Episodic nutrient transport to Florida coral reefs

Abstract

This study documents the changes in nutrient fluxes associated with internal tidal bores arriving on Florida Keys coral reefs and points to biological use of subthermocline nitrate brought onshore by this mechanism. Internal bores on Conch Reef, Florida Keys, are associated with concentrations of 1.0-4.0 mol L Ϫ1 nitrate (NO ) and 0.1-0.3mol L Ϫ1 soluble reactive phosphate (SRP) and onshore flow velocities of 0.1-0.3 m s Ϫ1 . The arrival of internal bores causes 10-40 fold increases in nutrient concentrations and 1-2 orders of magnitude increases in nutrient flux relative to ambient, nonbore conditions. The magnitude and duration of cool-water nutrient transport events increases significantly with increasing depth on reef slopes. In June 2001, the gradient of increased exposure to subsurface water with depth corresponded to increased percentage of N and ␦ 15 N and decreased C : N ratio in a common benthic macroalga, Codium isthmocladum. Internal tidal bores are widespread throughout the Florida Keys reef tract, with cool-water episodes influencing reefs up to 10%-25% of the time during summer months and with significant variability among years. Estimated inputs of nitrogen and phosphorus by internal tidal bores to Florida Keys reef slopes are as much as 40-fold larger than published estimates of inputs to near-shore waters from waste water and storm water runoff. Internal tidal upwelling represents an important, previously underestimated, episodic source of nutrients on the Florida Keys reef tract. In order to assess nutrient availability in this system accurately it is essential to understand natural sources of high-frequency variability.Concern over the recent, rapid decline of corals and the widespread shifts from coral to macroalgal dominance on many coral reefs has produced a focus of research attention on anthropogenic factors associated both with reductions in herbivore populations and the input of dissolved nutrients to reef environments (e.g

Characterization of Available Light for Seagrass and Patch Reef Productivity in Sugarloaf Key, Lower Florida Keys

“…Pulses of cooler, deeper oceanic water onto the shelf, such as those observed on 18 May (Figure 2A), were associated with an increase in CDOM pmq and turbidity ( Figure 3A,G). Upwelling and tidal bores accompanied by a decrease in temperature (>5˝C) have been previously described in the Florida Keys lasting up to about 4 h [60,61]. Our observations show that these upwelling events can result in a quick change in IOPs, with higher spectral c p , a p , b p , and lower E d in the water column over the patch reef during high tide (solid blue lines in Figure 5A,C,E,I).…”

Coastal circulation and water column properties along Kaloko-Honokohau National Historical Park, Hawaii. Part 1: Measurements of waves, currents, temperature, salinity and turbidity, April-October 2004

“…This is likely due to the advection of shallow, low-salinity water from submarine groundwater discharge warmed by insolation and then advected offshore as the tide falls, similar to the observations of West Maui by Storlazzi and Jaffe (2003). Leichter et al (2003) has shown the onshore advection of subthermocline waters that contain elevated nutrient loads from submarine groundwater discharge supply a large percentage of nutrients to the shallow coral reefs in the US Florida Keys. We have no evidence of elevated nutrient loads and without concurrent, co-located nutrient sampling, we cannot determine if these internal tidal bores are actively delivering nutrients to the reefs along the Kona Coast.…”

Intense Benthic Grazing on Phytoplankton in Coral Reefs Revealed Using the Control Volume Approach

“…Since the plankton biomass, expressed in terms of C, was roughly the same in both studies (,10 22 g C m 23 ), the difference in grazing was most probably due to the much higher density of suspension feeders in their flume, which had 100% coral cover and .5% cover of sponges, ascidians, and actinians (Ribes et al 2003). Our longterm measurements of currents and temperatures in Eilat (Genin and Paldor 1998; Monismith and Genin 2004, Monismith et al 2006) indicate that neither upwelling (Wolanski and Delesalle 1995) nor internal bores (Leichter et al 2003) are common at our study site. The import of N from terrestrial sources was also expected to be insignificant because the local climate is extremely arid and no rivers are found in the region.…”