Hoards but not seen

Hoards but not seen – the Tanaidacea

Knowledge of a significant but seldom heard of group of crustaceans is getting a fresh boost.

In its Crustacea section Te Papa has a good collection of New Zealand tanaids (tar-nay-ids) or ‘tanaidaceans’ (tar-nay-iday-see-ans). Tanaids are little marine crustaceans, mostly 2 – 5 millimetres long fully grown (see photo), that play a far more important role in our seas than you might imagine.

Our tanaid collection is helping to throw light on New Zealand’s marine biodiversity because we now have an expert working on them.

A new tanaid species in the genus Zeuxo from the Auckland Islands. All tanaids have a pair of quite large pinchers, as this one does. Note also the eggs under the body of this female, carried in a brood-pouch formed by membranes that grow from the inner base of its legs. (© Te Papa, photographer Jean-Claude Stahl).

A new tanaid species in the genus Zeuxo from the Auckland Islands. All tanaids have a pair of quite large pinchers, as this one does. Note also the eggs under the body of this female, carried in a brood-pouch formed by membranes that grow from the inner base of its legs. (© Te Papa, photographer Jean-Claude Stahl).

Dr Graham Bird, a specialist in tanaids (order Tanaidacea), settled here seven years ago. He quickly got to work identifying tanaids in New Zealand  collections and collecting more from various coastal localities.

Graham’s work has shown that we have at least 80 species of tanaids. Many of these are yet to be named but it is also obvious that there are still numerous species to be discovered on our beaches, rocky coasts, continental shelves and deeper slopes and trenches.

Dr Graham Bird at work in his laboratory, examining tanaids under a microscope (© Graham Bird)

Dr Graham Bird at work in his laboratory, examining tanaids under a microscope (© Graham Bird)

  

Thanks to Graham, we now have a grasp of what we know and don’t know about New Zealand tanaids but previously this was not the case. 

Back in 1982, world tanaid authority Dr Jurgen Sieg of Germany visited New Zealand to sort out the species here, most of which had not been given names.

Sieg examined the Te Papa and NIWA collections in detail and labelled each preserved lot with a species name, several of them new to science. He intended to write up and publish these findings on his return to Germany. After his visit to New Zealand he did publish a paper on tanaids from the RossSea, but he died before any of the new New Zealand species he had found in our collections were published.

Unfortunately this left knowledge of much of our tanaid fauna inadequate and some of it in a mess. Sieg had taken with him the reasons for giving them the names he did. After Sieg, no one had been able to identify most of our tanaids until the arrival of Graham Bird over 20 years later.

A jar of 25 lots of Zeuxoides identified and labelled by Dr. Jürgen Sieg (© Te Papa, Richard Webber)

A jar of 25 lots of Zeuxoides identified and labelled by Dr. Jürgen Sieg (© Te Papa, Richard Webber)

But why, you might ask, are tanaids of any interest? Which would be a fair question because we normally don’t see them, at all. The thing about tanaids is, they always live in shelter and generally do not swim, at any stage in their life cycle, apart from a few highly specialised exceptions.  

Tanaids are wizards at finding homes in crevices, in sand, gravel or mud, beneath stones, among the ‘holdfasts’ of seaweeds or in the cavities of sponges, corals or sea moss. In these protective spaces many species also build galleries of interconnected tubes to live in.

None of these places are easily visible to the naked eye, yet tanaids live there in great abundance. In a handful of sand or silt from a rock pool, or scrapings from an algae-covered rock, collectors who know what they are looking for might find 100 or more individuals. Their density is greater still in the deep sea  where they are sometimes second only to worms in abundance and variety.

This indicates that tanaids have a greater ecological significance than they might be given credit for, as consumers of food particles and as food for larger animals. In fact, in places they are far more abundant than their close relatives the hoppers and slaters which are also quite small but far more visible.  

A great deal more collecting and taxonomic work will be needed to get to know our tanaid fauna very well but right now great progress is being made.

Graham Bird (right) and Rick Webber (Curator of Crustacea at Te Papa) collecting tanaids and other small invertebrates from gravel and algae in tide pools on Mana Island during the 2011 Mana Marine Bioblitz. (© Graham Bird).

Graham Bird (right) and Rick Webber (Curator of Crustacea at Te Papa) collecting tanaids and other small invertebrates from gravel and algae in tide pools on Mana Island during the 2011 Mana Marine Bioblitz. (© Graham Bird).

Te Papa also holds substantial collections of the other small crustaceans of the order Amphipoda (land, sand and marine hoppers), and order Isopoda (woodlice, beach lice, fish lice and other-like forms). 

Interest in these groups has also grown recently because of their great importance to the world’s biodiversity. Stories about them and the scientists who specialise in them will appear in due course.

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