The influence
of turbidity on growth and survival of fish larvae: a numerical analysis
Ø.
Fiksen, D.L. Aksnes, M.H. Flyum, J. Giske-2002
Hydrobiologia, 484(1-3): 49-59
Abstract:
Growth and survival through the early larval phase
probably limit the production potential of many commercially important fish
stocks. Attempts to increase the production of these stocks by restocking of
juveniles have generally failed. Here, we analyse how enhanced
concentrations of phytoplankton and zooplankton affect the survival of fish
larvae during their early life stages. The analysis is developed for larvae
feeding on copepod eggs and nauplii, with fish and invertebrates as major
predators. A model of feeding and growth of fish larvae is applied to assess
the benefit of enhanced phytoplankton and zooplankton abundance. The
analysis shows that the shading effect of higher phytoplankton concentration
may reduce predation rates on fish larvae substantially. This `top-down'
effect may be more important for the cohort survivorship than the
`bottom-up' mechanism in situations when larval food is sufficiently
abundant. However, while increased algal biomass will improve recruitment at
high zooplankton concentration, it may also reduce recruitment at low
zooplankton concentrations and shallow mixing depths. Both the larvae and
their vertebrate predators are dependent on light to detect their prey, and
the longer reactive distance of the predators make them more susceptible
than the larvae to reduced light levels and increased turbidity. We discuss
the implications of reduced predation and increased zooplankton abundance on
recruitment and production of fish larvae, and point at environmental
conditions where changing algal biomass is likely to affect recruitment
success.
(Department of Fisheries and Marine
Biology, University of Bergen, P.O. Box 7800, N-5020 Bergen, Norway E-mail: oyvind.fiksen@ifm.uib.no)