77 — Burchard's whelk, Tritia burchardi

Some Tritia burchardi, moving
through mud, Point Chevalier,
Auckland, 14/6/15.

Burchard's whelk (Tritia burchardi (Dunker in Philippi, 1849)) is is a small snail (~12 mm long) and another recent non-indigenous species from southern Australia. It was first seen in the Waitemata Harbour in 2009 and has quickly become established there (also Whangarei Harbour and probably other northland harbours). They like sheltered areas with soft-sandy, to quite muddy sediments.

There are some closely related New Zealand species (Family: Nassariidae), but these are mostly found offshore or in much sandier conditions (and one in the deep-sea) (Powell, 1979). Very little is known about the ecology of the other nassariids found in New Zealand waters, but other closely related species overseas are considered to be scavengers.

Tritia burchardi, moving
through mud, Point Chevalier,
Auckland, 14/6/15.

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 by themselves. Otherwise, they’d probably be here already and would have been recorded before 2009. As mentioned in previous posts, New Zealand has a rich history of shell collectors and it is very unlikely that this whelk would have escaped their notice.

It's small, so why should anyone care? Well, it has the ability to out compete local species, particularly scavenging whelks such as Cominella (Cominista) glandiformis and C. adspersa. This competition could lead to a reduction in the numbers of local species. 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 can reach food before local species: it's faster than C. glandiformis. As on land, there are unforeseen effects caused by non-indigenous marine species and we don't really know what the impact of this animal will be.

Tritia burchardi,
in mud, Point Chevalier,
Auckland, 14/6/15.

More info:

Powell AWP, 1979. New Zealand Mollusca. Collins.

Images of Burchard's whelk: http://www.mollusca.co.nz/speciesdetail.php?speciesid=2798&species=Nassarius%20(Plicarcularia)%20burchardi

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.