MEPS 289:141-150 (2005)  -  doi:10.3354/meps289141

ABSTRACT: In this study, I evaluate the variability in light absorption efficiency of Thalassia testudinum leaves and the magnitude of the package effect affecting seagrass leaves. The large variability observed in pigment density and leaf absorptance of T. testudinum leaf segments, was compared to the variation in light absorption efficiency reported for leaves of Mentha aquatica, a species that maintains a specialized bifacial mesophyll and has 3 times higher leaf pigment content. Pigment light absorption efficiency of T. testudinum leaves was also compared to the interspecific variability reported for leaf sections of 12 seagrass species collected in 10 tropical (Mexican Caribbean and Philippine Indo-Pacific) and 31 temperate (Spanish Mediterranean, Portuguese Atlantic and Danish fjørds) coastal areas. The results of this comparison confirmed that T. testudinum leaves are affected by the package effect, because pigment light absorption efficiency decreases non-linearly as pigment content per unit area increases. The finding that M. aquatica leaves have a 1.5 times higher pigment light absorption efficiency than T. testudinum leaves for similar pigment content, does not necessarily indicate that the specialized leaf anatomy developed by seagrasses (i.e. a pigmented epidermis and an unpigmented leaf mesophyll) has led to a reduction in light absorption efficiency. This is because temperate seagrass leaves, which have a 2.5 times higher chlorophyll content than flat-shaped leaves of tropical species, exhibit a 1.4 times higher efficiency than M. aquatica leaves of similar pigment density. The possible effect of leaf morphology (i.e. leaf thickness and the specific leaf area) on the variation of leaf absorptance of T. testudinum was finally addressed to clarify the capacity of seagrass leaf morphology in counterbalancing pigment self-shading within the thin epidermis.

KEY WORDS: Seagrasses · Light absorption · Absorptance · Specific absorption · Package effect · Photoacclimation · Leaf thickness · Specific leaf area · Thalassia testudinum