Meandering Through the Mangroves

By Emily Arendsen

As a child, my parents had a love-hate relationship with my favorite pastime of competing with my sister about who could cake herself with more mud than the other. This competition got to the point that my father had to pull us out of the mud in the bucket of a tractor, leaving our boots buried under the sloppy ground. Never have I been as close to my childhood tendencies as I was today, and I couldn’t be happier about it. Today, we hiked through the roots of a mangrove forest, caked in mud, and learned about the unique functions that the organisms of the mangroves perform.

            Mangroves occur in coastal areas, growing in and near bodies of saltwater. The mangrove forest that we visited was situated on the banks of a small freshwater river, within sight of the Tempisque River, which contains saltwater. At the high tide, fine soil washes into the mangrove forest from the river, which doesn’t allow oxygen to enter it easily, meaning that the trees cannot use their roots for gas exchange. The trees themselves have many adaptations to their unique environment that we were able to see and taste. The soil doesn’t allow for the mangroves to grow deep, supportive roots underground because they desiccate too quickly, so they have specialized aboveground roots for support and gas exchange. The mangroves that we saw had stilt roots that came out of the trees well above our heads and that branched and extended far away from the tree until they reached the ground. For us, the stilt roots functioned as a resting spot to clean off the mud that had caked onto our hands and boots before having lunch. The mangrove trees also produce pneumatophores, which look like fingers sticking out of the ground, to do gas exchange to overcome the anoxic soil that they are rooted in and to provide more structural support.

Despite that mangroves live in a place that floods frequently, fresh water is a precious resource for them because of the high salinity of the water they receive. They have succulent leaves that can store the fresh water acquired when it rains or if they are near to a freshwater source. The roots also have a high calcium ion concentration that will encourage water to diffuse into the roots, leaving the salt behind because diffusion occurs until the two entities that are on either side of a water-permeable barrier are at an equal concentration. The high ion concentration inside of the roots forces water to diffuse into the roots. They also have the ability to secrete salt from their leaves, making the undersides iridescent with salt. If you were to lick the underside of a leaf, which I did several times, you would taste the salt. They also move salt to the older leaves that they are about to drop to get rid of as much salt as they can.

As children grow up, their learning experiences stop exposing them to what they are learning about. They shift from growing butterflies in their classrooms to having PowerPoint presentations about metamorphosis. Today I appreciated the ability to interact with the material that I was learning about in a way that hadn’t been considered important since the days that my sister and I paraded around in filthy clothes and were encouraged to learn about the world around us.