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Nico Koedam - One of the best experts on this subject based on the ideXlab platform.
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towards an unknown fate the floating behaviour of recently abscised Propagules from wide ranging rhizophoraceae mangrove species
Aquatic Botany, 2017Co-Authors: N Tonne, Elisabeth M. R. Robert, Hans Beeckman, Nico KoedamAbstract:Abstract The persistence of a mangrove ecosystem depends on the potential of its Propagules to disperse. In case of the Rhizophoraceae mangrove species, Propagules are elongated cylinder-shaped seedlings that have an initial ability to float upon abscission from the parent tree. During the hydrochoric dispersal period, Propagule traits (e.g. volume and density) change over time, which in parallel influences Propagule buoyancy behaviour. Recently abscised, mature Propagules of three rhizophoracean mangrove species (Bruguiera gymnorrhiza (L.) Sav., Ceriops tagal (Perr.) C.B. Rob., Rhizophora mucronata Lam.) were submitted to a three-month floating experiment to investigate the timing and pattern in their buoyancy behaviour linked to changes in Propagule density. Anatomical analyses of the aerenchymatous tissues complemented the floatation data. Initial Propagule density (between 0.96 (C. tagal) and 0.99 g cm−3 (B. gymnorrhiza and R. mucronata)) was on slightly lower than that of seawater and increased over time in all species but at dissimilar rates. Intra-individual density increased from the plumule- towards the radicle end, and corresponded with a decrease in proportion of intercellular surface area per unit area. The interplay between Propagule traits and surface water conditions determine the fate of each Propagule and its capacity to escape the local forest and reach open water. The combination of techniques used and hence combination of data obtained in this study, contribute to an increased understanding of mangrove forest dynamics: the potential and the limits therein to expand the species range or to replenish existing populations with new recruits.
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What regulates crab predation on mangrove Propagules
Acta Oecologica, 2015Co-Authors: Fleur Van Nedervelde, Nico Koedam, Stefano Cannicci, Jared O. Bosire, Farid Dahdouh-guebasAbstract:Crabs play a major role in some ecosystems. To increase our knowledge about the factors that influence crab predation on Propagules in mangrove forests, we performed experiments in Gazi Bay, Kenya in July 2009. We tested whether: (1) crab density influences Propagule predation rate; (2) crab size influences food competition and predation rate; (3) crabs depredate at different rates according to Propagule and canopy cover species; (4) vegetation density is correlated with crab density; (5) food preferences of herbivorous crabs are determined by size, shape and nutritional value. We found that (1) Propagule predation rate was positively correlated to crab density. (2) Crab competitive abilities were unrelated to their size. (3) Avicennia marina Propagules were consumed more quickly than Ceriops tagal except under C. tagal canopies. (4) Crab density was negatively correlated with the density of A. marina trees and pneumatophores. (5) Crabs prefer small items with a lower C:N ratio. Vegetation density influences crab density, and crab density affects Propagule availability and hence vegetation recruitment rate. Consequently, the mutual relationships between vegetation and crab populations could be important for forest restoration success and management.
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PRELIMINARY STUDY ON THE Propagule DEPENDENCY OF Rhizophora SEEDLINGS
2014Co-Authors: N. P. Dissanayake, Nico Koedam, Loku Pulukkuttige Jayatissa, S.k. Madarasinghe, Kodikara Arachchilage Sunanda Kodikara, A.j.d. Perera, F. Dahdouh GuebasAbstract:Early life of viviparous mangroves merely depends on the Propagule and it can be assumed that the period and the degree of dependency could depend on the size and the intrinsic factors of the Propagule as well as on the edaphic and environmental factors in which the seedlings are growing. However scientific studies on the Propagule dependency of mangrove seedlings is poorly studied, irrespective to the fact that such information is vital particularly in mangrove restoration programs. However, Propagule dependency of mangrove seedlings is poorly studied scientifically, irrespective to the fact that such information is vital particularly in mangrove restoration programs. This study was carried out to investigate the growth performances of seedlings and the variations in the content of carbohydrate foods (starch content) in the Propagule during the first 20 weeks period of the seedling growth of two viviparous species, Rhizophora apiculata and Rhizophora mucronata , which are having larger Propagules and commonly used in replanting programs. The experiment was conducted, under three salinity regimes (i.e. 5psu; 15psu; 30psu) in a planthouse. A separate set of Propagules was planted within the mangrove forest of Pambala lagoon under natural conditions and subjected to the same investigation as above. Growth performances of both species grown under high salinity regime were significantly lower than those grown in low and moderate salinity regimes. Total leaf area of the seedlings of R. mucronata increased in higher order compared to that of the R. apiculata during the study period. After an initial drop in the content of starch in the Propagules of both species, it started to increase slowly in the Propagule of R. mucronata seedlings whilst the reduction was continued in R. apiculata Propagules during the study period. However, the initial starch concentration of R. apiculata was remarkably higher than that of R. mucronata and hence, the starch content in R. apiculata, even after continued decreasing, was higher at the end of the study period. It can be hypothesized that the higher concentration of the stored food in smaller Propagule of R. apiculate, compared to lower concentration of the stored food in Propagules of R. mucronata, might lead to a similar longevity of viviparous mangrove seedlings of the two species allowing more or less the same chance to survive and establish in the same habitat as observed in many mangrove ecosystems. KEYWORDS: Mangroves, Restoration, Starch content, Propagule dependency, Rhizophora , Sri Lanka
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Modelling drivers of mangrove Propagule dispersal and restoration of abandoned shrimp farms
Biogeosciences, 2013Co-Authors: Diana Di Nitto, Paul L. A. Erftemeijer, J.k.l. Van Beek, Farid Dahdouh-guebas, L. Higazi, Katrien Quisthoudt, Loku Pulukkuttige Jayatissa, Nico KoedamAbstract:Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala–Chilaw Lagoon Complex (Sri Lanka) was studied by combining a hydrodynamic model with species-specific knowledge on Propagule dispersal behaviour. Propagule transport was simulated using a finite-volume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind), trapping agents (retention by vegetation) and seed characteristics (buoyancy) on Propagule dispersal patterns. Sensitivity analysis showed that smaller Propagules, like the oval-shaped Propagules of Avicennia officinalis , dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped Propagules of Rhizophora spp. and C. tagal . Directional Propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the Propagules being retained within the vegetation. Only a small proportion (max. 5%) of Propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once Propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows), was found to significantly affect the resultant quantities and species of inflowing Propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the value of Propagule dispersal modelling in guiding hydrological restoration efforts that aim to facilitate natural mangrove regeneration.
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size does matter but not only size two alternative dispersal strategies for viviparous mangrove Propagules
Aquatic Botany, 2012Co-Authors: Dennis De Ryck, Elisabeth M. R. Robert, Diana Di Nitto, Tom Van Der Stocken, Nele Schmitz, Farid Dahdouhguebas, Nico KoedamAbstract:We studied the Propagules of two widespread mangrove species, Ceriops tagal and Rhizophora mucronata, that are similar in shape but differ in other morpho-anatomical features (average length is 23.1 ± 2.2 cm and 44.4 ± 4.3 cm, resp., n = 180). We hypothesized the Propagules of both species to have a different hydrodynamic behavior and establishing capacity, resulting in a different dispersal strategy. More specifically, we hypothesized that C. tagal Propagules have a larger dispersal capacity than those of R. mucronata. The dispersal strategies of C. tagal and R. mucronata Propagules were elucidated through a combination of a Propagule tracking (n = 180 per species), predation (n = 20 per species) and root-growth experiment (n = 120 per species), carried out in the field. C. tagal and R. mucronata adopted two different dispersal strategies. C. tagal releases a large number of Propagules and disperses fast, having a slender morphology and low density (average ρ: 985.29 ± 19.02 g L−1), as well as a high agility (smaller size) when dispersing through dense root systems. C. tagal Propagules have a theoretical advantage to disperse over longer distances over the thicker, longer and denser R. mucronata Propagules (average ρ: 1003.92 ± 8.52 g L−1; t = 8.90, p < 0.0001, n = 197). C. tagal have, however, lower establishment chances due to slower root-growth, desiccation sensitivity and smaller size. In contrast to Ceriops’ tactic of releasing high numbers of Propagules and fast dispersal, R. mucronata has adopted a dispersal tactic of survival. Fewer Propagules are released, but they are more resistant to predators due to their larger size and they can anchor themselves faster due to quicker root-growth (Mann–Whitney U: p < 0.0001, nCt = 59, nRm = 57). Overall, Propagule characteristics of both species result in different and alternative dispersal strategies on a local scale, contradicting our initial hypothesis. On a global scale, we hypothesize this might lead to a similar capacity for long-distance dispersal, ending in successful establishment.
Angela M. Gurnell - One of the best experts on this subject based on the ideXlab platform.
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An investigation of the composition of the urban riparian soil Propagule bank along the River Brent, Greater London, UK, in comparison with previous Propagule bank studies in rural areas
Urban Ecosystems, 2011Co-Authors: Christopher P. Cockel, Angela M. GurnellAbstract:Most Propagule bank research has been conducted in rural areas and has emphasised agricultural soils, although research on rural riparian Propagule banks has expanded rapidly over the last decade. This paper presents observations of the species abundance of plant Propagules in urban riparian soils along the River Brent, Greater London, UK. The data are analysed to explore changes in species abundance of the Propagule bank with depth (0–5 cm compared with 5–10 cm soil layer), with distance from the river (0–1 m, 1–2 m, 2–3 m), and at different locations on the river network. No significant differences were found in Propagule abundance with soil depth or distance from the river’s edge, but significantly more species were found in the Propagule bank close to the river’s edge. The species composition of the Brent’s Propagule bank is then compared with riparian Propagule banks from the rural rivers Dove, Frome and Tern, UK. Species richness of the Brent Propagule bank samples was generally lower than was found in the three rural rivers and, in total, 21%, 4%, 5% and 4% of observed species were aliens in the Brent, Dove, Frome and Tern soil samples, respectively. When the species present in the Brent’s Propagule bank were compared with published data on urban garden soils in another UK city, the latter were found to support a higher number of alien species, suggesting that other Propagule sources to urban river systems support lower numbers of alien species in riparian zones than domestic gardens.
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Hydrological controls on the transport and deposition of plant Propagules within riparian zones
River Research and Applications, 2009Co-Authors: Helen L. Moggridge, Angela M. GurnellAbstract:The establishment of vegetation in riparian zones is dependent upon the availability of suitable habitat and the presence of viable Propagules. Studies have shown that Propagules are transported by rivers (hydrochory) and deposited in the riparian zone. However, there has been no detailed integrated study of fluvial Propagule transport and deposition in relation to the hydrological regime and relative to other key dispersal mechanisms, such as wind dispersal (anemochory) and direct fall from local riparian vegetation. This paper presents the findings of a 1 year study of the hydrological controls on Propagule input, transport and deposition in the riparian zone along two morphologically contrasting reaches of the River Frome (UK) and the potential importance of these processes for the riparian vegetation. Analysis of samples, taken every 6 weeks, shows that aerial seed dispersal delivered relatively few Propagules to the riparian zone and was highly spatially and temporally variable. The river transported and deposited large numbers of Propagules of high diversity, including many species which were not present in the local vegetation, although this varied with river water levels and with season. Winter high flows were particularly important for depositing diverse Propagules into the riparian zone along with local seed production during the summer. Despite contrasts in the planform and cross profile morphology of the two study reaches, they showed great similarity in patterns of Propagule deposition, which were largely driven by the inundation regime, the elevation of the sampling site, and the season of sampling.
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Propagule input, transport and deposition in riparian environments: the importance of connectivity for diversity
Journal of Vegetation Science, 2009Co-Authors: Helen L. Moggridge, Angela M. Gurnell, J. Owen MountfordAbstract:Question: How important is hydrochory for dispersing Propagules along riverbanks and to what extent do the quantity and species composition of deposited Propagules reflect the riparian vegetation, represent “new” species that are not present in the vegetation, and vary with river flow and season? Location: River Frome, Dorset, UK. Methods: Over 13 consecutive 6-week time periods, during which river water levels were continuously monitored, aerial inputs of Propagules to riverbanks were sampled using funnels, hydrochorous Propagule transport was sampled using drift nets, and deposition across the riverbanks was sampled using astroturf mats. A survey of the riparian vegetation enabled comparison between samples and the standing vegetation, so that “new” species could be identified. Differences in Propagule abundance and diversity between sampling methods, time periods and locations were tested using Mann-Whitney U-tests and Kruskall-Wallis ANOVA. DCA established contrasts in the floristic composition of all deposited Propagules and “new” Propagules between different sample types, time periods and locations. Results: Aerial seed fall generated few Propagules of low species richness. Hydrochory introduced large numbers of Propagules and new species, resulting in high Propagule deposition on the riverbank. The number and diversity of deposited Propagules was governed by seasonal patterns of seed release and the hydrological regime. Propagule deposition was significantly greater on the most frequently inundated parts of the riverbank and autumn floods were particularly important for transporting “new” species to the study site and for remobilizing previously released Propagules. Conclusions: The abundance and diversity of Propagules deposited along riverbanks is dependent upon high river flows, which facilitates connectivity between the channel and the riparian zone.
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Propagule deposition along river margins: linking hydrology and ecology
Journal of Ecology, 2008Co-Authors: Angela M. Gurnell, Ken Thompson, Joanne Goodson, Helen L. MoggridgeAbstract:Summary 1 Research has highlighted the importance of buoyancy for hydrochorous Propagule dispersal, but recently the river bed has been identified as a significant store of viable Propagules. 2 Over four consecutive 4-month periods, deposited Propagules (predominantly seeds) and sediment were sampled at 78 river bed, bank face and bank top sites within three river reaches in two catchments. Species of deposited Propagules were compared with the Propagule bank and standing vegetation to identify ‘new’ species. 3 Forty-four percent of deposited Propagule species were not present in the vegetation and the largest proportions were deposited in winter. New Propagules showed a higher proportion of species that establish long-term seed banks and produce light seeds, a higher proportion of R-strategists, and a lower proportion of C-strategists than species in the vegetation. 4 Ordination of Propagule species abundance data revealed differences in samples between reaches; bed and bank locations; and sampling periods. Within depositional samples there were significant positive correlations between average C scores and the proportion of species producing relatively heavy, short-lived seeds and scores on an ordination axis describing a gradient from channel bed to bank top. 5 Correlations and multiple regression models between species richness and abundance of deposited Propagules (total and new), and the quantity and calibre of river-deposited sediment, demonstrated a direct link between Propagule deposition and hydraulic conditions during inundation. 6 Synthesis. Riparian connectivity of river flows, varying hydraulic conditions and temporary storage of Propagules are all complex components of hydrochorous Propagule dispersal in the study reaches. Flood flows can transfer sediment particles and non-buoyant, viable Propagules from the river into the riparian zone. Propagules can pass in and out of storage within the channel bed and margins through a variety of dispersal processes and can then settle out of the water in suitable depositional environments generating distinct spatial and temporal patterns in total Propagule deposition. New Propagules show greatest floristic similarity to Propagule bank and bed samples. They are preferentially smaller, lighter and form longer term seed banks, making them particularly suitable for long distance transport over prolonged time periods and for widespread dispersal across river margins.
Jian Huang - One of the best experts on this subject based on the ideXlab platform.
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Soil Propagule bank of ectomycorrhizal fungi in natural forest of Pinus bungeana
Ying yong sheng tai xue bao = The journal of applied ecology, 2017Co-Authors: Nan Xing Zhao, Qi Sheng Han, Jian HuangAbstract:To conserve and restore the forest of Pinu bungeana, we investigated the soil Propagule bank of ectomycorrhizal (ECM) fungi in a severely disturbed natural forest of P. bungeana in Shaanxi Province, China. We used a seedling-bioassay method to bait the ECM fungal Propagules in the soils collected from the forest site. ECM was identified by combining morph typing with ITS-PCR-sequencing. We obtained 73 unique sequences from the ECM associated with P. bungeana seedlings, and assigned them into 12 ECM fungal OTUs at the threshold of 97% based on the sequence similarity. Rarefaction curve displayed almost all ECM fungi in the Propagule bank were detected. The most frequent OTU (80%) showed poor similarity (75%) with existing sequences in the online database, which suggested it might be a new species. Cenococcum geophilum, Tomentella sp., Tuber sp. were common species in the Propagule bank. Although C. geophilum and Tomentella sp. were frequently detected in other soil Propagule banks of pine forest, the most frequent OTU was not assigned to known genus or family, which indicated the host-specif of ECM Propagule banks associa-ted with P. bungeana. This result confirmed the importance of the special ECM Propagule banks associated with P. bungeana for natural forest restoration.
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soil Propagule banks of ectomycorrhizal fungi along forest development stages after mining
Microbial Ecology, 2015Co-Authors: Jian Huang, Kazuhide Nara, Kun Zong, Chunlan LianAbstract:Ectomycorrhizal fungal (EMF) Propagules play an important role in seedling establishment following distur- bance. However, little is known about how the EMF propa- gule community changes with forest development. In this study, EMF Propagules were examined using seedling bioas- says in rhizosphere soils collected from a recently closed Pb- Zn tailing (Taolin Pb-Zn tailing (TLT)), a Cu tailing (Dexing Cu No. 2 tailing (DXT)) that had undergone 21 years of restoration, and a mature Masson pine (Pinus massoniana) forest (DXC) outside the Cu mining areas. The corresponding EMF communities colonizing Masson pine at each site were also investigated for comparison. After 8 months of running bioassays, ectomycorrhizal colonization was poor for seed- lings grown in TLT (9.0 %±14.9 %) and DXTsoils (22.4 %± 17.7 %), while DXC seedlings were well colonized (47.5 %± 24.9 %). Internal transcribed spacer sequencing revealed that EMF species richness increased with forest development in boththePropagulebank(TLT,6;DXT,7;DXC,12) andinthe field (TLT, 8; DXT, 14; DXC, 26), though richness was lower in Propagule banks. Several lineages, such as Cenococcum, Rhizopogon,Inocybe,Suillus,andAtheliaceae,werefrequent- ly encountered in Propagule communities, but species assem- blages were different among the three sites. Canonical corre- spondence analysis revealed that several soil parameters, i.e., N, EC, Cu, Pb, Zn, etc., were responsible for the distribution of EMF in the field and bioassay seedlings. The highest overlap in EMF species composition between the Propagule bank and the field community was observed at the recently closed tailing (Morisita-Horn similarity=0.71 for TLT), whereas the lowest overlap occurred at the mature forest (0.26 for DXC). These results indicate that EMF Propagules in soil are less frequent and diverse in early primary succes- sion and become more frequent and diverse along forest development, due mainly to the accumulation of dormant spores of Rhizopogon spp. and sclerotia of Cenococcum spp. Thus, EMF Propagule communities in soil may diverge from those root-colonizing EMF communities along a gradient of forest development.
Diana Di Nitto - One of the best experts on this subject based on the ideXlab platform.
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Modelling drivers of mangrove Propagule dispersal and restoration of abandoned shrimp farms
Biogeosciences, 2013Co-Authors: Diana Di Nitto, Paul L. A. Erftemeijer, J.k.l. Van Beek, Farid Dahdouh-guebas, L. Higazi, Katrien Quisthoudt, Loku Pulukkuttige Jayatissa, Nico KoedamAbstract:Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala–Chilaw Lagoon Complex (Sri Lanka) was studied by combining a hydrodynamic model with species-specific knowledge on Propagule dispersal behaviour. Propagule transport was simulated using a finite-volume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind), trapping agents (retention by vegetation) and seed characteristics (buoyancy) on Propagule dispersal patterns. Sensitivity analysis showed that smaller Propagules, like the oval-shaped Propagules of Avicennia officinalis , dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped Propagules of Rhizophora spp. and C. tagal . Directional Propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the Propagules being retained within the vegetation. Only a small proportion (max. 5%) of Propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once Propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows), was found to significantly affect the resultant quantities and species of inflowing Propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the value of Propagule dispersal modelling in guiding hydrological restoration efforts that aim to facilitate natural mangrove regeneration.
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size does matter but not only size two alternative dispersal strategies for viviparous mangrove Propagules
Aquatic Botany, 2012Co-Authors: Dennis De Ryck, Elisabeth M. R. Robert, Diana Di Nitto, Tom Van Der Stocken, Nele Schmitz, Farid Dahdouhguebas, Nico KoedamAbstract:We studied the Propagules of two widespread mangrove species, Ceriops tagal and Rhizophora mucronata, that are similar in shape but differ in other morpho-anatomical features (average length is 23.1 ± 2.2 cm and 44.4 ± 4.3 cm, resp., n = 180). We hypothesized the Propagules of both species to have a different hydrodynamic behavior and establishing capacity, resulting in a different dispersal strategy. More specifically, we hypothesized that C. tagal Propagules have a larger dispersal capacity than those of R. mucronata. The dispersal strategies of C. tagal and R. mucronata Propagules were elucidated through a combination of a Propagule tracking (n = 180 per species), predation (n = 20 per species) and root-growth experiment (n = 120 per species), carried out in the field. C. tagal and R. mucronata adopted two different dispersal strategies. C. tagal releases a large number of Propagules and disperses fast, having a slender morphology and low density (average ρ: 985.29 ± 19.02 g L−1), as well as a high agility (smaller size) when dispersing through dense root systems. C. tagal Propagules have a theoretical advantage to disperse over longer distances over the thicker, longer and denser R. mucronata Propagules (average ρ: 1003.92 ± 8.52 g L−1; t = 8.90, p < 0.0001, n = 197). C. tagal have, however, lower establishment chances due to slower root-growth, desiccation sensitivity and smaller size. In contrast to Ceriops’ tactic of releasing high numbers of Propagules and fast dispersal, R. mucronata has adopted a dispersal tactic of survival. Fewer Propagules are released, but they are more resistant to predators due to their larger size and they can anchor themselves faster due to quicker root-growth (Mann–Whitney U: p < 0.0001, nCt = 59, nRm = 57). Overall, Propagule characteristics of both species result in different and alternative dispersal strategies on a local scale, contradicting our initial hypothesis. On a global scale, we hypothesize this might lead to a similar capacity for long-distance dispersal, ending in successful establishment.
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Biological and environmental drivers in mangrove Propagule dispersal and recruitment: a field and modelling approach
2012Co-Authors: Tom Van Der Stocken, Diana Di Nitto, Farid Dahdouh-guebas, Dennis De Ryck, James G. Kairo, Nico KoedamAbstract:Mangrove Propagule dispersal is a key driver of the architecture and functioning of mangrove populations and communities. Nevertheless, there is a lack of information on hydrochorous dispersal of Propagules, covering the period between Propagule abscission from the tree and Propagule stranding. The relative importance of current velocity, waves, wind and the absence/presence of roots/pneumatophores on Propagule movement out of the forest and on open water remain understudied. Such knowledge is however crucial, to obtain fundamental insight in relative dispersal behavior between species, and for the construction of mathematical (individual based) dispersal models. In this study, experiments were conducted in a flume tank to establish the effect of water velocity, presence/absence of wind and the density of roots/pneumatophores (0, 5, 10 and 20 m) on the dispersal speed of a Propagule. Propagules of four mangrove species were used to eludicate the effect of Propagule morphology. In a first experiment, dispersal velocities were calculated for two different water flow velocities (15 cm s and 30 cm s). In a second experiment wind was added as an additional dispersal force, firstly, in the same direction as the water flow, secondly, opposite to the water flow. The isolated effect of wind as a driver in Propagule dispersal, was investigated as well by using a zero water flow. In the third experiment, the behavior and dispersal speed of mangrove Propagules was examined, simulating three different root densities in the flume facility. Additionally, we added waves to the water flow for a fixed root density. We demonstrated that wind significantly affects the dispersal speed of mangrove Propagules, and that the combined effect of wind and water flow strongly depends on the species under consideration, as well as on the floating behavior within a single species. Propagules that float vertically, are much less influenced by wind than their horizontally floating counterparts. For root retention, Propagules of various species show widely varying dispersal speeds for the same root density.
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to go with the flow a field and modelling approach of hydrochorous mangrove Propagule dispersal
2010Co-Authors: Diana Di Nitto, Nico Koedam, Farid DahdouhguebasAbstract:Mangrove ecosystems thrive in (sub)tropical, intertidal areas where adaptationslike vivipary and the hydrochorous dispersal of Propagules become an absolutenecessity. As Propagule dispersal and early growth allow for the replenishment ofexisting stands and colonization of new habitats, many authors recognize theimportance of these stages in structuring mangrove populations and communities.However, when it comes to the actual Propagule dispersal and recruitmentmechanisms, there is an apparent lacuna in the current understanding ofmangrove ecology. The period between the mature Propagule falling from theparental mangrove tree and the early growth of the established seedling, undervarious possible circumstances, remains in the dark. In this study we focus on thisparticular period by investigating both the places where these Propagules end upas the pathways their dispersal units follow. And we go one step further.Mangrove forests are being destroyed worldwide at a threatening pace despitetheir tremendous asset to coastal human communities and associated biologicalspecies. The effect of human-induced (cutting and mangrove conversion toaquaculture ponds) as well as indirectly and/or ‘naturally’ evolving disturbances(sea level rise) on Propagule hydrochory occupies an important place in this study.Dispersal of water-buoyant Propagules of the family Rhizophoraceae andAcanthaceae (now including the Avicenniaceae) was studied in Gazi Bay (Kenya),Galle and the Pambala-Chilaw Lagoon Complex (Sri Lanka). The study sitesdiffer both in tidal regime and vegetation structure, covering an interesting varietyof ecological settings to examine Propagule dispersal. Field data and experimentsranging from micro/ mesotopographical measurements and successive Propagulecounts to hydrodynamic and Propagule dispersal experiments were collected orexecuted in situ.Two main methodological approaches were employed. Firstly, the question onmechanisms of Propagule recruitment was addressed by statistically investigatingthe effect of microtopography, top soil texture and above-ground-root complexes onthe stranding and self-planting of Propagules (Chapter 2&3). Afterwards,suitability maps were created using Geographical Information Systems (GIS) toassess whether a particular mangrove stand has the ability to succesfullyrejuvenate. Furthermore, the effect of degradation (tree cutting) (Chapter 2&3),sea level rise (Chapter 2&4) and microtopography-altering burrowing activities ofthe mangrove mud lobster Thalassina anomala (Chapter 3), was incoporated in theGIS-analyses. Secondly, the combined set-up of hydrodynamic modelling andecological dispersal modelling was developed to simulate Propagule dispersalpathways influenced by dispersal vectors (tidal flow, fresh water discharge, wind),trapping agents (retention by vegetation or aerial root complexes) and seedcharacteristics (buoyancy, obligated dispersal period) (Chapter 5&6). This type ofapproach provided the possibility to explore Propagule dispersal within itsecological context, but was also applied to an implication of shrimp pond arearestoration (Pambala-Chilaw Lagoon Complex, Sri Lanka) (Chapter 5) and toevaluate changes in Propagule dispersal when sea level rises (Gazi Bay, Kenya)(Chapter 6).The main findings regarding Propagule recruitment indicate that Propagules arenot distributed equally or randomly within a mangrove stand, yet species-specificdistribution for anchorage occurs. Characteristics of the environment(microtopography, top soil texture and above-ground root complex) influencePropagule recruitment in a way that complex root systems (e.g. pencil roots andprop roots) facilitate the entanglement of dispersal units and a more compact soiltexture (like clay and silt) and a predominant flat topography creates suitableareas for stranding and self-planting of Propagules. This combines effects ofexisting vegetation and abiotic factors on mangrove Propagule establishment.Since Propagule dispersal is not solely determined by species-specific Propagulecharacteristics (e.g. buoyancy, longevity, etc.), I emphasize that Propagule sortingby hydrochory has to be viewed within its ecological context. Propagule retentionby vegetation and wind as a dispersal vector, deserve a prominent role in studieson Propagule dispersal. The significance of dense vegetation obstructing longdistance dispersal (LDD in its definition of this work), mainly in inner mangrovezones, supports our main finding that Propagule dispersal is largely a shortdistance phenomenon. ‘Largely’ is here understood as quantitatively, notexcluding epic colonization events of rare but important nature.In accordance with the Tidal Sorting Hypothesis (TSH) of Rabinowitz (1978a),smaller, oval-shaped Propagules were found to disperse over larger distances thanbigger, torpedo-shaped Propagules. We can however not fully support the TSHbecause (1) these differences are no longer valid when comparing between torpedoshapedPropagules of different sizes and (2) Propagule dispersal is not alwaysdirected towards areas more inland, but can be strongly concentrated towards theedges of lagoons and channelsAnthropogenic pressure on mangrove ecosystems, more specifically clear-felling ormangrove conversion to aquaculture ponds, imposes limitations on Propagulerecruitment due to reduced Propagule availability and a decrease in suitablestranding areas where the architecture of certain root complexes, like prop rootsand pencil roots, function as Propagule traps. These types of pressure appear tohave more severe consequences on Propagule dispersal than the effect of sea levelrise on mangroves. Mangrove forests, which are not situated in an obviouslyvulnerable setting, can be resilient to a relative rise in sea level if a landward shiftof vegetation assemblages and successful early colonization is not obstructed byhuman-induced pressures. Also, and this renders mangrove forests vulnerable inspite of their intrinsic resilience, when the ‘capital’ of forest is severely reduced orimpoverished as happens extensively worldwide, the ‘interest’ on this capital,understood as Propagule availability, delivery and trapping, will not allow them toefficiently cope with sea level rise, putting sustainability of mangrove ecosystemservices and goods at risk.In a larger framework of mangrove vegetation dynamics, knowledge on Propaguledispersal will benefit management strategies for the conservation of mangrovesworldwide, besides its fundamental interest to fully fathom the ecology of thisparticular marine-terrestrial ecotone formation.
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digital terrain modelling to investigate the effects of sea level rise on mangrove Propagule establishment
Marine Ecology Progress Series, 2008Co-Authors: Diana Di Nitto, James G. Kairo, Farid Dahdouhguebas, Hugo Decleir, Nico KoedamAbstract:We studied the vegetation structure dynamics of mangroves, in order to contribute to an overall view on the conditions of Propagule establishment from the moment they detach from the parental tree. Microtopographical measurements, quantitative data on vegetation, and Propagule counts were collected in Gazi Bay (Kenya) and utilized in a 'geographical information systems' (GIS) environment where all modelling took place based on digital terrain modelling (DTM). Suitability maps were created for Propagules of Rhizophora mucronata and Ceriops tagal to analyse the disper- sal possibilities (through stranding or self-planting) for the present situation, and for cases of degra- dation and sea level change. The GIS-analyses take into account the available information derived from the field data, but alterations that go hand in hand with degradation and/or sea level changes (e.g. erosion patterns, rates of sediment supply, wave action) were not considered, since our main focus was the behaviour of Propagules. We found that the study area has the potential to successfully rejuvenate at present; however, increasing anthropogenic pressure may have severe consequences on Propagule dispersal within this mangrove stand, mainly through the loss of aerial root masses, as these were shown to provide stranding areas for Propagules. A relatively modest rise in sea level within a time span of 20 yr could affect the distribution pattern and the specific proportion of the juve- nile vegetation layer, leading to notable floristic modifications from a regional point of view.
Ulrich Sommer - One of the best experts on this subject based on the ideXlab platform.
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Propagule banks herbivory and nutrient supply control population development and dominance patterns in macroalgal blooms
Oikos, 2000Co-Authors: Heike K Lotze, Boris Worm, Ulrich SommerAbstract:Destructive macroalgal mass blooms threaten estuarine and coastal ecosystems worldwide. We asked which factors regulate macroalgal bloom intensity, distribution and species composition. In field experiments in the Baltic Sea, we analyzed the relative effects of nutrients, herbivores and algal Propagule banks on population development and dominance patterns in two co-occurring bloom-forming macroalgae, Enteromorpha intestinalis and Pilayella littoralis. Both species were highly affected by the combined effects of a Propagule bank, herbivory and nutrients. The magnitude of effects varied with season. The Propagule bank was an important overwintering mechanism for both algae, and allowed for recruitment two months earlier than recruitment via freshly dispersed Propagules. This provided a seasonal escape from intense herbivory and nutrient limitation later in the year. Favored by massive recruitment from the Propagule bank, Enteromorpha was the superior space occupier in early spring, thereby reducing recruitment of Pilayella. Elimination of the Propagule bank and recruitment via freshly dispersed Propagules favored Pilayella. Strong and selective herbivory on Enteromorpha supported Pilayella in the presence, but not in the absence of the Propagule bank. Nutrient enrichment in summer counteracted herbivore pressure on Enteromorpha, thereby negatively affecting Pilayella. Herbivore and nutrient effects were more pronounced for early life stages than adult algae. These results show that recruitment processes and forces affecting early life stages at the beginning of the vegetation period determine development and dominance patterns of macroalgal blooms. Herbivores naturally suppress blooms but increasing nutrient enrichment can override this important control mechanism. The Propagule bank plays a previously unrecognized role for population and community dynamics.
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marine diversity shift linked to interactions among grazers nutrients and Propagule banks
Marine Ecology Progress Series, 1999Co-Authors: Boris Worm, Heike K Lotze, Christoffer Bostrom, Roland Engkvist, Vytautas Labanauskas, Ulrich SommerAbstract:Diverse coastal seaweed communities dominated by perennial fucoids become replaced by species-poor turfs of annual algae throughout the Baltic Sea. A large-scale field survey and factorial field experiments indicated that grazers maintain the fucoid community through selective consumption of annual algae. Interactive effects between grazers and dormant Propagules of annual algae, stored in a 'marine seed bank', determine the response of this system to anthropogenic nutrient loading. Nutrients override grazer control and accelerate the loss of algal diversity in the presence but not in the absence of a Propagule bank. This implies a novel role of Propagule banks for community regulation and ecosystem response to marine eutrophication.
