Marine algae vary considerably in their nutritional, chemical, and structural composition, thus providing a heterogeneous and variable food resource for marine herbivores. However, Due to seasonal fluctuation in species composition and abundance of marine algae, herbivores usually encounter the environments with little tasty, highly nutritional food. Because herbivores eat foods that are much lower in nutrients than their own tissues, they display a diversity of behavioral and physiological adaptations to cope with the low nutritional value of their foods. Selective feeding on more nutritious plants, increasing consumption of lower quality foods (compensatory feeding) have all been proposed as important behaviors allowing herbivores to obtain adequate nourishment.
Amphipods were common benthic species in macroalgal-based communities. They may regulate the macroalgal community structure by their selective feeding behavior. This study investigated the feeding of amphipod Ampithoe valida on three dominant macroalgae (Ulva lactuca, Gracilaria tenuistipitata var. liui and Rhizoclonium sp.) of Yundang Lagoon, and analyzed how the nutritional quality in terms of dry mass/wet mass (DM/FM), total organic carbon (TOC), total nitrogen (TN), C/N ratio and protein level may affect the food selectivity in the amphipod. The results showed that there was negative correlation between the feeding rates and the DM/FM, or TOC/FM of the macroalgae when macroalgae was separately offered to A. valida, indicating compensatory feeding behavior in the amphipod, that is, A. valida can use quantity to compensate quality when nutritional value of macroalgae was low. A. valida preferentially fed on U. lactuca and Rhizoclonium sp., and their feeding rates negatively correlated to the TOC concentrations or protein levels in the macroalgae. However, no relationship was found between the feeding rates and TN. These results suggest there are no predictable effects of the nutritional quality on the feeding selectivity of amphipods. However, although A. valida have strong preference to green algae, Yundang Lagoon doesn't structure a macroalgal community dominated by red algae G. tenuistipitata var. liui.