First evidence of some dinoflagellates reducing male copepod fertilizationcapacity

Evidence is presented that hatching failure in Temora stylifera eggs can de pend on poor sperm quality. Three dinoflagellate diets, Prorocentrum micans , Gymnodinium sanguinium, and Gonyaulax polyedra, significantly modified sp ermatophore production and reduced the fertilization capacity of male sperm after 6-12 d of continuous feeding. Two other diets, the dinoflagellate P. minimum and the prymnesiophycean Isochrysis galbana, had no effect on hatc hing success, which remained high (>89%) and stable with time. A reduction in fertilization capacity was neither due to maternal effects nor to male a ge since hatching success returned to normal upon the introduction of fresh ly caught wild males or males conditioned with a good diet such as P. minim um for the same length of time as couples fed with the poor diets, P. mican s, G. sanguinium, and G. polyedra. Confocal microscope images of unhatched eggs colored with a nucleus-specific fluorescent dye confirmed that these e ggs had not been fertilized. Experiments with Calanus helgolandicus females , which did not require reinsemination and which were fed the same diets th at induced hatching failure in T. stylifera, showed no change in hatching s uccess with time.