Environmental preferences, impacts and population dynamics of the invasive screwshell Maoricolpus roseus
Creators: name: Probst, TA
Publisher: name: University Of Tasmania
Year: 2023

description: Biological invasions in the marine environment have become a major concern globally, as non - indigenous species can dramatically alter community composition and ecosystem functioning. A study on the turritellid Maoricolpus roseus (Quoy and Gaimard 1864) was conducted to increase the understanding of the invasive success of this native species and its potential impacts on the environment. Maoricolpus roseus is a prosobranch gastropod believed to have been introduced into Tasmania (Australia) in the 1920's, and despite its wide distribution, dense populations, and success in invading several different environments, knowledge of its habitat, reproductive biology and ecological impacts is poor. This thesis investigated habitat preferences of M. roseus, its impact on co - occurring macromolluscs and described its larvae. This information is important for effective management to understand the spread of this species and the extent and magnitude of its potential impacts on coastal ecosystems. Many of the previous surveys did not differentiate between live M. roseus or shells from dead animals, therefore many past descriptions on its preferred habitat are questionable. A survey was carried out in the D'Entrecasteaux Channel (SE Tasmania) to investigate M. roseus habitat. It was found that the spatial distribution of live and dead animals varied within the surveyed area and that differentiation between animal types was important to determine the patterns of distribution of M. roseus. High live animal density sites were generally characterised by sand. Some relatively high densities were also found on finer mud substrate, indicating its ability to adapt to different environments. The study also found that M. roseus were present at all the depths surveyed (down to 40 m) and that generally shell size class was larger at the shallower depths (&lt; 30m). From the survey it was noted that large densities of M. roseus on the finer mud substrate were located in close proximity to sites with the highest densities of live M. roseus and characterised by sand. Further laboratory experiments on habitat choice showed that there was a significant increase in the number of M. roseus that moved onto mud with an increase in the density of this gastropod on sand. This suggests that this response may be partially density - dependent. Investigation of the impact of M. roseus on the distribution of other macromolluscs in the D'Entrecasteaux Channel demonstrated that M. roseus live and dead animals and substrate type correlated in variable ways with macromollusc richness and abundance. Within its favoured habitat of sand, live M. roseus were significantly correlated with the macromollusc species community composition. Areas of higher live M. roseus densities had a lower number of suspension feeding macromolluscs, while the opposite occurred for areas with a lower density of live M. roseus. These results suggest that live M. roseus may be inhibiting the accumulation of other suspension feeding macromolluscs in its vicinity. Studies on two M. roseus populations in the D'Entrecasteaux Channel showed a sexual dimorphism, a 1:1 sex ratio, with females relatively larger than males, and up to 70 % of females carrying larvae over consecutive austral summer seasons. Larvae released from egg capsules were all relatively well developed and planktotrophic. This new information on planktonic larvae helps explain the expansion of this species around the Australian coastline. The results of this study are important to understanding the successful introduction and expansion of M. roseus, and its impact on the Tasmanian environment. This new knowledge will support improved management of this introduced species.