Abstract
Seagrasses provide valuable services and suffered decline worldwide due to anthropogenic activities and epiphyte related sunlight inhibition. This research addresses the causes and consequences of algal epiphyte growth on seagrasses in the Caloosahatchee River Estuary. The objectives for this research were: 1) bimonthly site monitoring at three sites within the estuary; 2) determining the effect of epiphytes; 3) assessing the impact of nutrient enrichment and invertebrate mesograzers on epiphytes. The manual removal of epiphytes field experiment in the Caloosahatchee ran for a total of sixteen days with epiphytes manually removed every fourth day. During the experimental timeframe, ambient epiphyte levels were low. There was no significant effect of epiphyte removal on any of the measured response variables (p>0.05).
The factorial manipulation of nutrient enrichment and invertebrate grazer-deterrent experiment was conducted from May 2016 through July 2016. During the experiment’s first month, all treatments experienced rapid increases in epiphyte levels. During week two, both deterrent and nutrient x deterrent treatments contained greater epiphyte loads, suggesting absence of the grazers allowed increased epiphyte accumulations. However, by week four, all treatments contained high numbers of epiphytes and none of the experimental manipulations showed significant effects for the measured response variables (p>0.05). Assessment of grazer communities at the end of the experiment suggested invertebrate grazers were not completely suppressed by the chemical deterrent. Assessment of stoichiometric ratios (CNP) in seagrass tissue from experimental plots indicated that even control treatments were nutrient replete, which may explain the lack of impact of nutrient addition.
Future experimental manipulations investigating nutrient, grazer, and epiphyte effects should take careful account of ambient conditions and their seasonal variation in order to maximize the chances of detecting effects. Overall, our results indicate epiphytes in the Caloosahatchee block a large percentage of light, and are not fully controlled by mesograzers in the highly nutrient-enriched conditions of the estuary. Efforts to conserve and restore seagrasses in the estuary should place serious focus on reducing nutrient loading.
