Dietary responses of the brackish cladoceran Daphniopsis australis fed on different marine microalgae.
Résumé
The effect of algal species on the life history of the euryhaline cladoceran, Daphniopsis australis was investigated under laboratory conditions. Three algal species, Tetraselmis suecica (T), Nannochloropsis oculata (N) and Isochrysis tahitian (I) were used to form three mono-alga species and four multi-algae species (T×N, I x N, I xT and I×T×N) to feed D. australis. The type of algal species significantly affected the life history of D. australis at both individual and population levels. The mono-alga T. suecica enhanced animal longevity and reproductive output but hampered animal body growth. In contrast, the mono-alga N. oculata and I. tahitian resulted in the highest growth rate of D. australis while the multi-algae I × N reduced the age at first reproduction with a possible cause of high carbon contents in the N. oculata and I. tahitian diets. The mono-alga I. tahitlan led to the shortest longevity and poorest reproduction output. Egg development was the fastest when animals fed on mono-algal species but was delayed by feeding animals on multi-algal species. The animals fed on the mono-algal species T. suecica showed the highest net reproduction (Ro) and the longest generation time (GT) while those fed on the mono-algal diet I. tahitian exhibited the lowest Ro and the shortest GT. The intrinsic growth rate was the highest when the animals fed either on the mono-alga T. suecica or on the multi-algae I ×N. This study indicates that species composition of algae in the diet can affect development, growth and reproduction of D. australis and thereby influence the population dynamic of cladocerans living in heterogeneous food environments