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AB 4:113-125 (2008)  -  DOI:

Depletion of plankton in a raft culture of Mytilus galloprovincialis in Ría de Vigo, NW Spain. I. Phytoplankton

Jens Kjerulf Petersen1,*, Torkel Gissel Nielsen1, Luca van Duren2,3, Marie Maar1

1National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, PO Box 358, 4000 Roskilde, Denmark
2Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands
3Present address: DELTARES, Rotterdamseweg 185, PO Box 177, 2600 MH Delft, The Netherlands

ABSTRACT: Food depletion in mussel cultivation has been rarely studied and seldom demonstrated. In this study, concentrations of phytoplankton in and around a blue mussel Mytilus galloprovincialis raft culture unit in the Ría de Vigo were measured during a 2 wk study period in July 2004. Flow direction and current speed were measured using an Aanderaa current meter and fine-scale Acoustic Doppler Velcimeter probes at different positions in the raft. Flow speeds were reduced compared to outside the raft, but a clear tidal signal and significant flow velocities could still be observed inside the raft. At the upstream corners of the raft, a zone of high turbulence but reduced advection was observed. Concentrations of chlorophyll a (chl a) were measured on 3 different spatial scales. On a macro-scale, fluorescence profiles were taken inside and outside the raft on several occasions and there was depletion of chlorophyll inside the raft corresponding to ~80% of the outside concentration, whereas there was no depletion below the ropes. On a meso-scale, from just upstream to just downstream of the raft, fluorescence profiles, as well as water samples, at several depths revealed similar depletion, however, with larger depletion of size-fractionated chl a >2 µm. On a micro-scale, water was sampled within 20 cm of the ropes using siphon mimics. In the middle of the raft, concentration profiles towards the mussel ropes could be observed at 2 depths, whereas less clear profiles were observed on the turbulent upstream corner. The present study documents food depletion in a mussel culture and emphasizes the importance of physical forcing and phytoplankton composition for food availability.

KEY WORDS: Depletion · Mussels · Phytoplankton · Raft culture · Scales · Hydrodynamics

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Cite this article as: Petersen JK, Nielsen TG, van Duren L, Maar M (2008) Depletion of plankton in a raft culture of Mytilus galloprovincialis in Ría de Vigo, NW Spain. I. Phytoplankton. Aquat Biol 4:113-125.

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