Relationships between habitat structure and fish communities on coral

The influence of habitat structure on reef-fish communities at Bar Reef Marine Sanctuary, Sri Lanka, was investigated. The relationship between habitat characteristics and the distribution and abundance of 135 species of fishes was examined on two reef types: coral and sandstone reefs. Results suggested that the reef-fish communities were strongly influenced by various aspects of reef structure. However, relationships between habitat variables and fish communities structure, varied between the two reef types. Fish species diversity was correlated with a number of habitat variables on the sandstone reefs, although structural complexity seemed to play the dominant role. There were no correlations between habitat structure and fish diversity on the coral reefs. Total abundance was not related to any one habitat parameter on either reef type. However, abundances of some species, families and trophic groups were correlated with habitat features. These specific correlations were commonly related to food or shelter availability. For example, coral feeders were correlated with live coral cover, and pomacentrid species, which used branching corals for protection, showed a significant relationship with the density of Acropora colonies. This shows that a summary statistic such as total abundance may hide important information. Effects of habitat structure on the distribution patterns of the fish communities was further investigated using multi-dimensional scaling ordination (MDS) and the RELATE-procedure. With the MDS ordinations for both habitat and fish-community composition it was possible to show that the multivariate pattern between the two ecological components was clearly correlated.     

Fish Colonization of an Artificial Reef in the Gulf of Elat, Northern Red Sea

A small near shore artificial reef was constructed in the Gulf of Elat, northern Red Sea at a depth of 22–24m. The colonization of fishes was monitored for a period of 728 days and a total of 94 species was recorded. Colonization was initially rapid. The first species to appear were Dascyllus trimaculatus and Chaetodon paucifasciatus (day 2). In the first seven months, a gradual increase in the number of species was observed, after which it leveled off. Subsequently, a reduction in the number of individuals increased diversity of the community, as measured by the Shannon & Weaver index. The low complexity of the major components of the artificial reef, in addition to its location on a muddy, silty substrate, resulted in a constant cover of fine grain particles which presumably discouraged settlement of invertebrates and small cryptic fish species on the artificial reef.     

A comparison of the deep-water demersal fish assemblages of the Rockall Trough and Porcupine Seabight, eastern North Atlantic: continental slope to rise

Fishery surveys of the continental slope to the west of the British Isles have shown quite marked differences between areas in both the proportion and abundance of marketable or potentially marketable species. In general, the northern slopes lying to the west of Scotland were considered to have a greater potential for exploitation than the southern slopes off Ireland. Subsequent detailed studies of a northern (Rockall Trough) and a southern slope area (Porcupine Seabight) sampled the demersal fish fauna using a Granton trawl fished on paired warps to depths of 1200 m, and a semi-balloon trawl fished on a single warp to depths of about 3000 m. The Granton trawl catches differed significantly between the two areas, especially at the greatest depths fished. The semi-balloon trawl catches did not differ between the areas. This slower trawl was poor at catching large, mobile species and efficient in the capture of the deep-waler eel Synaphobranchus kaupi. This eel was numerically dominant over the mid to lower slope and probably accounts for much of the similarity between areas at these depths.     

Riparian ecotones and spatial variation of fish assemblages in Portuguese lowland streams

The first results of a long-term study on the role of riparian ecotones on the population and community dynamics of Iberian stream fish are presented and discussed. Riparian and macrophyte cover, bank slope and depth were among the most important variables affecting fish distribution. In general small fish favoured shallow areas with high macrophyte cover, whereas large fish dominated in deep areas with a high riparian cover. Slight spatial changes in terrestrial prey use were found suggesting a minor role for this resource during autumn. Finally, no significant spatial differences were found for linear growth, although some differences were obtained for the condition factor.     

Spatio-temporal patterns of recruitment of labroid fishes (Pisces: Labridae and Scaridae) to damselfish territories

Recent studies have shown that recruitment variability is an important process structuring reef fish assemblages. The aim of this study is to describe the spatio-temporal patterns of recruitment of three abundant labroid taxa (Coris schroederi, Halichoeres melanurus and Scarus spp.), using damselfish territories as replicate units of habitat. Temporal recruitment patterns of each taxa were consistent among three sites along 2 km of reef tract, with small differences among sites probably the result of hydrological or random factors operating at that scale. Recruitment of only one species (C. schroederi) showed consistent differences in the magnitude of recruitment among sites, which was probably due to an overriding effect of habitat selection for the location of the territories on the reef profile at one site. Two taxa, C. schroederi and Scarus spp., recruited in low to moderate rates over many weeks with moderate recruitment peaks detected in one year only. This pattern may be characteristic of many labroid species that have protracted periods of production of larvae. In contrast, H. melanurus recruited in a single short pulse of high magnitude each summer, which suggests that production of larvae by this species may occur over a more restricted period of time. No strong pattern of lunar entrainment of recruitment was detected for any taxa, which may be due to a lack of lunar periodicity in production of larvae. Further studies are now required to identify the processes that are important in determining patterns of labroid recruitment. This revised version was published online in August 2006 with corrections to the Cover Date.     

西沙群岛礁栖鱼类物种多样性及其食性特征

通过新的方法(即潜水调查法)调查了西沙群岛浅水区的礁栖鱼类, 并从食性角度分析鱼类群落特征及其对水质环境变化的响应。2006年5-6月, 对西沙群岛6个岛礁(东岛、永兴岛、羚羊礁、金银岛、华光礁和中建岛)共10个站位的礁栖鱼类种类、数量和长度进行了调查, 结合公开资料(FishBase等)确定鱼类食性。共记录到29科71属119种鱼, 其中50种是新记录。至此, 西沙群岛的鱼类总记录已达到717种。从不同站位来看, 永兴岛西的种类数量和Shannon-Wiener多样性指数均最高。多数鱼种分布范围狭小。摄食浮游动物和底栖无脊椎动物的鱼类是优势类群, 而草食性、杂食性和食物链顶端食性的鱼类数量和生物量较低, 反映出西沙群岛珊瑚礁生态系统整体上健康稳定。永兴岛的杂食性鱼类的数量比例和生物量比例均高于其他岛礁, 反映出鱼类群落已对水体富营养化产生响应。     

A dynamic model of group-size choice in the coral reef fish Dascyllus albisella

We developed a dynamic programming model of group size choicefor settlingcoral reef fish to help understand variabilityin observed group sizes. Ratherthan calculating optimal groupsize, we modeled optimal choice and calculatedthe acceptablegroup sizes that arose from this choice. In the model, settlingindividualsweigh the fitness value of settling in a group against theexpectedfitness of searching another day and encountering other groups,choosingthe option with the higher value. Model results showed thatindividualssettling on any given day in the settling season have severalacceptablegroup sizes in which they can settle. The range of acceptablegroupsizes also changes across the season. Early in the season,when there is stilladequate time to grow, large groups (withhigher survival) have the highestfitness. Late in the season,when the ability to grow fast becomes moreimportant, smallgroups, which convey fast growth rates (although riskier),havehigher fitness. Thus, according to our model, even when fishall make thesame, simple decisions, a variety of outcomes arepossible, depending on thespecific options encountered andtemporally changing ecological pressures.Even when all fishbehave optimally, initial variability in group sizes willpersist.