Response of a mixed Philippine seagrass meadow to experimental burial

Abstract

ABSTRACT-The effect of burial due to sudden sediment loading was examined in a mixed Philippine seagrass meadow through the experimental deployment of sediment (0. 2. 4 , 8, and 16 cm deposited over the experimental plots). The responses in shoot density, vertical growth, and branching of the species present were assessed 2. 4, and 10 mo following disturbance. Shoot density responses were strongly species-specific. The large Enhalus acoroides maintained shoot density at all burial treatments, and only showed evidence of decline by the end of the expenment. Thalassia hempnchiiand, to a lesser extent. Cymodocea rotundata showed a sharp decllne In shoot density even at moderate burial treatments, from which they faded to recover. The accompanying species (Halodule uninervis, Syringodiurn isoetifolium, and Cyrnodocea serrulata) showed an initial decline In shoot density followed by recovery. The small Halophila ovalis showed an opportunistic growth in plots receiving intermediate (buried by 4 and 8 cm sediment) disturbance, reaching shoot densities well in excess of those on control plots. The results suggest a pattern of species loss following disturbance by sediment burial corresponding to the sequence, T hemprichii + (C. rotundata. S. isoetifolium, H uninervis) + C. serrulata + E. acoroides. Vertical growth increased significantly for all species with differentiated vertical shoots, except C, serrulata. The examination of the time course of vertical growth imprinted on the shoots of the dominant species, T hemprichii, revealed a rapid response to bunal through increased internodal length, which was maintained over 8 mo following the disturbance. The resulting cumulative vertical growth along the experiment was linearly correlated with the degree of burial in~posed on the plants. Branching of vertical shoots also increased significantly (73 to 96%, depending on the species) with burial. Experimental burial induced changes in shoot age distribution of some of the species, involving rearrangements, through selective mortality or recruitment, of the contribution of young shoots to the populations. The results obtained show major differences in species response to small-scale disturbance, closely linked to predictions derived from consideration of species growth rate and size, and provide evidence of the importance of small-scale disturbance in the maintenance of multispecific seagrass meadows.

Response and recovery dynamics of seagrasses Thalassia testudinum and Syringodium filiforme and macroalgae in experimental motor vessel disturbances

“…Regrowth into deeper disturbances was slow because it required vegetative growth from the scar margins and/or recruitment of seedlings, processes that are dependent on low densities of horizontal meristems and seedlings and the slow rate of clonal growth of T. testudinum (Van Tussenbroek et al 2000. Moreover, apical meristem tissue uncovered at the margins of the scar may be less likely to grow due to light exposure and may not possess the flexible rhizome architecture necessary to grow down into the remaining sediment (Marba et al 1994, Duarte et al 1997, Terrados 1997. Somewhere between 10 and 20 cm appears to be a critical depth beyond which the damage to T. testudinum is such that recovery takes significantly longer.…”

Rhizome elongation and seagrass clonal growth

“…Species with thin rhizomes (and long internodes) have, therefore, much faster horizontal rates of spread than large species with their thick and short internodes. In addition, the intraspecific variation in horizontal elongation rate is substantial ( Duarte et al 1997, Kenworthy pers. obs.)…”

Morphological and physiological differences between two morphotypes of Zostera noltii Hornem. from the south-western Iberian Peninsula

“…The higher (5-fold) net photosynthetic capacity in SM would contribute to its higher growth rates, allowing a faster regeneration of the meadow and a faster colonization of the substrate in disturbed or bare areas. In fact, Duarte et al (1997) have reported that mortality caused by burial increased with decreasing seagrass size, whereas the potential to recover from this disastrous situation is enhanced with decreasing seagrass size.…”