Data from: Coastal darkening substantially limits the contribution of kelp to coastal carbon cycles

Macroalgal-dominated habitats are rapidly gaining recognition as important
contributors to marine carbon cycles and sequestration. Despite this
recognition, relatively little is known about the production and fate of
carbon originating from these highly productive ecosystems, or how
anthropogenic and climate related stressors affect the role of macroalgae
in marine carbon cycles. Here, we examine the impact of increasing
turbidity on carbon storage, fixation and loss in southern hemisphere kelp
forests. We quantified net primary production (NPP) and biomass
accumulation (BA), and estimated carbon release via detritus and dissolved
organic carbon (DOC) across a large-scale turbidity gradient. We show that
increased turbidity, resulting in a 63 % reduction in light, can result in
a 95 % reduction in kelp productivity. When averaged annually, estimates
of NPP and BA per plant at high light sites were nearly 6 and 2 times
greater than those at low light sites, respectively. Furthermore, the
quantity of carbon fixed annually by kelp forests was up to 4.7 times
greater than that stored as average annual standing stock. At low light
sites, the majority of C goes directly into tissue growth and is
subsequently eroded. In contrast, excess production at high light sites
accounts for up to 39 % of the total carbon fixed and is likely released
as DOC. Turbidity is expected to increase in response to climate change
and our results suggest this will have significant impacts on the capacity
of kelp forests to contribute to carbon sequestration pathways. In
addition to demonstrating that turbidity significantly reduces the
quantity of carbon fixed by kelp forests, and subsequently released as
detritus, our results highlight the negative impacts of turbidity on a
large source of previously unaccounted for carbon.