shipworms, pillbugs and gribbles – oh my!

I've never heard of gribbles before, & did wonder if they were in some way related to tribbles (or a certain US politician's hair…). But no, it turns out that gribbles are small, wood-boring crustaceans. And they look rather cute: 

A magnified image of the gribble

Image by Prof Simon McQueen-Mason & Dr Simon Cragg 

However, their cuteness should not obscure the fact that gribbles (and their partners-in-crime, the molluscan shipworms & crustacean pillbugs) do a significant amount of damage to the wood of piers, jetties, & vessels. For this reason (Powell, 2012: 326)

Even in today's more ecologically oriented society, a motion to conserve the 'gribble' would receive little support along the world's waterfronts 

And how did I find out about gribbles? Well, a good friend & colleague is a co-author on a just-published paper on the environmental history of marine woodborers (Rayes, Beattie & Duggan, 2015). The authors begin by saying that

While depictions of mariners fighting fearsome sea monsters or battling terrifying storms entertain us to this day, it is perhaps ironic that one of the main threats to commerce over the last millennium or more has come from a series of very small organisms whose history has been submerged in historical accounts.
And they then go on to look at how these marine invertebrates have spread through the world's oceans, disrupting both travel & trade. In New Zealand they found a rich source of information on how European settlers tried to deal with the damage done by the woodborers (aka the "Termites of the Sea"), trying a range of (unsuccessful) techniques in an uncoordinated way.
The depredations of marine woodborers on these structures created headaches for governments, shipping companies and export industries alike, as authorities and companies grappled with the need to repair crumbling infrastructure and ships (ibid).
This was a continuous problem from at least the 2nd millenium BCE – when the Egyptians responded to borer attack by using much thicker ('sacrificial') wood on ocean-going ships & coating it with tar – until the advent of concrete-based infrastructure and ships of iron or steel. I found the history of human responses to the serious damage wrought by these little animals absolutely fascinating. At one point it reminded me of reading – in the 'Hornblower' books by C.S.Forester – of ships being careened in order to replace damaged hull timbers. It's worth noting, too, that some of the treatments applied to timber, while they may have reduced the depredations of gribbles & their ilk, were themselves quite harmful to the environment: think arsenic & mercury, for example.
I was surprised to discover that even in recent times, woodborers continue to do damage. For example
between 1995 and 1997, New York experienced severe woodborer damage, resulting in a 21-metre wharf section dropping into the East River and a six-metre section plunging from the Brooklyn pier (ibid).
New Zealand hasn't escaped scot-free. Shipworm fossils date back around 200 million years, and our native mangroves would have been part of their habitat. However, new niches would have opened up to them upon human arrival, dependent as we were on ships and related infrastructure. And in turn, Maori and then European movement to & around our coasts not only carried the native shipworms to new habitats but also introduced gribbles & pillbugs, now well-established here. However, for a long time after European settlement, responses to the problems posed by marine woodborers were handled in quite a parochial, disconnected manner – the authors have done a very thorough job of reviewing historical documents to pull together this aspect of New Zealand's maritime history. And they've found some fascinating little snippets: in 1889, in Timaru,
the effects of gribbles [on the Timaru wharf] were compared to 'the suckling of a sugar stick by a sweet-toothed infant' (ibid).
Incidentally, non-native woodborers can also do considerable harm to mangroves, which is of concern given the significant ecosystem roles that mangroves can play. However, Rayes & her co-authors also make the valuable point that the various woodborers – while they may be a right royal pain in the planking for mariners – also serve a valuable function in their own, original, tropical ecosystems:

Woodborers provide important ecological services within mangrove ecosystems and along coastlines by removing the build-up of dead woody debris, through increasing their rate of decomposition (ibid).
Indeed, it seems that an enzyme from this little wood-muncher may provide a useful biotechnological fix for recycling cellulose-based materials. (This is a valuable reminder that whether something is 'good' or 'bad' is often highly context-dependent; think also of the case of Helicobacter pylori.)
So why have we paid so little heed to the gribbles, shipworms, and pillbugs (oh my!)? Rayes et al. have this to say (but I really disagree on the claimed lack of cuteness of gribbles!)
There is nothing remotely heroic about fighting a minute-sized shipworm when one could be grappling with a terrifying octopus … [Marine woodborers] can offer neither the mystery nor appeal of a whale, still less the terror of a Great White Shark, or the cuteness of a dolphin. They have all the appeal of a snail or a slug, and probably induce the same inclinations …
Yet the fact that gribbles don't sell books or invite the same warm feeling or terror as larger creatures of the sea should not stop us from attempting to rescue them from the enormous condescension of posterity [that ignores their significant role in maritime history].

Powell, C.E. Jnr (2012) Isopods other than Cyathura. pp325 – 343 in Hart, C.W.Jnr (Ed) Pollution Ecology of Estuarine Invertebrates. pub Elsevier.

Rayes, C.A, Beattie, J., & Duggan, I.C. (2015) Boring through history: an environmental history of the extent, impact and management of marine woodborers in a global and local context, 500 BCE to 1930s CE. Environment and History 21(4): 477 – 512. doi: 10.3197/096734015X14414683716163


One thought on “shipworms, pillbugs and gribbles – oh my!”

  • Paul Riddler says:

    Hello, very interesting article on marine borers; Grubb less, I have been lucky enough to purchase an amazing piece of gem grade Kauri Gum; the piece is quite translucent, before I cleaned the crust off; I noticed multiple holes, after carefully sanding and polishing; this amazing piece of translucent Kauri gum I was amazed to see a veritable network of tunnels inside the copal, I believe these tunnels were bored by Gribbles or Ship worms, there are multiple exist and entry holes, I believe this stunning piece of very translucent Kauri copal has spent many years on New Zealand’s coast line; in tidal rock pool; or drifting the tides and currents after being washed down a river somewhere in the far North Island.

    I can send photos; before and after sanding and polishing this amazing piece of Kauri gum that provides a detailed window into the structure of the Grubb less secret tunnels.

    Paul Riddler.

Leave a Reply

Your email address will not be published. Required fields are marked *