Factors influencing primary production of seagrass beds (Zostera noltii Hornem.) in the Thau lagoon (French Mediterranean coast)

Abstract

The primary production and the respiration of Zostera noltii beds in the Thau lagoon were studied by means of the benthic bell jar technique. Concurrently, environmental data (temperature, light and nutrients) as well as morphological data of seagrass meadows (leaf width and height, density of shoots, above/below-ground biomass ratio) were collected with the purpose of explaining most of the observed variations in metabolism. Seagrass plus epiphyte respiration rates were influenced mainly by the water temperature, showing a typical exponential response to an increase in temperature. Surprisingly, measurements of production rates were not related to incoming light intensities recorded at the seagrass canopy level. An equation frequently used for terrestrial standing crops, involving the leaf area index (LAI) and the characteristics of the canopy architecture (parameter K, depending on leaves optical and geometrical properties), was applied to the seagrass ecosystem in order to estimate the light energy actually available for the plants, i.e. the light intercepted by the seagrass canopy (Q(abs)). Linear relationships were then validated between gross production rates and calculated Q(abs) for Z. noltii beds, and the best fits were obtained with K values nearing 0.6, confirming the similarities between terrestrial graminaceae and seagrasses. A linear regression model for primary production is proposed, involving the calculated Q(abs), the water temperature and the leaf nutrient content.

Community-level carbon flux variability over a tidal cycle in Zostera marina and Z. noltii beds

“…CR and GCP rates measured during immersion over the course of the year were within the range previously reported in the literature for both Zostera marina (Murray & Wetzel 1987, Barranguet & Alliot 1995, Martin et al 2005 and Z. noltii communities (Vermaat & Verhagen 1996, Viaroli et al 1996, Plus et al 2001. During emersion, CR and GCP rates were low but consistent with studies conducted on the same communities during 2008, when CR varied from 13.8 to 82.8 mg C m −2 h −1 and GCP from 43.9 to 251.5 mg C m −2 h −1 in the Z. marina community (authors' unpubl.…”

“…Some measurements have been performed at the community scale in Zostera marina beds under immersion (Martin et al 2005) and in Z. noltii beds under both immersion (Plus et al 2001) and emersion (Ouisse et al 2010). A direct comparison of aerial and underwater carbon metabolism has only been documented on a Z. noltii bed in the Banc d'Arguin, Mauritania (Clavier et al 2011), and investigations at the community scale over tidal cycles are still needed.…”

Measuring seagrass photosynthesis: methods and applications

“…Other significant differences, observed in the compensation intensity (I c ) and in respiration, highlighted the advantages of in situ measurements. Benthic chambers with continuous O 2 monitoring were also used by Plus et al (2001) to determine primary production and respiration of Zostera noltii beds in the Thau lagoon in South France.…”

Characterisation of the light environment and biophysical parameters of seagrass using remote sensing

“…LAI represents the total photosynthetic area of the plant canopy per unit area of sediment, which has been used as a diagnostic variable for crop growth rate, radiation intensity and above-ground height (Solana-Arellano et al, 2003). Biomass and LAI have also been used for modelling seagrass photosynthesis (Plus et al, 2001;Zimmerman et al, 2003, McPherson et al, 2011. While several studies have attempted to map biomass from remote sensing using various methods, only Dierssen et al (2003) and Wicaksono and Hafitz (2013) have explicitly attempted to map seagrass LAI using remote sensing data.…”

“…Consequently, LAI is often used as an input parameter for modelling of seagrass productivity (e.g., Plus et al, 2001;Zimmerman, 2003, McPherson et al, 2011. A high rate of oxygen production, which is a by-product of photosynthesis, is produced by high seagrass biomass, supporting life in coastal environment by supplying oxygen to the surrounding waters (Terrados and Borum, 2004).…”