An investigation into the composition, biomass and oxygen budget of the fouling community on a tuna aquaculture farm

Abstract

The composition, distribution and oxygen dynamics of a net fouling community on a tuna sea cage farm were studied to determine the changes in community composition over time, and the effects of this fouling on the oxygen status of the water body in the cage. The oxygen exchange was quantified using an in‐situ aquatic photosynthesis system in May and August 1995. Bio‐fouling of the seacage was considerable, with a community consisting of a diverse collection of organisms dominated by detrital feeding animals. The community was a net consumer of oxygen despite the high productivity of algae in the system. Respiration of the entire community ranged from 155–330μmol O₂g^‐1 FWd^‐1. Production of the algal component (which predominated in the upper portion of the cage) was higher in August (335umol O₂g FWd^‐1) than in May (90μmol O₂g^‐1 FWd^‐1). In comparison to other oxygen sources and sinks in the cage system, the fouling community consumed < 3% of the available oxygen. Whereas in a stressed system this may be sufficient to reduce oxygen levels below the critical values, it is probable that the restriction to mass water exchange (resulting from fouling) is more likely to lead to oxygen stresses in the cage system.

Key words:

• sea cage
• in situ aquatic photosynthesis system
• fouling community
• tuna
• aquaculture

Notes

Corresponding author; e‐mail: [email protected]