Abstract
Large herbivores such as sea urchins and fish consume a high proportion of benthic primary production and frequently control the biomass of marine macrophytes. By contrast, small mesograzers, including gastropods and peracarid crustaceans, are abundant on seaweeds but have low per capita feeding rates and their impacts on marine macrophytes are difficult to predict. To quantify how mesograzers can affect macrophytes, we examined feeding damage by the herbivorous amphipods Sunamphitoe lessoniophila and Bircenna sp., which construct burrows in the stipes of subtidal individuals of the kelp Lessonia berteroana in northern-central Chile, southeast Pacific. Infested stipes showed a characteristic sequence of progressive tissue degeneration. The composition of the amphipod assemblages inside the burrows varied between the different stages of infestation of the burrows. Aggregations of grazers within burrows and microhabitat preference of the amphipods result in localized feeding, leading to stipe breakage and loss of substantial algal biomass. The estimated loss of biomass of single stipes varied between 1 and 77%. For the local kelp population, the amphipods caused an estimated loss of biomass of 24–44%. Consequently, small herbivores can cause considerable damage to large kelp species if their feeding activity is concentrated on structurally valuable algal tissue.
Highlights
A significant proportion of primary production by marine macrophytes is consumed by herbivores [1,2]
To quantify how burrowing mesograzers can affect a large kelp, we studied herbivorous amphipods on subtidal individuals of the kelp Lessonia berteroana in a kelp forest in northern-central Chile
The same sigmoid regression model was used to visualize the observed biomass of stipes, the loss of biomass due to stipe breakage induced by amphipod domiciles and the loss of biomass due to all stipe breakages for stipes of different size, with a being the minimum biomass of the smallest stipe, which was set equal to zero. b is the maximum biomass of the largest stipe, c denotes the halfway biomass between a and b, and d is the slope of the curve
Summary
Large herbivores such as sea urchins and fish consume a high proportion of benthic primary production and frequently control the biomass of marine macrophytes. To quantify how mesograzers can affect macrophytes, we examined feeding damage by the herbivorous amphipods Sunamphitoe lessoniophila and Bircenna sp., which construct burrows in the stipes of subtidal individuals of the kelp Lessonia berteroana in northern-central Chile, southeast Pacific. Aggregations of grazers within burrows and microhabitat preference of the amphipods result in localized feeding, leading to stipe breakage and loss of substantial algal biomass. For the local kelp population, the amphipods caused an estimated loss of biomass of 24–44%. Small herbivores can cause considerable damage to large kelp species if their feeding activity is concentrated on structurally valuable algal tissue
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