Unique Fish Assemblages Research Articles

Influence of water-level variability on fish assemblage and natural reproduction following connectivity enhancement in a Typha dominated coastal wetland, USA.

We evaluated a wetland habitat modification strategy to contrast fish assemblage structure and the production of young-of-the-year (YOY) fish between different engineered habitats (i.e., spawning pool complexes and connectivity channels) relative to unmodified lateral channels in a large drowned river mouth tributary of the St. Lawrence River. Prior to habitat modifications, the coastal wetland was impaired by water level regulations, dominance of invasive hybrid cattail, Typha x glauca, that collectively replaced or created barriers to seasonally flooded spawning habitats important to fish. Connectivity enhancements provided fish access along a wetland habitat gradient from sedge-meadows to the deeper water robust emergent main-channel. Across an eight-year fish emigration dataset (2012, 2013, 2016-2021) more than 90% of all captured fish (Ntotal = 218,086 fish) were YOY and modified habitats outperformed the unmodified channels in total fish catch-per-unit-effort (CPUE) per year (both YOY and non-YOY). Spawning pool complexes had higher YOY species richness than unmodified channel habitats. Fish assemblage structure differed between the modified habitats, where connectivity channels and unmodified channels shared a more similar fish assemblage than spawning pool complexes. Modified habitats, however, supported warmer water and higher dissolved oxygen than the unmodified channels. Redundancy analysis and linear mixed-effect modeling with abiotic variables (hydrology, temperature and dissolved oxygen) showed significant effects on fish assemblage structure, species richness and CPUE of fish emigrating from the modified and unmodified habitats. Historic flooding in 2017 and 2019 was a primary driver of YOY fish production and fish assemblage structure, but also appeared associated with near anoxic conditions systemwide. YOY fish for several species was inversely affected by floods at spawning pool complexes, however CPUE of YOY fish for these species appeared unaffected at the connectivity channels despite low dissolved oxygen. Diversified habitat structure (i.e., connectivity channels and spawning pool complexes) offers a management option to enhance habitat for fish that allowed compensatory effects on the capture of YOY fish of several species during floods. This multi-faceted outcome from the habitat modifications resulted in unique fish assemblages between the channelized and spawning pool habitat. A connectivity-based habitat enhancement strategy provides adaptability for an uncertain climatic and regulatory future for the Laurentian Great Lakes and St. Lawrence River.

Sharks associated with a large sand shoal complex: Community insights from longline and acoustic telemetry surveys.

Offshore sand shoals are a coveted sand source for coastal restoration projects and as sites for wind energy development. Shoals often support unique fish assemblages but their habitat value to sharks is largely unknown due to the high mobility of most species in the open ocean. This study pairs multi-year longline and acoustic telemetry surveys to reveal depth-related and seasonal patterns in a shark community associated with the largest sand shoal complex in east Florida, USA. Monthly longline sampling from 2012-2017 yielded 2,595 sharks from 16 species with Atlantic sharpnose (Rhizoprionodon terraenovae), blacknose (Carcharhinus acronotus), and blacktip (C. limbatus) sharks being the most abundant species. A contemporaneous acoustic telemetry array detected 567 sharks from 16 species (14 in common with longlines) tagged locally and by researchers elsewhere along the US East Coast and Bahamas. PERMANOVA modeling of both datasets indicate that the shark species assemblage differed more across seasons than water depth although both factors were important. Moreover, the shark assemblage detected at an active sand dredge site was similar to that at nearby undisturbed sites. Water temperature, water clarity, and distance from shore were habitat factors that most strongly correlated to community composition. Both sampling approaches documented similar single-species and community trends but longlines underestimated the shark nursery value of the region while telemetry-based community assessments are inherently biased by the number of species under active study. Overall, this study confirms that sharks can be an important component of sand shoal fish communities but suggests that deeper water immediately adjacent to shoals (as opposed to shallow shoal ridges) is more valuable to some species. Potential impacts to these nearby habitats should be considered when planning for sand extraction and offshore wind infrastructure.

First records of two rays and three bony fishes for the Galapagos Islands

Abstract The Galapagos Islands lie within the oceanic ecoregion of the Tropical Eastern Pacific, which has a unique fish assemblage composition due to the influence of several ocean currents and El Niño Southern Oscillation (ENSO) events. In the El Niño phase of these events, water temperature changes facilitate the movement of fish species between oceanic ecoregions, as well as across the Eastern Pacific Barrier. Here, we present five new fish records for the Galapagos Marine Reserve based on underwater imagery. These include two rays (Mobula thurstoni and Myliobatis longirostris) and three bony fishes (Lobotes pacifica, Lutjanus colorado and Sphyraena stellata). Of these, the first species is proposed as potentially resident to the Galapagos, and the latter four as vagrant species in the Galapagos until further sightings can conclusively determine their status. The effects of ENSO, the use of underwater video technology, and the importance of up-to-date and accurate species listings to understand the impact of the climate crisis are discussed.

Turnover in fish species composition is related to water colour of Amazonian rivers

Abstract Variation in water colour is a remarkable characteristic of Amazonian rivers and reflects their limnological properties and the geomorphology of sub-basins. We present here a literature-based study to examine the relationships between fish species turnover and abiotic properties of Amazonian rivers with contrasting water colours. We analysed fish records and water physicochemical properties (pH, colour, turbidity, dissolved oxygen, ammonia and suspended solids) of eight Amazonian rivers with white-, black- and clearwaters. Rivers with similar water colour shared more fish species than those that contrasted in colour. Increased differences in abiotic parameters imply an increased dissimilarity in fish species composition. Species composition is also related to distance among rivers with high dissimilarity observed in rivers distant to each other. The fish species turnover could be ultimately driven by the geological history of rivers which provides different opportunities to speciation and biotic interchange. Water types likely influence species turnover by selecting fishes with different limits of physiological tolerance and specialized use of different habitat types. Our findings suggest that river water colours are reliable proxies for historical and ecological mechanisms affected fish species distribution. Antropic disturbances of Amazonian rivers with distinct water colours could threaten unique fish assemblages.

Co-occurrence of seagrass vegetation and coral colonies supports unique fish assemblages: a microhabitat-scale perspective.

Numerous studies have suggested that seagrass beds provide nursery habitats for juvenile fish in both tropical and subtropical regions. Most of these previous studies applied a landscape-scale perspective, in which seagrass beds and coral reefs are treated as independent, homogenous habitats. However, this perspective might overlook the microhabitat-scale perspective within the habitats, for example, the possibility that small-sized hard substrates (e.g., coral colonies) within seagrass beds might serve as fish nurseries. The present study aimed to examine the effects of the presence of microhabitats (small-sized coral colonies) within seagrass beds on the structure of fish assemblages. Fieldwork was conducted at Urasoko Bay, Ishigaki Island, Okinawa, Japan. Four habitat zones were selected: (1) seagrass bed with presence of massive coral colonies (SGCO), (2) seagrass bed without coral colonies (SG), (3) sandy bottom (without seagrass vegetation) with massive coral colonies (CO), and (4) sandy bottom without seagrass vegetation or coral colonies (SA). Six 20 m × 2 m line transects were established and monthly underwater observations were conducted between June and October in 2018 and 2019. A cluster analysis, analysis of similarity, and principal component analysis revealed that the fish assemblage at SGCO was significantly different from the other three habitat zones. This was because some fish species (e.g., Ostorhinchusishigakiensis and Lutjanus gibbus) were almost exclusively present at SGCO and rarely seen at CO, SG, and SA. Most individual fish belonging to these species were found on coral colonies at SGCO, suggesting that the co-occurrence of seagrass vegetation and coral colonies is essential for the habitats of these fish species. Although other fish species present at SGCO were also found at SG, three species, Parupeneus barberinus, Stethojulis strigiventer, and Lethrinus atkinsoni, were more abundant at SGCO with some found on coral colonies in this habitat zone. Several fish species that occurred at both SGCO and CO (e.g., Ostorhinchus properuptus, Cheilodispterus quinquelineatus, Chrysiptera cyanea, and Pomacentrus chrysurus) were more abundant or showed a greater size range at SGCO, suggesting greater survival rates in this habitat zone because of the co-occurrence of seagrass vegetation and coral colonies. This study demonstrated the existence of a unique fish assemblage structure at SGCO. Although the adoption of a landscape-scale perspective (three-dimensional structure of the vegetation) is necessary, a microhabitat-scale perspective that includes the presence of small hard substrates should also be considered to accurately evaluate the nursery function of seagrass beds.

Ensuring the Sustainability of Coastal Small-Scale Fisheries at Pitcairn Island (South Pacific) Within a Large Scale No-Take MPA

The Pitcairn Islands, located in the central South Pacific, contain near-pristine marine ecosystems which support unique fish assemblages, together with both endemic and threatened species. Pitcairn itself is the only inhabited island in the group and, before this study, the environmental impact of local fisheries was unclear, with little data to inform conservation and management. In 2014–2015 coastal fish populations were assessed using a mixed methods approach: a newly introduced system of fishers’ catch monitoring and Baited Remote Underwater Video Systems (BRUVS). Thirty-nine BRUVS deployments recorded 88 species in total, with small-bodied herbivores (e.g., Kyphosus pacificus) and mesopredators (e.g., Xanthichthys mento) dominating a “bottom heavy” assemblage. Several large pelagic predators were recorded, but reef-associated predators were rare with only one shark observed. Pitcairn’s top predator assemblage was relatively impoverished compared to global “pristine” sites, including other islands within the Pitcairn group. Top predator scarcity may be explained by local artisanal fisheries, which have historically targeted sharks and other large reef carnivores, and these taxa may not have recovered despite subsequent declines in fishing pressure. The dominant small-bodied species may have proliferated as a result of diminished top predator populations. Subsequent to BRUVS sampling, a local fisheries officer post was created to collate catch data from coastal fishers. Regular returns were obtained from over half of the active fishers (representing approximately 80% of catches), with K. pacificus also dominating catches and the small grouper Epinephelus fasciatus frequently targeted. Thirty fish species were represented in the recorded catch over a 12 month period. Results were shared with the local community, providing a basis for the cooperative design of a Fisheries Management Plan. This plan ensured traditional fisheries could continue in a sustainable manner within Coastal Conservation Zones around each of the four Pitcairn Islands, established within the large, no-take Marine Protected Area designated in 2016, covering the entire Pitcairn Exclusive Economic Zone. Monitoring of Pitcairn’s artisanal fisheries should be continued beyond this one-off study in order to inform adjustment of the Fisheries Management Plan, as the ongoing island fishery may still have consequences for long-term sustainability, particularly for pelagic species caught in coastal waters which remain a significant data gap.

Life-history traits, geographical range, and conservation aspects of reef fishes from the Atlantic and Eastern Pacific.

Reef fish represent one of the most diverse vertebrate groups on Earth, with over 7,000 species distributed around the globe. This richness is not evenly distributed geographically. The Atlantic (AT) and the Eastern Pacific (EP) encompass 30% of the global fish fauna. These areas have been considered the most isolated from the marine biodiversity hotspot in the Indo-Pacific due to distinct physical barriers, such as the Tethyan closure and the distance between the EP and the western Pacific. Despite their comparatively lower species richness, these realms host unique fish assemblages characterized by a remarkable proportion of regional endemics and species with large body size. Here, we present the largest database of life-history traits and biogeographical and conservation aspects presently available for the reef fish fauna of the AT and the EP realms. The database includes 21 traits distributed into behavioral (home range, diel activity, group size, level in the water column, three measures of preferred temperature), morphological (maximum body size, size class, body shape, aspect ratio, caudal fin, mouth position), and ecological (trophic level, diet, spawning strategy, depth of occurrence, two allometric constants, pelagic larval duration, and life span), as well as biogeographical (geographic range index, range extension, species distribution in 20 marine provinces, latitude north and south of occurrence, total number of provinces where species occur, occurrence in the AT and EP), and conservation aspects (IUCN status, vulnerability and global market price). We compiled these data through a careful review of 104 local checklists published between 1982 and 2020, online repositories, local reports, books, and monographs on specific families or genera. We limited our database to localities situated between latitudes 51°N and 45°S that including shallow and upper mesophotic biogenic and/or rocky reefs habitats. Our database covers 2,198 species belonging to 146 families and 655 reef fish genera distributed in two marine realms (1,458 in the AT, 829 in the EP, and 89 in both realms) and 20 marine provinces. This database of reef fish offers the opportunity to explore novel ecological and evolutionary questions at different scales and provides tools for species conservation based on these traits. There are no copyright or proprietary restrictions for research or teaching purposes.

Distribution of demersal fish assemblages along the west coast of St Lucia: Implications for planning no‐take marine reserves

Abstract Evidence‐based decisions relating to effective marine protected areas as a means of conserving biodiversity require a detailed understanding of the species present. The Caribbean island nation of St Lucia is expanding its current marine protected area network by designating additional no‐take marine reserves on the west coast. However, information on the distribution of fish species is currently limited. This study used baited remote underwater stereo‐video to address this shortcoming by investigating the effects of depth and seabed habitat structure on demersal fish assemblages and comparing these assemblages between regions currently afforded different protection measures. From the 87 stations visited a total of 5,921 fish were observed comprising 120 fish taxa across 22 families. Species richness and total abundance were higher within the highly managed region, which included no‐take reserves. Redundancy analysis explained 17% of the total variance in fish distribution, driven predominantly by the seabed habitats. The redundancy analysis identified four main groups of demersal fishes each associated with specific seabed habitats. The current no‐take marine reserves protected two of these groups (i.e. fishes associated with the ‘soft corals, hard corals or gorgonians’ and ‘seagrass’ groups). Importantly, habitats dominated by sponges, bacterial mats, algal turfs or macroalgae, which also supported unique fish assemblages, are not currently afforded protection via the marine reserve network (based on the five reserves studied). These results imply that incorporation of the full breadth of benthic habitat types present would improve the efficacy of the marine reserve network by ensuring all fish assemblages are protected.

Rehabilitation of a tropical storm-water drain creates a novel fish assemblage

A 2.7-km canalised section of the Kallang River, a major storm-water drain and reservoir spillway in Singapore, was rehabilitated into a 3-km naturalised, meandering river between 2009 and 2011. A combination of plants, natural materials, and civil engineering techniques were introduced to soften the edges of the waterway, to give it a more natural appearance and prevent soil erosion. Baseline data and published evidence of enhancement of aquatic biodiversity in this naturalised urban waterway are lacking, as there have not been any comprehensive biological surveys of the system to date. To determine the effect of rehabilitation, we quantitatively compared the fish assemblage and abiotic variables in the Kallang River after its rehabilitation (re-named Kallang River at Bishan-Ang Mo Kio Park or KRBAP; 2016–2018) against a downstream unrehabilitated section of the river (Kallang Canal; 2012). Secondly, we qualitatively compared fish assemblages and abiotic variables at the KRBAP and the Kallang Canal, to their source (upstream) reservoir, as well as to natural forest streams in close proximity. The KRBAP has a unique fish assemblage, which is dominated by two non-native cichlid taxa (quetzal cichlid, Vieja melanura (68%) and tilapia, Oreochromis spp. (17%)). Fish species richness (p < 0.001) and the percentage of native species (p = 0.015) was significantly higher in the KRBAP compared to the unrehabilitated canal. Moreover, the abiotic variables at the two sites are also significantly different. The fish assemblage and abiotic variables at the KRBAP resemble those of its (upstream) source reservoir, but contrasts with those of nearby natural forest streams. The unique fish assemblage in the KRBAP is shown to be stable, with similar species captured in high abundances across the three sampling years post-rehabilitation. Given the stability within the rehabilitated stream, further research and monitoring are needed to determine the established food web and predict the possible influence of future non-native species additions.

Conservation of fish communities: Extending the ‘research life cycle’ by achieving practical effects

Abstract This article highlights the practical impact of our 2018 Aquatic Conservation: Marine and Freshwater Ecosystems publication, ‘Importance of peripheral basins: Implications for the conservation of fish assemblages’, which described fish communities in a Polish river. Data on the fish assemblages of the Dniester River (Black Sea basin) are scarce; however, evidence indicates that the assemblages have declined. In our 2018 study, we hypothesized that the peripheral basin (the small basin on the edge) of the larger Upper Dniester River basin (the Strwiąż River) could maintain good ecological status and contained unique fish assemblages. To examine the influence of historical factors and assess the role of peripheral basins on fish conservation, data from the Strwiąż basin were compared with the adjacent but unconnected Wiar basin (the Vistula basin; Baltic Sea basin). The Strwiąż River fish assemblages featured higher species richness and a greater number of native Ponto–Caspian species that function near the edge of their ranges. This article focuses on four impacts of the 2018 publication: increasing awareness by various groups and organizations of the unique character of the surveyed river basin; highlighting important issues in assessing the ecological status of European rivers; driving the red‐listing of species and the development of stream fish conservation strategies; and identifying possible future impacts. Our 2018 publication demonstrated the value of studying peripheral basins, which may affect conservation strategy development and encourage study of the importance of other peripheral basins and their role in aquatic resources conservation. Our article influenced the interpretation of fish‐based biotic indices and the conduct of monitoring work and its evaluation. It also strongly emphasized the native origin of the racer goby (Babka gymnotrachelus) in the Strwiąż River, which was important for subsequent works seeking to change the legal status of the species in Poland.

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

AbstractCanopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%–43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries.

Differences in fish assemblage structures between tidal marsh and bare sandy littoral habitats in a brackish water lake, eastern Japan

Fish assemblage structures and environmental properties (e.g., water quality, sediment condition and prey abundance) were compared between tidal marshes, dominated by the common reed Phragmites australis, and bare sandy areas in the brackish-water Lake Hinuma, eastern Japan, by daytime seine net sampling in October 2014, and January, April and July 2015. A total of 4,076 fish individuals from 30 species and 5,431 individuals from 23 species were collected in the tidal marshes and sandy areas, respectively. Higher species richness in the former habitat was due to the restricted occurrence of ten species, including threatened or near threatened, only to that habitat. Species composition and the abundances of several dominant species, such as the commercially important icefish Salangichthys microdon and the goby Acanthogobius lactipes, also differed between the two habitats, although no interhabitat differences in the mean species and individual numbers per haul were found. Moreover, the individual number of small benthic and epiphytic crustacean feeders, including A. lactipes, was greater in the tidal marshes than in the sandy areas, whereas zooplankton feeders, including S. microdon, showed the opposite pattern. Such interhabitat differences in fish assemblage structures may be partly related to food availability, sediment condition and/or the presence or absence of vegetative structures. Because each of the two habitats harbored a unique fish assemblage, conservation efforts for both habitats are important for enhancing overall fish species diversity and sustaining fishery resources in Lake Hinuma.

Importance of peripheral basins: Implications for the conservation of fish assemblages

Abstract The upper Dniester River basin (Black Sea basin) contains unique fish assemblages. Although data on the fish of the basin are scarce, evidence indicates that these assemblages have declined. It was assumed that the peripheral basins (i.e. small basins on the edge of the larger basin) of the upper Dniester River basin could maintain good ecological status. To fill the knowledge gaps and assess the role of peripheral basins on fish species and assemblage conservation, research was conducted in the Strwiąż River basin. Data from the Strwiąż basin and the adjacent but unconnected upper Wiar basin (the Vistula basin; Baltic Sea basin) were compared in order to examine the influence of historical factors, and to confirm the unique characteristics of the fish assemblages of the peripheral area of the upper Dniester basin. A detailed analysis of the fish assemblages was performed, the primary morphological characteristics of sites that corresponded to the requirements of the fish assemblages were defined, and the human impacts were identified. The Strwiąż River basin is likely to be the only fragment of the upper Dniester basin with a well‐preserved fish assemblage. It features high species richness and numerous native Ponto–Caspian species that function near the edge of their ranges. The extant fish fauna of the Strwiąż River basin can provide a point of reference for other tributaries of the upper Dniester River that are degraded. We draw attention to the fact that peripheral basins, which are not usually considered in conservation biogeography, can be important for the protection of fish species and entire fish assemblages. This study provides one of the most convincing arguments for a more detailed investigation of peripheral populations.

Balancing lake ecological condition and agriculture irrigation needs in the Mississippi Alluvial Valley

Abstract The Mississippi Alluvial Valley includes hundreds of floodplain lakes that support unique fish assemblages and high biodiversity. Irrigation practices in the valley have lowered the water table, increasing the cost of pumping water, and necessitating the use of floodplain lakes as a source of water for irrigation. This development has prompted the need to regulate water withdrawals to protect aquatic resources, but it is unknown how much water can be withdrawn from lakes before ecological integrity is compromised. To estimate withdrawal limits, we examined descriptors of lake water quality (i.e., total nitrogen, total phosphorus, turbidity, Secchi visibility, chlorophyll-a) and fish assemblages (species richness, diversity, composition) relative to maximum depth in 59 floodplain lakes. Change-point regression analysis was applied to identify critical depths at which the relationships between depth and lake descriptors exhibited a rapid shift in slope, suggesting possible thresholds. All our water quality and fish assemblage descriptors showed rapid changes relative to depth near 1.2–2.0 m maximum depth. This threshold span may help inform regulatory decisions about water withdrawal limits. Alternatives to explain the triggers of the observed threshold span are considered.

Hidden Components in Tropical Seascapes: Deep-Estuary Habitats Support Unique Fish Assemblages

Tropical coastal seascapes are biodiverse and highly productive systems composed of an interacting mix of habitats. They provide crucial ecosystem services that support people’s livelihoods, yet key components of these seascapes remain unstudied. We know little about the deep (>2 m) subtidal areas of tropical estuaries, because, due to gear restrictions, there have been no detailed studies of the habitats they contain and the fish that use them. Consequently, potentially important functions and linkages with surrounding habitats remain unknown. Using unbaited videos, an approach capable of sampling the full breadth of benthic habitats and whole fish assemblages, we investigated patterns of fish occupancy of the deep subtidal habitats (2–20 m) in one of Australia’s largest tropical estuaries. We identified 19 taxa not previously recorded from estuaries of tropical eastern Australia, along with 36 previously identified estuary taxa. Three recognisable fish assemblages were associated with distinct benthic habitat types: open bottom fine sediment, seagrass and structurally complex rocky areas. In deep water, habitats often overlooked in shallow water become important, and there are sharp differences in habitat function. Deep subtidal habitats are potentially an important zone for direct interaction between estuary and marine fauna, with a range of consequences for intertidal habitat use and nursery ground functioning. The interface between marine areas and the shallow-water estuary may be richer and more complex than previously recognised.

Fishes in Paleochannels of the Lower Mississippi River Alluvial Valley: A National Treasure

Fluvial geomorphology of the alluvial valley of the Lower Mississippi River reveals a fascinating history. A prominent occupant of the valley was the Ohio River, estimated to have flowed 25,000 years ago over western Tennessee and Mississippi to join the Mississippi River north of Baton Rouge, Louisiana, 750–800 km south of the present confluence. Over time, shifts in the Mississippi and Ohio rivers toward their contemporary positions have left a legacy of abandoned paleochannels supportive of unique fish assemblages. Relative to channels abandoned in the last 500 years, paleochannels exhibit harsher environmental conditions characteristic of hypereutrophic lakes and support tolerant fish assemblages. Considering their ecological, geological, and historical importance, coupled with their primordial scenery, the hundreds of paleochannels in the valley represent a national treasure. Altogether, these waterscapes are endangered by human activities and would benefit from the conservation attention afforded to our national parks and wildlife refuges.

Effects of habitat change from a bare sand/mud area to a short seagrass Halophila ovalis bed on fish assemblage structure: a case study in an intertidal bay in Trang, southern Thailand

Fish assemblage structures in an intertidal sand/mud area invaded by short seagrass Halophila ovalis and a nearby non-invaded sand/mud area in Trang Province, Thailand, were examined in detail by visual census to elucidate the effects of such habitat change on assemblage structure. The assemblage structure in the newly established seagrass bed showed a significant shift from that in the sand/mud area, despite the total fish species numbers remaining similar to each other (i.e., 30 and 29 species, respectively). Total fish density was significantly lower in the seagrass bed. In addition, differences in density patterns of component species between seagrass and sand/mud fish assemblages were evident, some fish species being restricted to or more abundant in the alternative habitat. Such differences may have arisen, at least in part, from differences in practical food availability/accessibility between the two habitat types, and/or specific microhabitat preferences of the resident fishes. Although seagrass habitats are often regarded as supporting a richer fish assemblage compared with bare sand/mud areas, the present study clearly indicated that the latter also supported a unique fish assemblage, including juveniles of fishery target species. Accordingly, both seagrass and bare sand/mud habitats should be taken into consideration for both the conservation of greater overall biodiversity in the coastal environment and the continued existence of local fisheries.

Fish and Water Quality in the Forested Wetlands Adjacent to an Oxbow Lake

Forested wetlands represent some of the most distinct environments in the Lower Mississippi Alluvial Valley. Depending on season, water in forested wetlands can be warm, stagnant, and oxygen-depleted, yet may support high fish diversity. Fish assemblages in forested wetlands are not well studied because of difficulties in sampling heavily structured environments. During the April–July period, we surveyed and compared the water quality and assemblages of small fish in a margin wetland (forested fringe along a lake shore), contiguous wetland (forested wetland adjacent to a lake), and the open water of an oxbow lake. Dissolved-oxygen levels measured hourly 0.5 m below the surface were higher in the open water than in either of the forested wetlands. Despite reduced water quality, fish-species richness and catch rates estimated with light traps were greater in the forested wetlands than in the open water. The forested wetlands supported large numbers of fish and unique fish assemblages that included some rare species, likely because of their structural complexity. Programs developed to refine agricultural practices, preserve riparian zones, and restore lakes should include guidance to protect and reestablish forested wetlands.

Fish Assemblages of Shoal‐ and Shoreline‐Associated Seagrass Beds in Eastern Gulf of Mexico Estuaries

AbstractAssemblage structure of fishes associated with seagrasses (order Alismatales) is affected by factors such as depth, seagrass coverage, location of seagrass beds, and proximity of seagrass beds to adjacent habitats. Although these relationships have been well explored for small‐bodied fishes, few studies have examined seagrass habitat use by large‐bodied fishes (&gt;100 mm SL). To examine the effects of habitat characteristics on assemblages of large‐bodied fishes, two seagrass habitat types were sampled in three eastern Gulf of Mexico estuaries (2008–2010) with a 183‐m haul seine: (1) seagrasses immediately adjacent to shorelines and (2) seagrasses associated with shoals (seagrass beds &gt;100 m from shoreline). Within each estuary, fish density was greater (as much as two times greater) in shoal seagrass beds than in those along shorelines. Fish assemblage structure also differed significantly between the two habitat types. Species that distinguished the seagrass shoreline (e.g., Spot Leiostomus xanthurus, Redfin Needlefish Strongylura notata) had affinities for habitats that were relatively shallow, gently sloped, less saline, and muddy with less seagrass coverage. Species that distinguished seagrass shoals (e.g., Pigfish Orthopristis chrysoptera, Silver Perch Bairdiella chrysoura) had affinities for habitats that were deeper, steeply sloped, sandy, and more saline, with greater seagrass coverage. Among economically important fishes, some were more abundant along shorelines (e.g., Common Snook Centropomus undecimalis, Sheepshead Archosargus probatocephalus, and Striped Mullet Mugil cephalus), while others were more abundant on shoals (e.g., Gag Mycteroperca microlepis, Spotted Seatrout Cynoscion nebulosus, and Scaled Sardine Harengula jaguana). This study demonstrates that seagrass shoals, which are being lost in some estuaries, provide different environmental conditions than those along shorelines, support unique fish assemblages, and host greater densities of several economically important species.Received November 12, 2013; accepted March 18, 2014

Extreme flow variability and the ‘boom and bust’ ecology of fish in arid‐zone floodplain rivers: a case history with implications for environmental flows, conservation and management

AbstractFloodplain rivers in arid and semi‐arid regions may be the most threatened of all river systems because water resource developments typically dampen their most distinctive characteristics—extreme flow variability and ‘boom and bust’ ecological dynamics. This article shows how one of the world's most variable arid‐zone river systems—Cooper Creek in Australia's Lake Eyre Basin—functions and how it supports its unique fish assemblage and productive fisheries. The ecological roles of drought refugia, channel flows and flooding are reviewed in relation to fish persistence and losses, life history strategies, movement potential, food web processes and production levels. Comparisons are drawn with other floodplain rivers and fisheries to draw out common understandings and universal principles for conservation and management of arid‐zone rivers and their fish resources. Ecological implications of hydrologic alterations and land‐based activities are presented to highlight the importance of maintaining the hydrologic, geomorphic, sedimentary and biogeochemical processes of arid‐zone river systems. Preservation or restoration of natural flow intermittency, sequential flood pulses, complex habitat mosaics, connectivity and identification of the environmental flow requirements for highly valued species and processes are key scientific principles for the management of arid‐zone floodplain rivers. Copyright © 2011 John Wiley &amp; Sons, Ltd.