Relationship between fish and the number of horns in ceratium hirundinella (dinophyceae): a food-web-mediated effect on algal morphology
2010
Bertolo, Andrea | Lacroix, Gerard | Lescher-Moutoué, Françoise | Hjelm, Joakim
In a freshwater mesocosm experiment, we explored the potential for direct and indirect effects of roach (Rutilus rutilus) and Eurasian perch (Perca fluviatilis), two planktivorous fishes with different feeding behaviors, on the morphology of Ceratium hirundinella (O. F. Müll.) Dujard., a large dinoflagellate. Three morphs were detected: one with two hypothecal horns, one with a third rudimentary horn, and one with three well-developed horns. We observed a strong negative relationship between the presence of fish and the proportion of three-horned cells. The two fishes had strikingly similar effects on C. hirundinella morphology, despite their different capabilities to retain particles of the size of C. hirundinella. This finding suggests that the morphological variation in C. hirundinella was not related to selection by fish. Morphological variations in C. hirundinella could not be explained by fish-mediated variations in turbidity (i.e., light climate) or by predation pressure by the fish. In contrast, the proportion of three-horned cells was directly related to the biomass of filter-feeding cladocerans. This result was unexpected since cladocerans are not considered to consume C. hirundinella and they did not depress C. hirundinella numbers in our experiment. Without excluding other possible mechanisms, we suggest that the third horn might help these dinoflagellates avoid physical contact with the filtering apparatus of the cladocerans and the consequent potential damage caused by these herbivores, which were more abundant in the absence of planktivorous fish.
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