Biology Reference
In-Depth Information
Chapter 8
Grazers on Benthic Seaweeds
Katrin Iken
8.1 Common Classification Systems of Grazers
Seaweed grazers can be classified in several ways, most commonly by their feeding
mode, their size, or their diet specificity, with continua rather than distinct groups
within each of these classifications (Table
8.1
). These classifications are not only of
practical use for researchers but also have many ecological implications.
First, grazers can be distinguished by functional feeding mode, such as grazing,
browsing, rasping, biting, tearing, etc. Grazer mouthparts can be specifically
adapted to feeding on seaweeds, and even on particular algal functional groups
with different morphological thallus characteristics (thickness, branching, calcifi-
cation; Littler and Littler
1980
). For example, gastropod grazing has been distin-
guished based on specific radula types (Steneck and Watling
1982
), herbivorous
fishes can develop specialized mouthparts such as the “beak” in parrot fish, and the
Aristotle's lantern of sea urchins is particularly suitable for grazing on tough kelps.
The functional group approach is intriguing to ecologists because it may allow
detection of generalizable and predictable patterns in ecosystem functioning rather
than focusing on small differences among individual species. This approach,
however, may also overemphasize the functional redundancy in a system by
obscuring small but ecologically important differences in food selection or assimi-
lation within a particular functional group of grazers. For example, herbivorous
coral reef fishes classified within the same functional group displayed strong
species-specific food selectivity among algal species, suggesting a low degree of
functional redundancy within this feeding group and that species-specific herbivore
effects can be missed when looking at functional groups alone (Mantyka and
Bellwood
2007
).
K. Iken (
*
)
School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks,
AK 99775, USA
e-mail:
kbiken@alaska.edu
