72 — Asian file shell, Limaria orientalis

Limaria orientalis, from under Ngapipi
Bridge, Tamaki Drive, Auckland, 2015.

Limaria orientalis, from under Ngapipi Bridge,
Tamaki Drive, Auckland, 2015.

The asian file shell, Limaria orientalis (A. Adams & Reeve, 1850) is small bivalve species (to ~30mm) found in northern New Zealand. It has been thought that it was brought to New Zealand waters in the ballast water of ships during the early 1970's. Initially its population exploded, but these days they are less common between the tides and mostly found sub-tidally (down to ~30m). However, there is some evidence which suggests that it may have got here by itself.

Curiously, L. orientalis has a fossil history in New Zealand, dating back to the Duntroonian Oligocene (~23–33 million years ago). This fossil history suggests that L. orientalis may have become extinct and then re-established itself, so maybe it died out during periods of cold and returned during warmer interglacials. However, this doesn't explain why they seemingly appeared out of nowhere in 1972, so the ballast water explanation seems plausible.

They could have been were here all along, but somehow eluded detection, which seems unlikely given the current abundance of this species in the north of New Zealand. More so, if you consider the number of avid shell collectors in the Auckland region in the latter half of last century. I knew some of them, and if something was there to be found, they would have found it. Powell's surveys of the Waitemata Harbour in the 1930s also didn't detect any L. orientalis, which also suggests that they weren't around.

Limaria orientalis, Under Ngapipi
Bridge, Tamaki Drive,
Auckland, 2015.

Anyway, regardless of how it got here (again), Limaria orientalis has now become an important part of the benthic marine food web, being a notable dietary component of bottom-feeding fishes (snapper and gurnard) in Auckland's Waitemata Harbour.













More info:

http://www.thebookshelf.auckland.ac.nz/docs/Tane/Tane-29/6%20Changes%20to%20the%20marine%20biota%20of%20the%20Auckland.pdf

https://www.gns.cri.nz/static/Mollusca/taxa/BM494.html

http://www.tandfonline.com/doi/pdf/10.1080/03014223.1997.9517525

http://www.biosecurity.govt.nz/files/pests/salt-freshwater/2005-08-port-of-auckland.pdf