Biomass across space and tide: architecture of a kelp bed with implications for the abiotic environment
The complex, stratified seaweeds within kelp forests provide habitat to a multitude of organisms and can alter the physical and chemical parameters of their surrounding environment. It is unclear, however, how patterns in the architecture of these beds change as the tide ebbs and floods. We investigate biomass distribution of floating and stipitate canopies within a kelp bed during low and high slack tides to determine how biomass interacts with common environmental parameters (nutrients, light, and mass-transfer). Floating canopy biomass remained consistent despite differences in depth, likely driven by an interaction between stipe density and individual biomass. Biomass was distributed inconsistently throughout the water column, in which biomass at the surface roughly doubled at low tide relative to high. Despite an increase in kelp biomass at the surface of the water column during low tide, more light reached the benthos than at high tide, suggesting that seawater optical properties independent of algal canopy better explain light attenuation. Seawater nutrients were consistent throughout the bed. Rates of mass-transfer decreased from the exterior to the interior of the bed and also attenuated with depth. This study highlights the structural complexity of kelp beds and the localized effects on important environmental variables.
KeywordsMacrocystis Temperate reef Canopy Sub-canopy Light Nutrients Mass-transfer Water motion Tidal cycle Tidal height
We thank the staff and students of the University of Otago Marine Science Department, the Portobello Marine Laboratory, and Liina Pajusalu for aiding with fieldwork. We also thank those that provided critical reviews of this work, the constructive comments from which strengthened the final product. This work was funded by a University of Otago International Postgraduate Scholarship awarded to TAS, by postgraduate research funding awarded to TAS and MJD, and by supplemental departmental funding provided to CDH.
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