Shrimp on film
11 September 2010
Dr Zdeněk Ďuriš is interested in shrimp. As he tells me this, we are watching a tiny shrimp, less than a centimetre long, in exquisite detail as it goes about its business of cleaning a piece of coral.
"This is a Dasycaris zanzibarica. Its host, the sea whip, is a gorgonian coral. Corals have very delicate tissue and polyps which produce mucus. The mucus contains a lot of nutrients which are eaten by the symbiotic shrimps in the process of cleaning the host, and this stimulates the host to produce new portions of mucus," Dr Ďuriš explains.
Dr Ďuriš is videoing the shrimp through his microscope; the footage, he says, is an important tool in his work to describe and understand shrimp species.
Dr Ďuriš, an Associate Professor at the University of Ostrava in the Czech Republic, specialises in symbiotic shrimp of the Palaemonidae family. On the CReefs expedition to Lizard Island, he is looking for specimens of the subfamily Pontoniinae, which are usually found in marine habitats such as coral reefs.
"Some species are free-living on the reef, while others form strong relationships with host animals. This suggests a complex history of evolution from free-living forms to different kinds to hosts, host switching, and leaving hosts and living freely again on the bottom of the reefs," Dr Ďuriš explains.
Almost all species of Pontoniinae form relationships with hosts, usually larger marine invertebrates including sponges, molluscs, cnidarians (such as corals, anemones and jellyfish), molluscs (mainly bivalves), echinoderms (like sea urchins, sea stars, feather stars or sea cucumbers), as well as with sea squirts, and some are also fish cleaners.
These relationships are often considered to be commensal, that is, benefiting the shrimp but not affecting the host, or mutual, benefiting both the shrimp and the host. But, says Dr Ďuriš, sometimes the relationships are parasitic, benefiting the shrimp but causing some harm to the host.
"Most so-called symbionts may in some cases cause harm to their hosts. For example, some shrimp living on the sea anemones may, in periods of starvation, nip at the tentacles of the sea anemones," he says.
It probably doesn't happen very often, he says – but then again, research on the stomach contents of shrimps living in sponge hosts found ‘a lot' of sponge tissue.
"It would not be in the interest of the shrimp to kill its host, because in many cases the shrimp are unable to move to another host – instead the shrimp may feed on their host's body in very small quantities with the host being able to renew its tissues," he says.
To understand these relationships better, Dr Ďuriš is trying to observe and record the interaction between the shrimp and its host.
"I use underwater video of the shrimp habitats and video through the microscope of the feeding and cleaning behaviour of the shrimp," he explains.
"I can observe shrimp behaviour on the different hosts in a various habitats. In this way, I can see adaptation of colours, morphology, the way it moves on its host, and what it is doing with its mouth and other appendages," he says.
Dr Ďuriš refers to the videos when describing species. He has also provided footage for television documentaries in Poland and the Czech Republic, and may make his collection available to the scientific community in the future.