SBC LTER: REEF: Net primary production, growth and standing crop of Macrocystis pyrifera in Southern California

The giant kelp Macrocystis pyrifera forms
subtidal forests on shallow reefs in temperate regions of the
world. It is one of the fastest-growing multicellular autotrophs
on Earth and its high productivity supports diverse marine food
webs. In 2008, we published a method for estimating biomass and
net primary production (NPP) of giant kelp along with five years
of data, to provide a more integrated measure of NPP than those
yielded by previous methods. Our method combines monthly field
measurements of standing crop and loss rates with a model of kelp
biomass dynamics to estimate instantaneous mass-specific growth
rates and NPP for each season of each year. We have since improved
our approach to account for several previously unresolved sources
of biomass loss. These improvements have led to a near doubling of
our prior estimates of growth and NPP. At our site with the most
persistent stand of giant kelp, NPP averages ~5.2 kg dry mass
m-2 y-1 and
results from the rapid growth (~3.5% per day) of a relatively
small standing biomass (~ 0.4 kg dry mass
m-2 on average) that turns over ~ 12
times annually. Here we provide revised estimates of seasonal
biomass, growth and NPP for the five years covered by our previous
publication (2002-2006), along with an additional data collect
since then (2007-present). We also present updated relationships
for predicting giant kelp biomass and NPP from much more easily
obtained measurements of frond density. These data can be used to
understand the mechanisms that drive variation in giant kelp NPP
at a wide range of temporal scales.