In New Zealand marine ecology there is a long history of introduced species. For example, anyone who's spent time in either the Waitemata and Manukau Harbour's will have seen the banks of the Pacific oyster – Crassostrea gigas. Especially anyone who's had the misfortune to fall on them; these oyster shell banks did not exist before the 1960's. Marine invaders can be difficult to spot until they are established and their potential effects can be challenging to ascertain.
In 2009, Burchard’s whelk (Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849)) appeared in a survey of marine life in Auckland’s Waitemata Harbour (this survey is part of an ongoing monitoring programme) (Townsend et al. 2010). Burchard’s whelk is a small snail (~12 mm long) and is originally from southern and western Australia, where it is quite common. The habitat of this whelk tends to be sheltered, muddy areas (Figure 1).
Figure 1. Intertidal mud-flats at Point Chevalier, Waitemata Harbour, Auckland, New Zealand; habitat for Burchard’s whelk (Nassarius (Plicarcularia) burchardi).
Burchard’s whelk is most likely to have turned up from Australia as a result of ballast-water discharge. Nassariids are known to have a planktonic larval stage, so it seems plausible that larvae lived long enough to be transported across the Tasman Sea in the ballast water of a vessel, but not long enough to drift across through natural vectors. Otherwise, they’d be here already and would probably have been recorded before 2009. Although diminished in recent years, there has been a rich history of shell collectors in NZ and it is very unlikely that this whelk would have escaped their notice.
I first searched for this species in December 2010 and found it at Point Chevalier (mid-way up the Waitemata Harbour, Figure 1). In June 2015 I revisited the same location (Figure 3) and this whelk was still common, so it doesn’t seem to be going away. If anything, it's range has expanded as Burchard’s whelk has recently been found in the northern port of Whangarei (NZMollusca n.d.).
Figure 2. Burchard’s whelk, Point Chevalier, Waitemata Harbour, Auckland, New Zealand, 4/12/10.
Figure 3. Burchard’s whelk, Point Chevalier, Waitemata Harbour, Auckland, New Zealand, 14/06/15.
Ecological implications...
There are some closely related New Zealand whelks that are in the same family as Burchard's whelk (Nassariidae), but these are mostly found offshore or in much sandier conditions (and one in the deep-sea) (Powell, 1979). None of the NZ nassariids are particularly common and very little is known about their ecology. Other closely related species overseas are considered to be scavengers, so assuming that this invader is also a scavenger would be a good place to start.
Burchard’s whelk appears to share a common ecological niche with at least one other NZ whelk species (mud whelk (Cominella (Josepha) glandiformis, and speckled whelk (C. adspersa), both common intertidal whelks in sheltered waters (Powell, 1979). Burchard’s whelk appears to be quite a fast mover (for a snail), so it has the potential to get to food sources before local species. This means that Burchard’s whelk has the potential to compete with these local species for food and possibly other resources. At some stage Burchard’s whelk may replace the local whelk species in areas where they both occur. In addition, these local species may perform other ecosystem services that the newcomer does not. Predators may not recognise the newcomer, as they may look/smell/act differently to the local species and 'fly under their radar'. As such the invasion of this new species may upset the balance/functioning of the intertidal ecosystem.
However, there are many things that are as yet unknown…
• We don’t whether Burchard’s whelk is increasing in population, nor do we know it size or range.
• We don’t what it eats, although it is likely to be a scavenger feeding on carrion.
• We don’t what, if anything, eats it.
• We don’t know how Burchard’s whelk competes with local species for resources.
A recent conversation with Michael Townsend (NIWA), who authored the paper describing the first record of this species in NZ (see reference below) revealed that Burchard's whelk does indeed reach food before the local species. He is is currently researching the ecological effects of this invader, so it will be interesting to see what he finds out…
References
Powell 1979. New Zealand Mollusca. Collins.
Spurgeon A, n.d. New Zealand Mollusca. Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849). http://www.mollusca.co.nz/speciesdetail.php?speciesid=2798&species=Nassarius%20(Plicarcularia)%20burchardi Accessed 5/08/15.
Townsend M, Marshall BA, Greenfield BL, 2010. First records of the Australian dog whelk, Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849) (Mollusca: Gastropoda) from New Zealand. New Zealand Journal of Marine and Freshwater Research 44: 343–348.
