Figure 1. Tunicates live in complex environments! Here, a solitary tunicate, Styela plicata (identified by its white siphons), lives surrounded by a colonial tunicate species, Botryllus schlosseri (comprising hundreds of individual orange zooids) (photo by Jenny Norman, Macquarie Uni. Microscopy Unit).

I usually start research seminars with a photo of Balmoral Beach on Sydney's Middle Harbour. Its an incredibly beautiful place, and I show the slide to convince people that tunicates, the marine invertebrates that I study, live in wonderful places. Sydney's most common tunicate, cunjivoy (Pyura stolonifera....or "cunji" to the locals), is an icon. There are even poems about the stoic cunji! I can imagine a lone fisherman (probably in a terry toweling hat), solemnly reciting 'the ode to cunji'.....as he slices up another one for bait.

Idyllic stuff huh? Well, 2 comments. First, cunji, like all other marine invertebrates in New South Wales, are now protected (yes, we've got a permit to do our research!). Second, a cunji's life is not all that idyllic, even without the murderous fishermen. This morning, after 3 days of rain, Balmoral more resembled the Great Green Greasy Limpopo than the Great Barrier Reef. Tunicates, like all marine animals, live in a soup. Worse, cunji and their relatives are filter feeders, so they don't just live in it, they eat it. It makes sense that animals like cunji could be perfect sentinels to detect environmental pollution. After all, tunicates filter large amounts of seawater, and all its associated gunk, over extremely delicate internal membranes in order to extract food.

Figure 2. This light micrograph shows blood cells accumulating in the pharynx of a tunicate that has been living in water contaminated with toxic metals (tributyltin). We believe that those cells are transporting metals to the pharynx for expulsion (photo by Jane Radford).

Figure 3. This electron micrograph shows sub-cellular vesicles within epithelial cells of the pharynx which appear to be packed full of concentrated metals that are about to be expelled from the tunicate (photo by Jane Radford).

Our research group has already shown that common environmental pollutants can have profound affects on tunicates. However recent work by Jane Radford in our lab indicates that tunicates also have the capacity to fight back. Jane's work suggests that tunicate blood cells can concentrate and eliminate toxic metals that have penetrated from the environment. We believe the process goes something like this.....(although we still need to observe some critical components of this putative pathway to be sure). Certain blood cells concentrate and package metals into discrete sub-cellular compartments. Those cells then migrate to the outer membranes of the tunicate, that are in direct contact with the surrounding environment. There, the blood cells pass the packaged metals to the outermost layer of epithelial cells, which in turn, expel the metals back into the environment. This system indicates that tunicates have complex and adaptive mechanisms to sequester and expel foreign compounds. Perhaps that's not unexpected for an animal that lives in such a turbid environment. It might also be convenient. If we can identify the cellular mechanisms responsible for this process, we might be able to use tests of cellular activity as an early warning of pollution.

Staff working on this research:

The tunicate research group at Macquarie includes: David Raftos, Rebecca Newton, Jane Radford, Sham Nair, Peter Green, Dipal Patel (currently in the U.S.), Sarina Pearse and Gavin Hendersen. Aimee Hutchinson and Monika Burandt have also contributed to this work. Our studies have been funded in part by the Australian Research Council and the Macquarie University Research Grants scheme.

Interested in reading more?

Raftos, D.A. & Hutchinson, A. (1997). Effects of common estuarine pollutants on the immune reactions of tunicates. Biol. Bull. 192: 62-72.
Radford, J. & Raftos, D.A. (1998) A hemocyte classification scheme for the tunicate Styela plicata (Lesueur, 1823). Acta Zoologica. In Press.
Radford, J., Hutchinson, A. & Raftos, D.A. (1998) Effects of common estuarine pollutants on the hemocytes of Styela plicata. J. Invert. Pathol. Submitted.
Radford, J. & Raftos, D.A. Effects of environmental pollutants on tunicate hemocytes. 7th Congress of the International Society of Developmental and Comparative Immunology, Williamsburg, Virginia, 1997. Dev. Comp. Immunol. 21: 125.