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.

巨藻（Macrocystis pyrifera）在全球温带区域的浅海礁体上形成潮下带森林。它是地球上生长速度最快的多细胞自养生物之一，其高生产力支撑着多样的海洋食物网。2008年，我们发布了一种估算巨藻生物量与净初级生产力（NPP）的方法，并附带了五年的实测数据，旨在构建比既往方法更具整合性的净初级生产力测算方案。该方法将现存生物量与损失率的月度野外实测数据，与巨藻生物量动态模型相结合，用以估算每年各季节的瞬时质量比生长率与NPP。后续我们对该方法进行了优化，以纳入此前未被考量的多种生物量损失来源。这些优化使得此前估算的生长率与NPP提升了近一倍。在我们观测的巨藻存续最为稳定的样地中，NPP年均值约为5.2千克干重·平方米⁻¹·年⁻¹，这一结果源于相对较低的现存生物量（平均约0.4千克干重·平方米⁻¹）实现了每日约3.5%的快速生长，且年周转次数约为12次。本数据集提供了既往研究（2002-2006年）覆盖的五年的修正后季节生物量、生长率与NPP估算结果，同时补充了2007年至今的新增实测数据。此外，我们还更新了通过更易获取的叶状体密度实测数据，来预测巨藻生物量与NPP的相关关系模型。本数据集可用于解析不同时间尺度下驱动巨藻NPP变化的内在机制。