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The production of planktonic herbivorous food chains in large-scale continuous cultures Brown, Penelope Stevenson

Abstract

The production of planktonic herbivorous food chains was examined in large scale continuous cultures using a deep nutrient-rich source of seawater to promote high productivity rates. Both turbulent and non-turbulent upveiling systems were investigated in one-stage culture experiments with flushing rates ranging from 0.25/day to 0.7 5/day. The systems were analyzed in terms of the dynamics of the primary community and their suitability for the growth and survival of two bivalve molluscs, oysters (Crassostrea qigas) and scallops (Chlamys hastata hericia). The results indicated that a high flushing rate of the continuous culture system (0.75/day) was required for the growth of the scallops under natural forcing conditions. Maximum rates of 16.8% per month sere achieved at a depth of one metre, due to a reduced light intensity and temperature at this depth compared with surface conditions. In contrast, the one-stage culture system with a flushing rate of 0.25/day provided suitable environmental conditions for the growth of oysters, although an experimental comparison of two stocking densities indicated that the phytoplankton concentration limited the growth of Crassostrea qigas at densities below commercial levels. In the two-stage culture experiments, the dynamics of the of the primary communities were monitored at constant and variable flushing rates, ranging from 0.10/day to 1.00/day, in turbulent upwelling systems with natural forcing conditions. The dynamics of the primary community were predicted with reasonable accuracy using a numerical simulation model with experimentally determined parameters and values of the forcing variables. The growth of the oysters was also examined as a function of their size, their density and various primary communities as a food source, The results indicated that a primary system with a flushing rate of 1.0/day provided the most suitable environmental conditions for the production of oysters. The maximum growth rates attained during the experiment (18%/week) were greater than rates measured in an 'optimal' field location in British Columbia.

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