Differences in herbivory intensity between the seagrass Cymodocea nodosa and the green alga Caulerpa prolifera inhabiting the same habitat

- In field experiments, larger consumption on Caulerpa prolifera than the seagrass Cymodocea nodosa.
- Herbivorous fish abundance predicted the intensity of herbivory.
- Results contradicted the idea that Caulerpa spp. deter herbivorous fish.

Seagrasses are frequently found mixed with other macrophytes, e.g., green macroalgae. We aimed to assess whether the magnitude of herbivory differed between two coexisting macrophytes, the seagrass Cymodocea nodosa (Ucria) Ascherson and the green seaweed Caulerpa prolifera (ForsskÃ¥l) Lamouroux, at Gran Canaria Island (eastern Atlantic). Both in situ (field) and aquaria experimentation demonstrated a larger intensity of herbivory (between ca. 4-8 times) on C. prolifera than C. nodosa. At the scale of meadows, herbivorous fish abundance predicted the intensity of herbivory, in particular by the parrotfish Sparisoma cretense. A plant physical attribute (“force-to-fracture”) negatively correlated with a larger consumption on C. prolifera, while differences in total phenolic compounds between both macrophytes were insignificant. Importantly, herbivory marks (bites) were significantly larger (ca. two times) on C. nodosa leaves than in C. prolifera fronds, so differences in the magnitude of herbivory between C. nodosa and C. prolifera were dependent on herbivorous size.