san salvador island flora and fauna

This is a stylized scientific poster of key organisms I saw during my time studying abroad in San Salvador Island, the Bahamas, in the spring of 2020. It acted as my final project for my Oceanography course (2021).

All organisms pictured are essential players in the San Salvador Island ecosystem, which is governed by the processes of carbonate geology. Sea grapes (Coccoloba uvifera), coco plum (Chrysobalanus icaco), and bay lavender (Tournefortia gnaphalodes) shroud the sand dunes and sometimes creep onto the backshore, particularly in the case of bay lavender, protecting the dunes and inland area from erosion and weathering of sediment by wind and waves with their root systems. The tangled roots of mangroves (I saw red mangrove, Rhizophora mangle, most often) also perform sediment erosion control in quiet bays and intertidal sediment flats around the island (such as in Pigeon Creek), where they also serve as important nurseries for juvenile fishes, many of whom grow up to inhabit coral reefs not far offshore from the mangroves that sheltered them as young. (The protection of coral reefs is thus deeply connected to the protection of mangrove forests, both of which face anthropogenic threats like outright destruction and overfishing.)

The sediments these plants maintain are composed of mainly calcium carbonate fragments from biotic and abiotic sources. Ooids are one such carbonate grain; they are round, smooth, polished grains that form via accretion of carbonate particles around a nucleus as the nucleus is rolled across the sea bottom by wave activity. The nucleus can be another carbonate particle, a shark’s tooth, etc. The tiny tests of deceased Foraminifera (forams) also make up a significant component of carbonate sediments on San Salvador. And of course, one cannot discuss carbonate sediments without mentioning the contributions of hard coral fragments (such as brain coral, Diploria labyrinthiformis, which has just the coolest Latin name) by parrotfish (like the vibrant stoplight parrotfish, Sparisoma viride), who while grazing the algal symbionts off the hard corals frequently bite off chunks of the calcium carbonate itself and pass them later on. Echinoderm fragments like those of a sand dollar (Leodia sexiesperforata), though very rare, also occasionally make it into the sediment record. Over geologic time, these sediments are compressed by wind (forming aeolianites) and tide (forming beach facies like herringbone cross-stratification) to form the rock that supports the terrestrial inhabitants of San Salvador Island.

In the intertidal area, one can find a plethora of organisms grazing the algae, detritus, and bacteria that is highly available there, such as brittle stars (Ophiocoma), chitons (Polyplacophora), and red encrusting forams. In the sand flat between the intertidal zone and the coral reef, unoccupied conch shells (Strombus) shelter juvenile fish and other organisms. These shells may bear either a linear hole or a puncture hole indicating their age and how the conch met its fate: shells with linear holes like the one pictured were pierced by tools introduced to the Bahamian (Lucayan) people around the time of Columbus’ arrival, making them around 400 years old. Shells with puncture holes were pierced by the tip of another conch shell by the Lucayan people prior to Columbus' arrival. These punctured shells are often embedded in beach rock, which has been dated to around 4700 years old (Holocene).

On the coral reef itself, great barracuda (Sphyraena barracuda) float lazily and may even follow snorkelers in hopes of dining on the scraps of what it believes to be large ocean predators. Green sea turtles (Chelonia mydas) maintain the Thalassia grass beds in the shallows surrounding the reef, similar to a lawn mower, by eating just the tips of the blades.

Onshore, primarily at North Point and in their enclosure at the Gerace Research Center, San Salvador Rock Iguanas (Cyclura rileyi) bask in the sun. Buffy flower bats (Erophylla sezekorui) reside in abandoned, breached phreatic caves, which formed from the dissolution of limestone via rainwater that diffuses through the porous rock (i.e., vadose flow through eogenetic rock) and mixes with water in the water table. Even if the bats themselves are hidden inside the caves, one can find evidence of their activity in the discarded, almost entirely intact fruit peels that often surround cave entrances. The bats chew a single hole through the peel and eat the fruit out.

In these ways, and in countless others, the organisms on San Salvador Island are intimately tied to the carbonate geology processes that formed and continue to modify the island. These organisms and processes demonstrate nearly all aspects of the course material, including:

- Coral reef formation and ecology
- Ocean sediments, specifically biogenous sediments
- Intertidal zonation and mangrove forests
- Ecological habitats and niches, both marine and terrestrial