Fish Folks,

        I am working on a manuscript about Daphnia lumholtzi which is an
incredibly spiny daphnid native to Africa, Asia and Australia which has
shown up in the US in the past 5 years or so.  With the helmet and tail
spine, it can measure over 5 mm.
        I can't help but wonder why it bothers with such elaborate
structures (and the energetic cost which has shown to be substantial for
other species)when its body size is only about .8 mm from what I have
seen--which is smaller than plankters typically selected for by visually
feeding planktivores.  In addition, it is transparent and has lateral
spines coming off the carapace.
        Zooplankton spines are generally produced to deter invertebrate
predators, but I have found that these spines do deter bluegill < 50 mm
from preying on them effectively.
        It still strikes me as odd that this species has so many obvious
adaptations to deter visual predators when it's a bit on the small side
to make such adaptations a priority.  Does anyone have any ideas or
experience working with D. lumholtzi in its native range or knowledge of
African zooplankton?
Thanks in advance (I apologize from departing from the discussion of
strict fisheries).

Cindy Kolar
Research Biologist
Illinois Natural History Survey
Sam Parr Biological Station
6401 Meacham Road
Kinmundy, IL  62854
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