Zooplankton are usually transparent to avoid detection by visually oriented predators, such as fish. Occasionally,
though, vividly red or blue-coloured individuals are found, which acquire the pigments from their algal food,
phytoplankton. The adaptive advantage of body pigmentation in zooplankton is generally seen in the protection
from harmful solar radiation, especially UV light. This project seeks to assess the benefits, costs and trade-offs
different marine zooplankton may undergo in balancing both traits, pigmentation and predation risk.
In laboratory experiments, pigmented and transparent zooplankton will be submitted to predation by fish under
various conditions (e.g. different levels of light or water clarity). Thereby, visual conspicuousness will be
considered not only from body pigmentation but also from ingested algal pigments in the guts of zooplankton. In
field surveys, the vertical distribution and migration patterns of different zooplankton will be assessed. In
accordance with the solar (UV) protection hypothesis, pigmented animals are expected close to the surface during
daytime. In the opposite case - residence in deeper strata during the day - zooplankton may be avoiding visual
detection by fish, with pigmentation evidently serving other than solar protection purposes. Alternative hypotheses,
e.g., the enhancement of immunity or longevity, as reported for birds, fish and shrimps, and hitherto not tested in
zooplankton, will be examined in laboratory experiments.
Insights gained from this project on the adaptive significance of pigmentation in marine zooplankton will enhance
our understanding of this ecological issue on a general basis, and possibly reveal similarities between marine and
freshwater zooplankton of large, deep lakes, like Lake Constance.