9Chapter Controls Acting on Benthic Macrophyte Communities in a Temperate and a Tropical Estuary
Seagrass meadows and macro algal canopies are critical coastal habitats that are widely recognized for their vital ecological functions and services. Both seagrass and macro algal growth and community structure can be controlled by nutrients and herbivory. Although these benthic macrophyte groups have been studied extensively worldwide, there is still no consensus as to the relative roles of the different control mechanisms on their structure and function. To examine the relative influence of nutrients and herbivory on growth of seagrasses and macro algae, we conducted a set of field experiments, manipulating the nutrient supply, grazing pressure, or both in a temperate and a tropical estuary. In these estuarine systems, seagrass and macro algae were controlled by numerous and dynamic interactions between nutrients and herbivory, whereby nutrient supply considerably altered the potential for herbivore control of producer biomass. These results highlight the major role that human-driven nutrient loading from land plays in adjacent coastal habitats, and underscore the need for greater understanding of the benthic floral community dynamics in shallow estuarine environments.