Short-term foraging patterns of individual cornetfish, Fistularia commersonii, based on stomach content analysis

Stomach contents of 75 specimens of the cornetfish Fistularia commersonii, collected in shallow water off Kuchinoerabu-jima Island, southern Japan were analyzed. Many fish contained multiple prey. The prey were mostly fish, grouped into two types, pelagic and reef fishes. The size of prey increased as the size of F. commersonii increased. All the small individuals (<50 cm SL) had fed on only small reef fish. However, most of the large individuals (>50 cm SL) had fed on either prey type. Both pelagic and reef fishes usually occurred simultaneously in shallow water, suggesting that most of the large cornetfish may selectively hunt either type of prey. Received: February 27, 2001 / Revised: September 11, 2001 / Accepted: October 10, 2001     

Community Structure of Fishes and Habitat Complexity on a Tropical Rocky Shore

The relationship between the variables of reef fish community structure (fish richness, fish diversity and total number of fishes) and those of habitat complexity (total surface area, substratum diversity, topographic complexity, number of holes, percent cover of turf algae, zoanthids, millepores, massive corals, bare rock, encrusting calcareous algae, urchins, other sessile organisms and Sargassum) were examined on three different rocky shores (FA, FB and FT) at Arraial do Cabo, a tropical region located on Brazilian southeastern coast (23° S, 42° W). Fish abundance and vertical distribution were assessed by a visual census technique using strip transects. Percentage cover of benthic organisms and other substratum types were calculated by replicated transects using a chain laid down on the substratum. Topographic complexity was determined by the chain link method and number of holes were estimated by direct counts on replicated transects. More than 91 fishes belonging to 37 families were seen in all study sites during one year of visual census effort. FA and FB sites had similar fish community structure and habitat complexity characteristics, while FT showed different habitat characteristics and higher fish diversity and richness, plus total number of fishes. Vertical distribution of fishes along the rocky shores studied seemed to be predictable and was determined by factors such as feeding habits and behavior, availability of refuges and social interactions. The habitat variables that best explained the higher diversity and number of fishes observed in FT site were total surface area of rocky shores and the abundance of benthic sessile invertebrates; these conditions were typical of rocky shores more exposed to wave surge.     

南海永署礁泻湖1680年来微型腹足类丰度变化的环境意义

永署礁南永3井记录了近1680年来礁泻湖腹足类遗壳的沉积变化,其中腹足类丰度变化尤为显著,存在三个高丰度区和相间的三个低丰度区,全样单一的粉砂沉积,表明丰度的变化与底质类型无关,而高分异度显示了一部分腹足类遗壳为水动力搬动的结果,腹足类丰度与沉积速率的对比表明,高沉积速率和低沉积速率以及波动的沉积环境不利于腹足类的发展,而适中的沉积速率和稳定的沉积环境将是腹足类发展的有利因素,发现环境的变化大约以400－600年为周期,1459－1680年间为环境动荡期,腹足类为低丰度,1081－1459年间为环境稳定期,腹足类丰度高;559－1081年间为沉积速率急剧变化期,腹足类为低丰度,1－559年间沉积速率非常稳定,腹足类十分发育。     

The importance of chemical environmental cues for juvenile Lethrinus nebulosus Forsskål (Lethrinidae, Teleostei) when settling into their first benthic habitat

A commercially important coral-reef fish, the spangled emperor Lethrinus nebulosus, settles into seagrass beds at the end of its pelagic larval phase, but the mechanism for locating these beds is unknown. To investigate this mechanism we first used a wide-choice, ex situ setup to examine the ability of captivity-reared naïve L. nebulosus settlers to select their first benthic habitat by reference to chemical cues. Second, we examined the morphology and ultrastructure of the nasal olfactory organ in settling L. nebulosus juveniles. We obtained the first evidence of a tropical seagrass-settling coral reef fish that can use chemical environmental cues in selecting its first benthic habitat at ranges up to at least 2 m. The L. nebulosus settlers exhibited a well developed pair of nasal olfactory organs, positioned in nares on the dorsal side of the head. These organs were elliptical radial rosettes, one in each of the olfactory chambers, and each comprised 12 lamellae, six on each side of a midline raphe, which were totally covered with sensory and non-sensory cilia, except for the margins. This type of cilia distribution is thought to indicate an acute sense of smell. The olfactory epithelium contained mature and immature ciliated receptor neurons bearing three to five cilia, and a second type of receptor neuron bearing six to eight microvilli.     

POPULATION STRUCTURE OF A CLONAL GORGONIAN CORAL: THE INTERPLAY BETWEEN CLONAL REPRODUCTION AND DISTURBANCE

Clonality is a common feature of plants and benthic marine organisms. In some cases clonal propagation results in a modest increase in population density, while in other cases dense populations may be generated by the propagation of only a few clones. We analyzed the population structure of the clonal gorgonian Plexaura kuna across several reef habitats with a range of disturbance regimes in the San Blas Islands, Panama, and the Florida Keys, U.S.A. Using multilocus DNA fingerprinting to distinguish clones, we estimated that clones ranged in size from single individuals to 500 colonies. The number of genotypes identified on nine reefs ranged from three to 25. Population density and clonal structure varied markedly among reefs with G_O:G_E ranging from 0.03 to 1.00. On some reefs vegetative reproduction transformed P. kuna from a rare species to the numerically most abundant gorgonian. The effect of clonal propagation on P. kuna population structure was dependent on interactions between fragmentation and the reef environment (disturbance regime, substratum). We present a generalized model relating population structure of clonal species to disturbance and the mode of vegetative propagation. Disturbance promotes colony propagation and skews the size-frequency distribution of clones among P. kuna and many species that propagate via fragmentation. Propagation of these species is promoted by disturbance (disturbance sensitive), and they tend to have clones that are dispersed across local sites. Species that fragment and have dispersed clones, have high genotypic diversity in habitats with low levels of disturbance. Genotypic diversity then decreases at intermediate disturbance and increases again at the highest disturbance levels. Clonal species that do not rely on disturbance for vegetative propagation (disturbance insensitive) generally do not disperse and form aggregated clones. Among these taxa disturbance has a greater affect on individual survival than on propagation. Genotypic diversity is directly related to the level of disturbance until very high levels of disturbance, at which time genotypic diversity declines.     

Biogeography and the structure of coral reef fish communities on isolated islands

Aim To determine the applicability of biogeographical and ecological theory to marine species at two remote island locations. This study examines how biogeography, isolation and species geographic range size influence patterns of species richness, endemism, species composition and the abundance of coral reef fishes. Location Christmas Island and the Cocos (Keeling) Islands in the tropical eastern Indian Ocean. Methods Published species lists and underwater visual surveys were used to determine species richness, endemism, species composition and abundance of reef fishes at the islands. These data were statistically compared with patterns of species composition and abundance from the neighbouring ‘mainland’ Indonesian region. Results The two isolated reef fish communities were species‐poor and contained a distinct taxonomic composition with an overrepresentation of species with high dispersal potential. Despite low species richness, we found no evidence of density compensation, with population densities on the islands similar to those of species‐rich mainland assemblages. The mix of Indian and Pacific Ocean species and the proportional representations of the various regional faunas in the assemblages were not influenced by the relative proximity of the islands to different biogeographical provinces. Moreover, species at the edge of their range did not have a lower abundance than species at the centre of their range, and endemic species had substantially higher abundances than widespread species. At both locations, endemism was low (less than 1.2% of the community); this may be because the locations are not sufficiently isolated or old enough to promote the evolution of endemic species. Main conclusions The patterns observed generally conform to terrestrial biogeographical theory, suggesting that similar processes may be influencing species richness and community composition in reef fish communities at these remote islands. However, species abundances differed from typical terrestrial patterns, and this may be because of the life history of reef fishes and the processes maintaining isolated populations.     

Spatial and trophic partitioning in cryptic fish communities of shallow subtidal reefs in False Bay, South Africa

Thirty-nine species of cryptic fishes belonging to 16 families were captured on shallow reefs (0-20 m) in False Bay, South Africa using the ichthyocide rotenone. Five samples were collected in each of four depth zones (0-5, 6-10, 11-15 and 16-20 m). The area from which fish were collected in each sample was measured to give an estimate of density. The overall density of cryptic fishes in the area was 3.41 fish m^-2, with the families Congrogadidae and Clinidae being numerically dominant, representing 27.9% and 22.3% of the total sample respectively. The Clinidae were by far the most diverse group, being represented by 17 species, while no other family was represented by more than three species. Multivariate analysis of numerical density revealed that partitioning of spatial resources did occur, with the shallowest samples (0-5 m) forming a group discrete from the deeper samples (6-20 m). Further analysis indicated that the amount of algal cover present was the most important factor influencing community structure, although the abundance of algae is in turn related to depth. The shallowest samples were dominated by members of the families Clinidae, Gobiesocidae and Bythitidae, while the Cheilodactylidae, Tripterygiidae and Ariidae were more important components of deeper water communities (6–20 m). Analysis of percentage volume of prey items in the diets of 21 species revealed that only two species shared diets that were more than 50% similar, and that partitioning of trophic resources was considerable. This revised version was published online in July 2006 with corrections to the Cover Date.