Our lab has just published a new paper on dock piling “fouling” communities. In coastal ecosystems, one of the most important services that we value are the ability of filter feeding organisms (oysters, mussels, sponges, barnacles, etc.) to improve water quality. By removing particles from the water, and depositing them in the form of excretion on the ocean bottom, these organisms can significantly increase water clarity. This process is important to remove excess human-derived nutrients from the water column before tides and currents carry them to nearby seagrass beds and coral reefs.
In heavily developed estuaries, many native habitats (oyster reefs or mangrove prop roots) that support high densities of filter feeders have been substantially impacted by human activities. For example, in the Loxahatchee River, FL, the entire 7km of river shoreline from the ocean is completely developed, with no natural shoreline remaining. Yet the current artificial structures support very high densities of filter feeders (see the left hand dock piling photo above), which may provide significant filtration capacity. To explore this possibility, we counted every single dock in the Loxahatchee River (13,554 of them!), and used existing estimates of filtration rates of fouling organisms to estimate river-wide filtration capacity provided by docks. The result was impressive – docks supported a filtration capacity that approached that of all natural oyster reef in the river! One take home point is that the function of coastal ecosystems can not be fully quantified without explicit consideration of the services that artificial structures can have.
Obviously, this is not a suggestion that development of coastal shorelines is okay or advised. We write in the paper: “Conveying these ideas to resource managers and stakeholders may be challenging, as data could be couched as evidence to actually justify conversion of natural shorelines to human made structures. To the contrary, we categorically state that we are not equating dock pilings to healthy natural oyster reef. For example, it is important to remember that we only consider a single ecosystem service herein, and do not attempt a full assessment that would incorporate the numerous other ecosystems services that are compromised or lost with destruction of natural habitats. Urbanization of coastal areas also may lead to other unwanted consequences, e.g., facilitating the spread of invasive species.”
So how is this relevant in The Bahamas? We show that choice of building material has important implications for the level of ecosystem service provided. Compare the two pictures above: a concrete piling is loaded with critters, whereas the wooden piling covered with black wrap is specifically intended to reduce settlement of organisms. In the Loxahatchee River, concrete pilings supported 68% of total filtration, despite accounting for only 7% of all pilings. As such, in areas where developed shorelines are in place or inevitable (think Hope Town Harbour), choice of building materials may help create “living shorelines” that help mediate some of the other human impacts (nutrient loading). More generally, this role of filter feeders on dock pilings is another example how our we are fundamentally altering the way coastal ecosystems function in The Bahamas and globally.