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Pelagic tunicate grazing rates

Pelagic tunicates play a major role in food webs and ocean biogechemical cycles, yet they are the least investigated of all invertebrates.

As well as being an important prey item for many fish, turtles, albatross and even sea lions, pelagic tunicates can contribute significantly to the vertical carbon flux with clearance rates among the highest recorded in any pelagic grazer (values up to 35 l h-1) while migrating vertically between 90 and 760 m daily (Andersen & Sardou, 1994).  

Perissinotto et al. present measurements on ingestion rates, filtration rates, gut pigment content and gut pigment destruction efficiency for the tunicate Pyrosoma atlanticum. The samples, taken northwest of Kerguelen Islands during the ANTARES-4 cruise aboard the RV ‘Marion Dufresne’, were collected from the surface 200m using three different gear types.

Experiments with the freshly collected colonies show gut evacuation rates of 0.699 h-1 resulting in gut turnover time every 1.4 hours (standardized to 1 cm colony length). Individual colonies are reported to process on average 200 liters colony-1 day-1, ingesting 39.6 micrograms pigment day-1. 

The study claims to be the first study on the feeding dynamics of large pyrosomas from the Indian Ocean (see also Drits et al., 1992 for small colonies from the southeast Atlantic), and the first to estimate gut pigment destruction efficiencies of 54-100%, comparable to those of crustaceans. The data is also planned to be included into the database on vital rates of key species to ecosystem modeling (more).

Reference:
Perissinotto R,
Mayzaud P*, Nichols PD, Labat JP 2007. Grazing of Pyrosoma atlanticum (Tunicata, Thaliacea) in the South Indian Ocean. Mar Ecol Prog Ser , 330: 1–11 (pdf)
*EUR-OCEANS PIs

RELEVANT LINKS:

- Vital Rates Database – an effort to compile available data on vital rates of key species to ecosystem modeling;
- International Symposium on 'Parameterisation of Trophic Interactions in Ecosystem Modelling' - key speeches, discussions and recommendations to be published in a special issue in Progress in Oceanography in 2008. Key speeches, participants and status of the special issue available on the symposium website;



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