Spatial and Temporal Patterns in Assemblages of Temperate Reef Fish

SYNOPSIS. For reef fish in temperate marine regions, such componentsof local assemblage diversity (i.e., within a reef) as speciesrichness, total fish density, and rank order of abundance canremain relatively constantthrough time. Long-term data (17 years)for assemblages on 2 reefs in Southern California revealed that,despite high turnover in rare species, overall species richnesswas affected only moderately by major oceanographicdisturbances.This resilience of the assemblage is in marked contrast to hightemporal variation in densities exhibited by many local populationsof individual species, and it suggests that measurements ofdiversity to indicate status of an assemblage should be usedwith caution. Here we consider various processes and factors,together with the spatial and temporal scales over which theyoperate, that can influence local diversity (and its estimation)of reef fishes. Mechanisms that can "buffer" local diversityof reef fishes include dispersal of young that inter-connectssubpopulations, high "inertia" in relative abundance and populationstructures (especially for long-lived species), and broad ecologicalrequirements of many species. These considerations suggest thatthe effect of disturbances on local diversity of reef fisheswill depend in part on the magnitude, duration, frequency andspatial scale of the perturbation. While long-term data arefew, available information suggests that, due to life historycharacteristics of the fish and the spatial and temporal scalesat which disturbances are likely to occur, assemblages of temperatemarine reef fish might be relatively resilient to environmentalperturbations     

Multiscale habitat associations of detrivorous blennies (Blenniidae: Salariini)

The distribution and habitat associations of detrivorous blennies on a tropical coral reef were investigated at several spatial scales and compared with other fish that feed on the epilithic algal matrix to assess density and biomass contributions of small detrivorous fishes to these assemblages. At broad spatial scales total blenny abundance and biomass were highest on the tops of reefs exposed to prevailing winds. On the finer scale of microhabitat use, all species showed a preference for non-living corals, although the type of coral utilised differed between species. The high abundance of blennies on reef tops and non-living corals may be partially related to the quality and availability of detritus in these habitats. Comparisons of total blenny abundance and biomass with other territorial detrivores found that blennies accounted for approximately 60% of this functional group's density and 21% of their biomass on exposed reef tops. Overall, territorial detrivores were found to constitute approximately 37% of the density and 26% of the biomass of the detrivorous/herbivorous fish assemblage on exposed reef tops. Small detrivorous fish therefore represent a substantial proportion of fish assemblages that feed on epilithic algae and associated detritus on coral reefs.     

Spatial variation of reef fishes and the relative influence of biotic and abiotic habitat traits

Patterns of distribution of reef fishes were examined across three spatial scales and related to habitat traits along 25 km of the northern Portuguese coast. Response variables included the multivariate assemblage structure, the total number of taxa and individuals, and the abundance of single groups categorized according to their preference for the benthic, proximo-benthic or pelagic environment, feeding and reproductive behaviour. Habitat traits included topographic elements (small and large ‘drops’ like cracks and crevices) and the extent of dominant morpho-functional types of macroalgae (kelp, large foliose, small erect, turf-forming filamentous, and encrusting). All fish responses were characterized by the largest variance at the smallest scale (among transects tens m apart), followed by that among reefs (hundreds m to 1 km apart) and almost null variance among sites (some km apart). Small and large ‘drops’ of the substratum explained, respectively, considerable variation of assemblage structure and the total abundance of individuals, while the extent of bare rock influenced the richness of taxa and that of benthic fishes, fishes feeding on sessile invertebrates and fishes laying benthic eggs or having nesting behaviour. Combinations of abiotic and biotic structural attributes of reefs influenced proximo-benthic fishes, the predators of mobile animals and fishes releasing pelagic eggs. The here reported associations between patterns of distribution of reef fishes and habitat traits have implications for the design of future protection schemes suitable to guarantee the conservation of reef fish communities and of the processes responsible for their variation. Within the SLOSS (single-large vs. several-small) debate in the design of marine reserves, for example, effective protection to the studied reef fishes would be provided by a set of small reserves, rather than a single large which might be appropriate for fishes having wider home ranges.     

Relative Importance of Coral Cover,Habitat Complexity and Diversity in Determining the Structure of Reef Fish Communities

The structure of coral reef habitat has a pronounced influence on the diversity, composition and abundance of reef-associated fishes. However, the particular features of the habitat that are most critical are not always known. Coral habitats can vary in many characteristics, notably live coral cover, topographic complexity and coral diversity, but the relative effects of these habitat characteristics are often not distinguished. Here, we investigate the strength of the relationships between these habitat features and local fish diversity, abundance and community structure in the lagoon of Lizard Island, Great Barrier Reef. In a spatial comparison using sixty-six 2m² quadrats, fish species richness, total abundance and community structure were examined in relation to a wide range of habitat variables, including topographic complexity, habitat diversity, coral diversity, coral species richness, hard coral cover, branching coral cover and the cover of corymbose corals. Fish species richness and total abundance were strongly associated with coral species richness and cover, but only weakly associated with topographic complexity. Regression tree analysis showed that coral species richness accounted for most of the variation in fish species richness (63.6%), while hard coral cover explained more variation in total fish abundance (17.4%), than any other variable. In contrast, topographic complexity accounted for little spatial variation in reef fish assemblages. In degrading coral reef environments, the potential effects of loss of coral cover and topographic complexity are often emphasized, but these findings suggest that reduced coral biodiversity may ultimately have an equal, or greater, impact on reef-associated fish communities.     

Tropical Fishes Dominate Temperate Reef Fish Communities within Western Japan

Climate change is resulting in rapid poleward shifts in the geographical distribution of tropical and subtropical fish species. We can expect that such range shifts are likely to be limited by species-specific resource requirements, with temperate rocky reefs potentially lacking a range of settlement substrates or specific dietary components important in structuring the settlement and success of tropical and subtropical fish species. We examined the importance of resource use in structuring the distribution patterns of range shifting tropical and subtropical fishes, comparing this with resident temperate fish species within western Japan (Tosa Bay); the abundance, diversity, size class, functional structure and latitudinal range of reef fishes utilizing both coral reef and adjacent rocky reef habitat were quantified over a 2 year period (2008–2010). This region has undergone rapid poleward expansion of reef-building corals in response to increasing coastal water temperatures, and forms one of the global hotspots for rapid coastal changes. Despite the temperate latitude surveyed (33°N, 133°E) the fish assemblage was both numerically, and in terms of richness, dominated by tropical fishes. Such tropical faunal dominance was apparent within both coral, and rocky reef habitats. The size structure of the assemblage suggested that a relatively large number of tropical species are overwintering within both coral and rocky habitats, with a subset of these species being potentially reproductively active. The relatively high abundance and richness of tropical species with obligate associations with live coral resources (i.e., obligate corallivores) shows that this region holds the most well developed temperate-located tropical fish fauna globally. We argue that future tropicalisation of the fish fauna in western Japan, associated with increasing coral habitat development and reported increasing shifts in coastal water temperatures, may have considerable positive economic impacts to the local tourism industry and bring qualitative changes to both local and regional fisheries resources.     

Kenyan coral reef lagoon fish: effects of fishing,substrate complexity,and sea urchins

Population density, number of species, diversity, and species-area relationships of fish species in eight common coral reef-associated families were studied in three marine parks receiving total protection from fishing, four sites with unregulated fishing, and one reef which recently received protection from fishing (referred to as a transition reef). Data on coral cover, reef topographic complexity, and sea urchin abundance were collected and correlated with fish abundance and species richness. The most striking result of this survey is a consistent and large reduction in the population density and species richness of 5 families (surgeonfish, triggerfish, butterflyfish, angelfish, and parrotfish). Poor recovery of parrotfish in the transition reef, relative to other fish families, is interpreted as evidence for competitive exclusion of parrotfish by sea urchins. Reef substrate complexity is significantly associated with fish abundance and diversity, but data suggest different responses for protected versus fished reefs, protected reefs having higher species richness and numbers of individuals than unprotected reefs for the same reef complexity. Sea urchin abundance is negatively associated with numbers of fish and fish species but the interrelationship between sea urchins, substrate complexity, coral cover, and management make it difficult to attribute a set percent of variance to each factor-although fishing versus no fishing appears to be the strongest variable in predicting numbers of individuals and species of fish, and their community similarity. Localized species extirpation is evident for many species on fished reefs (for the sampled area of 1.0 ha). Fifty-two of 110 species found on protected reefs were not found on unprotected reefs.     

Coral and fish distribution patterns in Mafia Island Marine Park, Tanzania: fish–habitat interactions

We examined coral reef communities at 11 sites within Mafia Island Marine Park using a point count method for substrate and visually censused belt transects for fish populations. Multivariate ordinations showed that the benthic habitat differed among reefs. The patterns were mainly attributed to variations in depth, hydrodynamics and benthic composition. In total, the substratum was dominated by dead coral (49%) and algae (25%), with a live coral cover of only 14%. Three hundred and ninety-four fish species belonging to 56 families were recorded. According to MDS-ordinations and RELATE procedures, fish assemblage composition varied among sites in concordance with the habitats provided. Sites with highest proportion of dead coral exhibited highest degree of dispersion in the multivariate ordinations of fish assemblages. Stepwise multiple regression was used to determine the proportion of variance among sites which could be explained by depth, exposure, rugosity, substrate diversity, branching substrate, live coral cover, dead coral cover and different types of algae. The results showed that habitat variables explained up to 92% of the variation in species numbers and in total, and taxon-specific, abundance. Live coral cover was the foremost predictor of both numerical and species abundance, as well as of corallivores, invertivores, planktivores and of the families Pomacentridae, Chaetodontidae and Pomacanthidae. Our results suggest that habitat characteristics play a dominant role in determining fish assemblage composition on coral reefs.     

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems

We quantify the relative importance of multi‐scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo‐Pacific biogeographical provinces. Large (>30 cm), functionally‐important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km²). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local‐scale variables, ‘distance from port’, a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re‐emphasise the importance that historical processes play in structuring contemporary biotic communities.     

Ecological structure of assemblages of coral reef fishes on isolated patch reefs

A 9-year study of the structure of assemblages of fish on 20 coral patch reefs, based on 20 non-manipulative censuses, revealed a total of 141 species from 34 families, although 40 species accounted for over 95% of sightings of fish. The average patch reef was 8.5 m² in surface area, and supported 125 fish of 20 species at a census. All reefs showed at least a two-fold variation among censuses in total numbers of fish present, and 12 showed ten-fold variations. There was also substantial variation in the composition and relative abundances of species present on each patch reef, such that censuses of a single patch reef were on average about 50% different from each other in percent similarity of species composition (Czekanowski's index). Species differed substantially in the degree to which their numbers varied from census to census, and in the degree to which their dispersion among patch reefs was modified from census to census. We characterize the 40 most common species with respect to these attributes. The variations in assemblage structure cannot be attributed to responses of fish to a changing physical structure of patch reefs, nor to the comings and goings of numerous rare species. Our results support and extend earlier reports on this study, which have stressed the lack of persistant structure for assemblages on these patch reefs. While reef fishes clearly have microhabitat preferences which are expressed at settlement, the variations in microhabitat offered by the patch reefs are insufficient to segregate many species of fish by patch reef. Instead, at the scale of single patch reefs, and, to a degree, at the larger scale of the 20 patch reefs, most of the 141 species of fish are distributed without regard to differences in habitat structure among reefs, and patterns of distribution change over time. Implications for general understanding of assemblage dynamics for fish over more extensive patches of reef habitat are considered.     

The influence of coral reef benthic condition on associated fish assemblages

Accumulative disturbances can erode a coral reef's resilience, often leading to replacement of scleractinian corals by macroalgae or other non-coral organisms. These degraded reef systems have been mostly described based on changes in the composition of the reef benthos, and there is little understanding of how such changes are influenced by, and in turn influence, other components of the reef ecosystem. This study investigated the spatial variation in benthic communities on fringing reefs around the inner Seychelles islands. Specifically, relationships between benthic composition and the underlying substrata, as well as the associated fish assemblages were assessed. High variability in benthic composition was found among reefs, with a gradient from high coral cover (up to 58%) and high structural complexity to high macroalgae cover (up to 95%) and low structural complexity at the extremes. This gradient was associated with declining species richness of fishes, reduced diversity of fish functional groups, and lower abundance of corallivorous fishes. There were no reciprocal increases in herbivorous fish abundances, and relationships with other fish functional groups and total fish abundance were weak. Reefs grouping at the extremes of complex coral habitats or low-complexity macroalgal habitats displayed markedly different fish communities, with only two species of benthic invertebrate feeding fishes in greater abundance in the macroalgal habitat. These results have negative implications for the continuation of many coral reef ecosystem processes and services if more reefs shift to extreme degraded conditions dominated by macroalgae.     

Predators reduce abundance and species richness of coral reef fish recruits via non-selective predation

Predators have important effects on coral reef fish populations, but their effects on community structure have only recently been investigated and are not yet well understood. Here, the effect of predation on the diversity and abundance of young coral reef fishes was experimentally examined in Moorea, French Polynesia. Effects of predators were quantified by monitoring recruitment of fishes onto standardized patch reefs in predator-exclosure cages or uncaged reefs. At the end of the 54-day experiment, recruits were 74% less abundant on reefs exposed to predators than on caged ones, and species richness was 42% lower on reefs exposed to predators. Effects of predators varied somewhat among families, however, rarefaction analysis indicated that predators foraged non-selectively among species. These results indicate that predation can alter diversity of reef fish communities by indiscriminately reducing the abundance of fishes soon after settlement, thereby reducing the number of species present on reefs.     

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.

     

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     

Fish assemblages on sunken vessels and natural reefs in southeast Florida,USA

Derelict ships are commonly deployed as artificial reefs in the United States, mainly for recreational fishers and divers. Despite their popularity, few studies have rigorously examined fish assemblages on these structures and compared them to natural reefs. Six vessel-reefs off the coast of southeast Florida were censused quarterly (two ships per month) to characterize their associated fish assemblages. SCUBA divers used a non-destructive point-count method to visually assess the fish assemblages over 13- and 12-month intervals (March 2000 to March 2001 and March 2002 to February 2003). During the same intervals, fish assemblages at neighboring natural reefs were also censused. A total of 114,252 fishes of 177 species was counted on natural and vessel-reefs combined. Mean fish abundance and biomass were significantly greater on vessel-reefs in comparison to surrounding natural reef areas. Haemulidae was the most abundant family on vessel-reefs, where it represented 46% of total fish abundance. The most abundant family on natural reefs was Labridae, where it accounted for 24% of total fish abundance. Mean species richness was significantly greater on vessel-reefs than neighboring natural reefs and also differed among vessel-reefs. Both mean fish abundance and mean species richness were not significantly different between natural reefs neighboring vessel-reefs and natural reefs with no artificial structures nearby. This suggests the vessel-reefs are not, in general, attracting fish away from neighboring natural reefs in our area. Additionally, economically important fish species seem to prefer vessel-reefs, as there was a greater abundance of these species on vessel-reefs than surrounding natural reef areas. Fish assemblage structure on natural versus artificial reefs exhibited a low similarity (25.8%). Although no one species was responsible for more than 6% of the total dissimilarity, fish assemblage trophic structure differed strikingly between the two reef types. Planktivores dominated on vessel-reefs, accounting for 54% of the total abundance. Conversely, planktivores only made up 27% of total abundance on natural reefs. The results of this study indicate vessel-reef fish assemblages are unique and that these fishes may be utilizing food resources and habitat characteristics not accessible from or found at natural reefs in our area. Production may also be occurring at vessel-reefs as the attraction of fish species from nearby natural reefs seems to be minimal. Electronic supplementary material Supplementary material is available for this article at and accessible for authorised users     

Climate warming, marine protected areas and the ocean-scale integrity of coral reef ecosystems

Coral reefs have emerged as one of the ecosystems most vulnerable to climate variation and change. While the contribution of a warming climate to the loss of live coral cover has been well documented across large spatial and temporal scales, the associated effects on fish have not. Here, we respond to recent and repeated calls to assess the importance of local management in conserving coral reefs in the context of global climate change. Such information is important, as coral reef fish assemblages are the most species dense vertebrate communities on earth, contributing critical ecosystem functions and providing crucial ecosystem services to human societies in tropical countries. Our assessment of the impacts of the 1998 mass bleaching event on coral cover, reef structural complexity, and reef associated fishes spans 7 countries, 66 sites and 26 degrees of latitude in the Indian Ocean. Using Bayesian meta-analysis we show that changes in the size structure, diversity and trophic composition of the reef fish community have followed coral declines. Although the ocean scale integrity of these coral reef ecosystems has been lost, it is positive to see the effects are spatially variable at multiple scales, with impacts and vulnerability affected by geography but not management regime. Existing no-take marine protected areas still support high biomass of fish, however they had no positive affect on the ecosystem response to large-scale disturbance. This suggests a need for future conservation and management efforts to identify and protect regional refugia, which should be integrated into existing management frameworks and combined with policies to improve system-wide resilience to climate variation and change.     

Effect of simulated macroalgae on the fish assemblage associated with a temperate reef system

Increased habitat complexity is supposed to promote increased diversity, abundance and biomass. This study tested the effect of the macroalgal cover on temperate reef fishes by mimicking macroalgae on artificial reefs in NW Sicily (Mediterranean Sea). Macroalgal cover affected reef fishes in different ways and independently of intrinsic temporal trends. The fish assemblages of manipulated and control artificial reef units differed in the relative abundances of the associated species, but little in species composition. In line with studies in seagrass habitats, fishes were most abundant in reefs covered by artificial macroalgae. Three species (Boops boops, Serranus scriba and Symphodus ocellatus) exhibited consistently greater abundance on vegetated reef units than on control reef units. The total number of species and the abundance of three particular species (S. scriba, S. ocellatus and Thalassoma pavo) displayed temporal trends which were independent on short and large temporal scales. Only fish total biomass and one species (Spicara flexuosa) displayed strong effects of interaction among the experimental factors. Mechanisms to explain these findings are discussed from observational evidence on habitat use and interactions among multiple species. This study highlights that manipulative experiments involving repeated sampling of fish in artificial habitats appear to be a valid approach to study fish-habitat relationships in fluctuating environments. It is also concluded that macroalgae mimics may serve as a tool for restoring lost marine vegetated habitats when current human-induced conditions prevent the recovery of pristine macroalgal stands.     

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.     

The Eocene fishes of Monte Bolca: the earliest coral reef fish assemblage

The fish assemblage from the Eocene deposits of Monte Bolca, Northern Italy, are compared with those of Recent coral reefs. A family-level taxonomic definition of a Recent coral reef fish assemblage is formulated to permit direct comparisons. On this basis, the Monte Bolca fishes represent the earliest clearly defined coral reef fish assemblage. Quantitative analyses of the relative abundance of fish families revealed significant differences between the two assemblages. The Bolca assemblage has Mesozoic links (Pycnodontiformes) and non-perciform taxa are relatively abundant, particularly the Beryciformes (Holocentridae). However, Bolca represents the earliest record of a perciform-dominated benthic fish assemblage (68.4% of all non-clupeid taxa). Within the Perciformes, the abundance of the major reef fish lineages (higher squamipinnes and Labroidei) differs markedly between the two assemblages. The numerical dominance of labroid fishes on coral reefs appears to have been a relatively recent occurrence.     

A unified model explains commonness and rarity on coral reefs

Abundance patterns in ecological communities have important implications for biodiversity maintenance and ecosystem functioning. However, ecological theory has been largely unsuccessful at capturing multiple macroecological abundance patterns simultaneously. Here, we propose a parsimonious model that unifies widespread ecological relationships involving local aggregation, species‐abundance distributions, and species associations, and we test this model against the metacommunity structure of reef‐building corals and coral reef fishes across the western and central Pacific. For both corals and fishes, the unified model simultaneously captures extremely well local species‐abundance distributions, interspecific variation in the strength of spatial aggregation, patterns of community similarity, species accumulation, and regional species richness, performing far better than alternative models also examined here and in previous work on coral reefs. Our approach contributes to the development of synthetic theory for large‐scale patterns of community structure in nature, and to addressing ongoing challenges in biodiversity conservation at macroecological scales.     

Small-scale recruitment variation in a temperate fish: the roles of macrophytes and food supply

Synopsis The availability of reef-related resources, particularly food and shelter can play a significant role in determining the distribution and abundance of reef fishes. Much of the structure on temperate reefs is provided by macroalgae, and variability in the density of temperate reef fishes at large spatial scales (100's of meters) can often be explained by variation in macroalgal cover or density. In this study I investigated the role of macrophytes and associated food resources on the recruitment of a temperate fish, Tautogolabrus adspersus, at a small spatial scale (0.25 m²). No relationship between the density of new recruits and the percent cover of kelp, foliose or filamentous algae was observed. Multiple regressions revealed that less than 8% of variability in recruitment could be explained by variability in macroalgal cover. However, recruits were found in higher abundance in patches containing many functional forms of seaweeds than in patches dominated by a single form. A wide variety of prey were available for use by cunner recruits; however, crustaceans and mussels were the only common components of their diet, and crustaceans were clearly the most preferred prey. The prey composition in patches where fish were present was compared to randomly selected patches. Significantly greater numbers of isopods, amphipods and newly settled mussels were present in patches where fish were present than in randomly selected patches. The data presented in this study contradict previous work that has shown algal structure to be important in determining patterns of abundance and food supply to be of little significance. A conceptual model is proposed suggesting that settling fish select habitats in a hierarchical manner largely based on their dispersal tendencies. Hierarchical selection of habitats results in different attributes of the habitat being selected during different life-history intervals.