An introduced population at Peppermint Bay hybridized with an existing population of dwarf cushion star (Parvulastra exigua). For 10 years, three separate forms could be identified as pure P. exigua, pure P. vivipara and a hybrid form (Parsons 2020). Recently, further hybridization has occurred and eventually there was a hybrid collapse, causing most specimens to now look like P. exigua. The identification of individuals from the most recent survey at this location exhibited typical P. vivipara morphological features but further testing is required to confirm these observations.

This is an endemic species with a limited range and very low dispersal abilities found in south-east Tasmania, Australia. Its EOO is 2,542 km² and AOO is only 64 km². The rocky intertidal shoreline habitat is rapidly declining because of habitat degradation mainly due to nearby drain outlets, storm-water runoff, construction, as well as aquaculture and invasive species. These threats are likely to continue as the areas in which the sea star inhabits are near areas of human populations and coastal development. There are currently some conservation actions in place for one location, but the overall protection of the habitat required by this sea star is lacking.

This species is small (maximum radius = 13 mm) and is one of only six asteroid species known globally that viviparously produce their young, enhancing the scientific significance of this unusual species.

Previously, the Live-bearing Sea Star was considered extremely common, and prior to 2016, the species had been recorded from 15 sites. Since 2019, it has only been found at nine sites. The Live-bearing Sea Star is no longer found at multiple sites within its historical distribution and all current sites have experienced declines. The total population has decreased by an estimated 87% in the last 18 years (since 2006, three generations), with more than half of all individuals now found in two subpopulations. The species has experienced population decline, decrease in its area of occupancy, and is threatened by the impacts of pollutants and invasive species in its remaining population. We therefore list this species as Critically Endangered (CR A2bce).

The Live-bearing Sea Star is endemic to south-east Tasmania, covering a length of 4,973 km of shoreline. The species’ extent of occurrence (EOO) is 2,541.5 km² (based on total area within a minimum convex polygon around all known occurrence), but the area occupied within this EOO is estimated at 64 km² (based on a 2 x 2 km² grid overlay in the range map). This is a reduction from the previous EOO of 3,044.5 km² and an AOO of 84 km² over the last 20 years. The species occurs at nine locations within this range: Southport Lagoon, Peppermint Bay, Pipe Clay Lagoon, Bambra Reef, Pitt Water, Lewisham, Susan Bay, Tessellated Pavement, and Fortescue Bay (Polanowski 2002, DPIW 2005). Among these, one is a managed subpopulation (Pitt Water), and another is an introduced subpopulation (Peppermint Bay). The seastars in Pipe Clay Lagoon may represent two subpopulations, one of which was found in recent surveys (Strain et al. 2024).

The geographic position (in bays, separated by peninsulas etc) of each of these locations means that any single event related to threats caused by human intervention would not impact more than one of these locations at a time. The main global threats (climate change - rising temperatures and increasing storminess) and local threats (habitat degradation and invasive species) appear to affect each of these areas differently. The animals have limited dispersal potential because they lack any pelagic larval phase, and cannot swim.

Surveys of suitable habitat over the last 20 years around south-east Tasmania had not previously identified extensions to the current range or population size (Polanowski 2002, Parsons 2021) but observations published more recently indicate a potential expansion of one subpopulation into the south-west area of Pipe Clay Lagoon (Strain et al. 2024). Small and isolated subpopulations, combined with a non-dispersing reproductive strategy, and the diminutive size of the animal (Keever et al. 2013, Polanowski 2002, Gunn 2021), all would limit the species' ability to recover from potential disturbance.

Estimates for the population are for all individuals as the end point of incubation within the parent is variable and size at maturity is unclear (Byrne 1996). The size of brooding individuals varied (individuals with radius <6 mm had reproductive organs) and the size of juveniles emerging from the parents can be between 1.5–5 mm (Byrne 1996, Khan et al. 2009). Smaller adults give birth to smaller juveniles, while larger adults can give birth to juveniles up to 5 mm in size.

According to Prestedge (1998), 5 mm is the minimum size of parents observed to give birth (= 1.5–2 years old) and individuals of this species live from 8–10 years. Therefore, considering 2 years old as the age of maturity and 10 years as the longevity of the species, the generation length is calculated as: Age of first reproduction + [ z * (length of the reproductive period) ] = 2 + [0.5 * 8] = 6 years.

Large fluctuations in sea star numbers within one subpopulation (Pitt Water), in response to environmental variation and restricted monitoring windows, has made it difficult to provide reliable estimates of the total combined size of all populations (Parsons 2020).

Previously, the Live-bearing Sea Star was considered extremely common, making it hard to obtain accurate estimates due to high counts and limited survey time between tides (Rowland 2000, Prestedge 1998). Prior to 2016, there had been 15 sites where this species was recorded (Prestedge 2001a), but since 2019 it has only been found at 10 existing sites including one area of extended distribution (Strain et al. 2024). Based on existing information, at five of the historical sites this species has become locally extinct, and at all remaining sites the species is estimated to have experienced declines. The largest subpopulations are currently Pitt Water (13,422 individuals), Roches Beach (13,161 individuals) and Pipe Clay Lagoon (8,418 individuals).

The population was estimated to be ~500,000 based on surveys in 2000-2006, and has reduced to ~41,600 individuals in 2022 (Strain et al. 2024). Overall, there has been a genuine decline in the population surveys by almost 90% over the survey period, with over 87% population decline over the last three generations (18 years, in the period 2006-2024).

Most specimens have been found in the mid-littoral zone on rocky shorelines that gently slope in the sublittoral zone, which is also usually very shallow (M. Byrne pers. comm 2023). The sea star can be found at a maximum depth of 1.5 m below the high-water mark (Prestedge 2001a).

This sea star is not selective in the substrate upon which it lives, occupying sandstone, dolerite, sedimentary rock, basalt and even household bricks (Prestedge 2001a, Polanowski 2002). It is only found on cobbles or small boulders present, and not on exposed bedrock. A larger proportion of rocks they inhabit are between 1–20 cm, but they have been found on rocks 20–40 cm in size (Parsons 2020).

The sea star inhabits the space under and in between the rocks on the shoreline, migrating to the top to feed on microalgae. It is essential that these spaces do not infill with sediment and other deposits which impinge feeding, diurnal patterns of movement and create anoxic environments (Liversage and Bryne 2018, Parsons 2020).

This species is small (maximum radius = 13 mm) and is one of only six asteroid species known globally that viviparously produce their young (Byrne 1996, 2006). The Tasmanian Live-bearing Sea Star is a member of the family Asterinidae which exhibits a striking diversity of life histories along the broadcasting-brooding continuum seen in marine invertebrates, enhancing the scientific significance of this unusual species.

At the local scale this species is also threatened by extensive habitat degradation at key sites caused by sedimentation and nutrient enrichment, mainly from sewerage outfall, storm water run-off, urban encroachment (Prestedge 1998, Parsons 2014, DPIPWE 2012) and colonisation by invasive species (Prestedge 1998, Parsons 2014, DPIPWE 2012, Fitzpatrick 2023). Many of the Live-bearing Sea Star subpopulations inhabit areas being developed by humans, and are consequently impacted by the pollution created.

The intertidal zone in which the Tasmanian Live-bearing Sea Star inhabits is vulnerable to the effects of climate change (Pitt et al. 2010, Edgar et al. 2005). Many intertidal species can withstand high variation in environmental conditions, but Prestedge (2001b) has shown that consistent salinity levels outside of the normal range 20–37 ‰ can reduce the reproductive ability and life expectancy of this sea star species. The probability of increased severity of weather events, rising temperatures, and sea levels rising may lead to further habitat degradation and loss as the rocks and boulders are moved around or completely washed out of the narrow band of shoreline that the sea star inhabits (Scaefer et al. 2020).

At the local scale, increasing urbanisation and declining water quality is combined with threats from biofouling and invasive species. These species compete with the Live-bearing Sea Star for space and food (Parsons 2021, Fitzpatrick 2023). The Pacific Oyster (Crassostrea gigas) and Cunjevoi (Pyura stoloifera) and Porcelain crabs (Petrolisthes elongatus) are amongst the greatest threats to the Live-bearing Sea Star, as they occur in dense colonies and are most commonly responsible for cementation or colonising cryptic spaces under rocks (Fitzpatrick 2023). Biofouling, cementation and competition have reduced food availability, shelter, created anoxic mud beneath the rocks, and disrupted the diurnal movement patterns of the Live-bearing Sea Star (Parsons 2020, Fitzpatrick 2023).

Proximity to storm water and sewage outlets appears to cause a necrotic disease which leads to direct mortality of the Live-bearing Sea Star (Prestedge 1998). It has also led to the die-off of native mussel beds at Tessellated Pavement, which indirectly reduces the amount of shelter for the Live-bearing Sea Star (Prestedge 1998). The ongoing threat of urbanisation and declining water quality are particularly evident at Pitt Water and Tessellated Pavement (Parsons 2020), where the species has experienced the largest recent declines.

Finally, a threat that is localised to Pitt Water is habitat loss and disturbance caused by removal of substrate for construction, mainly due to Southeast Traffic Solutions (SETS) program. During construction, two regions (Sorrell and Midway Point causeway) where the sea star lives will be areas of high disturbance. Rocks will be removed and in areas where they are not, a significant increase in sedimentation and other disturbances is expected (Parsons 2021, Parsons 2022).

An additional risk factor, outside of global climate change and habitat degradation, is the reproductive strategy of the Live-bearing Sea Star. They are self-fertilising simultaneous hermaphrodites that give birth to only a few young, which are carried for long periods of time before birth (Prestedge 1998, Khan et al. 2019). These elements combined create one of the most restricted dispersal strategies among the asteroids.

There is no known trade in this taxon.

Currently, many Live-bearing Sea Stars are being relocated from Pitt Water to prevent localised extinction from road construction in an ongoing programme that started in 2024 (Parsons 2023a). Natural habitats along the shorelines within Pitt Water and Pipe Clay Lagoon are being used to temporarily relocate specimens before being returned to the artificial causeways after construction are complete. This was trialled in 2001–2005 and was deemed successful (Aquenal 2001). However, more recent observations suggest that specimens returned to the causeway eventually died. Attempts at using this type of management plan, i.e. relocation to natural areas, may be futile and could be more detrimental to populations in the long term.

Sites within Pitt Water are being augmented through the addition of rocky rubble material as a trial to increase the capacity of relocation sites, in an ongoing programme that started in 2023 (Parsons 2023b). Relocation of sea stars in Pitt Water without augmenting may not be successful because existing rubble may already be at capacity in terms of resources available to support sea star populations (Parsons 2021).

Trials have undertaken by CSIRO and the University of Tasmania to better understand sea star husbandry and aquarium carrying capacity (Trotter et al. 2023). Relocating to aquarium facilities is another precautionary action taken during construction at Pitt Water for a limited period in 2023, providing an "insurance" population to address scenarios in which numbers decline at the in situ receiver sites.

Some subpopulations of this species are located adjacent to terrestrial protected areas, e.g., Tessellated Pavement State reserve, Southport Lagoon Conservation Area. However, it is not clear whether the conservation areas extend to the low tide mark or below, which is required to encompass the range (DPIPWE 2012). These protected areas do not cover the AOO of the Live-bearing Sea Star.

Further survey work is required to determine the natural fluctuations in the population, with regards to environmental variables and to prioritise the key threats.