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

Abstract

Light availability is an important factor driving primary productivity in benthic ecosystems, but in situ and remote sensing measurements of light quality are limited for coral reefs and seagrass beds. We evaluated the productivity responses of a patch reef and a seagrass site in the Lower Florida Keys to ambient light availability and spectral quality. In situ optical properties were characterized utilizing moored and water column bio-optical and hydrographic measurements. Net ecosystem productivity (NEP) was also estimated for these study sites using benthic productivity chambers. Our results show higher spectral light attenuation and absorption, and lower irradiance during low tide in the patch reef, tracking the influx of materials from shallower coastal areas. In contrast, the intrusion of clearer surface Atlantic Ocean water caused lower values of spectral attenuation and absorption, and higher irradiance in the patch reef during high tide. Storms during the studied period, with winds >10 m¨s´1, caused higher spectral attenuation values. A spatial gradient of NEP was observed, from high productivity in the shallow seagrass area, to lower productivity in deeper patch reefs. The highest daytime NEP was observed in the seagrass, with values of almost 0.4 g¨O 2¨m´2¨h´1 . Productivity at the patch reef area was lower in May than during October 2012 (mean = 0.137 and 0.177 g¨O 2¨m´2¨h´1 , respectively). Higher photosynthetic active radiation (PAR) levels measured above water and lower light attenuation in the red region of the visible spectrum (~666 to~699 nm) had a positive correlation with NEP. Our results indicate that changes in light availability and quality by suspended or resuspended particles limit benthic productivity in the Florida Keys.

Water Column Optical Properties of Pacific Coral Reefs Across Geomorphic Zones and in Comparison to Offshore Waters

“…Similarly, CDOM was the dominant component of absorption at fore reef sites, and slightly under half of the lagoon and terrestrially influenced sites, with the majority of these two reef zones being mostly mixed-type. This is consistent with the findings of several studies [14,93]. Many models of benthic light availability in coastal systems are based largely on absorption by chlorophyll [94], which is clearly insufficient for CDOM-driven systems such as coral reefs.…”

“…As coastal environments, reefs are influenced by the input of dissolved organics, particulates, and nutrients from terrestrial systems, as well as those generated in place and advected from offshore. Some important research has been carried out describing light environments and attenuation on selected coral reefs [1,[9][10][11][12][13][14] or over small regional scales [15]. This study builds upon that research to present a snapshot of water column optical properties measured across diverse reef systems of the Pacific Ocean to better understand large-scale influences on water clarity and light regimes influencing the benthos.…”

“…On reef systems, the calcium carbonate skeletons of coral, as well as the structures of coralline algae, are broken down to fine particulate sand by physical and biological weathering [44][45][46]. Suspension of sediments through wind, wave, or other mechanisms increase the water column particulate load, limiting benthic PAR [14,47,48] in addition to other negative impacts on corals [49,50]. Particulate organic matter, i.e., detritus or marine snow, may remain suspended for long periods of time and can be produced on reefs from a variety of sources including coral mucus [51].…”

Mapping coral reef primary production and calcification from a light-use efficiency model with in-situ and remotely sensed data

“…The limitation of linear scaling approaches, such as the census-based and hydrochemical methods, is the inability to account for spatio-temporal variation due to light, temperature, water flow, etc., which heavily influences metabolism and calcification (Carpenter & Williams, 2007;Falter et al, 2013). Seagrass and patch reef productivity was observed to be highly variable in the Florida Keys due to light availability from changing water conditions, such as turbidity, resuspension of sediments, and chlorophyll a concentrations (Toro-Farmer et al, 2016). Census-based approaches rely on previously published linear extension rates to up-scale coral calcification.…”

“…The relationship between light and photosynthesis has been well studied for benthic marine phototrophs, which respond similarly to terrestrial plants. Photosynthesisirradiance curves show the reduction of photosynthesis occurs under light-limited conditions, and saturation at high irradiance levels (Carpenter, 1985;Chalker, 1981;Toro-Farmer et al, 2016) ( Figure 3-1). Photosynthetic organisms share commonality in the use of chlorophylls and accessory pigments packaged within the photosynthetic apparatus to absorb light in the photosynthetically active region (400-700 nm).…”