Major consequences of minor damage: impacts of small grazers on fast-growing kelps

Abstract

Damage by small herbivores can have disproportionately large effects on the fitness of individual plants if damage is concentrated on valuable tissues or on select individuals within a population. In marine systems, the impact of tissue loss on the growth rates of habitat-forming algae is poorly understood. We quantified the grazing damage by an isopod Amphoroidea typa on two species of large kelps, Lessonia spicata and Macrocystis pyrifera, in temperate Chile to test whether non-lethal grazing damage could reduce kelp growth rates and photosynthetic efficiency. For L. spicata, grazing damage was widespread in the field, unevenly distributed on several spatial scales (among individuals and among tissue types) and negatively correlated with blade growth rates. In field experiments, feeding by A. typa reduced the concentration of photosynthetic pigments and led to large reductions (~80%) in blade growth rates despite limited loss of kelp biomass (0.5% per day). For M. pyrifera, rates of damage in the field were lower and high densities of grazers were unable to reduce growth rates in field experiments. These results demonstrate that even low per capita grazing rates can result in large reductions in the growth of a kelp, due the spatial clustering of herbivores in the field and the selective removal of photosynthetically active tissues. The impacts of small herbivores on plant performance are thus not easily predicted from consumption rates or abundance in the field, and vary with plant species due to variation in their ability to compensate for damage.

Some Implications of High Biodiversity for Management of Tropical Marine Ecosystems—An Australian Perspective

“…These have provided reasonable coverage of the intertidal and shallow subtidal diversity of coral reef, seagrass, and mangrove habitats and of benthic species of fish, molluscs, crustaceans, and larger echinoderms of current or potential commercial interest. A similar pattern of knowledge is found for other groups with reasonable knowledge of intertidal and shallow biodiversity declining rapidly as one moves offshore [20,21]. We suggest that even in the relatively well-known groups of fish, molluscs, crustaceans, and larger echinoderms, biodiversity has been seriously underestimated and certainly the numbers of undescribed species increases with depth and distance from the coast.…”

Effect of grazing on distribution and recovery of harvested stands of Lessonia berteroana kelp in northern Chile

“…mollusks and echinoderms) increased the abundance of early stages of kelp Macrocystis pyrifera in comparison to treatments with low densities and/or total exclusion of herbivores (Henríquez et al 2011). Two reasons could explain this pattern: (1) the strong consequences of grazer abundance and identity on the intertidal landscape (see Poore et al 2012Poore et al , 2014 and (2) some biogenic habitats (e.g. calcareous algae, empty limpet shells) can provide protection from severe grazing for sporelings of macroalgae (see Camus 1994, Henríquez et al 2011.…”

“…Depending on the availability of food, foraging strategies, identity and abundance of grazers, and exploitation intensity, primary producer stands can change their spatial and temporal patterns of distribution (Adler et al 2001, Duffy 2002, Steneck et al 2013, Poore et al 2014. Herbivory influences both intra-and interspecific relationships in local communities and modifies the landscape structure (Duffy 2002, Poore et al 2012.…”

An experimental assessment of herbivory and nutrient effects on a small-scale in a coral reef macroalgal community

“…In seagrass communities, Ebrahim et al (2014) found exclusion of mesograzers resulted in a 233% increase in epiphyte biomass, which many associate with declines in seagrass abundance (Orth and Van Montfrans, 1984). In kelp forest communities, mesograzers can also strongly affect aquatic plants; Poore et al (2014) found that while non-lethal, small isopod grazers can reduce kelp blade growth by 80%. Given the importance of mesograzers in other ecosystems, it is important to revisit their role in regulating coral reef macroalgal communities, particularly under reduced herbivore abundance and increased nutrient conditions.…”