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 decade of data (2007-2017). 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.