Marsh crabs build creeks!

Some very cool new research has come out of the Pennings Lab at the University of Houston last month. Huy Vu et al reports, in Ecology, that purple marsh crabs Sesarma reticulatum can be responsible for massive changes in salt marsh hydrology! Through extensive burrowing and consumption of vegetation, crabs extend, build, and move salt marsh creeks.

Photo from Vu et al 2016

photo from Vu et al 2016

photo from Vu et al 2016

Vu found that the purple marsh crab excavates a massive amount of sediment per day, sometimes almost twice as much as other marsh crabs.  In addition, purple marsh crab density was highly correlated with decreases in above and belowground biomass and plant height.  These crab activities, especially when they were concentrated in the “dead zone” at the leading edge of a marsh creek as Vu calls it, drastically change the marsh sediment.  Speaking from experience, walking in these crab infested areas is very difficult! The soil stability is very low, so its not hard to imagine how constant water flow over those areas can enlarge creek heads.  To top it off, Vu et al simulated purple marsh crab herbivory at some of these creek heads and found that creeks expanded 38% more where plants were removed in similar ways as herbivory!

The purple marsh crab has been featured on MarshLife before and this is a very cool addition to the already exciting life history of this unique crab. Across its range the PMC can cause massive erosion (New England), prey on keystone consumers (Georgia), regulate ecosystem functions (Georgia), over-graze marsh grass (Southeast US), and change the whole flow of salt marsh creeks (SE). Considering that this crab is abundant all throughout marshes up and down the Atlantic coast it begs the question, is the purple marsh crab the most important salt marsh consumer?! I say yes 🙂

PMC at night


Check out this parasitoid!

We are slowly working our way through insect samples from salt marshes around New England and our undergrad Martina found something pretty insane recently.  The following picture is of a planthopper in a Nantucket salt marsh


If you zoooooooooooooooom in you can see a weird little bubble on the abdomen of these little hoppers.  If you zoooooooooooooooooooooooooooooooooooooooooooom in even further you can kind of see that that bubble has a head.  What the heck is that?!

I had to consult marsh arthropod expert, and all around awesome ecologist, Dr Gina Wimp on this.  Here is what she said:

This is one of my favorite things in the whole wide world – a parasitoid!!!  This is a Dryinid parasitoid (Haplogonatopus).  You are looking at the abdomen of the parasitoid protruding-out of the planthopper.  The parasitoid does not kill the planthopper (usually), but sterilizes it.  These planthoppers should consider themselves lucky, I have seen planthoppers with 3-4 parasitoids lined-up on the abdomen.

The other fun parasitoid that the planthoppers get is in the Strepsiptera (Elenchus).  The female just looks like a dark plate on the abdomen, but you can actually see the face of the male on the side of the planthopper’s abdomen!!  The male is winged, the female is not, and the male mates with her while she is still in the planthopper.”

Thanks Gina for that ID and if you want to hear more from her, check out the #MarshChat from a few months ago!