14 pages, 6 figures, 5 tables.The spatial scale and the magnitude of carbon and nitrogen translocation was examined in 5 tropical (Cymodocea serrulata, Halophila stipulacea, Halodule uninervis, Thalassodendron ciliatum, Thalassia hemprichii) and 3 temperate (Cymodocea nodosa, Posidonia oceanica, Zostera noltii) seagrass species using Carbon-13 (C-13) and Nitrogen-15 (N-15) as tracers in experiments conducted in situ. Seagrass leaf and rhizome production during the study period varied from <0.001 to 0.015 gDW shoot-1 d-1 and 0.002 to 0.017 gDW rhizomeapex-1 d-1, respectively. Based on measured leaf and rhizome growth rates, the demand of resources for leaf production varied from 0.19 to 4.99 mgC shoot-1 d-1, and from 0.01 to 0.24 mgN shoot-1 d-1, while the demand for rhizome production varied from 0.62 to 5.57 mgC rhizome apex-1 d-1 and from 0.02 to 0.12 mgN rhizomeapex-1 d-1. Seagrass leaves incorporated the isotopes at rates ranging from 0.04 to 0.63 µg C-13 gDW-1 h-1, and <0.01 to 0.35 µg N-15 g DW-1 h-1. After 4 d, all incubated shoots had shared part of the incorporated C-13 and N-15 with ramets placed at maximum distances ranging from 2.7 (H. stipulacea) to 81 cm (C. nodosa), indicating that seagrass clonal integration may be maintained between 1.6 d (H. stipulacea) and 5.4 yr (P. oceanica). Resource translocation within seagrass clones was stimulated towards horizontal rhizome apices. Seagrass ramets, in 4 d, shared with their neighbours between 0.37 and 390 µg C-13 and between 0.02 and 178 µg N-15. During the study period, resource translocation would supply <5% and up to 40% of the leaf carbon and nitrogen\ud required by a neighbouring developing ramet, respectively, and <5% and up to 36% of the carbon and nitrogen required for rhizome growth; provided that the incorporated resources over 1 d were mobilised at similar rates over 4 d. These results conclusively demonstrate physiological integration between seagrass ramets, and that resource translocation may be an important mechanism for young seagrass ramets to acquire resources and for seagrass clones to expand and persist.This study was funded by the grant no.\ud IC18-CT96-0065 of the Commission of the European Communities within the framework of the INCO Programme. N.M. was supported by a post-doctoral grant from the Spanish Ministry of Education, M.A.M. by a post-doctoral grant from the European Commission (MAS2-ct-94-5022), and J.T. and E.G. by return contracts of the Spanish Ministry of Education. This is the contribution number\ud 2852 of the NIOO Centre for Marine and Coastal Ecology Yerseke, The Netherlands.Peer reviewe

10 pages, 8 figures, 1 table.We demonstrate the utility of using the equivalent bottom roughness for calculating the friction factor and the drag coefficient of a seagrass meadow for conditions in which the meadow height is small compared to the water depth. Wave attenuation induced by the seagrass Posidonia oceanica is evaluated using field data from bottom-mounted acoustic doppler velocimeters (ADVs). Using the data from one storm event, the equivalent bottom roughness is calculated for the meadow as ks ~ 0.40 m. This equivalent roughness is used to predict the wave friction factor ƒw, the drag coefficient on the plant, CD, and ultimately the wave attenuation for other storms. Root mean squared wave height (Hrms) is reduced by around 50% for incident waves of 1.1 m propagating over ~1000 m of a meadow of P. oceanica with shoot density of ~600 shoots m−2.E. Infantes acknowledges the financial support received from the Spanish Ministerio de Educacion y Ciencia, FPI scholarship program (BES-2006-12850). G. Simarro is supported by the Spanish government through\ud the Ramón y Cajal program. A. Orfila and G. Simarro are grateful for financial support from Spanish MICINN through project CTM2010-12072. M. Luhar was supported on grant number 0751358 from the U.S. National Science Foundation Ocean Sciences Division.Peer reviewe

It is widely accepted that light availability sets the lower limit of seagrass bathymetric distribution, while the upper limit depends on the level of disturbance by currents and waves. The establishment of light requirements for seagrass growth has been a major focus of research in marine ecology, and different quantitative models provide predictions for seagrass lower depth limits. In contrast, the influence of energy levels on the establishment, growth, and maintenance of seagrasses has received less attention, and to date there are no quantitative models predicting the evolution of seagrasses as a function of hydrodynamics at a large scale level. Hence, it is not possible to predict either the upper depth limit of the distribution of seagrasses or the effects that different energy regimes will have on these limits. The aim of this work is to provide a comprehensible methodology for obtaining quantitative knowledge and predictive capacity for estimating the upper depth limit of seagrasses as a response to wave energy dissipated on the seafloor. The methodology has been applied using wave data from 1958 to 2001 in order to obtain the mean wave climate in deep water seaward from an open sandy beach in the Balearic Islands, western Mediterranean Sea where the seagrass Posidonia oceanica forms an extensive meadow. Mean wave conditions were propagated to the shore using a two-dimensional parabolic model over the detailed bathymetry. The resulting hydrodynamics were correlated with bottom type and the distribution of P. oceanica. Results showed a predicted near-bottom orbital velocity of between 38 and 42 cm s^-1 as a determinant of the upper depth limit of P. oceanica. This work shows the importance of interdisciplinary effort in ecological modeling and, in particular, the need for hydrodynamical studies to elucidate the distribution of seagrasses in shallow depths. Moreover, the use of predictive models would permit evaluation of the effects of coastal activities (construction of ports, artificial reefs, beach nutrient-input, dredging) on benthic ecosystems.

10 pages, 5 figures.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\ud 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 experiment. Thalassia hemprichii and, to a lesser extent, Cymodocea rotundata showed a sharp decline in shoot density even at moderate burial treatments, from which they failed to recover. The accompanying species (Halodule uninervis, Syringodium isoetifolium, and Cymodocea 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 burial 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 imposed 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\ud 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.This research was funded by the STD-3\ud programme of the Commission of the European Union (project TS3*-CT94-0301).Peer reviewe