Recruitment of Posidonia oceanica on rubble mounds: Substratum effects on biomass partitioning and leaf morphology

Leaf traits and biomass allocation to leaves (aboveground), roots and rhizomes (belowground) were assessed in Posidonia oceanica stands that had recently colonised rubble deposits at Capo Feto (Sicily). Comparisons were made with an adjacent pristine location (matte) at 5, 10 and 15 m depth and for crests, sides and valleys in the rubble deposits.Leaf traits of P. oceanica shoots were found to differ significantly between the rubble field and the matte. Leaf surface area was greater on the matte (mean adult leaves 200 ± 15 cm2/shoot) than at rubble locations (mean adult leaves 35 ± 5 cm2/shoot). At a smaller scale, differences also occurred within the rubble locations, with valley locations having greater leaf surface area than sides or crests. Overall, biomass allocation to the roots was higher in the rubble deposits with highest values in valleys (145.4 ± 22.5 g DW m−2) compared to the matte (12.6 ± 1.5 g DW m−2). An opposite pattern was recorded for leaf biomass, with highest values in the matte (1036.5 ± 64.7 g DW m−2) and no significant among between all other locations (average 13.8 ± 1.2 g DW m−2).We concluded that (1) P. oceanica leaf traits vary in relationship to substratum type (rubble versus matte); (2) once fragments recruit on rubble, biomass allocation is skewed towards the roots to increase anchorage; (3) root development affects biomass allocation to the leaves, so that above-ground biomass is reduced in plants on rubble mounds compared to the undisturbed meadow.