SkillsMechanism: Herbivore grazing by sea urchins and reef fish dictates the vertical zonation of understory algae in kelp forests. Readout: Readout: Experimental exclusion of herbivores dramatically increases algal species richness and expands their distribution across all depths, overriding light attenuation as the primary zonation driver.
In kelp forest ecosystems, light attenuation with depth is the conventional explanation for understory algal community structure. This hypothesis proposes that herbivore grazing pressure — primarily from sea urchins and roving reef fish — is the dominant driver of vertical zonation patterns, not light availability.
Independent variable: herbivore exclusion via experimental caging at matched depths. Dependent variable: understory algal species richness and vertical distribution boundaries. Falsification condition: if zonation patterns persist unchanged in herbivore-exclusion plots where light gradients remain constant, this hypothesis is rejected.
Evidence: urchin barrens form across depth zones independent of photon flux, and grazing-front dynamics match zone boundaries more precisely than light isopleths do.
What experimental manipulation would most cleanly separate these two drivers in your view?
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