Scarid Biomass on the Northern Great Barrier Reef: The Influence of Exposure, Depth and Substrata

Here I investigate whether patterns of scarid biomass across the continental shelf of the northern Great Barrier Reef can be explained by species associating with particular characteristics of the reef environment. Despite the widely documented tendency of scarids to graze and browse over exposed calcareous reef surfaces, scarid biomass was not significantly correlated with the availability of feeding substrata for any species investigated. Indeed positive correlations between biomass and substrata variables were rare for the 18 species investigated, indicating that biomass in these taxa was not strongly reliant on the availability of preferred substrata quantified at the spatial scale of sites (1620m²). Rather, species specific biomass was commonly highly variable between sites, suggesting that local aggregation of scarids commonly occurs at this scale. Such spatial patchiness potentially reflects the effects of spatially variable recruitment, fishes associating with unmeasured habitat characteristics or aggregating prior to spawning. Despite variability in the biomass of individual species between replicate sites within exposure regimes, exposure was generally a far more reliable predictor of biomass than the other variables quantified. This study provides little evidence to indicate that adult scarids have strict habitat requirements, rather they appear to be habitat generalists whose biomass is strongly influenced by exposure but weakly related to the cover of particular reef substratum.     

Effects of Mixed-species Foraging Groups on the Feeding and Aggression of Juvenile Parrotfishes

Many parrotfishes (Scaridae) co-occur in mixed-species aggregations as juveniles, but diverge in resource use and social structure as adults. Focal observations of three juvenile parrotfishes (Scarus coeruleus, Sparisoma aurofrenatum, and Sparisoma viride) were conducted on inshore patch reefs in the Florida Keys to determine how feeding and aggressive interactions vary with group participation. All three species spent more time in groups than alone, most often in groups of less than ten individuals. Feeding rates were significantly higher for S. viride when foraging in groups than when alone. All species fed most often from Halimeda, and overall diet composition was similar for fish whether feeding in groups or alone. The frequency of aggressive interactions varied with group participation. Focal S. aurofrenatum were more aggressive when in groups than when alone, and both S. aurofrenatum and S. viride were attacked more often by damselfishes when they were alone than when in groups. In contrast, feeding rates, diet breadth, and aggressive interactions of S. coeruleus were less affected by group participation. Small mixed-species aggregations of coral reef fishes may be large enough for individuals to assume some of the benefits of group participation while at the same time avoiding the costs of competition realized in larger groups.     

Habitat choice,recruitment and the response of coral reef fishes to coral degradation

The global degradation of coral reefs is having profound effects on the structure and species richness of associated reef fish assemblages. Historically, variation in the composition of fish communities has largely been attributed to factors affecting settlement of reef fish larvae. However, the mechanisms that determine how fish settlers respond to different stages of coral stress and the extent of coral loss on fish settlement are poorly understood. Here, we examined the effects of habitat degradation on fish settlement using a two-stage experimental approach. First, we employed laboratory choice experiments to test how settlers responded to early and terminal stages of coral degradation. We then quantified the settlement response of the whole reef fish assemblage in a field perturbation experiment. The laboratory choice experiments tested how juveniles from nine common Indo-Pacific fishes chose among live colonies, partially degraded colonies, and dead colonies with recent algal growth. Many species did not distinguish between live and partially degraded colonies, suggesting settlement patterns are resilient to the early stages of declining coral health. Several species preferred live or degraded corals, and none preferred to associate with dead, algal-covered colonies. In the field experiment, fish recruitment to coral colonies was monitored before and after the introduction of a coral predator (the crown-of-thorns starfish) and compared with undisturbed control colonies. Starfish reduced live coral cover by 95–100%, causing persistent negative effects on the recruitment of coral-associated fishes. Rapid reductions in new recruit abundance, greater numbers of unoccupied colonies and a shift in the recruit community structure from one dominated by coral-associated fishes before degradation to one predominantly composed of algal-associated fish species were observed. Our results suggest that while resistant to coral stress, coral death alters the process of replenishment of coral reef fish communities.     

Feeding Habits and Interspecific Feeding Associations of Caranx Latus (Carangidae) in a Subtropical Reef

I studied the feeding behavior and diet of the carangid jack Caranx latus in a subtropical reef at Búzios Island on the southeastern Brazilian coast. Caranx latus foraged alone or in small groups of up to three individuals during daytime employing two main feeding styles: searching for prey while swimming in mid-water and following individuals of other fish species which disturbed the substrate while foraging among the rocks. The labrid wrasse Bodianus rufus was the main fish species followed by the jack. The jack feeds on crustaceans and fishes some of which are benthic rocky bottom dwellers and are caught during following. The behavioral flexibility of C. latus enables this fish to consume both crustaceans from the water column and benthic rocky dweller fishes. There is little dietary overlap between C. latus and the followed B. rufus. The interspecific feeding associations could be regarded as advantageous for C. latus allowing access to a broader range of prey categories and increasing the food intake through the consumption of large benthic fish prey     

Community structure and biogeography of shore fishes in the Gulf of Aqaba,Red Sea

Shore fish community structure off the Jordanian Red Sea coast was determined on fringing coral reefs and in a seagrass-dominated bay at 6 m and 12 m depths. A total of 198 fish species belonging to 121 genera and 43 families was recorded. Labridae and Pomacentridae dominated the ichthyofauna in terms of species richness and Pomacentridae were most abundant. Neither diversity nor species richness was correlated to depth. The abundance of fishes was higher at the deep reef slope, due to schooling planktivorous fishes. At 12 m depth abundance of fishes at the seagrass-dominated site was higher than on the coral reefs. Multivariate analysis demonstrated a strong influence on the fish assemblages by depth and benthic habitat. Fish species richness was positively correlated with hard substrate cover and habitat diversity. Abundance of corallivores was positively linked with live hard coral cover. The assemblages of fishes were different on the shallow reef slope, deep reef slope and seagrass meadows. An analysis of the fish fauna showed that the Gulf of Aqaba harbours a higher species richness than previously reported. The comparison with fish communities on other reefs around the Arabian Peninsula and Indian Ocean supported the recognition of an Arabian subprovince within the Indian Ocean. The affinity of the Arabian Gulf ichthyofauna to the Red Sea is not clear. Received in revised form: 2 November 2001 Electronic Publication     

Varying responses of herbivorous and invertebrate-feeding fishes to macroalgal reduction on a coral reef

 The consequences of macroalgal overgrowth on reef fishes and means to reverse this condition have been little explored. An experimental reduction of macroalgae was conducted at a site in the Watamu Marine National Park in Kenya, where a documented increase in macroalgal cover has occurred over the last nine years. In four experimental 10 m by 10 m plots, macroalgae were greatly reduced (fleshy algal cover reduced by 84%) by scrubbing and shearing, while four similar plots acted as controls. The numerical abundance in all fish groups except wrasses and macroalgal-feeding parrotfishes (species in the genera Calotomus and Leptoscarus) increased in experimental algal reduction plots. Algal (Sargassum) and seagrass (Thalassia) assays, susceptible to scraping and excavating parrotfishes, were bitten more frequently in the algal reduction plots one month after the manipulation. Further, surgeonfish (Acanthurus leucosternon and A. nigrofuscus) foraging intensity increased in these algal reduction plots. The abundance of triggerfishes increased significantly in experimental plots relative to control plots, but densities remained low, and an index of sea urchin predation using tethered juvenile and adult Echinometra mathaei showed no differences between treatments following macroalgal reduction. Dominance of reefs by macrofleshy algae appears to reduce the abundance of fishes, mostly herbivores and their rates of herbivory, but also other groups such as predators of invertebrates (triggerfishes, butterflyfishes and angelfishes). Accepted: 2 February 1999     

Feeding patterns in eastern tropical Pacific blennioid fishes (Teleostei: Tripterygiidae,Labrisomidae, Chaenopsidae,Blenniidae)

Summary In terms of species number (47) and numerical abundance, blennioids are the most important primary resident rocky reef fishes in the Gulf of California, Mexico. We present the feeding patterns of the 34 most abundant species of blennioid fishes, 8 of which are Gulf endemics. A total of 2,144 specimens were sampled at 51 anaesthetic stations in 9 areas throughout the Gulf. Four feeding guilds were distinguished: 1) The majority (29 of 34 species) are microcarnivores exhibiting a number of different feeding strategies (ambush and stalking predators, active foragers, pickers, etc.). The more important prey categories were mobile invertebrates, and to some extent also sedentary fauna. Algae were of no importance for most of the latter species. 2) Hypsoblennius brevipinnis and H. gentilis are two omnivorous species, browsing mainly on sessile items including 52% and 13% (Vol.) algae in their diets. 3) Entomacrodus chiostictus and Ophioblennius steindachneri are herbivores, grazing on fine algae. 4) Plagiotremus azaleus specializes in cropping mucus and scales from the body surface of other fishes.Crustaceans account for 58.6% of the total volume of prey items in the 34 species investigated. Benthic amphipods were most important and made up 26% of the total volume of all prey items.Cluster analysis of percentage volumetric data using Squared Euclidian Distance and Horn's Index of Overlap produced distinct subgroups which coarsely reflected taxonomic grouping.The species are separated either by their geographic ranges, habitat and microhabitat preferences, feeding, or a combination thereof. Only rarely do sympatric species significantly overlap in diet.Trophic diversity as measured by the Shannon-index provides a tool for distinguishing: 1) specialists (6 species) from 2) low diversity feeders (18 species) and 3) high diversity generalists (10 species). Two different types of specialists can be distinguished: those which feed on the same items as the generalists but utilize only a very restricted prey spectrum (Stathmonotus sinuscalifornici and the chaenopsids Chaenopsis alepidota and Emblemaria hypacanthus). A second group of specialists (Entomacrodus chiostictus and Ophioblennius steindachneri as well as Plagiotremus azaleus) feed on items not utilized by any of the generalists.There is some evidence that high diversity generalists are numerically more abundant than the other trophic groups.In the labrisomids and blenniids a phylogenetic trend from microcarnivory towards feeding on sessile items appears to be expressed.     

Purification of β-N-Acetylhexosaminidase from Egg White and the Microsomal and Lysosomal Fractions of Hen Oviduct

β-N-Acetylhexosaminidase (NAHase) was purified from egg white and the lysosomal and microsomal fractions of hen oviduct. The purification procedure included affinity chromatography using Sepharose 4B coupled with IgG specific for NAHase of hen oviduct. The isoelectric points of the three enzymes were different, but their antigen determinants were identical. In sodium dodecyl sulfate polyacrylamide gel electrophoresis, both the egg white and lysosomal enzyme gave only one protein band each, corresponding to a MW of 68000 and 53000, respectively, but the microsomal enzyme gave two protein bands, corresponding to those of the lysosomal and egg white enzymes.     

Community structure and habitat associations of parrotfishes on Oahu,Hawaii

Despite their ecological importance as bioeroders and their economic importance in commercial, artisanal, and recreational fisheries, there have been relatively few studies on parrotfish (Scaridae) ecology in Hawaii. Belt transects were conducted around the island of Oahu to survey current parrotfish distributions, size structure, species composition and associated habitats. Scarid communities in this heavily fished region are dominated by smaller species and smaller individuals within all species. Specific habitat characteristics such as rugosity, substrate diversity, and percent live coral cover were positively correlated with scarid numerical abundance. Scarids, however, were patchily distributed and were often absent from preferable habitats, suggesting that intense fishing pressure may be an important factor preventing these fish from fully exploiting available habitats. This study is the first thorough, broad-scale investigation of scarid community structure in Hawaii, and provides important information that has management and conservation implications for parrotfish in Hawaii and throughout tropical coral reef ecosystems.