Bocas del Toro Research Station

Research Projects

Rosana M. da Rocha

Smithsonian Research Fellow
sabbatical year at Bocas Del Toro Station (2008-2009)

Tunicate distribution, reproduction and physiology

Tunicates, or sea squirts, are surprisingly diverse in Bocas del Toro. Rocha surveyed tunicates during the 1st Invertebrate Taxonomy Workshop in 2003. Her list of 58 species, including many species new to science and unique to the area, makes Bocas one of the five most diverse sites for tunicates in the Caribbean. In 2008, Rocha returned for a year’s sabbatical to collect more material and publish new species descriptions.

Her observation that some species in Bocas are widely distributed led her to new studies using tunicates as a model for biological invasions. Bocas is growing fast: more artificial structures, which often support exotic species, are being submerged. Passing ships carry tunicates and other invertebrates on their hulls.

Experimental plates deployed at five sites revealed more diversity and more colonial species near Bocas town. Ascidia sydneiensis and Styela canopus, both likely to be introduced species, were common at all sites. Species on artificial substrates close to natural mangrove habitats were not so different between sites, indicating that artificial substrates could act as stepping stones for introduced species that invade natural habitats.

Initial studies of salt tolerance of species in the Order Phlebobranchia revealed that some tunicates could control ion exchange and cellular volume in salinities as low as 15 parts per thousand indicating that these species have the potential to survive under different salinity conditions. Additional experiments will reveal behavioral and ecological differences between native and introduced species.

Pictures
1. Rocha snorkeling in mangrove habitat during plate monitoring.
2. Sandwich of experimental plates deployed at Bahia Honda for two months. Tunicates grow inside the sandwich and underneath the upper plate. Heavy sedimentation usually prohibits tunicate growth on top plate.
3. Styela canopus is a globally distributed species probably introduced to the West Atlantic by ship transport.
4. Mangrove (Rhizophora) prop roots covered by different tunicate species.



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