Latitudinal variation in abundance of herbivorous fishes: a comparison of temperate and tropical reefs

The aim of the study was to provide comparable estimates of abundance of herbivorous reef fishes at temperate and tropical localities using a standardized methodology. Faunas of herbivorous fish were sampled on the rocky reefs of temperate northern New Zealand and on the coral reefs of the northern Great Barrier Reef (GBR), Australia, and the San Blas Archipelago in the Caribbean. A pilot study established the most appropriate habitat setting and the scale and magnitude of replication for the sampling program in temperate waters. Herbivorous fishes, including members of families endemic to the southern hemisphere (Odacidae and Aplodactylidae), were most abundant in turbulent, shallow water (0 to 6 m) and had patchy distributions within this habitat. A hierarchical sampling program using 10-min transect counts within the 0 to 6 m depth stratum examined abundance patterns at a range of spatial scales including mainland and island coasts, localities separated by up to 100 km and sites separated by up to 10 km. This program identified a characteristic fauna of seven species of herbivorous fishes with mean total abundances ranging from 23 to 30 individuals per 10-min transect. Species composition of the fauna varied between islands and coasts. A similar methodology was used to sample the major families of herbivorous fish in a number of sites in each of the tropical regions. These sampling programs revealed a fauna dominated by acanthurids and scarids in both the GBR and Caribbean localities. Estimates of abundance from these regions were similar, with a mean of 108 individuals recorded on the GBR and 129 per 10-min transect in the Caribbean. Species richness varied between each region, with 44 taxa recorded from the GBR and 11 from the Caribbean. Abundances of temperate water herbivores in New Zealand were found to be 75 to 80% lower than those recorded from shallow water habitats sampled on coral reefs. This was not related to species richness, since both New Zealand and the Caribbean locality had patterns of low richness. We suggest that the differences in abundance found by our study between temperate and tropical regions are not restricted to herbivorous fishes, but are representative of general latitudinal trends in reef fish faunas. Received: 4 November 1996 / Accepted: 15 December 1996     

Effects of algal grazing and aggressive behaviour of the fishes Pomacentrus lividus and Acanthurus sohal on coral-reef ecology

Aggressive behaviour of the fishes Pomacentrus lividus Bl. Schn. and Acanthurus sohal Forskal from the Red Sea is briefly described, and its effect on intensity of algal grazing by herbivorous fish is demonstrated by settlement experiments. Green filamentous alga settles and grows at shallow depths over large areas of coral reefs, but is cropped by fishes to such an extent that it forms only a thin patchy matting on dead corals. Within pomacentrid territories, the alga forms a thicker matting on loosely cemented coralline rubble. Optimum depth range for growth occurs at less than 20 m. Rich growths of green filamentous alga, such as those which occur within pomacentrid territories or on settlement plates protected by wire netting cages, inhibit settlement of “lithothamnion” and invertebrates. While rasping and grazing fish feeders such as parrot fish and surgeon fish limit the distribution of certain invertebrates such as spirorbids, in shallow water it is also true that, were it not for such active removal of green filamentous alga, “lithothamnion” and many invertebrates would find ewer surfaces suitable for settlement.     

Geographical gradients of marine herbivorous fishes: patterns and processes

We present new data and the first rigorous analysis of latitudinal and thermal gradients of diversity, density and biomass of marine herbivorous fishes and review proposed explanatory mechanisms. Consistently, negative relationships between latitude, and positive relationships between sea surface temperature (SST), and relative richness and relative abundance of herbivorous fishes were found worldwide. Significant differences in the strength of gradients of richness and abundance with latitude and SST between tropical and extratropical zones were found consistently across ocean basins. Standardized sampling along the western Atlantic also showed negative relationships between latitude and total density and biomass. The trends, however, are driven by different components of the fish assemblages (i.e., scarids in the Caribbean and acanthurids in Brazil). Patterns of abundance along thermal gradients, generally associated with extensive latitudinal gradients, also were found at the local scale. Feeding rate of the ocean surgeonfish Acanthurus bahianus decreases with temperature more rapidly than the mean metabolic rate of teleost fishes. This relationship suggests a temperature-related physiological constraint. From the new standardized and comparative data presented and the review of the explanatory hypotheses, we conclude that temperature-related feeding and digestive processes are most likely involved in the distribution patterns of herbivorous fishes. Electronic Supplementary Material Supplementary material is available for this article at     

A re-evaluation of the diel feeding hypothesis for marine herbivorous fishes

We re-evaluated the "diel feeding hypothesis" by measuring diel variation in starch, protein, and floridoside in three algal "types" collected from a fringing coral reef at Lizard Island, Great Barrier Reef, Australia. Samples of two species of rhodophyte algae, Gracilaria arcuata and Acanthophora spicifera, and the turf assemblage from the territories of the herbivorous pomacentrid Stegastes nigricans were collected at four time periods through the day: 0630-0730, 1000-1100, 1330-1430, and 1630-1730 hours. We also measured the ability of several species of marine fish (the herbivores Acanthurus nigricans, A. lineatus, A. olivaceus, and Parma alboscapularis and the detritivore Ctenochaetus striatus) to hydrolyse floridoside by estimating !-galactosidase activity in tissue from the anterior intestine. We detected no diel pattern in protein content of the algae but found a significant steady increase in starch content throughout the day. Floridoside content increased in the morning and decreased in the afternoon, a pattern that may be driven by midday photoinhibition of the algae. All the fishes tested could utilise floridoside. Our results support the diel feeding hypothesis. Although floridoside content decreased in the afternoon, our results suggest floridoside was used during the day by the algae to synthesise starch. Thus the algae increased in nutritional value until photoinhibition occurred at midday then subsequently maintained their nutritional value during the afternoon. This pattern of algal nutrients increasing to a midday peak and remaining relatively constant throughout the afternoon correlates well with the diel feeding pattern in many species of marine herbivorous fish.     

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

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

Predicting structural complexity of reefs and fish abundance using acoustic remote sensing (RoxAnn)

This study determined whether the acoustic roughness of Caribbean reef habitats is an accurate proxy for their topographic complexity and a significant predictor of their fish abundance. Fish abundance was measured in 25 sites along the forereef of Glovers Atoll (Belize). At each site, in situ rugosity (ISR) was estimated using the “chain and tape” method, and acoustic roughness (E1) was acquired using RoxAnn. The relationships between E1 and ISR, and between both E1 and ISR and the abundance of 17 common species and the presence of 10 uncommon species were tested. E1 was a significant predictor of the topographic complexity (r ² = 0.66), the abundance of 10 common species of surgeonfishes, pomacentrids, scarids, grunts and serranids and the presence of 4 uncommon species of pomacentrids and snappers. Small differences in E1 (i.e. ∆0.05–0.07) reflected in subtle but significant differences in fish abundance (~1 individual 200 m⁻² and 116 g 200 m⁻²) among sites. Although we required the use of IKONOS data to obtain a large number of echoes per site, future studies will be able to utilise RoxAnn data alone to detect spatial patterns in substrate complexity and fish abundance, provided that a minimum of 50 RoxAnn echoes are collected per site.     

Herbivory by the Caribbean king crab on coral patch reefs

Caribbean coral reefs are increasingly dominated by macroalgae instead of corals due to several factors, including the decline of herbivores. Yet, virtually unknown is the role of crustacean macrograzers on coral reef macroalgae. We examined the effect of grazing by the Caribbean king crab (Mithrax spinosissimus) on coral patch reef algal communities in the Florida Keys, Florida (USA), by: (1) measuring crab selectivity and consumption of macroalgae, (2) estimating crab density, and (3) comparing the effect of crab herbivory to that of fishes. Mithrax prefers fleshy macroalgae, but it also consumes relatively unpalatable calcareous algae. Per capita grazing rates by Mithrax exceed those of most herbivorous fish, but Mithrax often occurs at low densities on reefs and its foraging activities are reduced in predator-rich environments. Therefore, the effects of grazing by Mithrax tend to be localized and when at low density contribute primarily to spatial heterogeneity in coral reef macroalgal communities.     

Increases in surgeonfish populations after mass mortality of the sea urchinDiadema antillarum in Panamá indicate food limitation

In 1983/1984,Diadema antillarum suffered mass mortalities throughout its West Atlantic range. Its populations were reduced by 95% and subsequently have failed to recover. These die-offs led to sustained increases in the abundance of soft algae, including types eaten by herbivorous reef fishes. I monitored adult populations of three herbivorous surgeonfishes (Acanthurus coeruleus, A. chirurugus andA. bahianus) between 1978 and 1990, and the recruitment of their pelagic juveniles between 1979 and 1989, on six patch reefs in Panamá. Adult populations ofA. coeruleus andA. chirurgus, which largely restrict their feeding to reef substrata, increased by averages of 250 and 160%, respectively, after the die-off ofD. antillarum in 1983. No increases occurred in the adult populations ofA. bahianus, which often feeds in off-reef habitats unaffected byD. antillarum. Average annual levels of juvenile recruitment of all three surgeonfishes did not differ before and after the die-off. These results support the hypothesis that adult populations of two herbivorous fishes that are strongly reliant on reef algae for food previously were limited by competition withD. antillarum.     

Importance of macroalgal fields as coral reef fish nursery habitat in north-west Australia

Macroalgal fields are a feature of the shallow tropical benthos, yet their importance for coral reef fish population dynamics remains poorly understood. The abundance of fish recruits was recorded using underwater visual census at six macroalgal and 11 coral reef sites in the Montebello and Barrow Islands. Surveys identified 6,935 individual recruit fish from 105 species, 54 genera and 20 families. Of these, 1,401 recruits from 48 species, 31 genera and 14 families were observed in macroalgal sites. Sixteen of the 105 recruit species (15.2 %) were observed exclusively at macroalgal sites. Forty-two (87.5 %) of these species have been observed as adults on adjacent coral reefs. Species composition of fish recruits differed significantly between the two habitats. Corallivore, small omnivore and zooplanktivore recruits had significantly higher numbers in the coral sites, while the results clearly demonstrate that juveniles, within the genera Lethrinus and Choerodon, as well as large algal croppers, are predominantly found at macroalgal (74–100 %) rather than coral-dominated sites. High-canopy macroalgae cover was positively correlated with abundance of these taxa, particularly Lethrinids (r ² = 0.40). This study is the first to highlight the important attributes of tropical macroalgal fields and suggests that they have a similar role to seagrass meadows as essential juvenile habitat, thus warranting greater attention in conservation planning and ecological studies.     

Mass mortality ofDiadema antillarum

It has been hypothesized that herbivorous fishes and the regular echinoidDiadema antillarum Philippi compete for benthic algae as their major food resource. Mass mortality ofD. antillarum in February 1984 provided the opportunity to test the hypothesis that herbivorous fishes and sea urchins were competing previously. Visual censuses of herbivorous fishes conducted over 4 yr in four reef zones on Tague Bay Reef, St. Croix, U.S. Virgin Islands, before and after the mass mortality indicated that population densities increased approximately three-fold in backreef and shallow (2m) forereef zones and two-fold, and four-fold in mid (5m) and deep (10m) forereef zones, respectively. Juvenile parrotfishes constituted the major component of these increases, except in the shallow forereef where acanthurids became most abundant. Grazing intensity by herbivorous fishes increased in three of the four reef zones immediately following the mass mortality. These data support the hypothesis that exploitative competition for algal resources was occurring prior to the sea urchin mass-mortality, although alternative hypotheses cannot be discounted completely. Despite the increases in the abundances of, and grazing by, herbivorous fishes, the algal community continued to increase in percent cover and biomass, indicating that increased grazing by fishes does not compensate for the loss of grazing byD. antillarum in controlling algal abundance and community structure.     

Daily feeding rates in herbivorous labroid fishes

Estimates of daily feeding rates were obtained for two groups of herbivorous labroid fishes, one confined to cold water and the other to tropical reef environments. These were the family Odacidae, represented by Odax pullus from New Zealand waters, (Goat Island Bay: Latitude 36° South; on the northeastern coast of New Zealand) and the family Scaridae, represented by Scarus rivulatus, S. schlegeli and S. sordidus from the northern Great Barrier Reef (Lizard Island; a mid-shelf reef at 14° South latitude). Observations on the odacid were made in 1984 and in 1992, and on the scarids in 1984 and 1988. O. pullus displayed a diurnal feeding pattern in which the rates (expressed as bites min^-1) are greatest early in the day. The mean combined feeding rate for three size groups (juveniles, subadults and adults) peaked (average of 2.9 bites) from 06.00 to 08.00 hrs and declined fourfold to a combined average of 0.7 bites min^-1 by midday. The greatest mean feeding rate recorded was 3.7 bites min^-1, with an overall mean of 1.8 bites min^-1. For subadults and adults there were consistent trends in feeding, with subadults feeding at a greater rate than adults and both groups displaying a decline in feeding rate during the day. The change in feeding rate with time of day was statistically significant in both groups. The pattern for juvenile O. pullus was different from that in the two larger size groups in that juveniles did not show a uniform decline in feeding with time of day. For scarids, the daily feeding rate varied by site, but the pattern was similar for all species, characterised by initial low rates increasing to higher but variable levels by midday. The influence of both site of feeding and time of day on feeding rate was confirmed by analysis. The overall mean values for each species were 20.1 bites min^-1 for S. rivulatus, 19.7 bites min^-1 for S. schlegeli and 14.9 bites min^-1 for S. sordidus. For scarids, the peak feeding rates varied from 19.3 to 32.8 bites min^-1, with overall rates from 14.9 to 21.1 bites min^-1. Estimates of activity and movement patterns during feeding were obtained for O. pullus. Distance moved per unit time was highly variable, 0.1 to 47.5 m min^-1, with a mean of 8.5 m min^-1 (SD=9.9). Trends in movement among sexes and size classes were obscured by the variable movement patterns of individual fishes.     

Seasonal rhythm in a Mediterranean coastal fish community as monitored by a cabled observatory

To adequately describe seasonal rhythms in habitat utilization by fish communities, observations are needed that occur at a relatively high frequency and over large temporal windows. For the first time, images collected from a cabled video-observatory (the western Mediterranean expandable SEAfloor OBservatory; OBSEA) were utilized to examine habitat utilization by coastal fishes. Over the course of a year, hourly digital images of the water column and an artificial reef were obtained during daylight hours. For each image, the total number of species, an estimate of the abundance of individuals, and the Shannon Diversity Index were quantified. A total of 22 fish species commonly associated with nearshore western Mediterranean habitats were identified, and significant spatial (water column vs. artificial reef), seasonal (spring, summer, autumn, and winter), and daily (morning, midday, and sunset) differences in habitat utilization occurred. Four species (Diplodus vulgaris, Diplodus cervinus, Diplodus sargus, and Scorpaena porcus) were associated with the artificial reef, while one species (Pagrus pagrus) chiefly occurred in the water column. Chromis chromis and Diplodus annularis occurred at the site more frequently in the winter and autumn, respectively, while 14 other species utilized the site more frequently in either the spring (8 spp) or summer (6 spp). In addition, Dentex dentex and Spicara maena occurred more frequently at sunset, while D. cervinus displayed a crepuscular rhythm (occurring more frequently in the morning and at sunset). Species diversity was highest in the summer and lowest in the winter. If not taken into account when planning in situ sampling, such seasonal and/or diel differences may lead to spurious estimates of population sizes and biodiversity. We suggest that cabled video-observatories offer a non-invasive and reliable technology for faunistic sampling and population assessment in coastal water of the Mediterranean and likely elsewhere.     

Coexistence of nine anemonefish species: differential host and habitat utilization, size and recruitment

The region of Madang, Papua New Guinea, has the highest reported species diversity of both anemonefishes (nine species) and their host anemones (ten species). To determine which factors may allow so many anemonefish species to coexist at this location, we studied their patterns of distribution, abundance, and recruitment. Population surveys at three replicate reef sites within four zones situated at varying distances from the mainland (nearshore, mid-lagoon, outer barrier, and offshore) indicated that each species of host anemone and anemonefish lived within a particular range of zones. Each species of anemonefish lived primarily with one species of host. Anemonefish species that lived with the same host species usually had different distribution patterns among zones (e.g., Amphiprion percula occupied Heteractis magnifica in nearshore zones, while A. perideraion occupied H. magnifica in offshore zones). Monitoring of natural populations showed that there were few changes (losses or recruitment) in the number or species of fishes associated with each individual anemone over periods ranging from 3 to 9 months. Recruitment was monitored on anemones with and without residents (resident fishes were removed) within each of three zones (nearshore, mid-lagoon, outer barrier). Significantly more anemonefishes recruited to anemones without resident fishes than to anemones with resident fishes. Each anemonefish species recruited to particular host species and zones. The distribution and abundance of the recruits of each fish species among zones were positively correlated with the distribution and abundance of resident fishes in the benthic habitat. This suggests that the spatial patterns of recruitment among zones strongly determined the distribution and abundance patterns of the benthic populations, and they were not the result of post-recruitment mortality or movement. Coexistence of the nine anemonefish species on the limited anemone resource was considered possible because of niche differentiation (i.e., differences in host and habitat utilization among zones), and the ability of two small species (i.e., Amphiprion sandaracinos and A. leucokranos) to cohabit individual anemones with other anemonefish species. Received: 29 July 1999 / Accepted: 1 September 2000     

Patterns of use of space in a guild of territorial reef fishes

There exists on Heron Reef, at the southern end of the Great Barrier Reef, an 8-species guild of ecologically very similar, territorial, herbivorous reef fishes. All individuals of these species maintain territories on rubble substrata throughout juvenile and adult life. Territories are defended from all other guild members. Three rubble patches, each containing residents of 3 guild species: Pomacentrus apicalis, P. wardi, and Abudafduf lachrymatus, have been monitored for 12 to 18 months. This paper examines the patterns of use of space as shown by the antecedent and subsequent histories of sites chosen by 43 new colonists, and sites vacated through the loss of 34 residents on the rubble patches. In addition, variation through time is examined in the total amount of space held in territories on each rubble patch. The 3 species show similar preferences for space as colonists, although adult and juvenile colonists behave differently. Numbers of colonists detected on rubble patches are not proportional to the resident populations of the 3 species. Residents of the 3 species are equal in their abilities to enter spaces vacated through mortality, although they differ slightly in methods used to enter sites. They do not respond preferentially to sites previously occupied by any particular species. P. wardi shows a higher rate of mortality than the other species, and residents of this species are more often dislodged by new colonists. The total amount of space held on any rubble patch did not vary during the year from September, 1972 to October, 1973. The data are interpreted as supporting the hypothesis that the 3 species do not differ in their requirements for space on rubble patches, and that they are in competition for a short supply of such space. Differences exist in their strategies for obtaining and holding such space. These differences are important for explaining the continued presence of P. wardi on rubble patches. P. apicalis and a. lachrymatus are both specialists in holding territories on the upper reef slope. No differences have been detected in their requirements or competitive abilities. P. wardi is a fugitive species on the upper reef slope, coexisting because it maintains a refuge from competition by occupying some un-preferred sites off rubble patches.     

Effects of fish feeding by snorkellers on the density and size distribution of fishes in a Mediterranean marine protected area

Although there is a great deal of evidence to show that supplementary feeding by humans in terrestrial environments causes pronounced changes in the distribution and behaviour of wild animals, at present very little is known about the potential for such effects on marine fish. This study evaluated the consequences of feeding by snorkellers on fish assemblages in the no-take area of the Ustica Island marine protected area (MPA; western Mediterranean) by (1) determining if reef fish assemblage structure is affected in space and time by tourists feeding the fish; (2) assessing the effects of feeding on the abundance of the most common fish species; and (3) assessing the effects of feeding on the size structure of the two most numerically dominant ones. In particular, we hypothesised that both the abundance and the size structure of some fish species would increase at the study site following supplementary feeding, since the additional food provided by humans would make the site more appealing to them. Fish feeding influenced the fish assemblages within the Ustica MPA, and significant spatio-temporal changes occurred. While fish feeding appeared to have no effect on the ornate wrasse Thalassoma pavo, there was a noticeable increase in the number of Oblada melanura and Epinephelus marginatus in the impacted location after feeding. It is very likely that aggregations of fishes that evolve as a result of fish feeding by the public may have negative effects on local populations of fishes and invertebrates that make up their prey. Recreational use of coastal areas and MPAs is increasing elsewhere, making fish feeding a generalised human activity. Accurate information about its effect on the fish assemblage is essential to make responsible management decisions.Communicated by R. Cattaneo-Vietti, Genova     

Demographic plasticity in tropical reef fishes

We use age-based analyses to demonstrate consistent differences in growth, mortality, and longevity of coral reef fishes from similar habitats (exposed reef crests) 20 km apart. On outer-shelf reef crests of the northern Great Barrier Reef (GBR), size in four taxa of reef fishes (Chlorurus sordidus, Scarus frenatus, and S. niger and the acanthurid Acanthurus lineatus) was systematically and significantly smaller when compared with the same taxa on adjacent mid-shelf reef crests. Differences in size could be attributed to differences in growth between habitats (shelf positions). On outer reef crests the species examined had consistently lower size at age profiles and also reduced life spans compared with populations from mid-shelf reefs. To confirm this relationship, two of the most abundant species (C. sordidus and S. frenatus) were selected for more detailed spatial analysis of demographic patterns. Sampling adults of both taxa from reef crests on three mid- and three outer-shelf reefs revealed that most of the variation in growth was explained by shelf position, although C. sordidus also displayed differences in growth among mid-shelf reefs. We conclude that differences in body sizes across the continental shelf of the northern GBR are primarily determined by these trends in growth. Strong spatial patterns also existed in the mean ages of populations and longevity estimates for C. sordidus and S. frenatus between shelf positions. Both species on outer-shelf reefs displayed less variable cohort sizes, significantly reduced mean ages, and foreshortened longevity compared with populations on mid-shelf reefs. Furthermore, differences in these parameters were rare among replicate reefs within mid- and outer-continental-shelf positions. Age-based catch curves suggested that rates of S. frenatus natural mortality on the outer shelf were nearly twice as high as on the mid shelf. Visual surveys indicated that total scarid densities on outer-shelf reef crests are on average fourfold higher than for equivalent mid-shelf habitats. This fact, coupled with significantly reduced growth rates, reduced mean ages, and increased mortality rates, suggests that density-dependent processes may be responsible for observed differences among localities.     

Diets of the demersal fishes on the shelf off Iwate,northern Japan

Diets of demersal fishes were determined on the shelf (ca. 130 m deep) off Iwate, Japan. Samples were taken in three different types of habitat, an artificial reef (AR) site, a natural reef (NR) site, and sandymud bottom (SB) site, from May 1987 to September 1991, mostly every two months. A total of 67 prey items were recognized in the stomachs of 45 predator fish species. The most important preys were the pelagic fishes Sardinops melanostictus and Engraulis japonicus, which comprised 37% wet wt of the overall stomach contents. The percentage of pelagic fishes was highest at AR site, where fish density was highest. The dominant ten species could be divided into five feeding types. The pelagic fish feeders Physiculus maximowiczi and Gadus macrocephalus fed mainly on S. melanostictus. The dietary breadth of P. maximowiczi was wide, while that of Gadus macrocephalus was narrow. The pelagic crustacean feeder Theragra chalcogramma mostly consumed Themisto japonica and euphausiids and showed the least dietary overlap with other fishes. Benthic fish feeders were Hemitripterus villosus and Liparis tanakai. The benthic crustacean feeders Alcichthys alcicornis and Hexagrammos otakii consumed benthic crustaceans as well as pelagic and benthic fishes and showed the largest dietary breadth. The benthic invertebrate feeders Gymnocanthus intermedius, Dexistes rikuzenius and Tanakius kitaharai fed mainly on polychaetes and benthic crustaceans. But Gymnocanthus intermedius consumed a significant proportion of pelagic fishes. Ontogenetic dietary shift was recognized for these fishes. Pelagic fishes were consumed more intensively by larger individuals, especially true of A. alcicornis, Theragra chalcogramma and Gadus macrocephalus. Predominancy of the two most adundant species, P. maximowiczi and A. alcicornis, may be supported by their wide dietary breadth and the significant proportion of pelagic fish in their diets. Interspecific dietary overlap was low in most cases suggesting that food resources were well partitioned, although some high overlap was observed among the pelagic fish feeders, A. alcicornis, and Gymnocanthus intermedius, and among the benthic invertebrate feeders. Interspecific competition seemed more likely in the benthic invertebrate feeders than in the pelagic fish feeders partly because of superabundance of the pelagic prey S. melanostictus.     

Toward pristine biomass: reef fish recovery in coral reef marine protected areas in Kenya.

Identifying the rates of recovery of fish in no-take areas is fundamental to designing protected area networks, managing fisheries, estimating yields, identifying ecological interactions, and informing stakeholders about the outcomes of this management. Here we study the recovery of coral reef fishes through 37 years of protection using a space-for-time chronosequence of four marine national parks in Kenya. Using AIC model selection techniques, we assessed recovery trends using five ecologically meaningful production models: asymptotic, Ricker, logistic, linear, and exponential. There were clear recovery trends with time for species richness, total and size class density, and wet masses at the level of the taxonomic family. Species richness recovered rapidly to an asymptote at 10 years. The two main herbivorous families displayed differing responses to protection, scarids recovering rapidly, but then exhibiting some decline while acanthurids recovered more slowly and steadily throughout the study. Recovery of the two invertebrate-eating groups suggested competitive interactions over resources, with the labrids recovering more rapidly before a decline and the balistids demonstrating a slower logistic recovery. Remaining families displayed differing trends with time, with a general pattern of decline in smaller size classes or small-bodied species after an initial recovery, which suggests that some species- and size-related competitive and predatory control occurs in older closures. There appears to be an ecological succession of dominance with an initial rapid rise in labrids and scarids, followed by a slower rise in balistids and acanthurids, an associated decline in sea urchins, and an ultimate dominance in calcifying algae. Our results indicate that the unfished "equilibrium" biomass of the fish assemblage > 10 cm is 1100-1200 kg/ha, but these small parks (< 10 km2) are likely to underestimate pre-human influence values due to edge effects and the rarity of taxa with large area requirement, such as apex predators, including sharks.     

Influence of habitat on abundance and size structure of a large temperate-reef fish, Achoerodus viridis (Pisces: Labridae)

The relationship between densities of Achoerodus viridis (Pisces: Labridae) and reef habitats at various localities within New South Wales (NSW), Australia was examined. Types of habitats were quantified at inner, mid and outer estuarine locations in each of two estuaries (Botany Bay and Port Jackson) to determine whether purported patterns of movement from estuaries could be related to differences in habitat. Although the same types of habitat were generally found at all locations, differences in the proportion of habitat types were found between shallow and deep reefs and among inner, mid and outer estuarine locations for both estuaries. Shallow habitats were usually dominated by Ecklonia radiata, turf and/or fringe habitat in Botany Bay, whereas deep sites were generally dominated by urchin-grazed barrens habitat and, sometimes, sponge- and ascidian-dominated deep reef. Shallow sites in Port Jackson were dominated by a mixture of habitats, as were deep reefs at mid-estuarine locations. Other deep reefs in Port Jackson were dominated by E. radiata (inner estuarine) or barrens (outer estuarine) habitat. Thus, patterns of habitat cover were not consistent between estuaries and numbers of fish could not be related to proportional representation of habitat on reefs along estuarine gradients. Univariate and multivariate analyses showed that there was little evidence that any size class of fish was correlated with the proportional representation of a particular habitat or group of habitats. Counts of fish that focused on barrens and E. radiata forest habitats over a period of 10 yr showed that similar numbers and all sizes of fish were found in the two types of habitat. Greater numbers of small fish were, however, found in the E. radiata forest habitat than in the barrens habitat. Estimates of abundance along the coast of NSW (100s to 1000 km) in a range of habitats (e.g. ascidian-dominated reef, kelp forest, urchin-grazed barrens) showed that there was no indication that a particular habitat consistently had greater numbers of A. viridis than other habitats. Therefore, A. viridis of a range of sizes appears to be flexible in its use of habitats on reefs. Received: 24 December 1997 / Accepted: 23 June 1998     

The trophic status of herbivorous fishes on coral reefs

Estimates of feeding rates, alimentary tract structure and temporal patterns of food processing obtained from twelve species of nominally herbivorous fishes on the northern Great Barrier Reef were compared. These included members of the families Acanthuridae, Scaridae and Kyphosidae. Based on an analysis of diet and short-chain fatty acid (SCFA) profiles from a previous study we initially partitioned the twelve species into four dietary categories, as follows: (a) Category 1: herbivores with a diet of macroscopic brown algae and high SCFA profiles in the hindgut region (Naso unicornis, Kyphosus vaigiensis); (b) Category 2: herbivores feeding on turfing and filamentous red and green algae with moderate SCFA profiles in the hindgut region (N. tonganus, K. cinerascens, Zebrasoma scopas, Acanthurus lineatus); (c) Category 3: zooplankton feeders with moderate SCFA profiles (N. vlamingii, N. brevirostris); (d) Category 4: species feeding on detrital and sedimentary materials with low levels of SCFA (Chlorurus microrhinos, Scarus schlegeli, Ctenochaetus striatus, A. olivaceus). The purpose of this comparison was to determine whether measures of feeding activity, alimentary tract structure, and food processing were concordant with diet. A dichotomy in feeding rates was observed. Species with a diet of algae and zooplankton (categories 1–3) had slower feeding rates than those feeding on detrital aggregates and sediment (category 4). The pattern of food processing also followed the same dichotomy with species of categories 1–3 retaining food in the alimentary tract overnight and commencing the feeding day with substantial amounts of food in the intestine and hindgut. Category-4 species commenced the feeding day with empty alimentary tracts suggesting a rapid turnover of gut contents. Within the herbivorous and zooplankton-feeding species neither alimentary tract structure nor food processing mode were predicted by diet or SCFA profiles. A hindgut fermentation chamber was present in K. vaigiensis but not in N. unicornis, a species with high levels of SCFA in the hindgut region and a diet of brown macroscopic algae. In contrast N. vlamingii, with a diet dominated by animal matter, retained large amounts of food material in a hindgut chamber over the entire feeding cycle. In tropical perciform fishes, herbivory and fermentation are not associated with the alimentary tract structures that characterise herbivorous terrestrial vertebrates. Estimates of the abundance of the different groupings of nominally herbivorous fishes indicated that the dominant elements in the reef grazing and browsing fauna were consumers of detrital and sedimentary materials. These could not be classified as herbivores. Members of this group were dominant in all habitats investigated. Explicitly herbivorous taxa were a minority component in all habitats investigated.Communicated by G.F. Humphrey, Sydney