ABSTRACT
Abstract Copepod dormancy evolved as an adaptation to precarious and temporary aquatic habitats. Large numbers of the world’s planktonic copepods exhibit some form of diapause. Many Calanoids in the family Centropagoidea produce dormant (and diapause) eggs, whereas some Megacalanoidea diapause as copepodids in deep oceanic waters. Numerous freshwater Cyclopoids undergo dormancy as copepodites and are widely distributed in freshwater habitats. Harpacticoids diapause only as adults in both fresh and marine waters. Historically, much of the work on copepod dormancy has been descriptive, examining life cycles and population dynamics of the copepods. Experimental work on cues inducing or terminating diapause has been done since 1980. To date, the proximate cues for inducing dormancy (and specifically diapause) are unknown; however, temperature and photoperiod are the two most common environmental cues suspected to induce or terminate diapause. Most researchers favour a combination of the two as necessary. Copepod dormancy is complex and widespread among the three free-living Orders. It is identical in most ways to diapause in insects, although less attention has been given to these aquatic invertebrates.
