Other formats

    Adobe Portable Document Format file (facsimile images)   TEI XML file   ePub eBook file  


    mail icontwitter iconBlogspot iconrss icon

The Settling and Growth of Wharf-pile Fauna in Port Nicholson, Wellington, New Zealand

Marine Borers

Marine Borers

As far as can be ascertained, the only published work on marine borers in New Zealand waters is a paper by Chilton in 1919. This is a general survey dealing with the systematics and habits of crustacean borers and the damage to wharves in Auckland, Lyttelton, Napier, and Wairoa. So far, in Port Nicholson waters, we have noted four species of borer. Two of them, a nereid, Nereis kerguelensis, and page 15 the Amphipod Chelura terebrans, seem to cause little damage. The burrows of Chelura terebrans are, however, very similar to those of Limnoria quadripunctata Holthius. It is possible that we have underestimated its damage, and that a greater amount of surface crumbling on some of the test blocks is caused by Chelura than is immediately apparent.

The third species of borer is the Isopod, commonly called the "gribble." At the request of Mr. Robert Menzies, of the Pacific Marine Station, California, specimens were sent to him. They were identified by him as Limnoria quadripunctata, a species described as new by Holthius in 1949, from Holland, and subsequently reported from Cape Town, Plymouth, and the Central Californian Coast. It had been assumed up to the time of Mr. Menzies' communication that the species present in Port Nicholson was Limnoria lignorum Rathke, as this species has been recorded from Auckland, Lyttelton, and Akaroa. Doubt has now arisen as to the correctness of Chilton's diagnosis of specimens from these three latter harbours. Since it is difficult to separate exactly the burrows of Chelura terebrans and Limnoria quadripunctata, we have referred in general terms to the damage done by these species as "Limnoria damage." Limnoria is undoubtedly responsible for the greatest visible destruction of the test blocks. The fourth species of borer found in the test blocks is the mollusc Bankia australis, commonly called the "ship worm," or "teredo."

Limnoria attacks the surface of the wood. As this becomes riddled with burrows, the surface disintegrates, and an accurate estimate of the attack can readily be made from month to month. Bankia, on the other hand, burrows below the surface, the burrows at first running with the grain, but later, as infestation becomes heavier, the burrows twist and turn in all directions. The only indication of "ship worm" in the wood is the presence of numerous small round respiratory holes on the surface. Although a count of these holes gives a fairly true measure of the numbers present, it gives no indication of the overall damage done to the interior of the wood. To obtain a more accurate picture of this damage and to obtain growth measurements, X-ray photographs were taken of the test blocks.