Mouths of the Bull

By Micaela Wells

The semester continues, and my sunburn deepens. Last week the program brought us just within the northern edge of Panama, in a tangled Caribbean island chain called Bocas del Toro Archipelago, literally “mouths of the bull.” Confusing twists and turns in the channels between islands stand ready to swallow any boat that ventures in unprepared. The mangrove tree roots weave a fine mesh along the coasts of the wilder islands, serving as excellent wind breaks and flood shields for the island inhabitants. Their submarine roots also provide important breeding and feeding grounds for many species of tropical fish who populate the surrounding coral reefs.

Those reefs are the reason for our visit, as they form surprisingly complex ecosystems beneath the waves. It’s easy to look at reefs and see only coral—colorful, lumpy, rock-like organisms, but their simple exterior belies a more intricately detailed reality. Each apparent individual is actually a clonal group composed of fused polyps, marine invertebrates that excrete the stony exoskeletons we recognize as coral growth! And just as terrestrial trees provide an environment for all sorts of species interactions, these animal colonies live in delicate balance with the other organisms of the sea.

Tropical fish weave their way between the many coral varieties, with some merely using it as temporary cover, while others carve out little territories along the coast. Not all of these fish solely leach off of the corals’ generous protection, but many contribute to the overall health of the reef in their own ways.

For example, herbivores are able to reduce the green algae constricting coral growth, making for a more healthy and diverse reef overall. Both microscopic algae and macro algae need to be grazed, and various species of fish happily serve that purpose. Damselfish delicately nibble at the algae they want, while parrotfish greedily snap off small chunks of the corals’ surface, grind them down, and filter out the algae growing in and around the bumpy structures. They produce the fine white sand that makes tropical beaches so picturesque in travel magazines, and also help the coral colonies to persist. Though these fish act entirely out of their selfish need for food, their actions protect their protectors and secure a habitat for future generations.

Tree-lined shores are familiar to me, but undersea communities are wholly new. I look forward to the next week of snorkeling and study beneath the mirror-like waves.