Rhizophora mangle and Crossostrea rhizophorae

They have an exhibit at the Smithsonian Marine Ecosystems Exhibit in Ft. Pierce where Red Mangroves thrive in a big indoor tank.   John and I have a lot of time invested in Red Mangroves, so we’re naturally interested in the captive individuals.  An odd and fascinating aspect of the indoor specimens is that Oysters grow on their prop roots, just as wild mangroves accumulate Oysters in the sea.

Oyster classification appears to be complex, with several different types sometimes mixed together.  Along the Southeast Coast of Florida there are mixed species, even on a Mangrove.    That said, one is a Red Mangrove specialist, the Mangrove being Rhizophora, and the Mangrove Oyster being Crossostrea rhizophorae, hanging out from Florida to South America.   It clusters on Red Mangrove roots below the high tide line, exposed when the tide is out.

Obviously the Mangrove helps the oysters, but how about the reverse?   A study in the Philippines on a different Oyster species on a different Mangrove species found the shellfish guilty of an unexplained mild detrimental effect on Mangrove growth.  

If the study was accurate, ya gottta wonder how some clinging seafood hurts the tree, but anything is possible.   The Mangrove roots “breathe” through big white valves (specialized lenticels) exposed to fresh air at low tide, so maybe a committee of oysters can cover the ventilation system.   A hypothesis to test, after first confirming oyster-impaired growth.

Harmless or pesky to the tree, the oysters are beneficial for hungry humans.   Some shell middens (ancient refuse piles) are almost entirely remains from the Mangrove Oyster, still showing tool marks from shucking a few thousand years ago. 

And speaking of tool marks, Bearded Capuchin Monkeys in Brazil bang the Mangrove Oysters open using clumps of other Oysters. (Although I have no image for that specifically, here is a link to Asian monkeys doing the same with other shellfish).  In Cuba historically Oyster harvesters cut off the mangrove roots and hauled them away in floating rectangular boxes.   In Puerto Rico as well, Mangrove Oysters were once an important harvest, sometimes approaching 100,000 pounds per year.