Brood-directed parental aggression and early brood loss in the coral reef fish, Acanthochromis polyacanthus (Pomacentridae)

Brood-directed parental aggression, in which parents attack and even kill their own young, is described for the coral reef fish Acanthochromis polyacanthus. This behaviour involves both parents, occurs on days 7–16 post-hatching, and is characteristic of all broods produced early in the spawning season. Such parental aggression appears to underlie widespread early brood loss in the species, i.e. disappearance of young before they reach an age at which they are viable in the absence of parental defence. Simultaneously, there is also a high frequency of sudden increases in the sizes of some tended broods. The data suggest that some brood-tending parents are forcibly expelling their broods from parental territories, and fostering them on to adults still tending broods. By expelling their young and re-spawning, pairs may realize a 7% increase in annual fecundity over pairs that do not expel their young, despite a low survival rate of expelled young.     

Relationships between coral reef substrata and fish

 The objective of this work is to identify which substrata characteristics (such as coral morphology, coral diversity, coral species richness, percentage coverage by live coral or by algae) influence the structure and abundance of fish communities. The study was carried out at Reunion Island, Indian Ocean, where six sites were sampled in two zones (reef flat and outer reef slope). Quantitative data were collected by visual census techniques, along a linear transect of 50 m for the substratum, and a belt of 50×2 m for the fish communities. Correspondence analysis (CA) and an optimising cluster analysis, called dynamic clustering method (DCM) were used to describe and compare fish assemblages with the benthic composition. The relationships between benthic and fish communities were examined using the classes revealed by the partitioning of the substratum with DCM. This partitioning allowed us to derive four classes of substratum: the non-disturbed reef flat, the non-disturbed outer reef slope, the perturbed reef habitat and the reef pass. The analysis of the partitioning based on the coral variables suggests that there are significant relationships between benthic and fish assemblages. Accepted: 26 July 1996     

Male morphological characteristics and mating success in a protogynous coral reef fish, Halichoeres melanurus

Morphological sexual differences and their effects on male mating success were investigated in the tailspot wrasse, Halichoeres melanurus, on a subtropical coral reef of Okinawa, southern Japan. Male mating territories were established along the reef edge from late April to early October, during which time pair-spawning occurred just before sunset in the male territories. Territorial males were larger and brighter than females in this protogynous fish. The males had longer, colorful ventral fins and colorful caudal fins, both of which were used during courtship. Multiple regression analysis of the effects of male characteristics on male mating success revealed that the yellow spot at the pectoral fin base was the most effective. It is suggested that large body size is favored in male–male competition for establishing mating territories and that conspicuous body color is favored in female mate choice. Received: June 16, 1999 / Accepted: September 22, 1999     

Evolution of mating systems in coral reef gobies and constraints on mating system plasticity

Social and mating systems can be influenced by the distribution, abundance, and economic defendability of breeding partners and essential resources. Polygyny is predicted where males can economically defend multiple females or essential resources used by females. In contrast, monogamy is predicted where neither sex can monopolise multiple partners, either directly or through resource control, but where one mate is economically defendable. The mating system and reproductive behaviour of five species of coral reef goby were investigated and contrasted with population density and individual mobility. The two most abundant species (Asterropteryx semipunctatus and Istigobius goldmanni) were polygynous. In contrast, the less populous and more widely dispersed epibenthic species (Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis) were pair forming and monogamous. All five species had low mobility, mostly remaining within metres (3 epibenthic species) or centimetres (2 cryptobenthic species) of a permanent shelter site. Interspecific differences in the mating system may have been shaped by differences in population density and the ability of reproductive individuals to economically defend breeding partners/sites. However, in a test of mating system plasticity, males of the three monogamous species did not mate polygynously when given the opportunity to do so in experimental manipulations of density and sex ratio. Mate guarding and complex spawning characteristics, which have likely co-evolved with the monogamous mating system, could contribute to mating system inflexibility by making polygynous mating unprofitable for individuals of the pair forming species, even when presented with current-day ecological conditions that usually favour polygyny.     

Spatial and temporal variation in predation on reef fishes by coral trout (Plectropomus leopardus,Serranidae)

The diet of coral trout Plectropomus leopardus (Serranidae) was studied over a two year period at One Tree Island, Great Barrier Reef, Australia. Rapid visual counts demonstrated that P. leopardus were most abundant on the reef slope habitat and inner edge of the enclosed lagoon. Few P. leopardus were found at sites from inner lagoon. It was hypothesized that diet would vary among habitats, times and size classes of coral trout. Ninety-two percent of P. leopardus that contained prey had consumed fish and 87% had only eaten fish. Many types of reef fish were taken by P. leopardus (e.g. Pomacentridae, Scaridae, Blenniidae and Labridae). Most pelagic prey (Clupeidae and Engraulididae) were taken on the reef slope, while some prey were solely or pimarily taken in the lagoon (e.g. Blenniidae and crustaceans). Most pelagic prey were taken on the reef slope in summer by P. leopardus>250 mm (SL). Plectropomus leopardus (<200 mm) from the lagoon had a higher proportion of invertebrates in the diet than fish from the reef slope. Plectropomus leopardus of all sizes ate small fish, while largest fish generally consumed largest prey (especially adult scarids and labrids). I argue that interactions among multiple species of prey and predators need more attention, because piscivores may respond to prey in different ways according to habitat type as well as the number and type of other prey types present. Furthermore, different sizes of fish (e.g. coral trout) may impact assemblages of prey in different ways.     

Relationships between structural complexity,coral traits,and reef fish assemblages

With the ongoing loss of coral cover and the associated flattening of reef architecture, understanding the links between coral habitat and reef fishes is of critical importance. Here, we investigate whether considering coral traits and functional diversity provides new insights into the relationship between structural complexity and reef fish communities, and whether coral traits and community composition can predict structural complexity. Across 157 sites in Seychelles, Maldives, the Chagos Archipelago, and Australia’s Great Barrier Reef, we find that structural complexity and reef zone are the strongest and most consistent predictors of reef fish abundance, biomass, species richness, and trophic structure. However, coral traits, diversity, and life histories provided additional predictive power for models of reef fish assemblages, and were key drivers of structural complexity. Our findings highlight that reef complexity relies on living corals—with different traits and life histories—continuing to build carbonate skeletons, and that these nuanced relationships between coral assemblages and habitat complexity can affect the structure of reef fish assemblages. Seascape-level estimates of structural complexity are rapid and cost effective with important implications for the structure and function of fish assemblages, and should be incorporated into monitoring programs.     

Protogynous hermaphroditism in the half-banded sea perch, Hypoplectrodes maccullochi (Serranidae)

The half-banded sea perch, Hypoplectrodes maccullochi (Serranidae) exhibits protogynous hermaphroditism, based on the presence of transitional individuals collected from rocky reefs along the coast of New South Wales, Australia. Males dominated the larger size and age classes, whereas females predominated the smaller size and age groups. Histological preparations suggested that sex change occurs between 55–85 mm s.l. and 1 + to 4+ years of age. Three transitional phases were identified which varied according to the proportion of gametogenic tissue and remnant oocytes present within their gonads. All individuals greater than 85 mm s.l. were functional males containing well defined crypts of spermatids and spermatozoa. Remnant oocytes within these testes indicated prior female function. H. maccullochi were sexually monochromatic. The occurrence of some small males derived from pre-spawning females suggested pre-maturational sex change occurred in some individuals. Sex changing individuals were found in all the months of the year that gonads were examined in detail (January, February, April and June 1989). Fish were ripe in August and November. H. maccullochi conforms with the pattern of reproduction evident within the genus Hypopleclrodes .     

Control of different mating systems in a coral reef fish by one environmental factor

The Red Sea coral-dwelling damselfish Dascyllus marginatus is organized in stable terri torial groups with males dominating all females. The fish live in pairs, harems or multi-male groups. Group size, and the number of sexually active males in a group, are correlated with coral size. Males monopolize and control the coral, attracting potential mates. The experimental alteration of coral sizes, using spherical Stylophora corals, resulted in an increase of male numbers, in artificially composed groups, with the increase of coral size. Thus pairs and harems were produced on small corals, multimale groups on big corals. Experiments with unisexual groups revealed a higher survival of females; males are more aggressive to each other, and cause a stronger emigration of subdominants. In D. marginatus, group size and the number of sexually active males are essentially restricted by one environmental factor: the number of available hiding places on a coral.     

The effect of territorial damselfish (family Pomacentridae) on the space use and behaviour of the coral reef fish, Halichoeres bivittatus (Bloch, 1791) (family Labridae)

Most demersal species of damselfish (family Pomacentridae) are territorial herbivores that aggressively chase other fishes away from their nests. This study investigates whether the aggressive territorial damselfish, Stegastes leucostictus, modifies behaviours and home range area use in a less aggressive, non-territorial species, the slippery dick wrasse, Halichoeres bivittatus (family Labridae). Damselfishes and wrasses are ubiquitous and abundant members of coral reef fish assemblages around the world; hence, this study has broader implications beyond the two Caribbean species chosen for this study. A manipulative field experiment consisted of transplanting one or three S. leucostictus into artificial shelters positioned within adult or adjacent to juvenile H. bivittatus home ranges. The introduction of damselfish had little effect on the size of home range areas of juvenile or adult wrasses, but had a significant effect on the location of their home ranges. The damselfish also affected adult microhabitat use but did not affect use by juveniles. In addition, there was an increase in damselfish-wrasse interactions that resulted in a significant reduction in the amount of time adult wrasses could spend foraging or in a foraging assemblage. It was concluded that aggressive interactions with territorial damselfish affect individual H. bivittatus space use and may consequently affect the spatial distribution of H. bivittatus populations.     

Temporal variation in the diet of a coral reef piscivore (Pisces: Serranidae) was not seasonal

Seasonal and smaller scale temporal variations in the diet of the large predatory grouper Plectropomus leopardus were examined on the central Great Barrier Reef, Australia. In 5 months over a 2-year period, 742 P. leopardus (₅ cm standard length) were collected for stomach content analysis. Despite intensive sampling, identified prey were spread over 20 families and much of the dietary variation was considered to be stochastic. Most aspects of the diet of P. leopardus did not vary seasonally. Frequency, rates of feeding, and proportion of fish consumed were consistent throughout the study. Size of fish prey did not vary significantly between seasons. Pomacentridae, Caesionidae, Scaridae, and Labridae were four of the five most important prey families consumed and did not vary seasonally in the diet. Prey in the other family, the small-sized schooling Clupeidae, were consumed sporadically among months with no seasonal patterns. One less common prey family variedseasonally in the diet; Synodontidae, which are small voracious predators of fish recruits, were consumed by P. leopardus more in summer than winter. Although the diet of P. leopardus is not influenced by the seasonal influx of small fishes recruiting to reefs, these large piscivores may indirectly improve recruit survival by consuming small and abundant predators of new recruits.     

Community structure,social organization and ecological requirements of coral reef fish (Pomacentridae)

In the Gulf of Aqaba (Red Sea), 25 species of damselfish (Pomacentridae) which form typical interspecific communities were studied. Several species are typical for different depth zones, others are ubiquitous. Damselfish are variously specialized in feeding (herbivore, omnivore, plankton-carnivore); habitat (bottom-dwelling, midwater); home-and-shelter site (selective or unselective). Environmental factors and social structures were found to be interlinked. Species with the same social structure are similarly specialized ecologically. A hypothetical flow diagram shows the effects of abiotic and biotic factors on group size, available food, and social structure. Damselfish are extremely flexible to environmental change, showing intraspecific modification of group structure, feeding habits, reproductive strategy etc. Experimental results suggest a strong selection against redundant males. This research is considered a pilot study for future field work, aimed at a prediction of environmental influences on behaviour.Supported by the Deutsche Forschungsgemeinschaft, Bad Godesberg, and the Max-Planck-Institut für Verhaltensphysiologie, Seewiesen.     

Spatio-temporal variability in fish recruitment to a coral reef (Moorea,French Polynesia)

Spatial and temporal patterns of recruitment of juvenile coral reef fishes were studied on the reefs of the high island of Moorea (Society Archipelago, French Polynesia) during the wet season (October 1988 to April 1989). Two size-classes of fishes (new-recruits and juveniles) were censused by visual counts within 24 quadrats along a transect across the lagoon. Correspondence analysis was used to calculate the hypothetical movements of the two size classes. Spatial variability was far more important than temporal variability; six main spatial communities were revealed, which could result from differences among habitats. Temporal variability in recuitment occurred only at nearshore stations; stations on the outer fringing reef and inner barrier reef displayed stable recruitment patterns.     

Variation in diversity of coral reef fish between French Polynesian atolls

The diversity of coral reef fish in seven atolls in French Polynesia is analyzed with respect to geomorphological characteristics of the atolls. The results show that size of the lagoon is more important than confinement in affecting overall fish diversity. This result suggests that island biogeographic theory, as developed by MacArthur and Wilson for terrestrial animals, also applies to reef fish in that more area gives more habitat complexity which, in turn, supports higher fish diversity. However, species diversity within a given family appears to be affected more by ecological parameters, such as living coral cover, food diversity, and reproductive behavior, than geomorphological features.     

Sex steroids relative to alternative mating behaviors in the simultaneous hermaphrodite Serranus subligarius (Perciformes: Serranidae)

This study is the first investigation of reproductive endocrinology in a simultaneously hermaphroditic teleost, the belted sandfish (Serranus subligarius). We address two questions: (1) Do steroid hormone levels vary during the spawning season or during the daily spawning cycle of sandfish? (2) Do hormone levels vary relative to an individual's phenotype-size, frequency of spawning and aggressive behaviors, and proportion of testis in the gonad? We analyzed circulating estradiol-17beta (E2), testosterone (T), 11-ketotestosterone (11KT), 17alpha,20beta,21-trihydroxy-4-pregnen-3-one (20betaS), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) concentrations in a field population. Only E2 levels were significantly higher at the new and full moon, suggesting peak periods of vitellogenesis at these times. Naturally spawning sandfish were sampled every 2 h during the photophase of a 25-h period (12 pm to 1 pm the following day) and gonadosomatic index, degree of oocyte hydration and ovulation, and plasma levels of E2, T, DHP, and 20betaS were analyzed. E2 and T levels did not vary during photophase, suggesting continuous recruitment of oocytes into vitellogenesis. The 20betaS levels peaked around the time of final oocyte maturation. Since frequency of spawning behaviors changes with body size, we captured individuals of various sizes throughout the spawning season and analyzed circulating levels of hormones. 11KT and 20betaS levels increased significantly with body size. In 1992, we quantified frequency of spawning and aggressive behaviors, circulating T and 11KT levels and testicular mass relative to ovotestis mass in focal animals. 11KT levels tended to be positively correlated with frequency of courting male behavior, but were unrelated to the frequency of aggressive behavior or testis mass. Because hormone levels increased with size and frequency of each spawning behavior changes with size, we propose that sex steroids influence growth-related changes in spawning tactics of individuals.     

The importance of light and food upon the early growth of the reef coral favia fragum (esper)

Planulae larvae of the reef coral Favia fragum (Esper) were allowed to settle and metamorphose to juveniles on glass microscope slides. The growth of the juveniles under conditions of light and darkness, with and without food, was measured for a period of about three months. Only those juveniles which were given food and incubated under a daily programme of 12 hours light continued to grow throughout the whole period of the experiment. Juveniles deprived of either light or food did not increase in size after the first week, but continued to survive for periods of up to three months with tissue atrophy.     

Habitat preference in newly settled coral trout (Plectropomus leopardus, Serranidae)

 The densities of newly settled coral trout (Plectropomus leopardus, Pisces, Serranidae) were monitored in a variety of habitats on Green Reef in the Cairns section of the Great Barrier Reef to assess whether spatial patterns of recruitment are influenced by physical features of the substratum, and whether this species uses different habitats during its ontogeny. Surveys showed that small juveniles used sites that were significantly different from random and that these habitat associations changed as the fish grew larger. Specifically, coral trout recruited to level patches of rubble substrata >5 m² and subsequently shifted to high relief features. Densities of recruits were related to the amount of rubble substrata available. Accepted: 4 July 1996     

The relationship between mating system and penis morphology in ischnuran damselflies (Odonata: Goenagrionidae)

Zygopterans belonging to the genus Ischnura are unusual amongst damselflies because of the variety of mate guarding techniques employed by males of different species. The lack of post-copulatory guarding combined with lengthy copulations in one group of ischnuran species suggest that these males guard females in copula. An examination of the accessory penes of species in this group indicates that all but one species have considerable microspination on the distal end (the flagella) of their penes that can function in sperm displacement. The flagella of these species are long and thin compared to those of other ischnurans. This is likely an adaptation to gain access to the spermatheca of the female. Two species tandem guard their mates during ovipositing. These species are the only ischnurans missing a stout pair of basal spines on the penultimate segments of their penes. They have considerable microspination over much of their penes but their flagella are of only moderate length and stout. Ischnurans that do not mate guard have short, stout flagella and most species examined from this group (5 of 7) have litde microspination on their flagella tips. It is proposed that females of these species mate only once and therefore their males do not displace sperm.     

Observations on the behaviour and coloration of some coral reef fish (family: Pomacentridae)

Observations were made on the behaviour of 16 pomacentrid coral reef fish living under natural conditions. On the basis of the habit recorded for the majority of individuals observed in each, the fish were divided into three groups (solitary, pairing and social). Correlations were established between coloration and behaviour. Six out of the 8 social species studied have patterns of black (or brown) and white (or yellow) dorso‐ventral stripes. All 6 of the solitary species have colours other than black, brown, grey‐green, and white.     

Effects of light and dark treatments on feeding by the reef coral Pocillopora damicornis (Linnaeus)

The feeding capability of Pocillopora damicornis (Linnaeus) was measured by exposing segments of the same colony to different densities of Artemia salina (L.) nauplii and determining the number of ingested prey. Feeding is directly related to prey density. No plateau in feeding capability was observed over the range of prey densities used.The effects of reduced photosynthesis on feeding capability and tissue dry weight were also examined in colonies maintained in unfiltered running sea water. Tissue samples from clonal segments of Pocilloporadamicornis colonies maintained in a covered (dark) sea table for 2 days or 15 to 17 days weighed significantly less than equivalent samples from segments maintained in a normal (light) sea table. Segments maintained in a darkened sea table for over 2 wk were unable to ingest as many Artemia nauplii as their light table equivalents. These data indicate that the amount of Zooplankton available to the colonies in the sea table was insufficient to meet their metabolic requirements and that feeding in Pocillopora damicornis was dependent upon energy derived from photosynthesis by the zooxanthellae.