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Growth models, age frequency and size frequency distributions of sea urchin populations (Heliocidaris erythrogramma) in native macroalgal beds and sea urchin barrens
Growth models were constructed for two sea urchin populations over a two-year period using a tag-recapture study in the Mercury Passage, Tasmania. Sea urchins were tagged using tetracycline and calcein and growth models constructed using measurements taken from sea urchin jaws.
Underwater visual census surveys were conducted at 15 sites in eastern Tasmania to quantify the abundance of the sea urchin Heliocidaris erythrogramma and several putative predators.
Sea urchin tagged using tetracycline display visible marks in jaw elements and test plates that can be used to determine growth and subsequently an individuals age. Natural growth lines in the same structures can be used to determine age if natural lines are deposited at a consistent rates independent of age. Sea urchins were tagged using tetracycline and age determined from both fitted growth models and the number of bands deposited. Rates of natural line deposition were also quantified.
Mortality rates of the sea urchin Heliocidaris erythrogramma where estimated under experimental conditions to determine the importance of natural and predation mortality in structuring sea urchin populations. Data was obtained from tethering, tagging and caging experiments at four sites within Mercury Passage and the Derwent Estuary in eastern Tasmania.
Growth and age across range extension region of Centrostephanus rodgersii in eastern Tasmania and morphometric comparison of urchins inhabiting kelp versus barrens habitats
The barrens-forming sea urchin Centrostephanus rodgersii has undergone poleward range extension to eastern Tasmania. This data compares growth, morphology, reproductive investment and gonad indices between individuals inhabiting barrens ('barrens-maintaining' urchins') with those found on kelp beds ('barrens-forming' urchins) in north eastern Tasmania. The data set is comprised of 3 files. The first (Centrostephanus_biometrics_kelp_vs_barrens_urch.xls) compares biometrics of urchins across 3 sites and 2 habitats in eastern Tasmania. The second (Copy_of_Centrostephanus_annual_jaw_growth_increments.xls) compares annual growth increments of urchins in kelp bed and barren habitat including an additional site in south eastern Tasmania (The Lanterns - Tasman Peninsula) to allow comparison of growth across the newly extended range. The third (Jaw_TD_allometery.xlsx) provides a conversion between the allometry of jaw length and test diameter. Ultimately a generalised growth model for the sea urchin in kelp bed habitat was obtained for eastern Tasmania.
Recent poleward range expansion of the barrens-forming sea urchin Centrostephanus rodgersii (Diadematidae) from mainland Australia to Tasmania, has emphasized the need to understand the population dynamics of this ecologically important species in Tasmania. This work informs potential population dynamics of C. rodgersii in Tasmania by examination of its reproductive ecology. Reproductive periodicity (gonad index and propensity to spawn) was assessed bimonthly for 18 months at 4 sites in eastern Tasmania. Gamete viability was assessed by fertilization and early development trials. Temperature tolerance of Tasmanian C. rodgersii larvae was also assessed to determine whether this species has undergone an adaptive shift to the cooler Tasmanian environment. There was also no evidence for an adaptive shift in reproductive phenology. Reproductive phenology was assessed by determination of peak spawning period (gonad index analysis).