Environmental variables driving horseshoe crab spawning behavior in a microtidal lagoon in Florida.

The timing of American horseshoe crab (Limulus polyphemus) spawning behavior along the coast of Florida (United States) is generally associated with the highest tides during the spring and fall lunar cycles. All Florida estuaries support horseshoe crab populations, but tidal characteristics vary markedly among locations, which may influence the timing of horseshoe crab spawning behavior. The Indian River Lagoon is a large microtidal estuary on Florida's east coast. Given the microtidal nature of the lagoon, it is unclear which environmental factors affect horseshoe spawning. In 2019, volunteers of Florida Horseshoe Crab Watch conducted daily surveys at two sites in the northern Indian River Lagoon during peak spawning months (February-April). During each survey, volunteers counted all spawning horseshoe crabs and recorded environmental variables, including water temperature, air temperature, wind speed, wind direction, salinity, and tide height. We developed a suite of negative-binomial regression models to quantify relationships between the number of spawning horseshoe crabs and environmental factors. Modeling results indicated a positive relationship between onshore wind speed and number of spawning horseshoe crabs. Our study suggests that in the absence of tidal cues, onshore wind speed may be an important driver of horseshoe crab spawning activity in microtidal estuarine systems.

Sources and concentrations of nutrients in surface runoff from waterfront homes with different landscape practices.

Development along Florida's coastal waterways has led to significant degradation in water quality over time. Numerous sources have contributed to increased nutrient loads in surface waters. Nitrogen (N) and phosphorus (P) pollution from urban fertilizer use has been addressed at the state, county, and municipality level yet the success of these efforts is rarely evaluated. This study aimed to validate these efforts by assessing the source and concentration of nutrients from surface water associated with waterfront homes with or without Florida Friendly Landscaping™, a nonstructural best management practice. The objectives were: to compare nutrient concentrations in runoff from differing landscape designs; compare the NO3- isotopic signature to that of known N sources; and evaluate the impact of a fertilizer ordinance blackout that is in effect during the wet season. Results from the study indicate no statistical reduction in the nutrient concentration of lawn runoff from either landscape design or the implementation of a fertilizer blackout ordinance. Results show that the sources of N in home landscapes are highly variable and cannot be solely attributed to fertilizer sources and highlight the influence of atmospheric depositions and soil nutrient pools which contribute 53-65% of the nitrate in lawn runoff. Nutrient management strategies need to address multiple sources of urban nutrients and mitigation efforts will not be immediate.