Inter‐ and intraspecific partitioning of food resources by six large and abundant fish species in a seasonally open estuary

Abstract

This study has tested the hypotheses that the dietary compositions of the six large and abundant fish species in the 46 km 2 basin of a seasonally open estuary (Wilson Inlet) will differ significantly, change with increasing body size and vary with water depth and season. These species comprise four marine species, the sea mullet Mugil cephalus, yellow-eye mullet Aldrichetta forsteri, King George whiting Sillaginodes punctata and Australian herring Arripis georgiana, and populations of two species that are confined to the estuary, the cobbler Cnidoglanis macrocephalus and the southern blue-spotted flathead Platycephalus speculator. Non-metric multidimensional ordination and associated tests showed that, overall, the dietary composition was influenced to a far greater extent by the species of fish than by either water depth or season. At even a relatively broad level of taxonomic discrimination, the dietary compositions of each pair of species were significantly different, except for those of A. georgiana v. P. speculator, and even in that case those of their larger individuals differed. Differences among the diets of the six species, which represented five families, are related to differences in feeding morphology and location within the water column. Mugil cephalus ingested almost exclusively sediment and fine organic material. Although A. forsteri and S. punctata both consumed substantial amounts of polychaetes (including nereids, capitellids and orbiniids), the former ingested relatively larger volumes of small crustaceans (copepods) and relatively lower volumes of large crustaceans (the carid Palaemonetes australis), nemertines and bivalve siphons. The diets of A. georgiana and P. speculator were both typified by the consistent and high contributions of large crustaceans and fishes. Among fish prey, however, A. georgiana focused to a far greater extent on the small clupeid Engraulis australis, whereas P. speculator consumed a wider range of teleosts, which included species of atherinid and goby. Although the diets of A. forsteri and C. macrocephalus both contained substantial amounts of coarse organic material, the latter differed markedly from those of all other species by the frequent presence of mytilids (mainly Xenostrobus spp.) and other bivalves (especially Tellina deltoidalis and Irus crenata). The diets of each species except M. cephalus changed with increasing body size and, for comparable size classes, did not differ between shallow and deeper waters. The partitioning of food resources within and among the six large and abundant fish species found in Wilson Inlet would reduce the potential for competition for these resources and help account for the large numbers of those species in this seasonally open estuary.

Dietary compositions of the sparid Acanthopagrus butcheri in three normally closed and variably hypersaline estuaries differ markedly

“…Almeida 2003;Maes et al 2003;Platell et al 2006). No study has explored the ways in which the dietary compositions of a species vary among estuaries in the same region, which, through exhibiting varying levels of degradation, are likely to differ in the relative species compositions of their potential prey.…”

Seasonal Diet Shifts and Overlap Between Two Sympatric Catfishes in an Estuarine Nursery

“…Many studies of trophic ecology infer mechanisms for fish coexistence using diet overlap data (Schoener 1974;Darnaude et al 2001;Platell et al 2006;Russo et al 2008;Sánchez-Hernández et al 2011), and the increasing amount of information on habitats and behavior may also shed new light on the feeding strategy of fishes (Sánchez-Hernández et al 2011). Thus, diet analysis has been proposed as a functional approach to understand mechanisms involved in predator-prey relationships (de Crispin de Billy and Usseglio-Polatera 2002;.…”

“…Consequently, it may be useful for understanding interspecific interactions and the mechanisms that determine food partitioning between species. Sympatric species will likely consume slightly different prey to minimize niche overlap (Schoener 1974), and a number of studies tested this hypothesis for fish that inhabit coastal ecosystems (Blaber et al 1994;Darnaude et al 2001;Platell et al 2006;Woodland et al 2011;Spilseth and Simenstad 2011). Competition for food can affect patterns of habitat selection, niche overlap, and distribution (Hilderbrand and Kershner 2004;David et al 2007).…”

Spatial and temporal patterns in the distribution of large bivalves in a permanently open temperate estuary: implications for management

“…While most visitor activities other than collecting are unlikely to directly affect these typically buried species, managers should also consider possible indirect effect, such as the disturbance of seagrass rhizomes or animals that may gather to feed on bivalves in this relatively confined area. Numerous fishes feed on bivalves (Sarre et al 2000, Platell et al 2006, including elasmobranchs like the southern eagle ray Myliobatis australis (Sommerville et al 2011), which are common in the Nornalup Inlet and make the system unique compared to other estuaries in the region (Potter and Hyndes 1994). The prominence of S. alba as the only large bivalve that is both abundant and widely distributed throughout shallow sand habitats in this system also highlights the limited functional redundancy that is common in estuaries (Elliott and Whitfield 2011).…”