Abstracts Category : Other

Life history characteristics of glassfish, Ambassis jacksoniensis, adjacent to saltmarsh within a large and permanently-open estuary

by Jack J McPhee

Research Doctorate - Doctor of Philosophy (PhD) Saltmarsh vegetation, which typically occurs in intertidal areas within estuaries globally, provides an important habitat and feeding ground for estuarine organisms such as crustaceans, gastropods, birds and fish (some of which are of economic importance). Within south-east Australian estuaries, saltmarsh vegetation is both typically bordered by mangroves and tidally inundated three or four times per month during the high tide of the spring tidal cycle (during the day high tide in summer and during the night high tide in winter). In recent decades, saltmarsh vegetation has declined globally due to anthropogenic influence, and in Australia, Coastal Saltmarsh is now listed as an Endangered Ecological Community under the Threatened Species Conservation Act 1995. This study was conducted within a representative and relatively unmodified saltmarsh habitat (Empire Bay Wetland) in a large and permanently open estuary, Brisbane Water Estuary, located in south-eastern Australia. This study, which was conducted at two markedly different times of the year during 2012, examined the general response of the estuarine fish (using seine nets) and zooplankton (using plankton nets) assemblages to tidal inundation, with further emphasis being placed on selected biological and ecological characteristics of the abundant estuarine ambassid, <i>Ambassis jacksoniensis</i>. Abundances of <i>A. jacksoniensis</i> (mean standard length=37.3 mm, 0.021 (SE)) and overall fish diversity were greater in nightly winter catches than daily summer catches, which is consistent with previous evidence of important feeding times for estuarine fish (including <i>A. jacksoniensis</i>) upon saltmarsh derived zooplankton (e.g. crab zoeae released by saltmarsh-dwelling grapsid crabs), during ebb tides that drain saltmarsh following its inundation. Indeed, zooplankton assemblages were dominated by crab zoeae during ebb tides following saltmarsh inundation, while calanoid copepods dominated these assemblages at other times. Moreover, stomach content analyses of <i>A. jacksoniensis</i> showed that crab zoeae were heavily preyed upon during such times, with dietary switching to caridean decapods being evident when crab zoeae were not abundantly present within the water column (i.e. during flood tides and during ebb tides that did not follow saltmarsh inundation; as shown within zooplankton assemblages). Despite their high abundance within zooplankton assemblages, calanoid copepods were not preyed upon by <i>A. jacksoniensis</i>, which is likely to reflect the relatively fast escape responses of calanoids to predators. Further, stomach fullnesses of <i>A. jacksoniensis</i> were generally highest during ebb tides on days of saltmarsh inundation, implying that feeding was most marked at these times. Trophic relay is an ecological model that involves the movement of biomass and energy from vegetation, such as saltmarshes, within estuaries to the open sea via a series of predator-prey relationships. Therefore,Advisors/Committee Members: University of Newcastle. Faculty of Science, School of Environmental and Life Sciences.