Description
Coastal marine systems host diverse communities of small invertebrate herbivores that link energy resources from primary producers to multiple trophic levels. Diverse assemblages of these invertebrates inhabit low-lying red algae (phylum Rhodophyta) on many temperate reefs and provide an important source of secondary production. Yet, despite the prevalence of red algae and the food resources that they provide, these habitats have been poorly studied. I conducted a series of field experiments to examine how algal identity and predation by microcarnivorous fishes influence the distribution of invertebrate prey in two species of common and structurally dissimilar red algae (Rhodymenia spp. and Plocamium pacificum) in San Diego, California. Invertebrate biomass was most strongly influenced by algal species, and predators decreased invertebrate biomass in the less structurally complex Rhodymenia but did not influence invertebrate biomass in the more structurally complex Plocamium, To investigate whether these differences were due to algal structural complexity or other algal characteristics, I conducted an additional field experiment to examine the response of invertebrate assemblages to structural complexity per se through increasing the amount of interstitial spaces between fronds of the focal alga, Rhodymenia spp. Invertebrate assemblages did not differ between altered and unaltered Rhodymenia treatments, suggesting that invertebrate-habitat associations may be driven by other algal characteristics. However, I observed in video recordings conducted in situ that fish predators foraged more in the structurally complex algae treatments, indicating that foraging patterns by transient fish predators may be influenced by benthic algal structural complexity. My research suggests that secondary production in red algae beds is driven by algal identity and that the diversity of red algae may play an important role on invertebrate prey assemblages and habitat utilization by microcarnivorous fishes.
