parks victoria technical series marine natural values study vol 2 ...

Parks Victoria Technical Series No. 79
Flinders and Twofold Shelf Bioregions Marine Natural Values Study
2.3.5 MAJOR THREATS
Threats to natural values in Point Hicks MNP were derived from lists of hazards and
associated risks in Carey et al. (2007b). These were the result of a statewide consultative
process to identify threats to MPAs. Through public and agency workshops, the natural
values in individual MPAs and the threats that could affect them over the next 10 years, were
considered and ranked to identify hazards. This list of hazards was then ranked (low,
medium, high and extreme) by the risk posed by each hazard (Carey et al. 2007b). Four
hazards with the potential to be extreme in Point Hicks MNP were identified by Carey et al.
(2007b). They are listed in rank order and the habitat or area at risk within the MNP is
indicated in brackets:
1. Introduced species from commercial vessels (including secondary introductions)
leading to changes in community structure (potentially all of MNP, benthic
communities most at risk);
2. Poaching of abalone in commercial quantities leading to decreased abalone
populations and consequent impacts on subtidal reef communities (subtidal reef);
3. Lack of ecological knowledge leading to inappropriate management and thus impacts
on habitats and communities (potentially all of MNP); and
4. Introduced marine pests from recreational boats leading to impacts on relevant
ecological communities (potentially all of MNP, benthic communities most at risk).
The introduction of marine pests threatens the integrity of marine biodiversity and may
reduce the social and economic benefits derived from the marine environment (Parks
Victoria 2003). Most marine pests known from Victorian waters are limited to Port Phillip
Bay (Parks Victoria 2003). Two introduced species or marine pest has been recorded Point
Hicks MNP, the screw shell Maoricolpus roseus (Holmes et al. 2007a) and the New Zealand
sea star Astrostole scabra (Edmunds et al. 2010b). It is presumed that the introduced green
meany or green shore crab Carcinus maenas occurs on the intertidal reefs of all the MPAs,
except Ninety Mile Beach which has no intertidal reef. Other species of particular concern
include the Northern Pacific seastar Asterias amurensis, European fanworm Sabella
spallanzanii, Japanese kelp Undaria pinnatifida and broccoli weed Codium fragile (subsp
fragile) (Parks Victoria 2003).
The screw shell Maoricolpus roseus has been recorded within the Point Hicks MNP (Heislers
and Parry 2007). This 5 cm long gastropod was introduced to Tasmania from New Zealand
in the 1920s (Bax et al. 2003). It has now spread out to the 80 m depth contour off the
eastern Victorian and New South Wales coasts (Patil et al. 2004). In New Zealand it is found
from soft sediments to exposed habitats. This habitat flexibility means there is a higher
potential for greater ecological and environmental impacts over larger areas than introduced
species restricted to specific inshore environments (Patil et al. 2004). The dense beds of this
invasive species change the benthic structure with unknown (and unexamined) effects on
ecosystem services (Patil et al. 2004). It can cover soft sediments with its hard shell, and
once dead, its shell provides abundant homes for a particular hermit crab that can use its
heavy tapered shell, thus potentially shifting the pre-invasion food web (Bax et al. 2003).
Dense beds of this burrowing filter feeder may have adverse impacts on native filter feeders,
with native turritellids numbers declining with increasing M. roseus numbers (Patil et al.
2004). In Point Hicks MNP where this invasive species was most abundant, the diversity of
infauna was reduced, suggesting that this exotic species poses a serious threat to the high
diversity of infauna that is characteristic of much of Bass Strait (Heislers and Parry 2007).
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