Sanibel Island Ecosystem Interactions

Marine Life Interactions at Sanibel Island
(sketch by Amy Coffman Phillips)

This iSite took place on an ecology tour through Tarpon Bay on the Ding Darling Natural Wildlife Refuge in Sanibel Island, FL.  A biologist, Brianna Coffman who turns out to be a distant unknown cousin of my dad (it's a small, interconnected world), led our tour with incredible knowledge and insight about this coastal marsh ecosystem.  In addition to the insights learned from the boat, our tour guide also gave us knowledge about how marine life interacts below the sea, interactions I've sketched above.  Because this was a boat tour and not a snorkeling tour, my photos of their aquarium will have to suffice for now.

my biologist guide's attempt to recreate tarpon bay's marine ecosystem
(photo by Faye Coffman)

Barnacles attach to any hard substrate they can find, including the shells of various marine organisms.  While walking the beach, I found beautiful pink and white barnacles attached to a pen shell (marine mollusk).  Given the amount of dead pen shells with barnacles I found on the beach, it is possible that the barnacles could get out of control and adversely affect the pen shell's ability to feed itself, developing a parasitic relationship. 

Whelks, such as the Lightening Whelk Conch, are carnivores that are able to eat the flesh of the barnacle by grinding down their outer shell.  The Conch uses its shell to grind and can repair and grow new shell using calcium from the ocean - talk about life friendly chemistry!   They also use suction to pry open the shells of their prey, and their favorite food seems to be the Arck, because their shells must number in the trillions and create Sanibel's white sand beaches.  These beaches create more land mass and continue the cycle of land creation.

Red Mangrove roots forming new islands
(photo by Amy Coffman Phillips)

As this sketch shows, terrestrial organisms are continually looking for new opportunities to colonize new land formed by the shells of marine life.  

Terrestrial Interactions at Sanibel Island
(sketch by Amy Coffman Phillips)

Intertidal zone sand bars are colonized by oysters, which form land by secreting a natural concrete-like compound and bind them together and with the land.  The interstitial spaces are filled by crabs and other organisms looking for shelter from the birds.  The birds land, looking for the crabs and find some, leaving feces to fertilize the sand bar with nitrogen, necessary for plant growth.

Sand bars that stay more or less above the tides are colonized by floating mangrove seedlings, which grow roots into the sand.  Barnacles and other organisms colonize the roots and trap more sediment, which stabilizes the roots and allows the plant to grow more roots.  Birds sit on these roots and look for food, giving nitrogen to the new soil with their feces.  This process grows an island and the sum of its parts are greater than they would be if each organism existed alone.

Mangroves have an impact on the ecosystem at the macro-scale as well.  This network of roots in the coastal marshes are the nurseries of the ocean and they help coastal nurseries respond to dynamic non-equilibrium by dampening hurricane winds and slowing flood waters.