Adkins, Merritt Elizabeth (2014) Large bodied fish communities and drivers of use in the shallow waters of a coastal habitat mosaic. Masters (Research) thesis, James Cook University.

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Abstract

Shallow coastal habitats support diverse communities of larval and juvenile fishes, providing refuge from predation while facilitating growth. The function of shallow coastal habitats as nurseries has created considerable interest in managing these areas. However, shallow coastal habitats may be important for benefits that extend beyond nursery function. Contemporary research suggests large bodied fishes also occur in shallow coastal habitats, and that predation may be a more common activity within nursery habitats than previously thought. Shallow coastal habitats may be utilised frequently by large bodied fishes and provide additional ecological functions for these poorly studied fish communities.

Few studies have considered cross-shore sampling of the shallow coastal habitat mosaic, thus current knowledge on how fish communities may differentially use micro-habitats within the shallow coastal habitats is limited. For this thesis the shallow coastal habitat mosaic was delineated into three continuous micro-habitats: the littoral, intertidal and subtidal habitats. The littoral habitat occurs at the interface of the terrestrial and the marine environment and is fully exposed during low tides. Contiguous from the littoral habitat, the intertidal habitat is exposed at varying depths depending on daily tidal cycles. Extending seaward from the intertidal habitat is the subtidal habitat that is always inundated with water. Although some research has focused individually within one of these micro-habitats, no research is yet to consider them as a broader connected ecosystem.

A shallow coastal habitat mosaic in Cleveland Bay, northern Queensland, Australia, was sampled using a large (115 mm) mesh monofilament gill net over a one year period. The community of large bodied fishes (> 200 mm) was defined and their distribution across the mosaic of littoral, intertidal and subtidal habitats identified. Further, the influence of salinity, temperature, and dissolved oxygen on fish community structures was also investigated. In an attempt to determine drivers of habitat use, ecological functions including life history stage, reproductive activity and foraging activity which may potentially influence how large bodied fishes use the habitat mosaic were investigated.

A total of 1119 individuals from 26 families and 36 species were sampled, though four families accounted for 79.1% of the total sample (Latidae, Polynemidae, Ariidae, and Carcharhinidae). Fish communities sampled were diverse and significant differences in community structure were present between habitats. The littoral and subtidal communities were significantly different from each other with the intertidal community sharing some species-specific characteristics with both the littoral and subtidal. Teleosts were the dominant group in the littoral and intertidal habitats while sharks dominated the subtidal habitat. Very few habitat generalists, species that occurred in all three habitats, were sampled. Clear habitat preferences and avoidance occurred with most of the dominant species entirely absent from at least one of the habitats. A relationship between environmental factors (temperature, dissolved oxygen and salinity) and fish assemblages was identified. These patterns are likely driven by a combination of biological and ecological processes, however further research will be necessary to better understand the role of these processes in shaping the large bodied fish communities of shallow coastal waters.

Life history stage was defined for 977 individuals from 26 families and 28 species. Reproductive and foraging activity was determined for the most abundantly sampled teleost and sharks. Ontogenetic shifts in habitats use were apparent with juvenile teleosts dominant in the littoral habitat while adult teleosts were dominant in the intertidal habitat (few teleosts were caught in the subtidal habitat). In contrast to teleosts, sharks were mostly present as young-of-the-year (YOY) and juveniles, suggesting the intertidal and subtidal habitats both act as a shark nursery (only three sharks were captured in the littoral habitat). Interestingly, YOY sharks were more common in the intertidal habitat as compared with the subtidal suggesting an ontogenetic shift in habitat use occurs for young sharks as well. Imminent spawning activity (defined by the presence of hydrated oocytes in the ovaries of females) was only observed in E. tetradactylum in all three habitats. Shark reproductive activity (defined by visible eggs or embryos and an enlarged/distended uterus) was observed in one shark, Rhizoprionodon taylori, with parturition observed in the subtidal habitat. Active foraging was evident in L. calcarifer, E. tetradactylum and P. argenteus with gut contents suggesting foraging occurred throughout the habitat mosaic. Some species specific foraging behaviours were identified with L. calcarifer consuming mostly teleosts in the littoral habitat, and crustaceans in the intertidal habitat. The behaviour of switching prey may allow L. calcarifer to exploit and dominate the littoral and intertidal habitats. Teleosts prey items were also predominant in the guts of R. taylori and Carcharhinus tilstoni/limbatus though opportunistic foraging was observed with Arius spp. eggs common in both shark guts. The use of the intertidal and subtidal habitats by young sharks may be encouraged by a seasonal abundance of nutrient rich food sources such as Arius spp. eggs.

This thesis illustrates that large bodied fish are common in the shallow coastal habitat mosaic and that the habitat mosaic provides many benefits beyond nursery function. Future research should sample both large and small fish communities simultaneously to completely understand the importance of shallow coastal waters to all fishes regardless of size or life history stage. The efficacy of future management will benefit from an understanding of all fish communities within, and ecological services provided by shallow coastal water ecosystems.

Item ID:	43744
Item Type:	Thesis (Masters (Research))
Keywords:	Australia; Cleveland Bay; fish communities; fish habitats; habitat mosaics; intertidal zone; large bodied fishes; life histories; littoral zone; North Queensland; shallow waters; subtidal zone; Townsville
Related URLs:	http://researchonline.jcu.edu.au/43763/
Additional Information:	Publications arising from this thesis are available from the Related URLs field. The publications are: Adkins, Merritt E., Simpfendorfer, Colin A., and Tobin, Andrew J. (2016) Large tropical fishes and their use of the nearshore littoral, intertidal and subtidal habitat mosaic. Marine and Freshwater Research, 67 (10). pp. 1534-1545.
Date Deposited:	20 Apr 2016 06:04
FoR Codes:	05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050102 Ecosystem Function @ 50% 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
SEO Codes:	96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 33% 96 ENVIRONMENT > 9609 Land and Water Management > 960903 Coastal and Estuarine Water Management @ 33% 97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 34%
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