Resource partitioning and habitat-specific dietary plasticity of two estuarine sparid fishes increase food-web complexity

Abstract

The diets of the co-occurring sparid fishes Acanthopagrus australis and A. pacificus were investigated to assess dietary overlap and resource partitioning, the extent of spatial variation and implications for the complexity of trophic interactions in tropical estuaries. Both species consumed a wide variety of prey, including bivalves, gastropods, crustaceans and polychaetes. There were clear differences in diet among sites separated by less than a kilometre. Site-specific substrata determined prey type, so diets at sites within a sandy bay were comprised largely of benthic infauna, whereas those at mangrove-lined sites contained substantial amounts of mangrove-associated prey. Although there was general dietary overlap between the two species, their diets differed substantially at any one site when viewed at a fine taxonomic resolution. A. pacificus displayed a very region- and site-specific diet, apparently feeding in different, and spatially separate, food chains at these different locations. Its main prey varied markedly among sites, seemingly because of habitat differences. By feeding in different food chains (and potentially different food webs) at different points in space and time, species such as A. pacificus have the potential both to link food webs operating in a variety of habitats and to add substantially to the complexity of tropical estuarine food webs.

Urbanisation supplements ecosystem functioning in disturbed estuaries

“…By contrast, yellowfin bream are large zoobenthivores that feed opportunistically on fish and benthic invertebrates across a range of coastal ecosystems; juveniles recruit into shallow seagrass meadows and migrate to structurally complex habitats (e.g. reefs, woody debris, artificial structures) as either sub-adults or adults (Meynecke et al 2008, Sheaves et al 2014b, Gilby et al 2018. Humans have, however, removed much of the natural subtidal structure from Australia's estuaries to improve their navigability for shipping, and through the combined effects trawling, dredging and channelization (Hindell 2007, Sheaves et al 2014a).…”

Use of mangroves by fish: new insights from in‑forest videos

“…The first featured similar rates of occurrence once they had entered the mangroves, and displayed broadly similar patterns in both seaward and landward zones. This profile was termed 'forager' because it appears to be characteristic of species dispersing to feed throughout the mangrove forest; the foragers were composed of species known to feed extensively on prey found in mangroves -sesarmid crabs: Acanthopagrus australis, A. pacificus (Sheaves et al 2014); L. argentimaculatus (Sheaves & Molony 2000); insects and small crabs: Toxotes chatareus (Allen 1991, Allen et al 2002) -or species that spent a large part of their time in mangroves picking from the substrate surface (Gerres filamentosus, G. oyena) or from mangrove pneumatophores and roots (S. lineatus). Variations among the foragers' patterns of oc cur rence indicated subtle differences in the mode and timing of entry and dispersal.…”

Demersal Fish and Shrimp Abundance in Relation to Mangrove Hydrogeomorphological Metrics

“…They proposed such tests that include an evaluation of life history strategies, comparative adult recruits per unit area of nursery habitat, comparison among habitats that juveniles use, movement patterns, and total biomass of individuals recruiting to adult populations. Dahlgren et al (2006) modified these factors but as pointed out by Sheaves et al (2014), these ideas basically focused on one aspect of the nursery ground value, i.e. the output of juveniles from nursery grounds to offshore areas.…”

“…It is hypothesized that the abundance or natural production of fish or shrimps in mangroves (or their nursery ground value) is related to the mangrove hydrogeomorphology. Here, we analyzed the inside of the black box (hydrogeomorphology) but not what that emerged at its end (Sheaves et al 2014). Nevertheless, the hydrogeomorphological metrics used here represent a subset of the comprehensive factors espoused by Sheaves et al (2014).…”

“…Here, we analyzed the inside of the black box (hydrogeomorphology) but not what that emerged at its end (Sheaves et al 2014). Nevertheless, the hydrogeomorphological metrics used here represent a subset of the comprehensive factors espoused by Sheaves et al (2014). We used multivariate analysis of the various hydrological and geomorphological parameters of five mangrove forests in Peninsular Malaysia to determine their influence on fish and shrimp abundance in the mangrove forest (swamp) itself.…”