Light availability in the coastal ocean: impact on the distribution of benthic photosynthetic organisms and their contribution to primary production

Abstract

Abstract. One of the major features of the coastal zone is that part of its sea floor receives a significant amount of sunlight and can therefore sustain benthic primary production by seagrasses, macroalgae, microphytobenthos and corals. However, the contribution of benthic communities to the primary production of the global coastal ocean is not known, partly because the surface area where benthic primary production can proceed is poorly quantified. Here, we use a new analysis of satellite (SeaWiFS) data collected between 1998 and 2003 to estimate, for the first time at a nearly global scale, the irradiance reaching the bottom of the coastal ocean. The following cumulative functions provide the percentage of the surface (S) of the coastal zone receiving an irradiance greater than Ez (in mol photons m−2 d−1): SNon-polar = 29.61 − 17.92 log10(Ez) + 0.72 log102(Ez) + 0.90 log103(Ez) SArctic = 15.99 − 13.56 log10(Ez) + 1.49 log102(Ez) + 0.70 log103(Ez) Data on the constraint of light availability on the major benthic primary producers and net community production are reviewed. Some photosynthetic organisms can grow deeper than the nominal bottom limit of the coastal ocean (200 m). The minimum irradiance required varies from 0.4 to 5.1 mol photons m−2 d−1 depending on the group considered. The daily compensation irradiance of benthic communities ranges from 0.24 to 4.4 mol photons m−2 d−1. Data on benthic irradiance and light requirements are combined to estimate the surface area of the coastal ocean where (1) light does not limit the distribution of primary producers and (2) net community production (NCP, the balance between gross primary production and community respiration) is positive. Positive benthic NCP can occur over 33% of the global shelf area. The limitations of this approach, related to the spatial resolution of the satellite data, the parameterization used to convert reflectance data to irradiance, the lack of global information on the benthic nepheloid layer, and the relatively limited biological information available, are discussed.

The influence of pore‐water advection, benthic photosynthesis, and respiration on calcium carbonate dynamics in reef sands

“…Benthic community metabolism-Photosynthesis in coastal sediments has long been known to depend on sediment PAR flux, leading to empirical parameterizations of benthic primary production dependent only on one variable, benthic light flux or water depth (Gattuso et al 2006). Our laboratory microsensor measurements, conducted in steady-state diffusive conditions, confirm that the photosynthetic activity of microphytobenthos at Heron Reef exhibits the expected light-saturating behavior (Webb et al 1974), although with light acclimation intensities (E k ; Table 4) that are lower than those previously observed in shallow tropical environments (Underwood 2002).…”

Expansion of vegetated coastal ecosystems in the future Arctic

“…Marine macrophytes, including seagrass and macroalgae grow in coastal waters down to the depth receiving about 1% of the incident solar radiation (Gattuso et al, 2006), with the deepest record of kelp (Agarum clathratum and Saccharina sp.) in the Arctic region reaching down to >60 m in Disko Bay, Greenland (Boertmann et al, 2013), records of foliose red algae to similar depths in Svalbard and slow-growing encrusted red algae to even larger depths (Wulff et al, 2009;Wiencke and Amsler, 2012).…”

Biological production in the Indian Ocean upwelling zones –Part 1: refined estimation via the use of a variable compensation depth in ocean carbon models

“…In addition to KPP, the model uses a background vertical diffusion reported by Bryan and Lewis (Bryan and Lewis, 1979). For horizontal mixing, the model incorporates Redi fluxes (Redi, 1982) and GM fluxes (Gent and McWilliams, 1990), which represent the eddy-induced variance in the mean tracer transport. A weak Laplacian diffusion is also included in the model for computational stability where the sharp gradient in concentration occurs.…”

“…Whenever the model phosphate exceeds the observational phosphate, it allows production. At Zc, the NCP is zero and above Zc the net primary production (NPP) exceeds the community respiration and the ecosystem will grow (Smetacek and Passow, 1990;Gattuso et al, 2006;Sarmiento and Gruber, 2006;Regaudix-de-Gioux and Duarte, 2010;Marra et al, 2014). However, Zc was held constant in time and space in OCMIP-II models (Najjar and Orr, 1998;Matsumoto et al, 2008) because the OCMIP-II protocol takes a minimalist approach to biology and simplifies the model calculations with a very limited set of state variables suitable for long-term simulations when implemented in coarse-resolution models (Orr et al, 2005).…”