I recently attended a conference at Michigan State University which highlighted the latest and greatest in Great Lakes research. Just to prove that I actually was paying attention, I wanted to bring you a simplified version of one of the papers. This gathering of minds showcased current work in the field of ecology, geo-morphology, chemistry, and something else which I’ve already forgotten. There was a lot of talk about detecting Asian Carp DNA in the Chicago water system and the dynamics of drowned river mouths (bet you didn’t know that rivers could drown, eh?) etc. Not all of it was stimulating, but all was potentially interesting to at least someone in the room at any given time.
The one that really stuck in my gray matter was a paper titled “The Invasive Spiny Water Flea: Disrupting Great Lakes Food Webs through Eating and Scaring Zooplankton Prey – Scott Peacor, Associate Professor, Department of Fisheries and Wildlife, Michigan State University, East Lansing.” I assumed that there was a typo which converted “Scarring” into “Scaring” – after all un-eaten prey are often scarred, right? You know, that torn ear or rump scar resulting from a failed attack. Although it was hard to visualize how this could possibly affect population dynamics (possibly rump scars are a turn-off for reproductive efforts or something?)
Well, this clever title turned out to be exactly as printed. It really was about how a dangerous new invader called the Spiny Water Flea (Bythotrephes longimanus) both consumes and scares the living daylights out of their prey species. These Water Fleas hitch-hiked into our regional waters from central Asia. They are one of the many hundreds of invasives that have wreaked havoc on the ecological systems of our Great Lakes. Unfortunately we already had a host of native water fleas here when this foreigner arrived. Not only are these natives in great danger, they are apparently suffering from PTSD as well.
Spiny Water Flea
Spiny Fleas look as nasty as they sound. Their dominant feature is an exceedingly long spine – a spine with smaller spines upon it, as a matter of fact (see my drawing above). Although only about half an inch long in total body length, most of this length is given over to this needle-like appendage. With a tail like that, our native fish are less than enthusiastic about eating them. The Spiny Water Flea, however, is very enthusiastic about eating any critter smaller than itself. High on that menu list are plant-eating water fleas called Daphnia. None of these guys are actually “fleas”, by the way, they are members of a crustacean group called the Cladocerans (a late 1960’s folk group that once played with Pete Seeger?)
Scott Peacor specifically studied the effect of Bathotrephes on Daphnia. Without taking any of his thunder, allow me to summarize what he found out. Spiny Water Fleas are visual predators equipped with a single huge eye. They need good light in order to track down their prey and generally keep to the upper waters during the day. Historically, Daphnia are also light-loving creatures that try to spend as much time as possible in those same well-lit upper waters. When the two populations collide, the Spiny Water Fleas tend to get fat and the Daphnia tend to get gone. This was pretty much already known and Peacor re-verified it in his study, but he also wondered what happened to those Daphnia that got away. Did they eventually learn to stay out of the upper waters?
In short, the answer was yes. Not all of them did, but a majority switched their routine so that they spent the daylight hours in the cold dark deeper waters and only returned to the surface at night when their new-found predator can’t see them. So, you could say that the living daylights were literally scared out of the Daphnia. You’d think this was a totally successful anti-predator tactic, but those scared shadow-seeking Daphina failed to thrive and eventually become pin-heads (my words not his). They didn’t reproduce well and their population plummeted. It can be assumed that the same thing is happening in nature. They are damned if they do and if they don’t -or “doubly screwed” if you want to put it in commoner style tongue.
Speaking of simplifying, I was inspired to draw up a cartoon that summarized the whole feeling of Scott’s talk. It is the very one that appears above. I sent my impromptu cartoon to the researcher, Scott Peacor, on the outside chance he might want to tape it on his door or use it for a future PowerPoint. He graciously wrote me back and said that he loved it and will use it. He was especially impressed at how I made the Daphnia looked so scared.
For those who are wondering, I did not draw the cartoon as I watched the conference. I paid full attention, although I must admit to spending an inordinate amount of time mulling over how I could make the starry-eyed Daphnia look scared.