The ecology of soft sediment tidepool dwelling gobies (Pisces: Gobiidae) in Moreton Bay, Australia

Craig Chargulaf (2010). The ecology of soft sediment tidepool dwelling gobies (Pisces: Gobiidae) in Moreton Bay, Australia PhD Thesis, School of Biological Sciences, The University of Queensland.

       
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Author Craig Chargulaf
Thesis Title The ecology of soft sediment tidepool dwelling gobies (Pisces: Gobiidae) in Moreton Bay, Australia
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 2010-04
Thesis type PhD Thesis
Total pages 167
Total black and white pages 167
Subjects 06 Biological Sciences
Abstract/Summary Tide pools are challenging environments. They can experience rapid changes in temperature, salinity and pH yet are occupied by fishes and other organisms. While more attention has been given to community composition, zonation and competition of intertidal rockpool faunas, soft sediment tidepools are potentially important in terms of biodiversity and fisheries. Gobies, dominate the communities of both rock- and soft sediment pools by virtue of physiological and behavioural adaptations. In part their great diversity is potentially a function of the ability to cope with great adversity. The combination of physiological challenges and low resource diversity offers and useful natural laboratory for examining resource partitioning and speciation processes in extreme environments. Moreton Bay, Australia contains extensive areas of soft sediment shores on which pools commonly occur. The objectives of this thesis were to: 1) quantify the use of soft sediment tidepools by fishes and their associated meiofaunal prey, and 2) examine more closely how several gobiid species are able to coexist in such a homogenous environment. A twelve month survey of fishes in soft sediment tidepools was undertaken between January and December 2009 at three sites: Dunwich, Manly and Godwin Beach, in south-east Queensland, Australia. The gobies Favonigobius lentiginosus, Favonigobius exquisitus, Pseudogobius sp., whiting Sillago spp. and the blenny Omobranchus punctatus were the most abundant species. The mean density of fish was between 0.29 ± 0.13 and 5.04 ± 1.74 fish L-1. Abundance of fish was positively correlated with pool volume. Most fish caught were juveniles, suggesting that soft sediment pools act as nurseries for some species. To assess prey availability and therefore the potential role of soft sediment pools as foraging areas during low tide, I assayed the meiofaunal occupation of soft sediment tidepools at each of the three intertidal shores. Mean maximum meiofaunal abundances were found at Godwin Beach (1389.2 ± 158.2 individuals per 20 cm3) and abundances differed significantly among months. Nematodes and copepods were the most abundant taxa while all other taxa contributed to <10% of the total abundances. Unlike fish abundances, pool volume did not correlate with the abundance of meiofauna and only at Dunwich did depth (p < 0.0001) and surface area (p < 0.01) have a positive correlation. The soft sediment pools found around Moreton Bay provide sufficient meiofaunal prey resources for juvenile and small fish that use them. The feeding ecology of two sympatric gobies, Favonigobius lentiginosus and F. exquisitus was investigated for tropic partitioning of resources. Gut contents were analysed to explore competition and temporal dietary shifts. Copepods dominated goby diets and there was no evidence of temporal partitioning between the congeners, even when sympatric. Food resource competition did not appear to be a limiting factor between F. lentiginosus and F. exquisitus despite cohabitation in such restricted environments, providing tentative support for the unified neutral theory hypothesis. Using scanning electron microscopy (SEM) character states for phylogenetic analysis were developed from images of the oral and pharyngeal jaws of six soft sediment tidepool dwelling gobies. The aim was to test if resource partitioning could be identified at a morphological level through divergence in pharyngeal and oral jaws. The genera Arenigobius, Acentrogobius and Favonigobius differed little morphologically, from which I infer that trophic resource competition is not a primary structuring agent in the evolution of gobies in such intertidal pools. Competition for food resources while the tide is in, partitioning of non-food resources, or spatial segregation by virtue of different physiological tolerances are suggested as mechanisms that might act to support the coexistence of such trophic isomorphs. Tank experiments were conducted assess whether Favonigobius lentiginosus, which typically occupies soft sediment tidepools, and Arenigobius frenatus, typically found in nearby subtidal seagrass beds, actually prefer those habitats. Both A. frenatus and F. lentiginosus preferred the seagrass habitat when alone. When in the same tank, F. lentiginosus significantly altered its preferred habitat towards sand (p < 0.01). Higher densities of F. lentiginosus also caused individuals to use more of the marginal habitats. I suggest that the use of soft sediment tidepools by F. lentiginosus may be a consequence of competition with A. frenatus for space in seagrass beds. Soft sediment tidepools are dynamic ecosystems that contain a small but potentially important group of fishes dominated by juveniles that mainly these pools as nursery refuges and, by virtue of pool dwelling meiofaunal communities, foraging areas during low tide. The intertidal gobies of Moreton Bay appear to be competing directly for prey, as most lack any apparent morphological or behavioural specializations that might allow them to segregate resources.
Keyword Gobiidae
tidepool
Meiofauna
Competition (ecology)
diet
Pharyngeal morphology

 
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Created: Fri, 29 Apr 2011, 20:28:22 EST by Mr Craig Chargulaf on behalf of Library - Information Access Service