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.     

Photosynthetic characteristics of dwarf and fringe Rhizophora mangle L. in a Belizean mangrove

Twin Cays (Belize) is a highly oligotrophic mangrove archipelago dominated by Rhizophora mangle L. Ocean‐fringing trees are 3–7 m tall with a leaf area index (LAI) of 2.3, whereas in the interior, dwarf zone, trees are 1.5 m or less, and the LAI is 0.7. P‐fertilization of dwarf trees dramatically increases growth. As a partial explanation of these characteristics, it was hypothesized that differences in stature and growth rates would reflect differences in leaf photosynthetic capacity, as determined by the photochemical and biochemical characteristics at the chloroplast level. Gas exchange and chlorophyll fluorescence were used to compare photosynthesis of dwarf, fringe and fertilized trees. Regardless of zonation or treatment, net CO₂ exchange (A) and photosynthetic electron transport were light saturated at less than 500 µmol photons m^?2 s^?1, and low‐light quantum efficiencies were typical for healthy C₃ plants. On the other hand, light‐saturated A was linearly related to stomatal conductance (g_s), with seasonal, zonal and treatment differences in photosynthesis corresponding linearly to differences in the mean g_s. Overall, photosynthetic capacity appeared to be co‐regulated with stomatal conductance, minimizing the variability of C_i at ambient CO₂ (and hence, C_i/C_a). Based on the results of in vitro assays, regulation of photosynthesis in R. mangle appeared to be accomplished, at least in part, by regulation of Rubisco activity.     

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.     

Standing crop and aboveground biomass partitioning of a dwarf mangrove forest in Taylor River Slough,Florida

The structure and standing crop biomass of a dwarf mangrove forest, located in the salinity transition zone ofTaylor River Slough in the Everglades National Park, were studied. Although the four mangrove species reported for Florida occurred at the study site, dwarf Rhizophora mangle trees dominated the forest. The structural characteristics of the mangrove forest were relatively simple: tree height varied from 0.9 to 1.2 meters, and tree density ranged from 7062 to 23 778 stems ha^–1. An allometric relationship was developed to estimate leaf, branch, prop root, and total aboveground biomass of dwarf Rhizophora mangle trees. Total aboveground biomass and their components were best estimated as a power function of the crown area times number of prop roots as an independent variable (Y = B × X^–0.5083). The allometric equation for each tree component was highly significant (p<0.0001), with all r² values greater than 0.90. The allometric relationship was used to estimate total aboveground biomass that ranged from 7.9 to 23.2 ton ha^–1. Rhizophora mangle contributed 85% of total standing crop biomass. Conocarpus erectus, Laguncularia racemosa, and Avicennia germinans contributed the remaining biomass. Average aboveground biomass allocation was 69% for prop roots, 25% for stem and branches, and 6% for leaves. This aboveground biomass partitioning pattern, which gives a major role to prop roots that have the potential to produce an extensive root system, may be an important biological strategy in response to low phosphorus availability and relatively reduced soils that characterize mangrove forests in South Florida.     

Rhizophora mangle L. Seedling Development into the Sapling Stage across Resource and Stress Gradients in Subtropical Florida1

Nutrient, light, salinity, soil redox potentials, and other soil characteristics were determined across a range of mangrove forest heights across the South Florida peninsula encompassing large-stature trees (> 10 m) on the west coast and dwarf forms (< 1 m) in the southeast Everglades. Relationships were established between abiotic factors and Rhizophora mangle seedling growth rates in four height (cm) classes, 25-40, > 40-55, > 55–70, and > 70–85. Light in open canopy gaps was an important determinant of seedling growth. Growth rates in gaps (0.32 ± 0.04 to 1.89 ± 0.18 mm/d) were two- to five-fold greater than adjacent closed canopy forests (0.14 ± 0.01 to 0.40 ± 0.07 mm/d). Among open canopy sites, labile soil phosphorus and soil redox potentials were significantly correlated to growth (P < 0.05; r= 0.98 and 0.89, respectively). Interstitial salinity ranged from 0 to 27 ppt across sites, well below hypersaline conditions. Thus, under low salinity stress and high light availabiliry, soil fertility is proposed to be the dominant factor controlling R. mangle seedling development to a sapling stage (> 85 cm) in South Florida mangrove forests. In addition, soil anoxia is hypothesized to be an important stressor in lagoonal-bay estuaries and marsh-mangrove ecotones with minimal tidal exchange.     

Nitrogen vs. phosphorus limitation across an ecotonal gradient in a mangrove forest

Mangrove forests are characterized by distinctive tree-height gradientsthat reflect complex spatial, within-stand differences in environmentalfactors,including nutrient dynamics, salinity, and tidal inundation, across narrowgradients. To determine patterns of nutrient limitation and the effects ofnutrient availability on plant growth and within-stand nutrient dynamics, weused a factorial experiment with three nutrient treatment levels (control, N,P)and three zones along a tree-height gradient (fringe, transition, dwarf) onoffshore islands in Belize. Transects were laid out perpendicular to theshoreline across a mangrove forest from a fringe stand along the seaward edge,through a stand of intermediate height, into a dwarf stand in the interior ofthe island. At three sites, three trees were fertilized per zone for 2yr. Although there was spatial variability in response, growth byR. mangle was generally nitrogen (N) -limited in thefringe zone;phosphorus (P) -limited in the dwarf zone; and, N- and/or P-limited in thetransition zone. Phosphorus-resorption efficiency decreased in all three zones,and N-resorption efficiency increased in the dwarf zone in response to Penrichment. The addition of N had no effect on either P or N resorptionefficiencies. Belowground decomposition was increased by P enrichment in allzones, whereas N enrichment had no effect. This study demonstrated thatessential nutrients are not uniformly distributed within mangrove ecosystems;that soil fertility can switch from conditions of N to P limitation acrossnarrow ecotonal gradients; and, that not all ecological processes respondsimilarly to, or are limited by, the same nutrient.     

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.     

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.     

Sun-shade adaptability of the red mangrove,Rhizophora mangle (Rhizophoraceae): Changes through ontogeny at several levels of biological organization

Rhizophora mangle L., the predominant neotropical mangrove species, occupies a gradient from low intertidal swamp margins with high insolation, to shaded sites at highest high water. Across a light gradient, R. mangle shows properties of both “light-demanding” and “shade-tolerant” species, and defies designation according to existing successional paradigms for rain forest trees. The mode and magnitude of its adaptability to light also change through ontogeny as it grows into the canopy. We characterized and compared phenotypic flexibility of R. mangle seedlings, saplings, and tree modules across changing light environments, from the level of leaf anatomy and photosynthesis, through stem and whole-plant architecture. We also examined growth and mortality differences among sun and shade populations of seedlings over 3 yr. Sun and shade seedling populations diverged in terms of four of six leaf anatomy traits (relative thickness of tissue layers and stomatal density), as well as leaf size and shape, specific leaf area (SLA), leaf internode distances, disparity in blade–petiole angles, canopy spread: height ratios, standing leaf numbers, summer (July) photosynthetic light curve shapes, and growth rates. Saplings showed significant sun/shade differences in fewer characters: leaf thickness, SLA, leaf overlap, disparity in bladepetiole angles, standing leaf numbers, stem volume and branching angle (first-order branches only), and summer photosynthesis. In trees, leaf anatomy was insensitive to light environment, but leaf length, width, and SLA, disparities in bladepetiole angles, and summer maximal photosynthetic rates varied among sun and shade leaf populations. Seedling and sapling photosynthetic rates were significantly depressed in winter (December), while photosynthetic rates in tree leaves did not differ in winter and summer. Seasonal and ontogenetic changes in response to light environment are apparent at several levels of biological organization in R. mangle, within constraints of its architectural baiiplan. Such variation has implications for models of stand carbon gain, and suggest that response flexibility may change with plant age.     

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     

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.     

Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

Two species of mangrove trees of Indo-Pacific origin have naturalized in tropical Atlantic mangrove forests in South Florida after they were planted and nurtured in botanic gardens. Two Bruguiera gymnorrhiza trees that were planted in the intertidal zone in 1940 have given rise to a population of at least 86 trees growing interspersed with native mangrove species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa along 100 m of shoreline; the population is expanding at a rate of 5.6% year⁻¹. Molecular genetic analyses confirm very low genetic diversity, as expected from a population founded by two individuals. The maximum number of alleles at any locus was three, and we measured reduced heterozygosity compared to native-range populations. Lumnitzera racemosa was introduced multiple times during the 1960s and 1970s, it has spread rapidly into a forest composed of native R. mangle, A. germinans, Laguncularia racemosa and Conocarpus erectus and now occupies 60,500 m² of mangrove forest with stem densities of 24,735 ha⁻¹. We estimate the population growth rate of Lumnitzera racemosa to be between 17 and 23% year⁻¹. Populations of both species of naturalized mangroves are dominated by young individuals. Given the long life and water-dispersed nature of propagules of the two exotic species, it is likely that they have spread beyond our survey area. We argue that the species-depauperate nature of tropical Atlantic mangrove forests and close taxonomic relatives in the more species-rich Indo-Pacific region result in the susceptibility of tropical Atlantic mangrove forests to invasion by Indo-Pacific mangrove species.     

Isolation and characterization of microsatellite loci in the red mangrove Rhizophora mangle (Rhizophoraceae) and its related species

Fourteen microsatellite markers were isolated from the red mangrove Rhizophora mangle (Rhizophoraceae), a widely distributed mangrove plant in the New World and West Africa. The range of expected heterozygosity of these markers was 0.000–0.672 in the two populations of R. mangle. Cross-species testing was examined for five other species of Rhizophora, and Kandelia candel and Bruguiera gymnorrhiza. All 14 markers could be amplified in R. samoensis, thirteen in R. racemosa, and six markers in all other species of Rhizophora. Our findings greatly increase the utility of these markers.     

Mangrove ecosystem changes during the Holocene at Spanish Lookout Cay, Belize

Mangroves are halophytic plants living at the land–sea interface and are therefore natural trackers of sea-level. Multiple proxies of a continuous (8 m) mangrove peat core (BT-79) from Spanish Lookout Cay, Belize illustrate mangrove ecosystem changes during the Holocene. Radiocarbon measurements show this site was colonized by mangroves ~ 8000 cal. yrs BP, with a significant decrease in the peat accumulation rate from ~ 6000 to 1000 cal. yrs BP. Stratigraphic characteristics of this peat core such as bulk density, magnetic susceptibility, and loss on ignition show relative uniformity, inferring an uninterrupted mangrove ecosystem during a majority of the Holocene. This is supported by pollen data from BT-79 that show that the site has been consistently dominated by Rhizophora mangle (red mangrove), with Avicennia germinans (black mangrove) and Laguncularia racemosa (white mangrove) present as well. Subfossil R. mangle leaves are used for stable nitrogen, carbon, and oxygen isotope (δ¹⁵N, δ¹³C, and δ¹⁸O) analyses. δ¹⁵N and δ¹³C values provide a proxy of this plant's past physiology and stand structure showing that dwarf (δ¹⁵N < − 3‰) and tall (δ¹³C < − 27‰) R. mangle stands were previously present at the site, which are a result of nutrient limitations that we equate with seawater inundation. δ¹⁸O values show differences in source water of R. mangle, with higher values attributed to the source water being composed of a greater proportion of seawater relative to precipitation. A decrease in inundation at the site is shown by lower δ¹⁸O values (< 19‰) from ~ 7000 to ~ 1000 cal. yrs BP that covary with the decreased sedimentation rate. Existing Caribbean sea-level data do not show evidence of a decrease in the rate of relative sea-level rise or fluctuations that we take to be the major causes of environmental changes at site BT-79.     

Predation on propagules and seedlings in mature and regenerating mangroves in the coast of Ceará, Brazil

Litterfall consumption and predation on propagules is high in Indo-west-Pacific mangroves and low in Atlantic-east-Pacific ones. However, data for the latter area comes only from Caribbean and subtropical North American mangroves. South American data on litterfall consumption contradicts this view but data on predation on propagules are scarce. We measured predation on Rhizophora mangle, Avicennia schaueriana and Laguncularia racemosa propagules and seedlings and related to densities of large (>1.5 m high) and small (1–1.5 m) plants in mature and regenerating mangroves in Ceará state, Brazil. Predation on propagules was the highest among American mangroves (R. mange, >47%; A. schaueriana, >97%; L. racemosa, >83%), especially in the regenerating area. Predation on seedlings was low (maximum of 14% for R. mangle) and did not hamper growth. The dominance of large R. mangle trees in the mature mangrove is consistent with the lower predation on its propagules but the high proportions of small plants of other species indicate that dominance is achieved by mechanisms other than predation. In the regenerating mangrove, dominance of large and small L. racemosa and A. schaueriana plants is not consistent with the high predation on their propagules. Therefore, predation is not the main determinant of the species composition in this mangrove system.     

Tropical forest and mangrove history from southeastern Mexico: a 5000 yr pollen record and implications for sea level rise

A 250 cm long core from El Palmar, a swamp area located along the Rio Hondo river in the south of the Yucatan Peninsula, near the Belizean border, reveals the environmental history of the mangrove and tropical forest of the last 5000 years. The period between 5000 and 4600 b.p. shows sandy deposits, which form the early infill and development of the swamp. A medium-statured tropical forest covered the area and members of the Moraceae and Fabacaeae dominated this early forest. The period between 4600 and 4000 b.p. presents a clear change to a mangrove system with Conocarpus erecta and Rhizophora mangle as dominant trees. This vegetational change is due to flooding of the Rio Hondo river, which deposits sediments of high salinity due to higher sea-level. The medium-statured forest became established at some distance from the swamp area. After 4400 b.p. C. erecta appears as the dominant mangrove species and the R. mangle stands are less predominant in the area. The tropical forest was close to the swamp area and was mainly composed of members of the Moraceae, Arecaceae and Fabaceae as dominant taxa of this vegetational mosaic.     

Regeneration in fringe mangrove forests damaged by Hurricane Andrew

Mangrove forests along many tropical coastlines are frequently andseverely damaged by hurricanes. The ability of mangrove forests to regeneratefollowing hurricanes has been noted, but changes that occur in vegetationfollowing disturbance by hurricane winds and storm tides have not been studied.We measured changes in plant community structure and environmental variables intwo fringe mangrove forests in south Florida, USA that experienced high windvelocities and storm tides associated with Hurricane Andrew (August1992). Loss of the forest canopy stimulated regeneration via seedlinggrowth and recruitment, as well as resprouting of some trees that survived thehurricane. Initial regeneration differed among species in both forests:Rhizophora mangle L. regenerated primarily via growth ofseedlings present at the time of the hurricane (i.e., release of advancerecruits), but many trees of Avicennia germinans(L.) Stearn and Laguncularia racemosa Gaertn.f.resprouted profusely from dormant epicormic buds. In one forest, which wasformerly dominated by Laguncularia, high densities ofRhizophora seedlings survived the hurricane and grew toform dense stands of saplings and small trees ofRhizophora. In the other forest, there were lowerdensitiesof surviving Rhizophora seedlings (possibly due tohigher storm tide), and extensive bare areas that were colonized byAvicennia, Laguncularia, andherbaceous species. This forest, predominantly Rhizophoraat the time of the hurricane, now contains stands of saplings and small treesofall three species, interspersed with patches dominated by herbaceous plants.These findings indicate that moderately damaged fringe forests may regenerateprimarily via release of Rhizophora advance recruits,leading to single-species stands. In severely damaged forests, seedlingrecruitment may be more important and lead to mixed-species stands.Regeneration of mangrove forests following hurricanes can involve differentpathways produced by complex interactions between resprouting capability,seedling survival, post-hurricane seedling recruitment, and colonizationby herbaceous vegetation. These differences in relative importance ofregeneration pathways, which may result in post-hurricane forestsdifferent from their pre-hurricane structure, suggest that models forregeneration of mangrove forests will be more complex than directregeneration models proposed for other tropical forests whereregeneration after hurricanes is dominated by resprouting.     

Genetic structure of the red mangrove (<Emphasis Type="Italic">Rhizophora mangle</Emphasis> L.) on the Colombian Pacific detected by microsatellite molecular markers

Rhizophora mangle, one of the five species of the genus Rhizophora, is found widely distributed along the American and West African coasts. This species is one of the principal constituents of the mangrove ecosystem in Colombia and is also found within the most important economic activities for the communities that inhabit the littoral. In order to assess the degree of genetic diversity of R. mangle in five populations of the Colombian Pacific, nuclear microsatellite molecular markers were used. In 92 individuals sampled, it was found that 100% of the loci were polymorphic , and no private alleles were detected. The population structure of R. mangle in the Colombian Pacific, was highly significant (P < 0.001); however, the greatest differentiation was detected at the within-population level (94.62%). For the populations of La Plata, Virudó and Charambirá, the tendency toward panmixia could be the cause of the low differentiation among these three locations. Within populations, the genetic diversity revealed a deviation from Hardy–Weinberg equilibrium with high significance in Virudó and Tumaco, where it appears the intense anthropogenic activity has exercised strong pressure on the red mangrove, resulting in the possible fragmentation of the local landscape and therefore an increase in the rate of endogamy within these populations. Despite this situation, our study―one of the first developed in genetics of the red mangrove in Colombia―did not show evidence of recent bottleneck effects or deterioration in its genetic composition, which could be exploited to propose management and restoration programs for the zones where the forests of this species are degraded. Handling editor: K. Martens     

Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: A field‐based experiment

Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.     

Herbivore responses to nutrient enrichment and landscape heterogeneity in a mangrove ecosystem

Complex gradients in forest structure across the landscape of offshore mangrove islands in Belize are associated with nutrient deficiency and flooding. While nutrient availability can affect many ecological processes, here we investigate how N and P enrichment interact with forest structure in three distinct zones (fringe, transition, dwarf) to alter patterns of herbivory as a function of folivory, loss of yield, and tissue mining. The effects of nutrient addition and zone varied by functional feeding group or specific herbivore. Folivory ranged from 0 to 0.4% leaf area damaged per month, but rates did not vary by either nutrient enrichment or zone. Leaf lifetime damage ranged from 3 to 10% of the total leaf area and was caused primarily by the omnivorous tree crab Aratus pisonii. We detected two distinct spatial scales of response by A. pisonii that were unrelated to nutrient treatment, i.e., most feeding damage occurred in the fringe zone and crabs fed primarily on the oldest leaves in the canopy. Loss of yield caused by the bud moth Ecdytolopha sp. varied by zone but not by nutrient treatment. A periderm-mining Marmara sp. responded positively to nutrient enrichment and closely mirrored the growth response by Rhizophora mangle across the tree height gradient. In contrast, a leaf-mining Marmara sp. was controlled by parasitoids and predators that killed >89% of its larvae. Thus, nutrient availability altered patterns of herbivory of some but not all mangrove herbivores. These findings support the hypothesis that landscape heterogeneity of the biotic and abiotic environment has species-specific effects on community structure and trophic interactions. Predicting how herbivores respond to nutrient over-enrichment in mangrove ecosystems also requires an assessment of habitat heterogeneity coupled with feeding strategies and species-specific behavior measured on multiple scales of response.