Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities

Growth form defines physiological photoprotective capacity in intertidal benthic diatoms

“…EPL is not only more abundant in muddy cohesive sediments where light penetration is more restricted than in sandy sediments (Paterson and Hagerthey 2001;Cartaxana et al, 2011), but, more importantly, their (micro-) migratory behaviour allows positioning at the optimal irradiance in the vertical light gradient and rapid escape from periodic excess light (Kromkamp et al, 1998;Conn et al, 2004;Consalvey et al, 2004;Serô dio et al, 2006). This alleviates the need to invest in a strong physiological capacity to respond to light stress as previously proposed Cartaxana et al, 2011), although the right balance between motility and physiology still remains essential (van Leeuwe et al, 2009;Perkins et al, 2010b;Cartaxana et al, 2011;Serô dio et al, 2012). Such balance is more crucial in the EPM-M species, which can move but have only limited control over their immediate light environment as movement is restricted, usually within the sphere of individual sand grains.…”

“…In most studies, diatom functional groups are defined on the basis of morphological growth form (for example, Gottschalk and Kahlert, 2012;Larson and Passy, 2012) and not physiological traits. In addition, photoprotective ability (limited to the measurement of the 'xanthophyll cycle', XC) and its relationship with ecology has only been studied in natural communities with mixed assemblages of functional groups (for example, Jesus et al, 2009;van Leeuwe et al, 2009;Cartaxana et al, 2011).…”

“…To prevent photoinhibition (Serô dio et al, 2008), benthic diatoms utilize behavioural and physiological responses (Mouget et al, 2008;van Leeuwe et al, 2009;Perkins et al, 2010b;Cartaxana et al, 2011;Serôdio et al, 2012). Behavioural photoprotection involves motility, allowing cells to position themselves in light gradients and escape from prolonged exposure to excess light (Admiraal, 1984;Kromkamp et al, 1998;Consalvey et al, 2004;Serô dio et al, 2006).…”

“…NPQ is controlled by several regulatory partners including the lightdependent conversion of diadinoxanthin (DD) to diatoxanthin (DT) by the DD de-epoxidase (that is, the XC) (Brunet and Lavaud, 2010;Goss and Jakob, 2010). In benthic diatoms, however, XC-NPQ has only rarely been studied, and mostly in situ: it has been shown to vary with diurnal and tidal cycles, season, latitude (Serôdio et al, 2005;van Leeuwe et al, 2009;Chevalier et al, 2010), the organisms' position within the sediments and along the intertidal elevation gradient Cartaxana et al, 2011). On the basis of their in situ measurements, the latter authors hypothesized the existence of a trade-off between behavioural and physiological photoprotection mechanisms in benthic diatoms, as a stronger XC was shown to occur in sandy vs muddy sediments.…”

“…On the basis of their in situ measurements, the latter authors hypothesized the existence of a trade-off between behavioural and physiological photoprotection mechanisms in benthic diatoms, as a stronger XC was shown to occur in sandy vs muddy sediments. However, at least the sandy sediments contained a mix of both epipsammic and epipelic forms Cartaxana et al, 2011), and even when the latter are not numerically dominant, they can still make a substantial contribution to biomass because of their much larger biovolumes (see for example, Hamels et al 1998).…”