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Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/25789
- The ecology of three species of wrasse (Pisces: Labridae) on temperate rocky reefs of New South Wales, Australia
Morton, Jason Kyle
- University of Newcastle. Faculty of Science and Information Technology, School of Environmental and Life Sciences
- Research Doctorate - Doctor of Philosophy (PhD)
- In temperate New South Wales, most fish species in the family Labridae have not previously been investigated with available knowledge restricted primarily to photographic identification guides providing brief notes on species distribution, habitat preferences and identification. This information is inadequate for assessing the impact of labrid harvesting on rocky reef systems and for making informed management decisions for the protection of these fishes. Therefore, this study aimed to fill some of the significant gaps in the understanding of labrid assemblages associated with rocky reefs of temperate eastern Australia. This was accomplished by concentrating primarily on three species - Ophthalmolepis lineolatus, Notolabrus gymnogenis and Pictilabrus laticlavius - which are abundant and co-occur in shallow waters (less than 20 m depth) on the central coast of New South Wales. The methods used in this study included SCUBA surveys of labrid assemblages; in situ observations of labrid behaviour on SCUBA; and acquisition of labrid specimens for the extraction of intestines, gonads and otoliths, and for measurements of fish weight and length.
Labrids were found to be the most species rich family in the study region and were the most abundant of all non-planktivorous fishes. Overall, a higher number of labrid species and a higher number of labrid individuals occurred in sponge garden habitat (15-22 m depth) compared to fringe (3-7 m) and barrens (8-15 m), owing to greater densities of O. lineolatus, Austrolabrus gymnogenis and Eupetrichthyes angustipes. The common labrids, N. gymnogenis, Achoerodus viridis and P. laticlavius, occurred at higher densities in fringe habitat due mostly to a higher representation of juveniles in this habitat. The effect of habitat on labrid assemblages was subject to small-scale variation between sites (separated by hundreds of metres) and experienced temporal changes due primarily to a substantial increase in the abundance of recruits coinciding with late summer and autumn (April-May). Behavioural observations revealed that the three focal species differed substantially in their spatial structure. O. lineolatus were found to be temporary reef residents using home ranges in excess of 2500 m2 for periods of up to 1 year before permanently emigrating outside these temporary home ranges. In contrast, N. gymnogenis exhibit strong site fidelity to reef patches of less than 600 m2 in which they remain for periods in excess of 2 years. Reef patches are shared by up to at least 10 juvenile and female individuals and a single, highly territorial male in a mating system suggestive of resource defence polygyny. An understanding of the spatial structure of P. laticlavius was constrained by its cryptic behaviour, but behavioural observations suggest this species is home ranging and establishes temporary territories for the purpose of feeding and/or reproduction. Intensive ethological observations allowed for the description and quantifying of several major behaviours in which all species typically engaged including encounters and interactions with other fishes, lying, use of shelter, side-swiping, bending, gaping, cleaning by clingfishes (Gobiesocidae) and colour change. The occurrence of these behaviours often demonstrated substantial differences among species (e.g. lying, shelter and bending) and/or experienced shifts with ontogeny (e.g. interactions and area usage). These trends generally remained consistent at different times of the day and periods of the year, and at both locations. Dietary analyses revealed O. lineolatus, N. gymnogenis and P. laticlavius are generalist carnivores feeding on a variety of benthic invertebrates including polychaetes, amphipods, decapods, gastropods, bivalves, polyplacophorans, echinoderms and cirripedes. Differences in the volumetric contribution of prey items in the guts of each species showed that food resources are partitioned among species and observations of foraging behaviour demonstrated a partitioning of microhabitats used for feeding. Ontogenetic shifts in diet and feeding microhabitats demonstrate that food resources are further partitioned within a species. However, overall morphological and behavioural similarities within a species results in greater competition occurring among individuals of the same species than among individuals of different species. This was reflected in higher rates of intra-specific interactions compared with interactions between labrid individuals of different species. Observations of feeding episodes revealed the bite rates of all species were typically unaffected by the time of day and period of year in which sampling occurred, but a location effect occurred for O. lineolatus and P. laticlavius. A reduction in bite rate with ontogeny occurred for N. gymnogenis. The population structure of the three species suggests each exhibits the typical labrid reproductive strategy of protogynous hermaphroditism. O. lineolatus and N. gymnogenis are both monandrous species, but the occurrence of some P. laticlavius males at small sizes and young ages suggests this species may be diandrous. Similarities occurred between O. lineolatus and N. gymnogenis in the size/age at which individuals sexually matured (c.a. 180 mm, 2 years) and changed sex (c.a. 280 mm, 4.6 years), but these events occurred at substantially smaller sizes (95 and 138 mm, respectively) and younger ages (les than 0.9 and 1.9 years, respectively) in P. laticlavius. Sectioned otoliths were used to determine that the longevity of O. lineolatus, N. gymnogenis and P. laticlavius was at least 13.4, 9.6 and 4.8 years, respectively. Ages were validated using marginal increment analysis. Timing of reproduction in each species was asynchronous with peaks in the reproductive activity occurring in late summer to early autumn (February-March) for O. lineolatus, mid winter (July) for N. gymnogenis and mid spring to early summer (October-December) in P. laticlavius.
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- Copyright 2007 Jason Kyle Morton