Mangrove litter dynamics in La Mancha Lagoon,Veracruz, Mexico

In the mangrove surrounding the coastal lagoon of La Mancha, Veracruz, Mexico, we studied litter fall, litter standing crop, and turnover rates in four different mangrove settings, based on the ecological classification of Lugo and Snedaker (1974). We studied those three prominent ecological processes at the basin, fringe and riverine mangrove settings, being the last one a relict riverine stand. The aim was to describe and compare litter dynamics among mangrove types in a lagoon with an ephemeral inlet, as a way of understanding functional heterogeneity within this coastal ecosystem. The daily average values of litter fall were different (P < 0.01) among mangrove site basin I, formed by Avicennia germinans and Rhizophora mangle (2.35 g/m²/day); basin II, formed by Laguncularia racemosa, Avicennia germinans, and Rhizophora mangle (2.93 g/m²/day); fringe with Rhizophora mangle (2.13 g/m²/day); and relic riverine, also with R. mangle (4.70 g/m²/day). The amount of litter standing crop was different among sites (P < 0.001), and also between the dry and rainy season, for each mangrove type (P < 0.001). Turnover ratios were higher in basin I and basin II sites (6.34 and 7.44 times per year) than in relic riverine and fringe mangroves (1.49 and 2.39 times per year). Interstitial salinity and sediment nutrients varied among mangrove types and could influence litter production. Since this lagoon has an ephemeral inlet, continuous inundation throughout 7–8 months per year has an important effect on litter dynamics.     

Small Gap Creation in Belizean Mangrove Forests by a Wood–Boring Insect1

We investigated the role of wood-boring insects in the creation of light gaps within mangrove forests. We compared the frequency of gaps caused by wood borers to other gap-forming processes and characterized the physical attributes of light gaps in mangrove forests on small islands in Belize. Methods of quantifying light gaps included aerial photography, ground surveys, and experimental plots. Small light gaps (≤12 m²) were very common in Rhizophom mangle fringe, comprising almost 22 percent of these forests. Rhizophora mangle gaps were smaller than gaps in Avicennia germinans forests. In R. mangle forests, gaps were caused by branch death, and in A. germinans forests, gaps were caused primarily by downed trees. More than 91 percent of the gap-forming branches and boles in the R. mangle fringe were killed by a wood-boring cerambycid beetle, Elaphidion mimeticum, indicating that it is the major cause of small-scale disturbances in these forests. No trees or branches in the A. germinans forest were attacked by this beetle. In R. mangle forests, small gaps had significantly higher light levels and soil temperatures than areas under the closed canopy; however, soil conditions for sulfide concentrations, porewater salinity, and redox potentials were similar in small gaps and under the closed canopy. Survival of R. mangle, A. germinans, and Laguncularia racemosa seedlings was also higher inside these small gaps, indicating their importance in regeneration of mangrove forests. Feeding by wood borers is thus an important type of indirect herbivory in mangrove forests, with a critical role in ecological processes such as gap dynamics.     

REEXAMINATION OF PORE WATER SULFIDE CONCENTRATIONS AND REDOX POTENTIALS NEAR THE AERIAL ROOTS OF RHIZOPHORA MANGLE AND AVICENNIA GERMINANS

Soil redox potentials and pore water sulfide concentrations on a mangrove island in the Belizean barrier reef system were significantly correlated with the presence of the aerial roots of mangrove trees. Sulfide concentrations were three to five times lower near the prop roots of Rhizophora mangle (red mangrove) and the pneumatophores of Avicennia germinans (black mangrove) than in adjacent (≤ 1 meter away) unvegetated sediment. Soil redox potentials were also significantly higher near the aerial roots. A comparison of the two species revealed that sulfide concentrations in the rhizosphere of R. mangle were as low as that of A. germinans. However, sulfide concentrations in areas occupied by the black mangrove were variable and a function of pneumatophore density. The occurrence of an oxidized rhizosphere around the roots of both species suggests that the adult trees are equally capable of exploiting reduced sediments as long as their respective pathways for root aeration are functional.     

Leaf Longevity,Construction, and Maintenance Costs of Three Mangrove Species Under Field Conditions

This study assessed the effect of leaf age on construction cost (CC) in the mangrove species Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle growing in their natural habitat. Leaf osmolality values were species-specific, the highest in A. germinans (1 693 mmol kg^–1) and the lowest in L. racemosa (1 270 mmol kg^–1). In the three species, contents of chlorophyll (a+b) (Chl_a+b) and nitrogen (N) per unit of leaf area were maximal in adult leaves and tended to decline with age. Leaf mass to leaf area ratio (LMA) and ash content increased during leaf ageing. Similarly, as leaves aged, a significant increase in leaf construction cost per leaf area (CC_a) was observed, while per leaf mass (CC_m) it remained almost constant, suggesting a sustained production of leaf compounds as leaves became older. CC was positively correlated with LMA and heat of combustion (Hc) per leaf area, suggesting differences among species in the quantity and composition of expensive compounds. Leaf half lifetime (t_0.5) showed contrasting values in the three mangrove species (60, 111, and 160 d in L. racemosa, R. mangle, and A. germinans, respectively). Overall, L. racemosa was the species with less expensive leaves to construct while leaves of A. germinans and R. mangle had the highest CC_m and CC_a, respectively. Leaf longevity was positively correlated with the ratio between CC and maximum photosynthetic rate (P _max), clearly showing the existence of a balance between leaf costs and benefits.     

Evaluation of triterpenols and sterols as organic matter biomarkers in a mangrove ecosystem in northern Brazil

Mangrove leaves, sediment, and excrementfrom the mangrove crab Ucidescordatus from the coastal areas of theBragança peninsula in North Brazil wereanalysed to determine suitable biomarkersfor mangrove-derived organic matter. Leavesof Rhizophora mangle (red mangrove),the dominant species in the area, werecharacterised by high amounts of-amyrin, germanicol, taraxerol, andlupeol. Avicennia germinans (blackmangrove) mainly contained betulin, lupeol,and -sitosterol, whereas significantquantities of -sitosterol and lupeolwere typical of Laguncularia racemosa(white mangrove), the locally leastabundant species. Except for betulin, theexcrement of U. cordatus containedall of the above substances, but moststrongly reflected the triterpenolsignature of R. mangle leaves, thepredominant diet of this crab. Surfacesediments from various mangrove locationshad relatively uniform compositions thatpossibly reflect tidal mixing. Sedimentextracts were dominated by taraxerol andcontained smaller amounts of-amyrin, germanicol, and lupeol.Only sediments in a marsh area, dominatedby Sporobolus virginicus (seashoredropseed) and Eleocharis sp. (spikerush), revealed a differentbiomarker distribution. Core samples ofsubrecent sediment (up to 4000 ¹⁴C yrBP), for which previous pollen analysisindicated vegetation dominated bymangroves, had compositions similar to thatof the surface sediment. Taraxerol was themain component in the examined mangrovesediments and may be a marker for mangrovematter in this region, although analysis ofplant material did not unequivocallysupport this. Germanicol is suggested to bea biomarker for organic matter from R.mangle in North Brazil. It was detected inolder sediments, and was not significantlyaffected by ingestion by land crabs.     

Selective feeding by larval dytiscids (Coleoptera:Dytiscidae) and effects of fish predation on upper littoral zone macroinvertebrate communities of arctic lakes

Carbon and nitrogen stable isotopic data from the primary producers in mangrove ecosystems are needed to investigate trophic links and biogeochemical cycling. Compared with other mangrove species (e.g. Rhizophora mangle) very few measurements have been conducted on the white mangrove, Laguncularia racemosa. The carbon and nitrogen stable isotopic and elemental compositions of L. racemosa were analyzed and compared from Florida and Belize. ¹³C values of L. racemosa from Florida (mean = –26.4) were slightly higher than those from Twin Cays, Belize (mean = -27.4), which may be due to higher salinity in some parts of the Florida site. There was no difference between the ¹⁵N values from L. racemosa from these two sites (Florida mean = 0.6; Belize mean = 0.3), which are indicative of nitrogen derived from nitrogen fixation in a planktonic marine system. However, higher ¹⁵N values from L. racemosa at Man of War Cay in Belize (11.4 and 12.3), which is fertilized by roosting marine birds (14.0), illustrate that L. racemosa can sensitively reflect alternative nitrogen sources. Although the isotopic data could not distinguish between Avicennia germinans, R. mangle and L. racemosa in Belize the L. racemosa had considerably higher C/N ratios (46.5 – 116.1) compared with the Florida samples (42.2 – 76.0) or the other mangrove species. Unlike some previous findings from R. mangle, substrate characteristics (e.g. salinity, NH₄ ⁺, and H₂S) were not related to the isotopic or elemental composition of L. racemosa. ¹³C, ¹⁵N and C/N were analyzed for ecosystem components from L. racemosa habitats at Twin Cays, including other plants (e.g. R. mangle, A. germinans and seagrass), detritus, microbial mats and sediments. Results from mass-balance calculations show that mangrove detritus composes very little of the sediment, which is principally composed of microbial biomass (80 – 90%). Detritus at some sites is also influenced by sources other than that from L. racemosa, including seagrass leaves.     

Long-Term Growth and Succession in Restored and Natural Mangrove Forests in Southwestern Florida

We compared colonization, growth and succession from 1989 to 2000 in a restored mangrove site and in gap and closed canopy sites in a natural mangrove forest. The restored site was created in 1982 and planted with Rhizophora mangle (≈2 m⁻²) propagules. By 1989, Laguncularia racemosa, with densities up to 12.9 tree m⁻², was a dominant in all plots, although densities were greater at edge plots relative to inner plots, and near open water (west plots) relative to further inland (east plots), and in tall mangrove plots relative to scrub plots. Rhizophora mangle (1989 tree densities about 2 m⁻²) was a codominant in inner and scrub plots, while Avicennia germinans had the lowest densities (<1 tree m⁻²) in all plots. From 1989 to 2000 L. racemosa experienced reduced recruitment and apparent density-dependent mortality of canopy individuals in plots with high initial densities. Scrub plots experienced high rates of colonization by R. mangle and L. racemosa, rapid growth in height of all species (1989–1996), followed by a dieoff of L. racemosa in later years (1997–2000) as the canopy came to resemble that of tall mangrove plots. Colonization and growth rates were lower in gap and closed canopy regions of the natural forest relative to rates in the restored site. After 11 years, densities of L. racemosa were 10–20× lower and R. mangle slightly less in the gap relative to densities in tall mangrove plots in the restored site at the same age. Although the restored stand had converged with the natural forest by 2000 in terms of some factors such as species richness, vegetation cover, litterfall, and light penetration, trees were still much smaller and stem densities much higher. Full development of mature structure and ecological function will likely require decades more development.     

Structure of a unique inland mangrove forest assemblage in fossil lagoons on the Caribbean Coast of Mexico

Scrub mangrove wetlands colonize the intertidal zone of fossil lagoons located in carbonate continental margins along the Yucatan Peninsula of Mexico. These unique ecological types were investigated in October, 1994, by locating transects in several mangrove forests along the Caribbean coast of the peninsula. Four species of mangrove occurred at these sites including Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta. This is one of the first examples of a species rich scrub forest. The mangroves fell into three height categories: short scrub less than 1.5 m, tall scrub to 3.0 m, and basin forests between 4.5 and 6 m. Average height, diameter (dbh), basal area, and complexity index generally increased from short scrub to basin forests. Basal area, ranged from 0.16 m² ha^–1 in a short scrub forest intermixed with Cladium jamaicense to 12.9 m² ha^–1 in a basin forest. Density ranged from 1520 trees ha^–1 to over 25,000 trees ha^–1 in a short scrub forest dominated by R. mangle. The complexity index ranged from 0.01 to 8.3. Height, dbh, basal area, and complexity index were positively related. A number of trees were growing as sprouts from larger downed trunks, suggesting that hurricanes, such as Gilbert that occurred in 1988, are important in controlling the structure of these forests. These forests appear isolated from the sea, but are influenced by groundwater exchange occurring at the land-margin zone.     

Distribution of mangrove vegetation along inundation, phosphorus, and salinity gradients on the Bragança Peninsula in Northern Brazil

Background and aims

The Bragança Peninsula, in northern Brazil is characterized by macrotides (4 m) and specific edaphic conditions, which determine the local mangrove forest’s development. This study, conducted during the dry season evaluated the spatial patterns of Rhizophora mangle and Avicennia germinans species across an inundation gradient.

Methods

Along a transect of 700 m, measurements of structure forest, soil moisture, porewater salinity, extractable phosphorus (extr.-P) in sediments, and phosphorus in the leaves (leaf-P) were conducted.

Result

The A. germinans (100 %) occurred in high intertidal (HI) zone. A. germinans (59 %) and R. mangle (41 %) co-occurred in mid intertidal (MI) zone, while R. mangle (58 %) predominated in low intertidal (LI) zone, followed by A. germinans (37 %) and Laguncularia racemosa (5 %). Covariance analysis (ANCOVA) indicated that salinity and soil moisture means are significantly different between the mangrove forests, but do not correlate with inundation frequency (IF). The means of extr.-P were significantly different in mangrove forests and correlated with IF and leaf-P.

Conclusion

The inundation frequency, the availability of P in the sediments, phosphorus in the leaves and interstitial salinity are all important factors contributing to the distribution of the mangrove tree species A. germinans and R. mangle on the Bragança Peninsula.     

Mangroves found in Dominica (West Indies)

Mangroves has been described for the whole Caribbean are in their different habitats. The island of Dominica (West Indies) has always been excluded from the distribution area due to supposed inadequated conditions for mangrove growth. However, there are small areas with proper edaphic conditions for mangal in which black mangrove (Avicennia germinans L.) and white mangrove (Laguncularia racemosa L.) has been found. Even the occurrence of an additional Avicennia species is under discussion.     

Effect of environment and gibberellins on the early growth and development of the red mangrove, Rhizophora mangle L.

Seedlings of the red mangrove, Rhizophora mangle L., were subjected to a variety of salinity, light, and plant growth regulator treatments to examine the influence of these factors on early development. Stem, leaf, and root growth were significantly enhanced in both low salinity seawater and under reduced intensities of solar radiation. Semi-quantitative analyses of GAs by enzyme-linked immunoabsorbant assays (ELISA) suggest that under these conditions the early 3/13 hydroxylation GA₁ biosynthetic pathway is predominant in R. mangle. Concentrations of GA₁ and GA₁₉-like substances were highest in propagules exhibiting enhanced development. Attempts to identify the endogenous GAs by GC-MS were unsuccessful, most likely due to undetermined impurities present in mangroves. Exogenous applications of GA₃ to R. mangle were moderately successful in alleviating shoot growth inhibitions observed at higher salinities and light levels. The role of gibberellins is discussed in terms of metabolic responses to the external environment and possible impacts upon the distribution of this species.     

Microbial Nitrogen Cycling Processes in a Sulfidic Coastal Marsh

Sulfide distribution is a key controller of vegetation zonation in coastal ecosystems, but data are limited regarding its impact on the spatial distribution of important N cycling processes. We assessed vegetation distribution and density and, mineral N pool sizes, composition and transformations in a sulfidic coastal marsh in relation to distance from sulfur springs. We observed strong relationships between vegetation attributes (species and density) and mineral N status with greater total inorganic N, NO₃⁻ and denitrification enzyme activity (DEA) in sediment samples from areas populated by Crithmum maritimum (mid-way between S springs and sea shore) than in sediments from areas colonized by either Agropyron repens (closest to the S springs) or mangrove (Rhizophora mangleL., farthest from the springs). Our data also suggest close links between N cycling and SO₄⁻² reduction. The latter resulted in net release of NH₄⁺ ranging from 0.9 mg N kg⁻¹ in the low density C. maritimum to 3.2 mg N kg⁻¹ in the high-density A. repens, during a 3-day incubation. We also tested for microbial adaptation to long-term high sulfide exposure by measuring DEA using the C₂H₂ block method (which has been found to be strongly affected by the presence of sulfide) and amendment of marsh sediment samples with NaMoO₄ to suppress reduced S production. In sediments extracted from sites near the sulfur springs (A. repens and C. maritimum), the C₂H₂ blockage assay yielded similar results without and with NaMoO₄ addition. However, in samples from a mangrove located further downstream from the springs, DEA was substantially lower (2.3 vs. 6.8 mg N₂O-N kg⁻¹ sediment d⁻¹) when production of reduced S was not inhibited by NaMoO₄. These results suggest that denitrifying microbes in the high sulfide areas may have adapted to the presence of sulfide, allowing for high rates of N and S cycling to occur simultaneously in these marshes.     

DIFFERENTIAL OXIDATION OF MANGROVE SUBSTRATE BY AVICENNIA GERMINANS AND RHIZOPHORA MANGLE

Both Avicennia germinans (black mangrove) and Rhizophora mangle (red mangrove) are commonly found in anaerobic substrate. Black mangrove roots create oxidized rhizospheres substantially larger than those described for other plant species. When air cannot enter the root system through the pneumatophores, the rhizospheres become as reduced as nearby un vegetated soil. The presence of red mangrove, in contrast, appears to have no effect on the oxidation state of surrounding anaerobic soils. It is likely that these data help to explain the distributions of both species in intertidal associations.     

Sulfide permeability in the marine invertebrate Urechis caupo

Summary Hydrogen sulfide can reach toxic concentrations in the burrow-water of the echiuran worm Urechis caupo during low tide. Its two large epithelial surfaces, the thick muscular body wall and the thin-walled hindgut are in constant contact with the environment. Hindgut inflation of up to 2 ml water·g wet weight^-1 causes tissue stretch. To determine if these body surfaces present a barrier to sulfide influx, the total permeability coefficient P_T was measured at different degrees of stretch in diffusion chambers at pH 6.0, 7.0, and 8.0, and specific permeability coefficients P_{H 2}S and P_HS ^- were calculated. Both the body wall and the hindgut were more permeable to H₂S than HS^-. The body wall showed no significant increase in sulfide permeability with natural degrees of stretch, and the mean P_{H 2}S and P_HS ^- were 0.17 and 0.063 cm·h^-1, respectively. The sulfide permeability of the hindgut was increased by stretch, with the relative permeability of H₂S increasing faster than that of HS^-. Unstretched hindgut mean P_{H 2}S and P_HS ^- were 0.095 and 0.11 cm·h^-1, respectively, and stretched hindgut mean P_{H 2}S and P_HS ^- were 1.8 and 0.16 cm·h^-1, respectively. A model of sulfide influx in the natural environment indicates that even if the hindgut is kept uninflated, the coelomic fluid of U. caupo would have toxic sulfide concentrations well before the end of a 2-h tidal exposure in the absence of a sulfide elimination mechanism.Abbreviations P permeability coefficient - P_T total permeability coefficient - PD transepithelial potential difference     

Spatial structure of a leaf-removing crab population in a mangrove of North-Brazil

The leaf-removing decapod crab, Ucides cordatus plays a key role as ecological engineer in Brazilian mangrove ecosystems. We analyzed the spatial distribution of a specific population at two different scales to observe how individual behavior could alter spatial population structure. First, we conducted a spatial point pattern analysis of the burrow entrances and the Rhizophora mangle prop roots on the mangrove floor at a scale of few meters. Secondly, we analyzed at a large scale (10–100 m) the potential effects of surface elevation, light intensity, prop root coverage, species of neighboring tree (R. mangle, Laguncularia racemosa, Avicennia germinans) and pneumatophore density on the size and number of burrow entrances. At the same large scale, we conducted an analysis of clustering of the crabs around the R. mangle trees. At small scale, the burrow entrances, although aggregated around the prop roots, showed a regularly spaced distribution (∼25 cm) signaling an intraspecific competition among the crabs. At large scale, crabs preferred to install their burrows at an intermediate level of surface elevation and prop root coverage, and in R. mangle-dominated areas. At the same kind of habitats, the largest burrows, and thus potentially the largest crabs, were found in higher number than on other habitats. The R. mangle-dominated areas preference was confirmed by an aggregating around R. mangle trees in R. mangle-dominated forest, but only of large individuals in L. racemosa-dominated forest. These observations lead us to the definition of a preferred habitat for U. cordatus. Competition leading to the small-scale regular patterns was proposed as an explanation for exclusion of smaller crabs from preferred habitats seen at large scale. We hypothesize that this preferred habitat might explain at regional scale the variation of U. cordatus importance in Neotropical mangroves.     

Where temperate meets tropical: multi-factorial effects of elevated CO2, nitrogen enrichment, and competition on a mangrove-salt marsh community

Our understanding of how elevated CO₂ and interactions with other factors will affect coastal plant communities is limited. Such information is particularly needed for transitional communities where major vegetation types converge. Tropical mangroves (Avicennia germinans) intergrade with temperate salt marshes (Spartina alterniflora) in the northern Gulf of Mexico, and this transitional community represents an important experimental system to test hypotheses about global change impacts on critical ecosystems. We examined the responses of A. germinans (C₃) and S. alterniflora (C₄), grown in monoculture and mixture in mesocosms for 18 months, to interactive effects of atmospheric CO₂ and pore water nitrogen (N) concentrations typical of these marshes. A. germinans, grown without competition from S. alterniflora, increased final biomass (35%) under elevated CO₂ treatment and higher N availability. Growth of A. germinans was severely curtailed, however, when grown in mixture with S. alterniflora, and enrichment with CO₂ and N could not reverse this growth suppression. A field experiment using mangrove seedlings produced by CO₂‐ and N‐enriched trees confirmed that competition from S. alterniflora suppressed growth under natural conditions and further showed that herbivory greatly reduced survival of all seedlings. Thus, mangroves will not supplant marsh vegetation due to elevated CO₂ alone, but instead will require changes in climate, environmental stress, or disturbance to alter the competitive balance between these species. However, where competition and herbivory are low, elevated CO₂ may accelerate mangrove transition from the seedling to sapling stage and also increase above‐ and belowground production of existing mangrove stands, particularly in combination with higher soil N.     

Relation of water transport to leaf gas exchange properties in three mangrove species

Mangrove species more tolerant to salinity may function with less efficient water transport, which may be related to more conservative water use. To test the hypothesis, we investigate the gas exchange and hydraulic properties of three mangrove species: Rhizophora mangle L., Laguncularia racemosa Gaert and Avicennia germinans (L.)L. Experiments were performed with adult plants growing naturally in the field under a salinity of 35‰. Gas exchange parameters showed that A. germinans had significantly higher photosynthetic rates, and lower stomatal conductance and transpiration rates, compared to the other two mangroves. In concert with this, instantaneous water use efficiency was significantly high in A. germinans, intermediate in L. racemosa and lowest in R. mangle. The hydraulic parameters of the three mangrove species were in the lowest end of the range reported for tropical trees. However, the three mangrove species exhibited measurable differences in hydraulic parameters related to the control of water requirements for maintenance of carbon gain. L. racemosa and A. germinans showed less efficient water transport at shoot level but were the more efficient species in water use at the leaf level in comparison to R. mangle. Received: 7 April 1999 / Accepted: 25 July 1999     

Seedling recruitment patterns in a Belizean mangrove forest: effects of establishment ability and physico-chemical factors

A field study was conducted to evaluate the relative importance of factors affecting seedling establishment and survival on a mangrove-dominated island in Belize. An examination of spatial patterns of seedling relative densities in relation to reproductive adults and physico-chemical conditions provided correlative information on factors affecting mangrove regeneration patterns. Distance from reproductive adults explained 89–94% of the variation in relative density of Rhizophora mangle seedlings, whereas availability of resources (light and NH₄) explained 73–80% of variation in Avicennia germinans seedling relative density. Just after dispersal (December), 89% of the variation in Laguncularia racemosa seedling relative density was attributable to distance from reproductive adults, but 7 months later (July) 74% of the variation was explained by intensity of flooding- and salinity-related stresses. Survivorship (after 2.5 years) of propagules and seedlings of R. mangle and A. germinans transplanted to zones of contrasting physico-chemical conditions demonstrated that: (1) mortality was highest during the establishment phase and major causes were failure to strand before viability was lost, consumption by predators and desiccation; and (2) after establishment, differences in sensitivity to physicochemical stress factors such as flooding (A. germinans) and initial orientation of the seedling axis (R. mangle) exerted a further influence on seedling survival. The results indicate that seedling recruitment in these neotropical forests is strongly influenced by dispersal patterns, differential establishment abilities and effects of physico-chemical factors that vary with elevation and distance from the shoreline.     

Herbivore feeding preferences as measured by leaf damage and stomatal ingestion: a mangrove crab example

The diet of the mangrove crab, Aratus pisonii, was assessed by determining the percent of damaged leaves at selected mangrove communities and by examining herbivore gut contents. This study compared the utility of both methods and tested if comparable levels of damage and dietary preference occurred using the methods. Percent of damaged leaves was determined for the three species of mangroves within Tampa Bay, FL, USA, including: the red, black, and white mangroves (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa, respectively) in four 5×10-m quadrats during summer 2001. For each species, in each of the quadrats, 200 leaves per tree were assessed for the presence or absence of crab damage. A. pisonii were sampled from the same quadrats from which leaf damage data were collected. Stomach contents were dissected and food items were classified into a number of categories.Species damaged and preferred were determined by comparing relative numbers of mangrove leaf stomata from the three mangrove species in gut contents. Results suggested that both methods provide similar estimates of preference. R. mangle leaves were preferred over those of A. germinans and L. racemosa. The percent of R. mangle leaves with damage was about 20-30 times greater than the other species, and R. mangle leaf stomata were 3 to 20 times more abundant in crab guts compared to leaf stomata of the other species. Gut contents indicated that A. pisonii is omnivorous, that average-sized adult crabs (1.4-1.7-cm width) prefer R. mangle, and that the diet of males is more varied than of females. While use of both percent leaf damage and crab gut contents reliably indicates preference, gut contents may describe better the actual diet and elucidate trends for different size or sex classes within a population.     

Root biomechanics in Rhizophora mangle: anatomy,morphology and ecology of mangrove’s flying buttresses

Background and Aims Rhizophora species of mangroves have a conspicuous system of stilt-like roots (rhizophores) that grow from the main stem and resemble flying buttresses. As such, the development of rhizophores can be predicted to be important for the effective transmission of dynamic loads from the top of the tree to the ground, especially where the substrate is unstable, as is often the case in the habitats where Rhizophora species typically grow. This study tests the hypothesis that rhizophore architecture in R. mangle co-varies with their proximity to the main stem, and with stem size and crown position.Methods The allometry and wood mechanical properties of R. mangle (red mangrove) trees growing in a mangrove basin forest within a coastal lagoon in Mexico were compared with those of coexisting, non-buttressed mangrove trees of Avicennia germinans. The anatomy of rhizophores was related to mechanical stress due to crown orientation (static load) and to prevailing winds (dynamic load) at the study site.Key Results Rhizophores buttressed between 10 and 33 % of tree height. There were significant and direct scaling relationships between the number, height and length of rhizophores vs. basal area, tree height and crown area. Wood mechanical resistance was significantly higher in the buttressed R. mangle (modulus of elasticity, MOE = 18·1 ± 2 GPa) than in A. germinans (MOE = 12·1 ± 0·5 GPa). Slenderness ratios (total height/stem diameter) were higher in R. mangle, but there were no interspecies differences in critical buckling height. When in proximity to the main stem, rhizophores had a lower length/height ratio, higher eccentricity and higher xylem/bark and pith proportions. However, there were no directional trends with regard to prevailing winds or tree leaning.Conclusions In comparison with A. germinans, a tree species with wide girth and flare at the base, R. mangle supports a thinner stem of higher mechanical resistance that is stabilized by rhizophores resembling flying buttresses. This provides a unique strategy to increase tree slenderness and height in the typically unstable substrate on which the trees grow, at a site that is subject to frequent storms.