Positive indirect effects of reef fishes on kelp performance: the importance of mesograzers (funded by National Undersea Research Program; National Science Foundation; SDSU Master's Program in Ecology)

Andy Davenport's thesis project --

The señorita, Oxyjulis californica, and the kelp surfperch, Brachyistius frenatus, are important microcarnivorous reef fishes in kelp forest communities. Previous studies suggest that these fishes may significantly reduce kelp-associated mesoherbivores and encrusting epifauna. The goal of Andy Davenport's research was to quantify invertebrate herbivore and epiphyte biomass on plots of giant kelp (Macrocystis pyrifera) in treatments of 'fish access', 'fish exclusion', and a cage control, and to in turn examine the effects of mesoherbivores and encrusting epifauna on the performance of giant kelp at Santa Catalina Island.

Experimental plots of kelp were deployed in a randomized block design, with each predator-exclusion plot enclosed by a 5-m diameter nylon mesh pen. The biomass of herbivores was determined by collecting blades within mesh bags, identifying herbivores, and converting their lengths to weight. The weight of epiphytes and percentage cover of blades was measured directly. Data on CHN ratios, growth rates of blades, and the number of fronds and apical meristems were collected as metrics of performance of giant kelp.

Experiments on both isolates of kelp habitat and on a continuous reef were similar in reducing herbivore populations on giant kelp, and in turn, also positively affecting the performance of giant kelp. A further experiment was completed in which each species of fish (señorita and kelp perch) were placed at different densities within the pens surrounding plots of kelp to examine their separate effects and how herbivore populations and kelp performance may vary with the density of these fishes. Andy also examined observationally the relationship between the density of microcarnivorous reef fishes and herbivore biomass among kelp-forested reefs over several kilometers. Taken together, these experiments and observations point to the importance of mesograzers and their fish predators in kelp forest ecosystems.

This page was last modified on August 3, 2007.

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