Seagrass-associated Fish Research Articles

Tropical cyclone impacts on seagrass-associated fishes in a temperate-subtropical estuary.

Major storms can alter coastal ecosystems in several direct and indirect ways including habitat destruction, stormwater-related water quality degradation, and organism mortality. From 2010–2020, ten tropical cyclones impacted coastal North Carolina, providing an opportunity to explore ecosystem responses across multiple storms. Using monthly trawl and contemporaneous seagrass surveys conducted in Back Sound, NC, we evaluated how cyclones may affect the nursery role of shallow-water biogenic habitats by examining seagrass-associated fish responses within a temperate-subtropical estuary. We employed a general before-after-control-impact approach using trawls conducted prior (before) and subsequent (after) to storm arrival and years either without (control) or with (impact) storms. We examined whether effects were apparent over short (within ~three weeks of impact) and seasonal (May-October) timescales, as well as if the magnitude of storm-related shifts varied as a function of storm intensity. Our findings suggest that the ability of these shallow-water habitats to support juvenile fishes was not dramatically altered by hurricanes. The resilience exhibited by fishes was likely underpinned by the relative persistence of the seagrass habitat, which appeared principally undamaged by storms based upon review of available–albeit limited seagrass surveys. Increasing cyclone intensity, however, was correlated with greater declines in catch and may potentially underlie the emigration and return rate of fish after cyclones. Whether estuarine fishes will continue to be resilient to acute storm impacts despite chronic environmental degradation and predicted increases major tropical cyclone frequency and intensity remains a pressing question.

Linking seagrass ecosystem services to food security: The example of southwestern Madagascar’s small-scale fisheries

Small-scale fisheries(SSF) are crucialfor food security and poverty alleviation. Many SSF are however under pressure, and in need of better management paying special attention to the key seascape ecosystems which are supporting them. This study investigates the importance of seagrass beds for SSF households and their food security in southwestern Madagascar. The specific aims of this study were to: i) analyze if and how seagrass-associated fish contributes to subsistence and/or the economy of local fishing households, ii) identify and compare seagrass ecosystem goods and services valued by local fishers in a rural and an urban setting, and iii) analyze links between local people and seagrasses in terms of local ecological knowledge, use and traditions. The results showed that seagrasses were the most important fishing habitats for most fishers. Seagrass-associated fish species were both the economically most important and most commonly fished species, and are a major source of protein in the region. Further, seagrass-derived sea urchins are important complements to local people’s diets. Thefindings illustrate that seagrasses contribute both through subsistence and income generation to food security and wellbeing of coastal people in southwestern Madagascar. This highlights the need to consider seagrass ecosystems in management towards sustainable SSFand their ability to sustain food security for future generations.

Seagrass-associated fish species’ richness: evidence to support conservation along the south coast of Lombok Island, Indonesia

Abstract. Syukur A, Al-Idrus A, Zulkifli L. 2021. Seagrass-associated fish species’ richness: evidence to support conservation along the South Coast of Lombok Island, Indonesia. Biodiversitas 22: 988-998. The concept of seagrass conservation at a global scale tends to be less appropriate with regard to the environmental conditions at the regional and local scales, and thus, there is a need for scientific studies at the regional and local scales to support conservation measures. This research aimed to describe the importance of seagrass conservation based on the species richness of seagrass-associated fish. Data were collected from seven seagrass locations using surveys and observation. Data on the fish species present were collected with the gear used by small-scale fishermen to catch fish in the seagrass area and the surrounding waters. Data analysis was descriptive; the statistical analyses performed included calculation of the Shannon-Wiener index of diversity (H '), the Simpson evenness index (E), and the Morisita species richness index (D) as well as cluster analysis. All statistical analyses were performed in IBM SPSS Statistics 25. We found 104 fish species belonging to 38 families. Leiognathidae, Apogonidae, Clupeidae, Carangidae, Channidae, Sillaginidae, and Mullidae are families with high abundance, and 16 fish species have an abundance of individuals above the average value (192 individuals) of the total number of individuals (20,352). Meanwhile, 94.37% of the fish families are the target catch of small-scale fishermen (commercial fish). The diversity of fish species associated with seagrass in the study location is evidence of the survival of seagrass provision services at the local scale for fish. Therefore, scientific evidence of the species richness of fish, species yang domina, and its importance for small-scale fisheries at each seagrass bed in the study location can be used as a source of information for increasing and improving seagrass conservation efforts at the local scale.

Diel Variability and Influence of Artificial Light on Fish and Macroinvertebrate Communities in Gulf of Mexico Seagrass Beds

Seagrasses are productive habitats that support diverse communities of economically and ecologically important fishes and macroinvertebrates. However, most seagrass faunal assessments are conducted only during daylight hours. Here, we documented diel patterns in seagrass-associated fish and macroinvertebrate community structure in seagrass near Seahorse Key, Florida (USA). Artificial light is prevalent in many coastal areas and may influence day/night assemblages; therefore, we added lights to the natural environment to get a better understanding of its effect on community composition. Seagrass inhabitants were quantified using 25-m seine transects during different diel periods (day or night) and in areas where light was manipulated to mimic light pollution (artificial + natural light or natural light). Results suggest that the magnitude of diel effects exceeded that of light addition. While total abundance was similar between day and night, communities did change, with Lagodon rhomboides (Pinfish) dominating day samples and Farfantepenaeus duorarum (pink shrimp) most abundant at night. Other fishes such as Orthopristis chrysoptera (Pigfish) and Strongylura notata (Needlefish) had higher catches during the day, while invertebrates such as Callinectes sapidus (blue crab) and Palaeomonetes spp. (grass shrimp) were more prominent at night. In addition to the differences in abundance and community structure, we also identified diel differences in sizes for some species. No clear patterns were observed with the short-term addition of artificial light. This research highlights the role of diel variability in seagrass communities and suggests that diel movement of organisms may represent an important conduit for the transfer of energy to adjacent habitats.

Fish assemblage structure response to seagrass bed degradation due to overgrazing by the green sea turtle Chelonia mydas at Iriomote Island, southern Japan

The fish assemblage structure response to rapid degradation of Enhalus acoroides seagrass beds due to overgrazing by green sea turtles (Chelonia mydas) was investigated at Iriomote Island, southern Japan, by visual censusing of fish species in several microhabitats in and around the beds (i.e., dense seagrass bed, grazed bed, their boundaries, and adjacent sandy area). Fish assemblage structure differed among the seagrass microhabitats, both species and individual numbers being higher in microhabitats with seagrass compared to overgrazed beds and unvegetated sandy areas, together with different species composition. In the dense seagrass beds and boundary areas (the border area between dense seagrass beds and grazed areas), seagrass-associated fishes such as the rabbit fish Siganus fuscescens and cardinal fish Ostorhinchus ishigakiensis were abundant and comparable with those in other seagrass beds in the area. In addition, the fish assemblages in those microhabitats varied seasonally, fish abundance being greater in summer due to higher levels of recruitment. In the grazed bed, benthic gobies, such as Ctenogobiops crocineus and Cryptocentrus caeruleomaculatus, were dominant (similarly so in unvegetated sandy areas), and seasonal variations in such assemblages were relatively low compared to those in dense seagrass microhabitats. The decrease in the abundance and diversity of seagrass-associated fish in the grazed areas could be explained partly by the shortage of vegetation (< 20 cm in leaf length) for shelter and feeding throughout the year. The results suggested that the degradation of seagrass beds due to overgrazing by green turtles has a deleterious effect on fish assemblages, and that future conservation and management strategies for seagrass beds should consider both their associated fish communities and green turtles.

Complex yet fauna-deficient seagrass ecosystems at risk in southern Myanmar

AbstractDependence on seafood across Southeast Asia is extensive. Myanmar is no exception, but the country’s provisioning marine ecosystems are threatened. Seagrass is one habitat that is frequently overlooked in management as an important fisheries resource, despite its nursery function. In Myanmar, research on seagrass habitats is particularly sparse, and as a result, our understanding of seagrass exploitation remains limited. In this study, we provide a baseline assessment of the seagrass-associated fish assemblages at four locations in the Myeik Archipelago in southern Myanmar using mono Baited Remote Underwater Video systems. Across the sites surveyed only 12 taxa of motile fauna were recorded. Relative to other regional and global studies, this figure is meagre. Our data adds to a growing literature suggesting that the marine ecosystems of Myanmar are in a worrying state. Despite the lack of recorded seagrass associated fauna, our study revealed minimal impacts to seagrass meadows from eutrophication or sedimentation, and the meadows included appeared to be healthy. The sites with the highest number of motile fauna were within Myanmar’s only National Marine Park offering some optimism for the effectiveness of protection, but further assessments are required to allow targeted management of Myanmar’s seagrass meadows.

Feeding Relationships among Six Seagrass-associated Fishes in the Northeastern Gwangyang Bay, Southern Korea

We conducted dietary analyses of six seagrass-associated fish species inhabiting northeastern Gwangyang Bay, Korea. These six species consumed a variety of benthic invertebrates and teleosts, but their preferences for different food resources varied. Although all species consumed crustaceans, the contributions of different crustacean taxa differed among the species’ diets. Caridean shrimps and crabs were a significant part of the Hexagrammos agrammus and H. otakii diets, respectively, while amphipods were consumed mainly by Sebastes inermis. Caridean shrimps and prawns were abundant within the Lateolabrax japonicas diet, but were not common prey resources for Pseudopleuronectes yokohamae or S. schlegelii. Polychaetes and ophiurids were ingested by P. yokohamae, and the former prey taxon also made moderate contributions to the diets of H. agrammus and L. japonicus. With the exception of P. yokohamae, the diets of all species included teleosts. Teleosts contributed the largest proportion of the S. schlegelii diet, followed by the S. inermis and L. japonicas diets; however, H. agrammus and H. otakii rarely consumed teleosts. Non-metric multidimensional scaling (nMDS) ordination plots and permutational analysis of variance (PERMANOVA) revealed the variation in dietary composition among species and the contributions of each prey taxon. These interspecific differences in diet increase the range of food resources available to these fishes, thereby reducing competition for resources within the fish community in this region.

Marine protected areas increase temporal stability of community structure, but not density or diversity, of tropical seagrass fish communities.

Marine protected areas (MPAs) have been shown to increase long-term temporal stability of fish communities and enhance ecosystem resilience to anthropogenic disturbance. Yet, the potential ability of MPAs to buffer effects of environmental variability at shorter time scales remains widely unknown. In the tropics, the yearly monsoon cycle is a major natural force affecting marine organisms in tropical regions, and its timing and severity are predicted to change over the coming century, with potentially severe effects on marine organisms, ecosystems and ecosystem services. Here, we assessed the ability of MPAs to buffer effects of monsoon seasonality on seagrass-associated fish communities, using a field survey in two MPAs (no-take zones) and two unprotected (open-access) sites around Zanzibar (Tanzania). We assessed the temporal stability of fish density and community structure within and outside MPAs during three monsoon seasons in 2014–2015, and investigated several possible mechanisms that could regulate temporal stability. Our results show that MPAs did not affect fish density and diversity, but that juvenile fish densities were temporally more stable within MPAs. Second, fish community structure was more stable within MPAs for juvenile and adult fish, but not for subadult fish or the total fish community. Third, the observed effects may be due to a combination of direct and indirect (seagrass-mediated) effects of seasonality and, potentially, fluctuating fishing pressure outside MPAs. In summary, these MPAs may not have the ability to enhance fish density and diversity and to buffer effects of monsoon seasonality on the whole fish community. However, they may increase the temporal stability of certain groups, such as juvenile fish. Consequently, our results question whether MPAs play a general role in the maintenance of biodiversity and ecosystem functioning under changing environmental conditions in tropical seagrass fish communities.

Fish, Macroinvertebrate and Epifaunal Communities in Shallow Coastal Lagoons with Varying Seagrass Cover of the Northern Gulf of Mexico

Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0–18.8 %), and four had high cover (83.8–97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems.

Single and joint effects of regional- and local-scale variables on tropical seagrass fish assemblages

Seagrass beds are highly important for tropical ecosystems by supporting abundant and diverse fish assemblages that form the basis for artisanal fisheries. Although a number of local- and regional-scale variables are known to influence the abundance, diversity and assemblage structure of seagrass-associated fish assemblages, few studies have evaluated the relative and joint (interacting) influences of variables, especially those acting at different scales. Here, we examined the relative importance of local- and regional-scale factors structuring seagrass-associated fish assemblages, using a field survey in six seagrass (Thalassodendron ciliatum) areas around Unguja Island (Zanzibar, Tanzania). Fish density and assemblage structure were mostly affected by two regional-scale variables; distance to coral reefs, which positively affected fish density, and level of human development, which negatively affected fish density. On the local scale, seagrass biomass had a positive (but weaker) influence on fish density. However, the positive effect of seagrass biomass decreased with increasing level of human development. In summary, our results highlight the importance of assessing how multiple local and regional variables, alone and together, influence fish communities, in order to improve management of seagrass ecosystems and their services.

Variation with Depth in Temperate Seagrass-Associated Fish Assemblages in Southern Victoria, Australia

Variability in the abundance and distribution of seagrass-associated fish assemblages was examined at different depths in a temperate bay in southern Australia. Depth differences in seagrass-associated fish assemblages are poorly known but this information is critical given that seagrass loss can occur at specific depths depending on the cause. Overall, 69 species of fish from 26 families were recorded, with higher species richness in shallow than deep beds, with 12 species found only in deep beds and 22 species found only in shallow beds. While the total fish abundance (i.e. abundance of all species recorded) varied between years and seasons, and to some extent between sites, it was significantly higher in shallow than deep seagrass beds in the majority of cases. Although there was some variation between sites, seagrass tended to be longer and have a higher biomass in shallow than deep beds during both spring and autumn throughout the study. A positive relationship between seagrass biomass/length and total fish abundance/species richness was apparent. Assemblage structure tended to be distinct at each depth, with the largest species recorded in shallow seagrass. Large numbers of small schooling fish, such as atherinids, dominated in shallow seagrass but were not found in deep seagrass. Loss of seagrass could therefore have varying implications for distinct assemblages found at different depths.

Variation in larval growth can predict the recruitment of a temperate, seagrass-associated fish

Understanding the factors leading to inter-annual variation in recruitment of animals with complex life cycles is a key goal for ecology and the sustainable management of animal resources, such as fisheries. We used otolith microstructure to determine larval growth rates of post-larval King George whiting, Sillaginodes punctata, in seagrass beds of Port Phillip Bay, Australia. Inter-annual variation in growth determined early in the pelagic, offshore larval-stage was highly correlated with post-larval abundance (a predictor of fishery recruitment). Sea surface temperature measured near the presumed spawning area off Western Victoria was significantly correlated with larval growth, and was also significantly correlated with post-larval abundance in Port Phillip Bay. Increased water temperature would have had the direct effect of increasing larval growth and therefore contributing to larval survival, but may also have been indicative of enhanced physical transport and/or plankton productivity. Overall, larval growth rate of King George whiting is a very strong predictor of post-larval abundance, which in turn will influence fishery recruitment in 3-5 years' time.

Assessing the trophic link between seagrass habitats and piscivorous fishes

Links between piscivorous fishes and seagrass habitat were investigated in Port Phillip Bay, Australia. Abundances of piscivorous fish were estimated, the contribution of fish to their diets was measured and the trophic link between these fish and seagrass beds was assessed with stable isotopes. Piscivorous fishes were common in seagrass and included eight species from seven families (33% by abundance). They consumed at least eight families of teleost prey, including juveniles of seagrass-associated taxa, such as monacanthids (e.g. Meuschenia freycineti) and syngnathids (Stigmatopora argus). No fish were exclusively piscivorous and contribution of fish to the diets of the most common species (Arripis truttacea and Kestratherina esox) varied strongly through time. Putative contributions of each source (primary producer – plant) to the nutrition of piscivorous fishes were: (1) fishes whose base for nutritional support was driven mostly (&gt;50%) by seagrass (e.g. Platycephalus speculator and Platycephalus laevigatus); and (2) fishes whose base for nutritional support was not driven by any particular primary producer (e.g. Arripis truttacea and Pseudocaranx dentex). The propensity for piscivorous fish to include seagrass-associated fish in their diets, their perennial presence in seagrass and the strong putative contribution by seagrass to their nutrition, suggest that seagrass habitats can be valuable habitat for piscivorous fishes.

Influence of climate on the fishery recruitment of a temperate, seagrass-associated fish, the King George whiting Sillaginodes punctata

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 288:263-271 (2005) - doi:10.3354/meps288263 The influence of climate on the fishery recruitment of a temperate, seagrass-associated fish, the King George whiting Sillaginodes punctata Gregory P. Jenkins* Primary Industries Research Victoria, Marine and Freshwater Systems, and Department of Zoology,University of Melbourne, PO Box 114, Queenscliff, Victoria 3225, Australia *Email: greg.jenkins@dpi.vic.gov.au ABSTRACT: The King George whiting fishery in Victoria, Australia, is based on sub-adult fish of 3 to 5 yr old in bays and inlets. Previously, Zonal Westerly Winds (ZWW) and the El Niño southern oscillation index (ENSO) cycle have been found to influence the larval stages and subsequent catches of some fishery species in southeastern Australia. Offshore spawning and long larval life, together with a fishery based on a few year classes of sub-adult fish, led to the hypothesis that the fishery would be strongly influenced by climatic conditions in the larval stage. A significant positive correlation was found between the strength of ZWW in the region and the catch 3 to 5 yr later. These conditions may have influenced larval transport rates, or alternatively may have led to increased plankton productivity and therefore larval food supply. The ENSO cycle, however, was found to have a positive influence on catch at 0 lag. This positive correlation suggested that La Niña conditions may have led to increased catchability of King George whiting. Post-larval abundances at a seagrass site in Port Phillip Bay were strongly correlated with ZWW, confirming that the effect of these winds occurred in the larval to post-larval stages. Overall, results suggest that climatic conditions exert a strong influence on the larval to post-larval stages that subsequently affect the catch in the fishery. KEY WORDS: Climate · Zonal Westerly Winds · ENSO cycle · King George whiting · Catch trend · Southeast Australia · Sillaginodes punctata Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 288. Online publication date: March 10, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Links between humans and seagrasses—an example from tropical East Africa

The concept of ecosystem goods and services and the approach of a linked social–ecological system were used to identify and describe the interactions between humans and seagrasses in a rural tropical economy in the East Coast of Zanzibar (Chwaka village). The main stakeholders in the population are fishermen and seaweed farmers. Through in-depth and semi-structured interviews, questionnaires, market data analysis and participant observation, we found a diversity of social–ecological links that are important for the welfare of the local population. Fishing grounds for finfish and invertebrates, substrate for seaweed cultivation and sites for bait collection were among the most important ecological support areas for fishermen and farmers. Seagrass-associated fisheries in the form of trap fisheries (“dema”) provided the highest daily average income per fisherman. Furthermore, seagrass-associated fish constituted the primary source of animal protein for the local people. Seagrasses were also used as traditional medicine and fertilizers. They provided a wide range of ecological services including aesthetical, instrumental, spiritual and religious. The amount of local ecological knowledge (LEK) among fishermen was substantial. No institution directly dealing with seagrasses in the area was identified. The use of a seascape management approach is recommended to improve and develop social–ecological resilience.

The Effects of Season and Proximity to Fringing Mangroves on Seagrass-Associated Fish Communities in Charlotte Harbor, Florida

Little has been published on habitat use by fishes in Charlotte Harbor, one of Florida's largest-and still relatively pristine-estuaries. Multivariate analyses of data from 21.3-m-seine samples (1996-2000) were used to examine spatiotemporal patterns of seagrass habitat use by Charlotte Harbor fishes. Two habitats (mangrove-associated seagrass shorelines and offshore seagrass flats) were examined. Throughout the year, the mangrove-seagrass habitat was distinguished by Menidia spp., Mugil gyrans, Eucinostomus harengulus, and Floridichthys carpio, and the offshore seagrass flats habitat was distinguished by Bairdiella chrysoura, Orthopristis chrysoptera, and Cynoscion nebulosus. The dry season (Dec.-May) was distinguished by Lagodon rhomboides, Leiostomus xanthurus, and O. chrysoptera in both habitats and by Mugil cephalus in the mangrove-seagrass habitat. The wet season (June-Nov.) was distinguished by Lucania parva, F. carpio, and Fundulus grandis in the mangrove-seagrass habitat and by Eucinostomus gula, Microgobius gulosus, C. nebulosus, and E. harengulus in the offshore seagrass flats habitat. Eucinostomus spp., Anchoa mitchilli, and Strongylura notata were abundant in both habitats during the wet season. In general, many species were collected in both habitats and were widely distributed in the estuary. Various combinations of four environmental variables (i.e., water temperature, salinity, dissolved oxygen, water depth) and their coefficients of variation were well correlated with the biotic community patterns. These results show that different fish communities use different seagrass habitats in Charlotte Harbor, depending on the season and the proximity of the seagrasses to fringing mangroves.

Changes in Seagrass-Associated Fish and Crustacean Communities on Florida Bay Mud Banks: The Effects of Recent Ecosystem Changes?

The fauna of seagrass-covered mud banks in Florida Bay, documented in the mid 1980s prior to recent seagrass die-off, phytoplankton blooms, and other ecosystem changes, was reexamined in the mid 1990s for faunal changes that might be associated with environmental perturbations. During both decades, decapod crustaceans and fishes were collected with 1-m2 throw traps from seagrass beds at six sites that differ in the amount of freshwater and/or marine influence and in seagrass community metrics. The most common faunal changes were declines in seagrass-canopydwelling forms and increases in benthic forms. At three sites with relatively lush seagrass meadows, above-ground seagrass standing crop declined and abundance of the benthic predatory fishOpsanus beta increased. The degree of faunal change among these sites appeared to be related either to salinity variability or to the degree of exposure to the ecosystem changes that have taken place in Florida Bay. At two sites with poorly developed seagrass meadows, seagrass standing crop and canopy height did not change significantly between decades, but there was an increase in shoot density and total leaf area. The animal communities at these sites were characterized by significant increases in the abundance of benthic crustaceans. At the site on the edge of Rankin Lake, the basin where seagrass die-off was first observed in Florida Bay during 1987, seagrass standing crop, canopy height, shoot density, and leaf area declined significantly between decades, but species richness of both crustaceans and fishes increased. The abundance of canopy-dwelling crustaceans and fishes declined markedly at this site, whereas the abundance of benthic forms less dependent on seagrass cover generally increased. In retrospect, we believe the fauma at this site during the 1980s, characterized by high productivity but few species, was already showing signs of the stresses that led to the seagrass die-off that began in 1987.

The contributions of habitat structure and larval supply to broad-scale recruitment variability in a temperate zone, seagrass-associated fish

The contribution of habitat structure and larval supply to broad-scale spatial variability in recruitment of a temperate zone, seagrass associated fish, Sillaginodes punctata (Cuvier and Valenciennes), was investigated in Port Phillip Bay, Australia, from September to November, 1994. Replicate artificial seagrass beds were placed at five sites over a 50 km section of coastline, and artificial and adjacent natural seagrass were sampled approximately fortnightly for Sillaginodes punctata recruitment. Significant differences in recruitment amongst sites were apparent for both natural and artificial seagrass. A small but significant effect of habitat was detected where more recruits occurred in artificial relative to natural seagrass at sites with longer plant stems in the natural seagrass. The contribution of larval supply to spatial variability in recruitment was investigated by sampling natural seagrass, and concomitantly sampling the plankton immediately offshore for pre-settlement larvae. There was no significant correlation between larval abundances and recruitment, or between habitat structure and recruitment, over nine sites. We hypothesise that the high spatial variability in recruitment attributable to location is probably related to a combination of factors. These factors may include variation in larval supply, and also variation in the physical exposure of the location that influences mortality and movement of recruits in the early post-settlement stage.

Temporal and spatial variability in recruitment of a temperate, seagrass-associated fish is largely determined by physical processes in the pre- and post-settlement phases

Temporal and spatial variability in recruitment of a temperate, seagrass-associated fish is largely determined by physical processes in the pre- and post-settlement phases

The production and trophic ecology of shallow-water fish assemblages in southern Australia II. Diets of fishes and trophic relationships between fishes and benthos at Western Port, Victoria

A total of 5113 fishes belonging to 91 species was collected from seagrass and unvegetated habitats at Western Port for dietary analysis between August 1989 and November 1990, with 720 animals having empty guts. None of the common species was found to have a highly specialised diet. Crustaceans were the dominant component in the diets of the majority (69%) of the 88 species with non-empty guts, with five species (a girellid, a mugilid, a monacanthid and two gobiids) consuming large amounts of algal material, and only one species [the garfish Hyporhamphus melanochir (Valenciennes)] ingesting seagrass in any quantity. In general, dietary differences between juveniles and adults of a species were as great as dietary differences between fish belonging to different species when at the same body size. Amongst the crustacean feeders, diets generally changed from predominantly copepods to predominantly peracarids (amphipods, isopods and mysids) at ≈0.1 g wet body weight, and from predominantly peracarids to predominantly crabs and shrimps at ≈100 g. Across the range of species examined, there was a close relationship between the size of ingested prey and fish biomass. Prey length averaged 7.5% of predator length. The dominant species in gillnet catches, the mullet Aldrichetta forsteri (Cuvier & Valenciennes), possessed an unusual diet because prey were smaller than for other fishes of the same body size and large quantities of algal material were also consumed. Similar trophic pathways leading to fishes were found in different habitats, with the major linkages being from benthic microalgae and detritus through epifaunal crustaceans to the smaller fishes. The major predators of small fishes were locally-resident species, the rock flathead Platycephalus laevigatus Cuvier & Valenciennes in seagrass beds and the sand flathead Platycephalus bassensis Cuvier & Valenciennes at unvegetated sites. Crustaceans supplied most of the dietary intake for the small fish communities at all sites, with molluscs and polychaetes also important but supplying >25% of food consumed at only two sites. When daily rates of consumption were compared with daily production of food, the production of crustaceans >1 mm sieve size was calculated to be all consumed by fish. The production of the non-crustacean benthos was an order of magnitude higher than that consumed by fish predators. These results indicate that the availability of high quality crustacean prey may limit the production of fishes, and that fishes are likely to compete diffusively for crustacean prey. Additional support for this hypothesis is provided by the observations that the condition of seagrass-associated fish declined, and mortality rates were high, during the autumn season when total fish consumption could not be supported by crustacean production.