Big fish in shallow water; use of an intertidal surf-zone habitat by large-bodied teleosts and elasmobranchs in tropical northern Australia

Shallow intertidal habitats are recognised as critical for larval and juvenile fish, and are often assumed to function as refuge areas where predation risk is reduced. Yet there is growing evidence that suggest these areas may also be regularly inhabited by large bodied fish and be the site of high levels of juvenile fish predation. In the present study we examined the use of an intermittently available surf zone habitat in tropical northern Australia by a diverse community of large-bodied teleosts (mean total length 444 mm), sharks (mean total stretched length 658 mm) and rays (mean total stretched length 1,108 mm). Drawing on the methods and ecological knowledge of a local commercial fishery, gillnets were used to capture fish as they entered the surf zone on the flooding tide. Monthly surveys over a one-year period revealed a dynamic assemblage consisting of 30 species of teleosts (mostly caught as adults) and 14 species of sharks and rays (mostly caught as juveniles or young of the year). Although it is unclear why these fish use this habitat, we conclude that it may support a broad range of biological benefits including spawning for teleosts, parturition for elasmobranchs, as well as foraging and refuge. The unique findings of this study highlight existing knowledge gaps and the need to better understand what fish use the intertidal zone and why. This should be a high priority given the increasing anthropogenic pressures on coastal margins.     

A review on the early life history and ecology of Japanese sea bass and implication for recruitment

Recruitment in marine fishes is regulated largely by the demographic changes that occur during the early life stages; therefore, a thorough understanding of early life stages is essential for predicting recruitment variability in fishes. Japanese sea bass (JSB), Lateolabrax japonicus, is a coastal marine fish distributed in East Asian coastal waters, and is regarded as highly important for commercial and recreational fisheries, for marine and brackish water aquaculture as well as for stock enhancement. JSB is a typical estuarine dependent temperate fish, which spawns in shelf areas and coastal embayments and the larvae and juveniles are dispersed and transported into shallow nearshore habitats and estuaries where they spend the early life. In this paper, we provide insight into the early life history and ecology of JSB through a revision of the available information and using the data we obtained from a relatively long-term research. We review and discuss the distribution and habitat use, food and feeding, age and growth, mortality and recruitment of larval and juvenile JSB in coastal waters around Japan. We extend our discussions in all available dimensions: habitat-specific, ontogenetic, and spatio-temporal, and highlight the importance of nursery habitats. We also discuss the implications of early life history for recruitment of JSB as well as the possible effects of climate change. At the end, we point out potential areas for future research.     

Benefits of Turbid River Plume Habitat for Lake Erie Yellow Perch (Perca flavescens) Recruitment Determined by Juvenile to Larval Genotype Assignment

Nutrient-rich, turbid river plumes that are common to large lakes and coastal marine ecosystems have been hypothesized to benefit survival of fish during early life stages by increasing food availability and (or) reducing vulnerability to visual predators. However, evidence that river plumes truly benefit the recruitment process remains meager for both freshwater and marine fishes. Here, we use genotype assignment between juvenile and larval yellow perch (Perca flavescens) from western Lake Erie to estimate and compare recruitment to the age-0 juvenile stage for larvae residing inside the highly turbid, south-shore Maumee River plume versus those occupying the less turbid, more northerly Detroit River plume. Bayesian genotype assignment of a mixed assemblage of juvenile (age-0) yellow perch to putative larval source populations established that recruitment of larvae was higher from the turbid Maumee River plume than for the less turbid Detroit River plume during 2006 and 2007, but not in 2008. Our findings add to the growing evidence that turbid river plumes can indeed enhance survival of fish larvae to recruited life stages, and also demonstrate how novel population genetic analyses of early life stages can contribute to determining critical early life stage processes in the fish recruitment process.     

Larval fish assemblage recovery: a reflection of environmental change in a large degraded river

Estuaries are globally important to fisheries but face many anthropogenic stressors that reduce water quality and degrade benthic habitat. The Maumee River estuary has been degraded by industrial contaminants, high sediment and nutrient loads, channelization and elimination of surrounding wetlands, lessening its value as spawning habitat for fishes of Lake Erie. Regulation and better management practices (BMPs) in the watershed have improved the water quality in this estuary, which should result in a response of the biotic community. We compared recent (2010/2011) larval fish assemblage data to similar data from the 1970s (1976/1977) in order to identify changes due to improved water and habitat quality. Family‐level diversity was greater in recent study years compared to the 1970s and family richness increased from 6 to 10. In addition, the abundance of lithophilic spawning fishes was significantly greater in the recent study years. Increased diversity and family richness were consistent with increased water quality in the Maumee River whereas the observed increase in abundance of lithophilic spawners was consistent with an increase in the amount or quality of benthic habitat used by species in these families for spawning. Better wastewater management and agricultural practices in coastal watersheds can benefit the early life stages of fishes, thus benefitting coastal fisheries. Furthermore, larval fish assemblages may be useful indicators of biological integrity because of their sensitivities to environmental change. Routine sampling of estuarine larval fish assemblages could provide practitioners with insight into ecosystem changes and measure the response of the biotic community to restoration.     

Distribution of fishes in the Río Guayalejo-Río Tamesí system and relationships with environmental factors in northeastern Mexico

A priority issue in ecology and biogeography is understanding the patterns in species diversity and the causal factors of their distribution, which allows the generation of information for conservation strategies. The longitudinal distribution of fishes and their relationships with environmental variables were studied in the Guayalejo-Río Tamesí system (northeastern Mexico) from February 2000 to July 2001. A total of 5918 fish were caught in 27 collections along an altitudinal gradient in the main river course, from high mountain (1500 masl) to coastal plain near Tampico. Forty-three native and five exotic species, belonging to 35 genera in 23 families, were identified. Cluster analyses identified four major fish habitats in the river system. A distinctive euryhaline marine fish habitat (1) occurs near the mouth with native and two exotic species. Two other habitats consist essentially of freshwater fish species that are distributed along the longitudinal gradient. One of these habitats (habitat 4) shows greater diversity, as per the Shannon index value, and also includes amphidromous fish, in addition to two exotic freshwater fish; the other (habitat 2) includes freshwater, euryhaline and three exotic species. The changes in the frequency of occurrence and the abundance of Gambusia vittata, Astyanax mexicanus, and Xiphophorus variatus contribute to explaining differences between these habitats. Another habitat (3) is represented by two sampling sites located near the mouth and consist of freshwater and euryhaline fish and three exotic cyprinids with broad salinity tolerance. The low abundance and richness of exotic species suggest little impact on native fish fauna in this river. The fish assemblage of the Guayalejo-Tamesí river system species changes along a longitudinal gradient with the addition, replacement and presence of indicator species. Upstream fish fauna is mostly composed of freshwater species, some of them generalists that inhabit the entire longitudinal gradient, others that are restricted to certain sites, and the remainder of species is an assemblage composed of a mixture of euryhaline freshwater and marine species near the mouth.     

Habitat and resource use by larval and juvenile fishes in an arid-land river (Rio Grande, New Mexico)

1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In arid‐land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an arid‐land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon (¹³C : ¹²C) and nitrogen (¹⁵N : ¹⁴N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young‐of‐year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low‐flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid‐summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid‐summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.     

Linkages between seagrass,mangrove and saltmarsh as fish habitat in the Botany Bay estuary,New South Wales

Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh utility as fish habitat may in some situations be linked to the proximity of available seagrass.     

Habitat specialization in tropical continental shelf demersal fish assemblages

The implications of shallow water impacts such as fishing and climate change on fish assemblages are generally considered in isolation from the distribution and abundance of these fish assemblages in adjacent deeper waters. We investigate the abundance and length of demersal fish assemblages across a section of tropical continental shelf at Ningaloo Reef, Western Australia, to identify fish and fish habitat relationships across steep gradients in depth and in different benthic habitat types. The assemblage composition of demersal fish were assessed from baited remote underwater stereo-video samples (n = 304) collected from 16 depth and habitat combinations. Samples were collected across a depth range poorly represented in the literature from the fringing reef lagoon (1-10 m depth), down the fore reef slope to the reef base (10-30 m depth) then across the adjacent continental shelf (30-110 m depth). Multivariate analyses showed that there were distinctive fish assemblages and different sized fish were associated with each habitat/depth category. Species richness, MaxN and diversity declined with depth, while average length and trophic level increased. The assemblage structure, diversity, size and trophic structure of demersal fishes changes from shallow inshore habitats to deeper water habitats. More habitat specialists (unique species per habitat/depth category) were associated with the reef slope and reef base than other habitats, but offshore sponge-dominated habitats and inshore coral-dominated reef also supported unique species. This suggests that marine protected areas in shallow coral-dominated reef habitats may not adequately protect those species whose depth distribution extends beyond shallow habitats, or other significant elements of demersal fish biodiversity. The ontogenetic habitat partitioning which is characteristic of many species, suggests that to maintain entire species life histories it is necessary to protect corridors of connected habitats through which fish can migrate.     

Habitat Use by Fishes in Coral Reefs,Seagrass Beds and Mangrove Habitats in the Philippines

Understanding the interconnectivity of organisms among different habitats is a key requirement for generating effective management plans in coastal ecosystems, particularly when determining component habitat structures in marine protected areas. To elucidate the patterns of habitat use by fishes among coral, seagrass, and mangrove habitats, and between natural and transplanted mangroves, visual censuses were conducted semiannually at two sites in the Philippines during September and March 2010–2012. In total, 265 species and 15,930 individuals were recorded. Species richness and abundance of fishes were significantly higher in coral reefs (234 species, 12,306 individuals) than in seagrass (38 species, 1,198 individuals) and mangrove (47 species, 2,426 individuals) habitats. Similarity tests revealed a highly significant difference among the three habitats. Fishes exhibited two different strategies for habitat use, inhabiting either a single (85.6% of recorded species) or several habitats (14.4%). Some fish that utilized multiple habitats, such as Lutjanus monostigma and Parupeneus barberinus, showed possible ontogenetic habitat shifts from mangroves and/or seagrass habitats to coral reefs. Moreover, over 20% of commercial fish species used multiple habitats, highlighting the importance of including different habitat types within marine protected areas to achieve efficient and effective resource management. Neither species richness nor abundance of fishes significantly differed between natural and transplanted mangroves. In addition, 14 fish species were recorded in a 20-year-old transplanted mangrove area, and over 90% of these species used multiple habitats, further demonstrating the key role of transplanted mangroves as a reef fish habitat in this region.     

Distribution of early life history stages of fishes in selected pools of the Upper Mississippi River

Effective management of the fishery resources of the Upper Mississippi River and successful mitigation of the loss of critical habitat depend in part on an understanding of the reproductive and early life history requirements of the affected fishes. However, little is known about the use of nursery areas by fishes in the river. Of the nearly 130 species identified in the adult ichthyofauna, only a few are represented proportionally in the available data on early life stages because study designs have not included consideration of the early stages, collection gears have not adequately sampled the young, and eggs and larvae of some species are difficult to sample by conventional approaches. For the species collected, information is available on seasonal variations in total densities, composition, and catch among different habitat types. However, the data are most accurate for species with buoyant early life stages, such as freshwater drum (Aplodinotus grunniens) and gizzard shad (Dorosoma cepedianum). Eggs and larvae of freshwater drum dominate collections made in the main channel, whereas other larval fishes are usually most abundant in backwater habitats. The species found there usually deposit eggs on the substrate or on vegetation. Habitat preferences (as indicated by relative abundance) often shift as development proceeds and physical and behavioral changes occur in the larvae. Only limited information is available on the distribution of larvae within habitats, but it is clear that variations within habitats are significant.     

Population Dynamics and Spatial Distribution of Coral Reef Fishes: Comparison Between Continuous and Isolated Habitats

Recent studies have shown that there are high degrees of spatial and temporal stability in coral reef fish assemblage structures in a continuous habitat, in contrast to results of observations in isolated habitats. In order to determine the reason for the difference in temporal stability of fish assemblage structures in a continuous habitat site and an isolated habitat site, population dynamics and spatial distributions of coral reef fishes (six species of pomacentrids and two species of apogonids) in the two habitat site were investigated over a 2-year period in an Okinawan coral reef. The population densities of pomacentrid and apogonid species increased in juvenile settlement periods at both sites, but the magnitude of seasonal fluctuation in population density was significantly greater at the isolated habitat site, indicating that the rate of juvenile settlement and mortality rate in the isolated habitat were greater than those in the continuous habitat. The magnitude of aggregation of fishes, which affects density-dependent biological interactions that modify population density such as competition and predation, was also significantly greater at the isolated habitat site, especially in the juvenile settlement season. Most of the fishes at the isolated habitat site exhibited more generalized patterns of microhabitat selection because of less coral coverage and diversity. The seasonal stability in the species composition of fishes was greater at the continuous habitat site than that at the isolated habitat. Our findings suggest that the relative importance of various ecological factors responsible for regulation of the population density of coral reef fishes (e.g., competition, predation, microhabitat selection and post-settlement movement) in a continuous habitat site and the isolated habitat site are different.     

Changes in rocky reef fish assemblages throughout an estuary with a restricted inlet

Rocky reef habitat is common in many estuaries, yet its role as a habitat for fishes is poorly understood. There is also limited understanding of how access of coastal species into estuaries and habitat quality can affect the distribution of rocky reef fishes within estuaries. This study used baited remote underwater video stations to determine spatial patterns in fish assemblages associated with rocky reef habitat throughout a barrier estuary with a permanently open but restricted inlet. Estuarine rocky reefs provided habitat for a diverse assemblage of fishes, many of which were large juveniles and subadults. In the absence of a pronounced salinity or temperature gradient, a clear transition in fish assemblages occurred from coastal waters, through the inlet channel, to the central estuary, and into the inner estuary. The inlet channel, notably its narrowness and length, limits tidal input into this estuary, which acts as a significant impediment to the dispersal of many coastal fishes, and insufficient habitat excludes many coastal rocky reef species from the inner estuary. This study highlights the need to recognise estuarine rocky reefs as providing habitat for diverse fish assemblages and the role inlets play in restricting access of coastal species.     

枸杞岛潮下带沙地生境鱼类群落结构和季节变化

为了解岛礁水域沙地生境的鱼类群落结构特征,评估该生境对鱼类资源养护的潜在作用,于2009年采用多网目组合刺网对枸杞岛潮下带沙质区域进行了逐月采样,同步设置岩礁为对照生境.应用α和β多样性指数结合相对重要性指数、相对渔获率、ABC曲线和聚类排序方法对两种生境中的鱼类组成、多样性变化和群落格局与变化进行了全面探讨.全年在沙地和岩礁生境共采集鱼类63种,隶属11目38科56属,2种生境各自出现的鱼类皆为46种.受暖水种频繁出现在沙地生境的影响,潮下带沙质区域鱼类区系比岩礁生境略显丰富,且春夏季的渔获量普遍高于岩礁生境;由于种类组成均匀度较低,沙地生境各季节的α多样性普遍较低,夏季显著低于岩礁生境.日本须鳎是沙地生境的指示种,为早春、夏末和秋冬季沙地底层优势鱼种.5-7月鳀、多数月份鲻和10月份鳗鲇等种类对沙地生境的阶段性利用,使其形成了区别于以趋礁性鱼类为优势类群的岩礁生境的群落格局和季节动态.沙地是多种鱼类幼鱼阶段的庇护所和饵料场,是鲆鲽类的良好栖息地.沙地生境在维持鱼类区系和养护鱼类资源方面具有重要作用.     

Mangrove Habitat Use by Juvenile Reef Fish: Meta-Analysis Reveals that Tidal Regime Matters More than Biogeographic Region

Identification of critical life-stage habitats is key to successful conservation efforts. Juveniles of some species show great flexibility in habitat use while other species rely heavily on a restricted number of juvenile habitats for protection and food. Considering the rapid degradation of coastal marine habitats worldwide, it is important to evaluate which species are more susceptible to loss of juvenile nursery habitats and how this differs across large biogeographic regions. Here we used a meta-analysis approach to investigate habitat use by juvenile reef fish species in tropical coastal ecosystems across the globe. Densities of juvenile fish species were compared among mangrove, seagrass and coral reef habitats. In the Caribbean, the majority of species showed significantly higher juvenile densities in mangroves as compared to seagrass beds and coral reefs, while for the Indo-Pacific region seagrass beds harbored the highest overall densities. Further analysis indicated that differences in tidal amplitude, irrespective of biogeographic region, appeared to be the major driver for this phenomenon. In addition, juvenile reef fish use of mangroves increased with increasing water salinity. In the Caribbean, species of specific families (e.g. Lutjanidae, Haemulidae) showed a higher reliance on mangroves or seagrass beds as juvenile habitats than other species, whereas in the Indo-Pacific family-specific trends of juvenile habitat utilization were less apparent. The findings of this study highlight the importance of incorporating region-specific tidal inundation regimes into marine spatial conservation planning and ecosystem based management. Furthermore, the significant role of water salinity and tidal access as drivers of mangrove fish habitat use implies that changes in seawater level and rainfall due to climate change may have important effects on how juvenile reef fish use nearshore seascapes in the future.     

Habitat rehabilitation for juvenile fish in urban waterways: A case study from Berlin,Germany

This study examines the improvement of juvenile fish recruitment by technical rehabilitation measures implemented in two urban waterways in Berlin, Germany: the River Spree and the Teltow Canal. Rehabilitation sites provide new littoral habitats protected from navigation‐induced flow and wake wash and are intended to improve habitat quality for juvenile fish and to support urban fish diversity. Both sites and four control sites with common embankments have been sampled monthly by point electric fishing (875 dips in total) from May to September 2009. In total, 6,243 fish were caught representing 12 species. Two of the species, roach (Rutilus rutilus) and perch (Perca fluviatilis), dominated the fish community, comprising 81.5% and 16.1% of the total catch. Nine species were rare, with relative abundances <1%, which hampered more detailed species‐specific analyses. Of the dips 33% contained no fish, causing zero‐inflation of the dataset. A hurdle regression model confirmed positive effects of reduced hydraulic disturbances and resulting vegetation cover on juvenile fish occurrence. However, it also showed low oxygen concentrations limiting habitat quality, as observed at the older, densely vegetated rehabilitation site in the River Spree. The general improvement of the juvenile fish assemblage by the rehabilitation measure appeared rather low, as partially vegetated, rectangle trapeze and trapeze profile banks had even higher fish abundance. The study also revealed a need for adaptive maintenance to improve the long‐term performance of this type of rehabilitation structure. With the recovery of aquatic vegetation, the technical bank protection should be adaptively removed to retain the connectivity with the main channel for a sufficient oxygen supply for the long‐term functionality as a fish habitat.     

Fish assemblage patterns in the littoral zone of a European reservoir

1. Although reservoirs are common aquatic habitats in Europe, there is little quantitative information on the spatial organisation of fish assemblages inhabiting their littoral zones. Consequently, we characterised fish assemblage structure in the littoral zone of a reservoir (Lake Pareloup) in SW France during late spring, summer and early autumn (the growing season).
2. We measured the relative abundance of fish weekly, from mid-May to mid-October, using point abundance sampling by electrofishing. We identified temporal patterns in assemblage structure using hierarchical cluster analysis, and then characterised the spatial distribution of 17 defined ecospecies using a Kohonen self-organising map (SOM, an unsupervised Artificial Neural Network).
3. Our analyses revealed three distinct faunal structures within the littoral zone. From mid-May to mid-July, adults and young-of-the-year (0+) occupied separate habitats, with most 0+ fish in vegetated habitats and adults in open water. From mid-July to late August, some 0+ co-occurred with adults, but most 0+ fishes remained in vegetated areas. Finally, from late August to mid-October, most fish (both 0+ and adults) left the vegetation for unvegetated littoral habitats, the exception being fish species known to be dependent on macrophytes.
4. Contrary to patterns for adult fishes, the 0+ fish assemblage was dynamic. These dynamics were driven by ontogenetic species-specific habitat changes. Consequently, there was little evidence of stable assemblages or strong assemblage–habitat relationships that would be expected of an 'interactive' assemblage. It is likely that the patterns observed are a result of species-specific response to habitat availability in the lake.     

The Mangrove Nursery Paradigm Revisited: Otolith Stable Isotopes Support Nursery-to-Reef Movements by Indo-Pacific Fishes

Mangroves and seagrass beds have long been perceived as important nurseries for many fish species. While there is growing evidence from the Western Atlantic that mangrove habitats are intricately connected to coral reefs through ontogenetic fish migrations, there is an ongoing debate of the value of these coastal ecosystems in the Indo-Pacific. The present study used natural tags, viz. otolith stable carbon and oxygen isotopes, to investigate for the first time the degree to which multiple tropical juvenile habitats subsidize coral reef fish populations in the Indo Pacific (Tanzania). Otoliths of three reef fish species (Lethrinus harak, L. lentjan and Lutjanus fulviflamma) were collected in mangrove, seagrass and coral reef habitats and analyzed for stable isotope ratios in the juvenile and adult otolith zones. δ¹³C signatures were significantly depleted in the juvenile compared to the adult zones, indicative of different habitat use through ontogeny. Maximum likelihood analysis identified that 82% of adult reef L. harak had resided in either mangrove (29%) or seagrass (53%) or reef (18%) habitats as juveniles. Of adult L. fulviflamma caught from offshore reefs, 99% had passed through mangroves habitats as juveniles. In contrast, L. lentjan adults originated predominantly from coral reefs (65–72%) as opposed to inshore vegetated habitats (28–35%). This study presents conclusive evidence for a nursery role of Indo-Pacific mangrove habitats for reef fish populations. It shows that intertidal habitats that are only temporarily available can form an important juvenile habitat for some species, and that reef fish populations are often replenished by multiple coastal habitats. Maintaining connectivity between inshore vegetated habitats and coral reefs, and conserving habitat mosaics rather than single nursery habitats, is a major priority for the sustainability of various Indo Pacific fish populations.     

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.     

Effects of Habitat Connectivity on the Abundance and Species Richness of Coral Reef Fishes: Comparison of an Experimental Habitat Established at a Rocky Reef Flat and at a Sandy Sea Bottom

Coral reef fish assemblages are widely recognized for the coexistence of numerous species, which are likely governed by both coral diversity and substratum complexity. However, since coral reefs provide diverse habitats due to their physical structure and different spatial arrangements of coral, findings obtained from an isolated habitat cannot necessarily be applied to fish assemblages in other habitats (e.g. continuous habitats). The aim of this study, therefore, was to determine by a field experiment whether habitat connectivity (spatial arrangement of coral colonies) affects abundance and species richness of fishes in an Okinawan coral reef. The experiment consisted of transplanted branching coral colonies at a 4m×8m quadrat at both a rocky reef flat and sandy sea bottom. Generally, the abundance of fishes was greater at the sandy sea bottom, especially for three species of pomacentrids, one species of labrids, one species of chaetodontids and two species of apogonids. Species–area curves showed that the species richness of fishes was significantly greater in the quadrat at the sandy sea bottom at 3, 6 and 9 months after the start of the experiment. The rate of increase in abundance of fishes per area was significantly greater in the quadrat at the sandy sea bottom over the study period. The results of rarefaction analyses showed that the rate of increase in species richness per abundance was significantly higher in the quadrat at the sandy sea bottom in the juvenile settlement period, indicating that the magnitude of dominance by particular species was greater at the sandy sea bottom habitat. Our findings suggest that habitat connectivity affects the abundance and species richness of coral reef fishes, i.e. the isolated habitat was significantly more attractive for fishes than was the continuous habitat. Our findings also suggest that the main ecological factors responsible for organization of fish assemblage at a continuous habitat and at an isolated habitat are different.     

Macrohabitat associations of fishes in shallow waters of the Detroit River

Seasonal variation in large‐scale habitat selection by fishes in shallow, Canadian waters of the Detroit River was examined. Fish communities were compared among three river segments (upstream, middle and downstream) consisting of areas of shallow water habitat separated by wide hydrologic barriers of deep, flowing water and between inshore and offshore areas. In spring, the most unique, diverse and abundant fish assemblages were found at inshore sites in the middle segment where the largest remaining wetland habitats are located. Fishes used inshore habitat to spawn and probably avoided offshore areas because macrophyte cover was not available in spring. In summer, juvenile gizzard shad Dorosoma cepedianum and white bass Morone chrysops were observed in high densities in the upstream segment, probably migrating downstream from Lake St Clair. There was little difference in the fish assemblage among macrohabitats in autumn. The upstream segment appeared to be the most degraded, because it contained no species that were not found in the other segments, had a paucity of uncommon species and had significantly more non‐native species. This state was attributed to the infilling of coastal wetlands by urban land use and a resulting loss of habitat heterogeneity. The middle segment, with the only remaining wetland habitats, had the greatest occurrence of uncommon species and the only species at risk found in this study. Conservation and restoration efforts should be greatest for wetlands; however, shallow offshore areas provide important fish habitat in summer and autumn.