The next few, or many, posts are going to be about cladoceran reproduction. An obvious question is why spend so much time writing about the sex life of this tiny crustacean? What does cladoceran sex have to do with vernal pools? I think it tells us quite a bit actually and speaks yet again to the uniqueness of these habitats and their worthiness as more than just homes and mating sites of amphibians. Let me explain.
Cladocerans are found in virtually every aquatic habitat across the globe. There are marine species but they are relatively rare; among crustaceans the oceans are dominated by copepods and things such as krill. The ocean is filled with all sorts of non-crustacean zooplankton as well so the overall effect is limit cladoceran diversity and biomass. The cladocerans in lakes have greater diversity and relative biomass than those oceans. Lakes are shared with copepods that are often competitive dominants as well as predators of cladocerans. The fish of lakes are often planktivorous putting further stress on zooplankton. The result is that cladocerans of lakes are usually small species often outnumbered by copepods and even smaller rotifers.
Ah, but in vernal ponds, and in temporary waters of all types by any name, cladocerans are in their glory. The diversity is great among genera and among the fine scale habitats that I have written about previously. Why are they so successful in temporary waters? I would like to suggest it is the close match between the short-lived cyclic nature of the habitat and the reproductive mode of cladocerans. The habitats are short lived but unless they are around for less than a few weeks there is plenty of time for cladocerans to do all their business and be ready for the next dry period. Not that there aren’t other crustaceans that manage as well, but it is the cladocerans that have been most successful at exploiting the brief season of vernal ponds.
So I write about the peculiarities of cladoceran egg production and cell division (and eventually the production of males and resting eggs) because this is ultimately what allows them to not only survive, but also thrive. No other habitat of which I am aware is so thoroughly dominated by animals that reproduce clonally. Understanding cladoceran reproduction is one way to marvel at how special vernal ponds are. This underscores the need to study all the organisms that live in such habitats and to appreciate such a unique habitat whose attributes promote clonally reproduction.
