The impact of sediment burial and erosion on seagrasses: A review (original) (raw)
Related papers
Response of a mixed Philippine seagrass meadow to experimental burial
Marine Ecology …, 2009
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.
Seagrass roots strongly reduce cliff erosion rates in sandy sediments
Marine Ecology Progress Series, 700:1-12, 2022
Vegetated coastal ecosystems such as saltmarshes, mangroves and seagrass beds are in- creasingly promoted as sustainable storm and flood defence solutions by reducing wave energy. Yet, there is still intense debate on the ability of root mats to mitigate erosion, with some studies arguing that the direct contribution of roots in preventing sediment erosion is minor, while others consider them of major importance. Here, we hypothesized that the contrasting findings on the role of sea- grass root mats in preventing erosion may stem from differences in sediment type. To test this idea, we investigated how root mats of seagrass that thrives in both sandy and muddy sediments mitigate wave-induced cliff erosion using Zostera marina in manipulative flume experiments. Results demon- strate that roots are very effective in reducing cliff erosion rates in sandy sediments. Cliff erosion rates were reduced up to 70% in sandy sediment with high seagrass root biomass. In contrast, cliff erosion rates in cohesive muddy sediments were low and unaffected by seagrass roots. This highlights the important role of seagrass roots in erosion miti- gation, which has been overlooked compared to the role of canopies, which has received more at- tention. We suggest that management strategies should be developed to enhance the stabilization of sandy sediment, such as (1) using species with high belowground biomass, (2) using fast-growing pioneer species and (3) applying temporary stabilising measures.
Estuarine, Coastal and Shelf Science, 2010
Seagrasses are well-known ecosystem engineers. They reduce water dynamics and sediment resuspension, and trap fine sediments. However, exceptions of this paradigm have been reported. To test whether these exceptions could be related to plant cover and environmental conditions, we investigated sediment modification under influence of seagrass presence in various annual eelgrass (Zostera marina) beds with varying plant cover and sediment composition. At the relatively wave-exposed, sandy sites, dense vegetation caused muddification (increase in fine sediments and organic content) of the sediments. Sparse vegetation (<35% cover) had no effect, as such confirming the classical sediment trapping paradigm. In contrast, at the sheltered sites with muddy sediments, dense vegetation had no effect on the sediment composition, and in sparse vegetation sandification (decrease in fine sediments and organic content) was recorded. Sandification was never recorded before and was probably related to turbulence enhancement. Both, muddification and sandification are likely to provide a feedback on seagrass performance. Muddification may increase the nutrient input and, depending on the nutrient status of the system, either stimulate or reduce seagrass development. Similarly, sandification may postpone and even prevent extinction of seagrass beds when it occurs in areas that may have become too muddy for seagrass growth.
2017
Sediment burial stress response, bio-indicators and thresholds for a tropical multi-species seagrass assemblage John Statton1,3, Kathryn McMahon2,3, Roisin McCallum2,3, Gary Kendrick 1,3, Paul Lavery2,3 1 The Oceans Institute, The University of Western Australia, Crawley, Western Australia, Australia 2 Edith Cowan University, Joondalup, Western Australia, Australia 3 Western Australian Marine Science Institution (WAMSI), Perth, Western Australia, Australia
Are seagrass growth and survival constrained by the reducing conditions of the sediment?
Aquatic Botany, 1999
A literature review of the effects of the reducing conditions of the sediment on seagrass metabolism, growth and survival, and of the morphological and physiological adaptations that seagrasses show to cope with sediment anoxia is presented and major gaps in knowledge are identified. The hypothesis that sediment anoxia controls the survival of seagrasses was tested experimentally by increasing the oxygen demand of the sediment with the addition of sucrose. Experiments were performed in a tropical (Southeast Asia) multispecific seagrass meadow, a Mediterranean Cymodocea nodosa meadow, and a temperate Zostera marina meadow. Sulfide levels in pore water and vertical redox profiles were used to characterise the effects of the sucrose additions on the sediment, while plant responses were quantified through the changes in shoot density and leaf growth. Sulfide levels in pore water increased and sediment redox potential decreased after the addition of sucrose to the sediment of different seagrass meadows. The effect of the addition of sucrose to the sediment of seagrasses was species-specific. Leaf growth was reduced and shoot mortality increased in some of the tropical species (e.g., Thalassia hemprichii), but not in others. Neither mortality nor leaf growth of the Mediterranean species C. nodosa was affected by sucrose additions, and only leaf growth was reduced two months after the addition of sucrose in Z. marina. Our results suggest that increased sediment anoxia might be a factor promoting growth inhibition and mortality in seagrasses, although strong differences have been found among different species and environments.
Seagrass mortality due to oversedimentation: an experimental approach
Journal of Coastal Conservation, 1998
Mortality due to oversedimentation of the Mediterranean seagrass Posidonia oceanica was experimentally evaluated by field manipulations of the sediment level. Increased levels of sediment placed over plant shoots and rhizomes induced significant shoot mortality, even at moderate burial levels (ca. 5 cm). When sediment was added to reach levels 15 cm higher than the initial one, a 100 % mortality was observed after 200 -300 days. The response of the plant was independent of site and depth. These results can be used in ecological risk assessment of coastal activities which potentially affect sediment deposition.
Sedimentation that leads to periodic, and often prolonged, burial events is becoming more common on the world's coastlines as human populations expand and create urbanised marine environments. Different seagrass species react differently to sediment burial but many species in the southern hemisphere are yet to be examined. How seagrasses react to burial has restoration implications. There is a need to critically assess seagrass transplant propagule responses to periodic (pulse) and prolonged (press) burial events before selecting the most appropriate species, transplant propagule, and transplant site. In my study, meso-cosm experiments, coupled with field measurements were used to assess how sexual (seedlings) and vegetative (sprigs) propagules of Posidonia australis responded to pulse and press burial events. Seedlings were highly susceptible to burial (both pulse and press), with no survival at the end of the experimental period. In contrast, rhizome growth in vegetative propa-gules was stimulated by pulse burial, although press burial events resulted in mortality. The implication for Posidonia australis restoration efforts in areas where burial is periodic, was that vegetative propagules are optimal transplant units, in comparison to seedlings. Press burial however, renders a transplant site sub-optimal for both seedling and sprig transplants.
Effects of burial and erosion on the seagrass Zostera noltii
Journal of Experimental Marine Biology and Ecology, 2007
The effects of experimental burial and erosion on the seagrass Zostera noltii were assessed through in situ manipulation of the sediment level (−2 cm, 0 cm, + 2 cm, + 4 cm, + 8 cm and +16 cm). Shoot density, leaf and sheath length, internode length, C and N content and carbohydrates of leaves and rhizomes were examined 1, 2, 4 and 8 weeks after disturbance. Both burial and erosion resulted in the decrease of shoot density for all the sediment levels. The threshold for total shoot loss was between 4 cm and 8 cm of burial, particularly during the 2nd week. A laboratory experiment confirmed that shoots did not survive more than 2 weeks under complete burial. There was no evidence of induced flowering by burial or erosion. As well, no clear evidence was found of sediment level effects on leaf and sheath length. Longer rhizome internodes were observed as a response to both burial and erosion, suggesting a plant attempt to relocate the leaf-producing meristems closer to sediment surface or in search of new sediment avoiding the eroded area. The C content of leaves and rhizomes, as well as the non-structural carbohydrates (mainly the starch in rhizomes), decreased significantly along the experimental period, indicating the internal mobilization of carbon to meet the plant demands as a consequence of light deprivation. The significant decrease of N content in leaves, and its simultaneous increase in rhizomes, suggests the internal translocation of nitrogen from leaves to rhizomes. About 50% of the N lost by the leaves was recovered by the rhizomes. Our results indicated that Z. noltii has a high sensitivity to burial and erosion disturbance, which should be considered in the management of coastal activities.
Effects of sediment burial on tropical ruderal seagrasses are moderated by clonal integration
Continental Shelf Research, 2011
Seagrasses are clonal plants that grow submerged in dynamic sedimentary environments where burial is a common occurrence. Clonal organisms may respond to burial in very different ways depending on how strongly integrated they are through horizontal rhizomes, but the effect of clonal integration under conditions of stress such as burial is poorly studied for seagrasses. We test the effect of burial on tropical seagrasses that occur in multispecific meadows by subjecting plants in mixed stands to burial of 0, 2, 4, 8 and 16 cm for 27 days. Treatments were divided into those where rhizomes were severed and those where rhizomes were left intact. We hypothesize that species withstand burial better if clonal integration is maintained (intact rhizomes). Results showed that all species tolerated burial of up to 4 cm without adverse effects but significant reductions in shoot density and biomass become evident at 8 cm of burial. Furthermore, Cymodocea serrulata and Syringodium isoetifolium were strong integrators, i.e. they provide support for buried shoots, whereas Halophila ovalis and Halodule uninervis were weak integrators that did not show evidence of subsidizing buried shoots. Vertical elongation was observed for C. serrulata and H. uninervis as a response to burial only when rhizomes were severed, leading us to speculate on whether species rely on vertical elongation as an escape strategy only in the absence of resource translocation. Our distinction between the responses of treatments with intact rhizomes from those with severed rhizomes may be extended to an interpretation of burial scale (intact rhizomes ¼ broad spatial À scale burial; severed rhizomes ¼ fine spatial À scale burial). We concluded that broad spatial À scale burial exceeding 4 cm leads to rapid loss or reduction of all species. However, fine spatial-scale burial exceeding 4 cm, such as those caused by shrimp mounds (bioturbation), is expected to favor C. serrulata and S. isoetifolium, while H. ovalis and H. uninervis are disadvantaged. Clonal integration is an important trait in moderating the response of seagrasses to sediment burial and in this way, helps them to cope in high-stress habitats.