Utilisation of the introduced New Zealand screwshell (Maoricolpus roseus) by native hermit crabs in eastern Tasmania - spatial variability in occupancy

Interactions between native and introduced species can help to elucidate the impact of exotic species on the broader community. This work examines utilisation of an introduced gastropod, the New Zealand screwshell (Maoricolpus roseus) by native hermit crabs in eastern Tasmania. Samples of screwshells were collected from Bass Strait, Maria Island, Pirates Bay and Dennes Point using a modified scallop dredge or collected by divers. Site location, date, depth, dredge opening size were recorded, and random sub-samples of shells were measured for length and width, and spire damage was scored. Hermit crabs, if present, were identified to species, sexed and measured.

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.

Larval transport of the introduced Northern Pacific Seastar (Asterias amurensis) in the Derwent Estuary, SE Tasmania

This study assessed the spatial and temporal (horizontal and vertical) distribution of Asterias amurensis larvae in the Derwent Estuary and adjacent Storm Bay, SE Tasmania. Horizontal transport and development was assessed by collecting plankton samples at 2 or 4 week intervals, from July to December 2001, at 4 sites in the Derwent Estuary and 6 sites in Storm Bay. The effects of light and salinity on vertical distribution of larvae was examined over a 24 hour tidal and diel cycle.

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.

Population structure and movement of Octopus maorum and Octopus pallidus, and predation on rock lobster

Samples of Octopus maorum and O. pallidus have been collected from the Eaglehawk fishery and as bycatch from southern rock lobster fishery to determine population structure and spatial and temporal trends. Tag recapture study of O. maorum and O. pallidus in Taroona reserve using PIT tags and movement study using acoustic tracking at Taroona reserve and Eaglehawk neck examine the temporal and spatial scales of movement and habitat use. Octopus tracked using VR2's (presence/absence data) and VRAP (triangulated positional data) at both sites.

Impacts of New Zealand screwshells (Maoricolpus roseus) on native scallop distribution and behaviour

The impact of the introduction of the New Zealand screwshell (Maoricolpus roseus) on scallop distribution and behaviour in the D'Entrecasteaux Channel, SE Tasmania was investigated. The impact of both live and dead and empty M. roseus shells on the distribution of two sympatric scallop species, queen scallop (Equichlamys bifrons) and doughboy scallop (Chlamys asperrimus) was quantified at large spatial scales. Also quantified was the impact of M. roseus on the distribution and behaviour of the commercial scallop (Pecten fumatus), at both large and small spatial scales.

Community level impacts of Maoricolpus roseus on the function of native soft sediment assemblages

The impact of the introduced New Zealand screw shell, Maoricolpus roseus, were assessed using a cageing experiment in SE Tasmania (Bligh Point, D'Entrecasteaux Channel). Three treatments consisted of different substratum type (live, dead and empty shells, and dead shells with 50% occupancy by hermit crabs); which were crossed with 2 levels of screwshell density (high and low). Treatment groups were artificially maintained for 20 months before metabolic chambers were used to quantify the community metabolism of different treatment groups.

Range expansion of the sea urchin Centrostephanus rodgersii leads to loss of taxonomic diversity in a kelp bed habitat, eastern Tasmania

The long spined sea urchin Centrostephanus rodgersii (Diadematidae) has recently undergone poleward range expansion to eastern Tasmania (southeast Australia). This species is associated with barrens habitat which has been grazed free of macroalgae, and therefore has potentially important consequences for reef structure and biodiversity. This study used urchin removal experiments from barrens patches in eastern Tasmania to monitor the subsequent response of the macroalgae relative to unmanipulated barrens patches. In removal patches, there was a rapid proliferation of canopy-forming macroalgae (Ecklonia radiata and Phyllospora comosa), and within 24 months the algae community structure had converged with that of nearby areas without urchins. Faunal species richness was comparatively low in barrens habitat, with C. rodgersii grazing activity resulting in an estimated minimum net loss of approximately 150 taxa compared with intact macroalgal habitats.

Reproductive potential of the long spined sea urchin Centrostephanus rodgersii in 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).

The effect of anthropogenic structures on reproductive output of the northern Pacific seastar (Asterias amurensis) in the Derwent River estuary, SE Tasmania

In the Derwent Estuary (south eastern Tasmania, Australia), the introduced northern Pacific seastar Asterias amurensis is highly abundant and fecund when associated with anthropogenic structures (wharves and marinas). Based on modelled predictions of fertilisation success, seastars at wharf 'hotspots', whilst representing <10% of the total population in the Derwent Estuary, and concentrated in <0.1% of the total area, contribute up to >80% of total larval production in the estuary. Reproductive potential of populations at wharf and control sites was quantified (in terms of individual capacity and spatial characteristics of the population. A large scale survey was undertaken in the Derwent estuary (to 27m) to determine spatial distribution of the species. Zygote production (i.e. number of fertilised eggs) was used as a measure of reproductive output and was simulated using empirical estimates of spatial and reproductive parameters of the adult seastars in a spatially explicit model of fertilization (developed by A. Morris and C. Johnson).

2008