Species species of the Week week #2 OR Emily's FAVORITE Tautonym

Gemma gemma

(The Amethyst Gem Clam)

As it's at least supposed to be a molluscan marine blog it seemed worthy to start (1) with a redundant local marine mollusk.  Unfortunately, it turns out that very few, if any, tautonomical invertebrates are native to the Pacific Northwest (2).  So why not a non-native? It turns out this one is also my very, very favorite tautonym.

Figure 1. Peterson (of field guide fame) refers to G. gemma as, "a handsome ... clam, easily overlooked because of its small size".  Just so, sir.  Just so.

Photo Credit: Fisheries and Oceans Canada. Melissa Wong.

In addition to being the name of my wireless network, Gemma gemma (3) is the diminutive Amethyst Gem clam (Disambiguation).  These tiny bivalves are native to the east and Gulf coasts of North America, from Nova Scotia to Texas. They were introduced along the west coast of the US around 1960, but have only recently become very abundant in San Francisco Bay - but hey, what hasn't these days?! Am I right, folks?! (<---- NOTE: That was an excellent/horrible invasive species joke.  Insert rim shot here ... plz.)  

But seriously...

Ted Grosholz (UC Davis) tried to figure out why the gem clam population didn't really take off until decades after it was actually introduced (4).  It looks like the gem clam populations used to be held in check by competition (Figure 2) with native clams of the genus Nutricola (which I'm pretty sure are referred to as "Nut" clams).  

Figure 2. Schematic depicting San Francisco Bay pre-Green Crab Invasion (5).  Native Nutricola spp. (Pink, Yellow, and White individuals) originally kept non-native Gemma gemma (Green individual) at low abundances by eating up all of the food (phytoplankton represented by dinoflagellates, chain-forming and pennate diatoms and coccolithophores) leaving only scraps for poor G. gemma. 

Gem clams were kept at such low abundances that they were not, apparently, worthy of much notice or concern.  That is, until the arrival of the [non-whimsically named] European green crab, Carcinus maenas, which came to SF bay as a stow-away in the late 1980's.  The invasive crab, embracing the gastronomic culture of its host country, prefers to eat the biggest thing is can get its little green claws on, which in SF bay is the native Nutricola spp. The tiny gem clams get overlooked - lucky Gemma gemma devils!  That means no more selfish native clams hogging all the delicious phytoplankton (Figure 3)! Time for tiny gem clams to make tiny gem babies! 

Figure 3. My, how the tables have turned!  Schematic representing San Francisco Bay post-Green crab invasion.  Crabs (lower left) preferentially consume native Nutricola spp. (lonely yellow individual), freeing up more food for non-native gem clams (prolific green individuals) to make gem babies! 

Cool, huh?!  In many cases like this one, non-native species are present at low abundances for years after they are introduced, leading people to be all like, "ohhhhhhh....whateverrrr...it's no big deallll...I mean, who cares about some dumb clam anyway..."  And then something changes.  Maybe the non-native population develops a key adaptation that enables it to make more babies than before, or something else in the environment frees up resources (*cough, cough* I'm looking at you C. maenas), and the population of the non-native explodes and messes things up for EVERYONE.  And people are all like, "whaaa!? But how could we have known!?"  And I'm all like, "because it happens every time!"  Well, not every time, but surprisingly often. 


So called "lag times" are a pretty common property of biological invasions, and one extremely good reason that, notwithstanding any aesthetic arguments(6) for the moral equivalence of human and non-human invasions, all introductions of non-native species deserve to be treated with caution. 

References and miscellany:
(1) Yes "start" more than a month later, this is the first second species species of the week week. I did warn the one of you that reads this that these would be irregular and unlikley to actually appear on a weekly basis.
(2) I'm tempted do some arm waving here about how this probably has something to do with the idea that the tautonym species are so-named because they were the first of the genus to be described, and most of the marine genera in the PNW were first described in Europe or the east coast of North America.  But that arm waving will only appear in small print in the foot notes.
(3) On the pronunciation of Gemma gemma: "gemma" comes from Latin for "jewel". I assume it SHOULD be a hard G if you're being true to Latin pronunciation, but I have only ever heard it pronounced with a soft G, presumably in honor of the common name - which also pretty much comes from Latin for "jewel" but has since been bastardized.
(4) Grosholz, E., (2005) PNAS. 102(4): 1088. 
(5) If you have to look this game up, and don't have age as an excuse, your childhood was misspent.
(6) Drew Christie is a great Seattle animator and illustrator whose work I actually really like, but this piece got under my skin (really really far under my skin), for making a tenuous aesthetic (but it's cute!) and moral (humans are invasive too, who are we to point the finger?!) argument that manipulates feelings about a legitimate conservation issue.