and spawning behavior is described for the grouper Cephalopholis spiloparaea from Rota, Mariana Islands. Daily courtship behavior began late in the afternoon and proceeded until after sunset. Males repeatedly visited females in single-male, multiple-female mating groups during each period and engaged in courtship bouts. Mating was observed only twice, was paired and pelagic. Two congeners, C. argus and C. urodeta, with overlapping geographical distributions, were also examined. Cephalopholis urodeta appeared to have a mating group organization similar to that of C. spiloparaea, with some similarity in courtship behavior. Cephalopholis argus also had a similar mating group organization but differed in courtship behavior. This species' behavior more closely resembled that of similarity-sized Epinephelus spp.     

Elemental signatures of Acanthochromis polyacanthus otoliths from the Great Barrier Reef have significant temporal, spatial, and between-brood variation

We evaluated the spatial and temporal scales over which otolith signatures varied in a reef fish on the Great Barrier Reef (GBR) using the non-dispersing damselfish Acanthochromis polyacanthus. We found a robust multi-element separation in otolith signatures from reef clusters in the northern and southern GBR. Variance components indicated that this spatial scale accounted for the majority of the variation in two elemental ratios (Ba/Ca and Sr/Ca) over the 2 years of the study. There was also significant variation in elemental signatures between otoliths collected over two consecutive years, as well as within a season. Individual reefs within clusters were less distinguishable based on otolith chemistry and were probably observed by differences within reefs (among sites and broods within sites). These results indicate that it may be difficult to determine the reef of origin for individual fish using otolith chemistry, while determining natal region seems a realistic goal.     

Resolution of the early life history of a reef fish using otolith chemistry

We used the elemental signatures in otoliths of the damselfish Pomacentrus coelestis as a proxy for conditions experienced prior to settlement. Fish from the southern Great Barrier Reef (GBR) differed in their pre-settlement otolith chemistry, indicating that they had occupied different water masses during their pelagic stage, thus suggesting multiple larval sources. Fish from reefs in the northern GBR did not differ greatly in their pre-settlement otolith chemistry, suggesting a single larval source. Using near-natal signatures, we determined that ~67% of these signatures matched the signature established for Lizard Island (LZ), suggesting LZ could be a source reef. However, these results could also be the result of poor separation among reefs caused by reefs sharing water masses. Otolith chemistry also revealed that 50–70% of all fish examined settled on the reef the day they encountered it, while some fish spent up to 4 days near the reef prior to settlement.