Micro- and mesozooplankton
response to enhanced nutrient input – a
mesocosm study
I. Gismervik, Y. Olsen, O. Vadstein-2002
Hydrobiologia, 484(1-3): 75-87
Abstract:
An 18-day mesocosm study was performed in central
Norway to assess the effect of enhanced nutrient input to the marine
plankton community. This paper reports the responses of micro- and
mesozooplankton to increased food supply due to elevated nutrient input.
Seven mesocosms (M1–M7) were added variable
doses of N, ranging from 0 to 2.19 μm N
l-1 d-1. Phosphorus and silicate was added in Redfield
ratios. The ciliate community responded rapidly to the treatment, and
reached maximum biomass of 88 μg C l-1
within a week in the most fertilised mesocosm (M7). Tontonia sp.
and a small Strombidium sp. dominated biomass and numbers,
respectively. Ciliate biomass declined rapidly after the peak, returning to
initial values by the end of the experiment (Day 18). Mesozooplankton
biomass increased from the second week, due to recruitment of Acartia
spp., Centropages spp. and Oithona sp. Numbers of Temora
longicornis and Pseudocalanus sp. remained low. Highest
biomass of mesozooplankton (116 μg C l-1)
was recorded in M6 by Day 18. Egg production rates for Acartia spp.
peaked in M3 at Day 11, while calculated mortality rates for juvenile
copepods was highest in M1 and M7. Estimated community net growth rates were
highest in the most fertilised mesocosms for both copepods and ciliates. It
is concluded that enhanced nutrient input affected both biomass and the
relative species composition of the zooplankton community.
(Section of Marine Zoology and
Chemistry, University of Oslo, P.O. Box 1064, Blindern, N-0316 Oslo, Norway)