Effects of shade from multiple kelp canopies on an understory algal assemblage

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Clark, R. P., Edwards, M. S., & Foster, M. S. (2004). Effects of shade from multiple kelp canopies on an understory algal assemblage. Marine Ecology Progress Series, 267, 107-119.
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TitleEffects of shade from multiple kelp canopies on an understory algal assemblage
AuthorsR. Clark, M. Edwards, M. Foster
AbstractWe examined the effects of shade from multiple kelp canopy layers (surface Macrocystis pyrifera canopy, understory Pterygophora californica canopy), both individually and in combination, on an understory algal assemblage in a central Californian kelp forest. The removal of both kelp canopies resulted in a dense recruitment of the understory brown alga Desmarestia ligulata that formed a third canopy layer, which significantly decreased bottom light and the abundance of understory red algae. We subsequently created an additional canopy treatment by removing this third canopy layer. In general, the understory red algae fluctuated seasonally with winter swell intensity, changes in kelp canopy cover, and grazing; and although species richness increased significantly with increased bottom light, red algal bottom cover did not respond significantly to the canopy clearings until 2 yr after the canopies were initially cleared. Red algal cover within the Pterygophora canopy treatment was similar to that in the control treatment. In the absence of Pterygophora, the Macrocystis canopy treatment and 'no canopy' treatment were found to have greater red algal cover and species richness. Individual understory species were rare, which resulted in small effects sizes and thus low statistical power. However, when grouped post hoc, according to how they responded to the canopy clearings (i.e. response groups), we were able to detect canopy treatment effects as much as 1 yr earlier. This method identified that some understory red algae adapted to areas of canopy removal (light-adapted), and others adapted to a variety of light regimes (shade-tolerant). We were able to classify the light-adapted algae into 2 subgroups: the high-light species and the intermediate-light species. Although this method of grouping was done post hoc, our results indicate that it may provide the clearest assessment of how understory algae respond to shading from kelp canopies.
JournalMarine Ecology Progress Series
Date2004
Volume267
Start page107
End page119
ISSN0171-8630
Subjectscommunity structure, kelp forest, red alga, shade tolerance, understory, California Margin, Pacific Ocean, algae, Desmarestia, Desmarestia ligulata, Eukaryota, Macrocystis, Macrocystis pyrifera, Phaeophyceae, Pterygophora, Pterygophora californica, Rhodophyta
NoteCited By (since 1996):40, Seaweeds, CODEN: MESED

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