Modeling daily production of aquatic macrophytes from irradiance measurements: a comparative analysis

Abstract

The importance of submerged aquatlc macrophytes to coastal ecosystems has generated a need for knowledge of minlmum l~g h t levels that wlll support the m a~n t e n a n c e and restoration of healthy populations Our goals were (1) to evaluate the s e n s~t~v~t y to natural, non-sinusoidal fluctuatlons in irradiance I of analytical integration techniques for calculating daily carbon gain (2) to evaluate the H,,, (the daily period of I-saturated photosynthesis) model of daily production relat~ve to models based on Instantaneous photosynthesis vs Irradiance ( P v s I ) and (3) to provlde some guidance for the temporal d e n s~t y of Irradiance data r e q u~r e d for accurate estimation of dally carbon gain Monthly measures of the P v s I response of an eelgrass Zostera m a n n a L population were used to p~e d l c t rates of dally carbon galn from continuous in sjtu recordings of I Dally ~n t e g r a t e d I was not a reliable predictor of daily product~on Numencal (iterative) integration of H,,, was much more r e l~a b l e but r e q u~r e d repeated measures of I within a day as did numencal integrat~on of P vs I Analytical (non-iterative) models based only on observations of l,, (noon) could not p r e d~c t daily production accurately Analyt~cal models of P v s I and H,,, agreed with each other, however, indicating that the analyt~cal models may be useful where the daily pattern of I is sinusoidal Given the h~g h degree of temporal vanability in coastal 11ght environments continuous monltonng of hght a v a~l a b~l i t y may be required for calculation of daily production and rehable management of aquatlc macrophyte populations

Annual metabolic carbon balance of the seagrass Posidonia oceanica: the importance of carbohydrate reserves

“…This is due to (1) the relative shallowness of our study site (5 m), and (2) the specificity of the Mediterranean waters, including the lack of tidal movements generating daily cycles of turbidity and the scarcity of nutrients (and associated high transparency; Poole & Atkins 1929, Weinberg 1976, Ivanoff 1977. This is in contrast with the large variability found by other authors in quite different marine environments, such as areas under the influence of upwelling waters or estuaries (Dunton 1994, Zimmerman et al 1994, which precludes a correct assessment of underwater light except when using continuous recording. This is not the case for the much more predictable Mediterranean area.…”

“…The accuracy in the measurement (or estimation) of photosynthetic active radiation reaching the plant canopy seems a crucial aspect in the reliability of any carbon balance (Zimmerman et al 1994). Our calculations show that most of the variability of the underwater irradiance can be attributed to variability of the surface solar irradiance.…”

“…Despite the importance of seagrasses in the global carbon cycle, few attempts have been made to integrate all the processes into carbon budgets, and only few studies have considered seasonality and extreme values of light availability, dependent on either sun angle, weather conditions or water transparency throughout the year (Pérez & Romero 1992, Dunton 1994, Zimmerman et al 1994, Lee & Dunton 1997, Herzka & Dunton 1998.…”

Annual and perennial life history strategies of Zostera marina populations under different light regimes

“…Because compensation irradiance represents the minimum light requirement for plant survival, the duration of PFDs above light compensation points (H comp ) is closely related to the survival of seagrasses (Dennison 1987). The duration of PFDs above light saturation points (H sat ) has also been used to predict carbon balance and seagrass production (Dennison & Alberte 1982, 1985, Zimmerman et al 1994. Therefore, reduction in underwater light intensity and/or duration is one of the main environmental stresses leading to seagrass declines and affecting distribution patterns (Cabello-Pasini et al 2002, Holmer & Laursen 2002, Thom et al 2008, Biber et al 2009).…”

Photosynthesis and daily metabolic carbon balance of the invasive <i>Caulerpa racemosa</i> var. <i>cylindracea</i> (Chlorophyta: Caulerpales) along a depth gradient

“…To this end a carbon balance approach was taken, based on the numerical integration of photosynthesis vs irradiance (P vs E) models throughout continuous measurement of instantaneous irradiance recorded at the sea floor. This mechanistic approach has been previously demonstrated to provide reliable estimates of primary productivity in marine macrophytes (Matta and Chapman, 1991;Zimmerman et al, 1994). Photosynthesis and respiration rates of C. racemosa fronds, together with continuous irradiance field data, were measured at three different locations of contrasting depth and light on the coast of the Murcia Region of SE Spain, a part of the Spanish Mediterranean coast invaded by the alga since 2005 (Ruiz et al, 2011).…”