Physiological responses of Acartia and Eurytemora spp. to changes in the nitrogen:phosphorus quality of their food

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This study addressed how copepods respond to varying nutrient content in their prey. Copepod physiological responses were measured along a gradient of prey nitrogen:phosphorus (N:P) ratios created by altering the P content in diatom prey grown at a constant rate. Acartia tonsa, a broadcast spawner, and Eurytemora carolleeae, a brood spawner, increased excretion of P as prey N:P declined (i.e. P increased). E. carolleeae had higher somatic tissue nutrient content, while A. tonsa had higher egg nutrient content overall and higher P in eggs as N:P decreased. E. carolleeae egg production was greatest when eating high N:P prey while A. tonsa showed the opposite. Egg viability declined at high N:P for both copepods, yet A. tonsa viability was always greater than E. carolleeae viability. Both copepods responded physiologically to food of varying quality, yet regulated their homeostasis differently. Prey nutrient content may be significant in the environmental selection of different copepods.