Elemental and biochemical nutrient limitation of zooplankton: A meta-analysis

Primary consumers in aquatic ecosystems are frequently limited by the
quality of their food, often expressed as phytoplankton elemental and
biochemical composition. However, effects of these food quality indicators
vary across studies, and we lack an integrated understanding of how
elemental (e.g., nitrogen, phosphorus) and biochemical (e.g., fatty acid,
sterol) limitations interactively influence aquatic food webs. Here we
present results of a meta-analysis using >100 experimental studies,
confirming that limitation by N, P, fatty acids, and sterols all have
significant negative effects on zooplankton performance. However, effects
varied by grazer response (growth versus reproduction), specific
manipulation, and across taxa. While P limitation had greater effects on
zooplankton growth than fatty acids overall, P and fatty acid limitation
had equal effects on reproduction. Furthermore, we show that: nutrient
co-limitation in zooplankton is strong; effects of essential fatty acid
limitation depend on P availability; indirect effects induced by P
limitation exceed direct effects of mineral P limitation; and effects of
nutrient amendments using laboratory phytoplankton isolates exceed those
using natural field communities. Our meta-analysis reconciles contrasting
views about the role of various food quality indicators, and their
interactions, for zooplankton performance, and provides a mechanistic
understanding of trophic transfer in aquatic environments.