Wigeongrass is Unexpectedly Cool

In my professional life I work on addressing stormwater pollution (among other things). Recently this got me thinking: what all was in the bay water I used to swim in?

Wigeongrass may appear unassuming, but don’t be fooled!  It’ll send pollinated bubbles after you.  Image courtesy of stonebird via flickr.

As a child I swam in Langford Creek, a broad and slow water body that flows into the Chester River and from there to the Chesapeake Bay.  Back then, I enjoyed seeing ospreys overhead, and I loved swimming under docks to check out barnacle colonies and birds’ nests.  And love doesn’t even quite capture the feeling of peeing off a boat at night to see the water respond by glowing green (perhaps a topic for another post?).  But I didn’t think much about the question of water quality, despite being vaguely aware that runoff from chicken farms was reaching the Chesapeake, and that the Chester River was directly between some of the farms and the Bay.

Now that I am accustomed to thinking about water quality, I figured I could likely pick out some interesting fecal coliform bacterium I shared the water with once upon a time.  Or maybe an obnoxious alga.  Instead, I found something more pleasant: wigeongrass.

A 1997 survey of submerged aquatic vegetation in the Chesapeake Bay [pdf] reported the following underwater plants in Langford Creek: “R. maritima, M. spicatum, E. canadensis, P. perfoliatus, and Z. palustris.”  I liked what I saw from R. maritima and looked no further.

R. maritima is more lengthily known as Ruppia maritima, or colloquially as wigeongrass.  According to Harold Kantrud, writing back in 1991 for the U.S. Fish and Wildlife ServiceR. maritima received its name from Linnaeus in the mid 1700s.  And wigeongrass may be essential to ducks (which makes sense given that a wigeon is a kind of duck): Kantrud quotes a 1915 author writing “bays that have kept their wigeon-grass have kept their ducks; those in which the plant has been destroyed by influxes of mud and filling up of the inlets have lost them.”  So that in itself is moderately interesting.

What’s more interesting to me are a couple odd properties of R. maritima.

First, R. maritima devotes considerable energy to growing roots that it doesn’t seem to use.  The plant apparently grows fine when free-floating and draws in no nutrients through its roots; nevertheless, even “detached plant parts” will immediately send out roots.  Given this energy expenditure, Kantrud concludes that “roots probably serve some function.”  We just don’t seem to know what.  I tried to confirm this with a search of more recent scholarship on Google scholar and still came up empty.  But then again, I haven’t studied plants properly since high school biology about fifteen years ago, so this might just be my ignorance showing through.

Second, R. maritima can reproduce in three ways, one of which is unexpectedly cool.  Maybe you prefer methods one (asexual reproduction) or two (self-pollination), but my favorite method is number three: bubble-assisted.  The anther of R. maritima‘s flower — the part responsible for pollen release — “burst[s] and release[s] pollen, aided by gas bubbles that accumulate inside the anther sac.”  The pollen grains then ride the bubbles in search of other R. maritima specimens to cross-pollinate with.  Sounds like fun!

And bubble-riding pollen naturally leads to some good news: apparently R. maritima is a bedrock species of a healthy estuary.  Here’s a lightly edited summary of why R. maritima and other sea grasses matter, from the Narragansett Bay Estuary Program: “Seagrass beds provide shelter and feeding grounds for juvenile fish, crabs, shellfish, and birds, and act as a biological filters and erosion control by trapping sediments in interconnected root structures known as rhizomes.”  So the abundance of wigeongrass in Langford Creek in 1997 — a year I must have swum there — was a sign of good health.  Phew.

(Then again, I also used to fish in Langford Creek, and apparently PCBs have been discovered in fish there — eek.)


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