Effects of elevated pH on marine copepods in mass cultivation systems: practical implications

Female tolerance to pH (8.0-9.5) by six marine copepods, Oithona similis, Temora longicornis, Acartia spp., Centropages typicus, Pseudocalanus elongatus and Eurytemora affinis was investigated to identify robust species for live feed production. The species with the most oceanic-neritic distribution, O. similis, exhibited 72 h LC50 at pH 8.39 +/- 0.11 (+/-95% CL) whereas the most estuarine E. affinis had LC50 at pH 9.51 +/- 0.04. The rest had LC50 at intermediary pH's. Egg hatching by a selection of species, Acartia spp., C. typicus and E. affinis, was unaffected by pH up to 9.0-9.5. Nauplii from both Acartia spp. and C. typicus had higher mortality at pH 9.5 than at the other pH regimes while E. affinis nauplii were not affected by pH. Wild Acartia spp. and A. tonsa from a culture showed some differences in response although of minor practical importance for aquaculture; both produced no eggs at pH 9.5, A. tonsa exhibited significantly higher egg production at all other pH's than 9.5, both showed egg hatching invariant of pH, but gradually increasing nauplii mortality with pH. We suggest active/passive selection to obtain the most pH robust species able to cope with accidently, but frequently, elevated pH in aquaculture systems.