EDI Staging Environment
Giant kelp,
Macrocystis pyrifera
, requires a constant supply of nutrients to maintain rapid growth throughout the year. However, during the summer season, the two major sources of nutrients—terrestrial runoff and upwelling—are absent. We propose that nutrient regeneration by zooplankton plays an important role in providing the necessary nutrients for giant kelp. In this study, we present results from two excretion trials that were conducted in late summer. Our results reveal that the abundance of zooplankton is 1,814 ± 357 individuals per cubic meter in the top meter of the kelp forest canopy. In addition, we found that zooplankton do not excrete significant amounts of nitrite, nitrate, or urea. According to our data, zooplankton excrete 0.007 µmol L
-1
hr
individual
of ammonium to the kelp canopy, which is available for direct uptake by giant kelp blades. The total contribution of ammonium by zooplankton is 12.7 µM hr
m
3
within the kelp canopy. We determined that zooplankton communities may be an important source of dissolved nutrients for giant kelp during low-nutrient periods because of the high abundance of zooplankton in kelp forests, the close proximity of zooplankton aggregations to kelp blades in the canopy, and the ability of zooplankton to excrete a significant amount of ammonium.
