Rhizophora Zone Research Articles

Crab Species-Specific Excavation and Architecture of Burrows in Restored Mangrove Habitat

Burrowing crabs are considered to be ecosystem engineers, playing a vital role in mangrove ecosystems through bio-geochemical transformation. This process depends on the size and shape of burrows. The present study analyzes the architecture of burrows constructed by crabs in a restored mangrove habitat. Fourteen crab species were found to construct burrows of 13 different shapes, with a predominance of I-, J-, and L-shapes. Sesarmids were larger in size than fiddlers, and made burrows with wider openings mostly in the Rhizophora zone. Fiddlers constructed complex burrows with a vertical position, and made longer and deeper burrows in contrast to sesarmids, which formed simple burrows with a horizontal position, digging shorter and shallower burrows in Avicennia or open zones. The sesarmids had smaller burrows without branching in mangrove zones, whereas the fiddlers had larger burrows with or without branching in open and Avicennia zones. The burrows of fiddler crabs, especially Austruca occidentalis and A. annulipes, had separate openings and passages for exit and entry as an adaptation against predators. The present work identified Austruca occidentalis and A. annulipes as the most potent bioturbating crab species in restored mangrove habitats due to their efficiency in soil excavation and formation of large-sized burrows.

Mangrove zonation, community structure and healthiness in Kei Islands, Maluku, Indonesia

Abstract. Dharmawan IWE, Renyaan J, Nurdiansah D. 2022. Mangrove zonation, community structure and healthiness in Kei Islands, Maluku, Indonesia. Biodiversitas 23: 4918-4927. Forest structure and quality were studied in an archipelagic site in Indonesia which consists of estuarine and oceanic mangrove habitats. This study aimed to determine mangrove structure and estimate the spatial distribution of forest healthiness along the zones dominated by different genera. Forest zones were investigated using the Random Forest method utilizing a cloud-free Harmonized Sentinel-2A-Surface Reflectance image. Community structure measurement followed a stratified purposive sampling design along forest zonation. A spatial-based mangrove health index (MHI) model was applied to analyze forest healthiness distribution in each zone. Mangrove area was clearly classified into six genera-dominated zones such as Sonneratia, Rhizophora, Bruguiera, Ceriops, Xylocarpus and Lumnitzera from seaward to landward. The Rhizophora zone had the most extensive area proportion at approximately 68% of the total mangrove area. This study revealed that S. alba species dominated in the outmost zone at about 200% of IVI, while X. granatum and C. tagal were calculated in a larger IVI value in the more landward area. On the other hand, R. stylosa had a majority species composition in Rhizophora forest. According to spatial analysis of MHI, most zones had a majority area of excellent condition, emphasizing that the entire mangrove forest was pristine.

Spatial distribution of mangrove health index on three genera dominated zones in Benoa Bay, Bali, Indonesia

Abstract. Sugiana IP, Andiani AAE, Dewi IGAIP, Karang IWGA, As-Syakur AR, Fharmawan IWE. 2022. Spatial distribution of mangrove health index on three genera dominated zones in Benoa Bay, Bali, Indonesia. Biodiversitas 23: 3407-3418. A study of mangrove forest stratification was conducted in Benoa Bay which experienced high coastal development pressures during the last decade. The study aimed to determine mangrove health index distribution (MHI) and forest community structures along three genera-dominated zones which were Sonneratia, Rhizophora and Bruguiera. Random forest method was applied to classify the areas of distributed genera along the bay. Forest structure was assessed with 54 plots. The forest was mainly composed of Rhizophora and Sonneratia-dominated zones in a respective forest area proportion at approximately 51% and 45%. Those zones were dominated by R. mucronata and S. alba with an importance value index (IVI) at 266.35% and 145.57%, respectively. A narrow Bruguiera zone composed of B. gymnorrhiza domination was found in the most landward area, only covering 4% of the mangrove area. Overall accuracy and a kappa coefficient indicated high accuracy of forest classification at 97% and 0.94 respectively. We found that 47.44% of mangrove areas could be classified into the highest healthiness category indicating that the mangrove forest in Benoa Bay is in excellent condition. The Rhizophora zone made a significant contribution to the entire forest state since the excellent category coverage in this zone was approximately 73.80%.

Benthic Meiofaunal Diversity in Four Zones of Pichavaram Mangrove Forest, India

ABSTRACTThe community structure of meiofauna was assessed relative to environmental parameters in four zones (non-mangrove, Avicennia zone, mixed zone, and Rhizophora zone) of Pichavaram Mangrove Forest, which is located along the southeast coast of India. Field sampling was carried out from June 2016–May 2017. The meiofaunal data were evaluated using univariate and multivariate statistics. The highest abundance of meiofauna (434 ind/10 cm−2) was recorded in the Rhizophora zone and the lowest (270 ind/10 cm−2) in the non-mangrove zone. A total of 62 species representing four meiofaunal groups were recorded, including 38 species of foraminifera, 12 species of nematodes, seven species of ostracods, and five species of harpacticoids. Diversity (Shannon H′) mostly ranged from 3–4, and was highest (3.86±0.26) in the Avicennia zone and averaged ∼3.3 in the other three zones. The Margalef richness index was ∼6 in the Avicennia and Rhizophora zones and ∼5 in the non-mangrove and mixed zones. The BIO-ENV and CCA analyses identified sediment texture and organic matter as key variables influencing the distribution of meiofauna, while % calcium carbonate, salinity, and sediment pH were also important. Monitoring studies of meiofaunal taxa may help elucidate their roles in coastal blue-carbon cycling and will also contribute to understanding how mangrove-associated habitats influence meiofaunal distributions.

Development of a Rapid Mangrove Zonation Mapping Workflow Using Sentinel 2-Derived Indices and Biophysical Dataset

Moderate to high resolution satellite imageries are commonly used in mapping mangrove cover from local to global scales. In addition to extent information, studies such as mangrove composition, ecology, and distribution analysis require further information on mangrove zonation. Mangrove zonation refers to unique sections within a mangrove forest being dominated by a similar family, genus, or species. This can be observed both in natural and planted mangrove forests. In this study, a mapping workflow was developed to detect zonation in test mangrove forest sites in Katunggan-It Ibajay (KII) Ecopark (Aklan), Bintuan (Coron), Bogtong, and Sagrada (Busuanga) in the Philippines and Fukido Mangrove Park (Ishigaki, Japan) using Sentinel-2 imagery. The methodology was then applied to generate a nationwide mangrove zonation map of the Philippines for year 2020. Combination of biophysical products, water, and vegetation indices were used as classification inputs including leaf area index (LAI), fractional vegetation cover (FVC), fraction of photosynthetically-active radiation (FAPAR), Canopy chlorophyll content (Cab), canopy water content (Cw), Normalized Difference Vegetation Index (NDVI), modified normalized difference water index (MNDWI), modified chlorophyll absorption in reflectance index (MCARI), and red-edge inflection point (REIP). Mangrove extents were first mapped using either the Maximum Likelihood Classification (MLC) algorithm or the Mangrove Vegetation Index (MVI)-based methodology. The biophysical and vegetation indices within these areas were stacked and transformed through Principal Component Analysis (PCA). Regions of Interest (ROIs) were selected on the PCA bands as training input to the MLC. Results show that mangrove zonation maps can highlight the major mangrove zones in the study sites, commonly limited up to genera level only except for genera with only one known species thriving in the area. Four zones were detected in KII Ecopark: Avicennia zone, Nypa zone, Avicennia mixed with Nypa zone, and mixed mangroves zones. For Coron and Busuanga, the mapped mangrove zones are mixed mangroves, Rhizophora zone and sparse/damaged zones. Three zones were detected in Fukido site: Rhizophora stylosa-dominant zone, Bruguiera gymnorrhiza-dominant zone, and mixed mangrove zones. The zonation maps were validated using field plot data and orthophotos generated from Unmanned Aerial System (UAS) surveys, with accuracies ranging from 75 to 100%.

The Abundance and Distribution of Mangrove Gastropods from Kuala Selangor Nature Park, Selangor

This study reports on the abundance and distribution of mangrove gastropods from Kuala Selangor Nature Park, Malaysia (KSNP). The line transect method with quadrats (5m x 5m) was employed to sample the gastropods. Gastropods were collected from the leaves, branches, stems and roots of trees and the mangrove floor. Nineteen gastropod taxa from seven families were recorded from the Bruguiera, mixed (Bruguiera, Avicennia and Rhizophora), Avicennia and Rhizophora zones. Avicennia sp. recorded the largest Girth at Breast Height (GBH) (mean±sd=37.3±18.2 cm) while Bruguiera sp. recorded the smallest GBH (mean=22.36±8 cm). The overall density of the gastropods at KSNP was 0.85 no/m2. The gastropod density was higher at the Avicennia & Rhizophora zone (150-200m (closer to the mudflats) (0.064±0.084 no/m2) followed by the mixed zone (50-150m) (0.046±0.30 no/m2) and lowest at the Bruguiera zone (0-50m) (0.08±0.080 no/m2) (closer to the coastal bund). Gastropod density between sampling zones did not vary significantly (p>0.05) but generally increased from the bund towards the mudflat edge. Further studies of the role of gastropods in the coastal food chain, as bio-indicators of habitat change and as potential food source for local populace are needed.

Use of airborne Lidar to investigate mangrove accommodation space in macrotidal estuaries of northern Australia

Extensive mangroves in the Northern Territory of Australia reflect the large tidal range along that coast. Airborne Lidar enables interpretation of ground elevation along transects through mangroves and across coastal and estuarine plains, supplementing past levelling surveys of elevation range of the principal mangrove taxa. Mangrove distribution in the upper intertidal varies geographically in response to tidal variations. In the well-mapped Darwin and Bynoe Harbours, Sonneratia alba grows at elevations below mean sea level, whereas Rhizophora occupies a prominent zone that is inundated by neap tides. Ceriops is generally found at higher elevations, often showing a canopy height gradation. A number of mangroves, including Avicennia, occur at the upper bound of the mangrove forest adjacent to the hinterland, which occurs at ~2.8 m above Australian Height Datum (AHD) on the open coast and at ~3.6 m AHD, reflecting tidal amplification, in the embayments. Along the less known macrotidal estuaries of the Alligator Rivers, accommodation space and species distribution varies with distance from the open coast. On the coastal plain that has formed along the southern margin of van Diemen Gulf, Lidar reveals that landwardmost mangroves also occur up to an elevation of ~2.8 m AHD. Amplification of tides in the cuspate-meandering middle sections of the South and East Alligator Rivers enables mangroves to occur up to 3.5–3.6 m AHD, in contrast to the less infilled West Alligator River. The Lidar reveals substrate topography and vegetation structure. The Rhizophora zone is particularly distinct and its steeper gradient implies rapid sediment accretion; Rhizophora has played a disproportionately large role in the sequestration of blue carbon. Low-lying parts of these estuarine plains, particularly former channels, are already experiencing tidal creek extension and saline intrusion, and topography of the landscape behind the mangroves will mean many areas will be vulnerable to future salinization in response to rising sea level.

Mapping of mangrove extent and zonation using high and low tide composites of Landsat data

Monitoring mangrove health and distribution requires reliable methods that can be undertaken rapidly and at a resolution that optimises costs and accuracy. The Landsat record has been used for this purpose, but its application has been limited by the capacity to provide accurate results that distinguish mangrove from adjoining communities. The Australian Geoscience Data Cube provides a framework for exploring the Landsat record from 1987 onwards, and as pre-processing has already been undertaken there are efficiencies gained using this resource. Using the Data Cube, we exploited the differential spectral signature of mangrove under high tide and low tide conditions at Darwin Harbour, Australia, a relatively stable mangrove ecosystem, using image composites that combined imagery corresponding to the highest 10% and lowest 10% of tides. By applying the automated RandomForest classification technique, we demonstrate the capacity to accurately determine the extent of mangrove zones. Classification identified five mangrove zones: (1) seaward margin dominated by Sonneratia alba, (2) Rhizophora zone dominated by Rhizophora stylosa, (3) tidal flat dominated by Ceriops tagal, (4) landward salt flat and (5) marginal hinterland. Image composites that included high and low tide images achieved the best outcomes with kappa co-efficient of 0.81 and overall accuracy of 82%.

Mangrove zonation and utilization by the local people in Ajuy and Pedada Bays, Panay Island, Philippines

The study was conducted in order to establish and describe the mangrove zones and the resource uses in Ajuy and Pedada Bays, Panay Island, Iloilo, Philippines. Plot or quadrat method coupled with informal community folk interviews were done. Cluster and principal component analyses indicated four mangrove zones: Zone 1 – Avicennia–Sonneratia zone; Zone 2 – Avicennia–Rhizophora zone; Zone 3 – Avicennia–Excoecaria–Bruguiera–Ceriops zone; and Zone 4 – Avicennia zone. Fishpond establishment was the main dominant activity. Additionally, subsistent and apparently sustainable localized fuel wood gathering was still evidently practiced by the fisherfolks. With the bays’ natural mangrove landscape greatly deformed and transformed, the study recommends two strategies which could serve as its turning point leading to a more sustainable utilization and conservation of the mangroves. First we recommend the creation of a landscape corridor and secondly, adoption of a mangrove aquasilviculture system as an alternative to the current extensive fishpond practice. Implementation of these two strategies can be facilitated by a strong biodiversity education program and a local ordinance.

Cross-shore gradients of physical disturbance in mangroves: implications for seedling establishment

Abstract. Mangroves may grow in an active sedimentary environment and are therefore closely linked to physical coastal processes. Seedlings colonize dynamic tidal flats, after which mangroves have the potential to change their physical environment by attenuating hydrodynamic energy and trapping sediments. Disturbance from hydrodynamic energy of waves or currents and the resulting sediment dynamics appear to be a critical bottleneck for seedling establishment on tidal flats and at the forest fringe. However, knowledge about the mechanisms at the single plant level and the spatial pattern of disturbance is limited. By means of a flume study, we demonstrate that a surface erosion threshold of as little as 1–3 cm depth can lead to failure of young seedlings. By monitoring accretion/erosion for 8 months along cross-shore transects in southwest Thailand, we show that, especially on the bare mudflat, the physical sediment disturbance regularly exceeds the critical erosion thresholds derived from the flume study. Physical sediment parameters along the same transects were analysed to deduct patterns of hydrodynamic energy attenuation. Grain size analysis and erosion/accretion data showed only limited energy dissipation within the fringing Avicennia/Sonneratia zone; sediment dynamics only dropped below lethal values for seedlings within the denser Rhizophora zone. Overall, present results emphasize that (i) seedling survival is extremely sensitive to physically driven sediment dynamics and (ii) that such physical disturbances are not only present on the tidal flats but can penetrate a significant distance into the forest. Spatio-temporal patterns in sediment dynamics should hence be considered when conducting restoration of mangrove ecosystems.

Species composition, comparative size and abundance of the genus Littoraria (Gastropoda: Littorinidae) from different mangrove strata along the East African coast

Variation in the abundance, distribution and size of four species of mangrove littorinid gastropods (genus Littoraria) was investigated using a nested sampling design at different spatial scales along the East African coast, from Tanzania to South Africa. Littorinid abundance and diversity decreased abruptly south of Inhaca Island at the southern end of the study area. All species presented a large-scale spatial variation in abundance, with L. subvittata showing the greatest abundance while L. intermedia was rare. Littoraria scabra and L. intermedia were found mainly at the seaward edge of the forests. Littoraria subvittata increased in abundance in the middle of the forest and towards the landward side. Littoraria pallescens occurred mainly at the seaward edge and in the middle areas in the Rhizophora zone. These small-scale variations show contrasting specific distribution patterns within the mangrove, likely reflecting different tolerances to physical factors and biological interactions. All species appeared decreased in shell height from north to south. Littoraria scabra was always significantly larger than other species at all mangrove study sites.

Mangrove sesarmid crab feeding experiments in Peninsular Malaysia

The feeding ecology of mangrove sesarmid crabs in Peninsular Malaysia was investigated by field and laboratory experiments using four mangrove leaf species ( Avicennia officinalis, Bruguiera gymnorrhiza, B. parviflora and Rhizophora apiculata) and leaves of different condition (fresh and senescent). Leaves tethered on strings at high ( Bruguiera zone) and low ( Rhizophora zone) intertidal positions, both upstream (Sungai Pasir) and downstream (Lower Merbok) showed significant amounts of leaf litter removal in 24 h (mean 79±3% initial dry mass). Significantly more B. gymnorrhiza was consumed in Bruguiera zones and significantly less senescent A. officinalis in the upstream Rhizophora zone. In Bruguiera zones, significant numbers of leaves were taken down burrows but there were no preferences for leaf species or condition of leaf taken down burrows at all sites. In 24 h, under laboratory conditions, the sesarmid crabs Sesarma (Perisesarma) eumolpe and S. (Perisesarma) onychophorum were offered with a mangrove species choice of either fresh or senescent leaves. There was no difference in mangrove species taken when the leaves were senescent for both crab species, but when the leaves were fresh, significantly more A. officinalis leaves were consumed by both sesarmid crab species. S. onychophorum ate significantly more B. parviflora than did S. eumolpe. The crab distribution in the field was related to the preferred tree species dominance, indicating that tree species may be important for crab species distribution, or vice versa. The mean rate of leaf consumption was not significantly different between the crab species; S. eumolpe was 29.9±5.9 and S. onychophorum was 35.3±7.2 mg dry mass per wet mass gram of crab in 24 h. Rhizophora spp. were the least preferred species in all feeding experiments, a finding which may have implications for ecosystem functioning in monoculture rehabilitation projects.

Abundance, Zonation and Foraging Ecology of Birds in Mangroves of Darwin Harbour, Northern Territory.

The density, seasonality, habitat utilization and foraging ecology of birds in mangals (mangrove forests) at a site on the upper reaches of Darwin Harbour were investigated by transect censusing and colour-banding over three years. Despite having only 10 species of plants, the site supported 17 confirmed and five probable breeding resident species of birds, and was visited by 30 more. From variable-width transect censuses, the mean density of birds on a 4-ha plot was estimated to be 25 ha-1, fairly consistent with densities obtained from territory mapping of colour-banded birds. Nearly 70% of the individuals belonged to just 4 species: two mangal-dependent species, the red-headed honeyeater (Myzomela erythrocephala) and the yellow white-eye (Zosterops lutea) and two more generalised species, the large-billed gerygone (Gerygone magnirostris) and the brown honeyeater (Lichmera indistincta). Only the red-headed honeyeater showed significant seasonal variation in abundance, with highest numbers during the late dry season after breeding. This coincided with the period of greatest food (nectar) availability in the mangal, due to flowering Bruguiera exaristata. Lowest numbers of the red-headed honeyeater (and the brown honeyeater) occurred in the late wet season when nectar was scarce in the mangal but abundant in Melaleuca cajuputi fringing the mangal. Several resident species held permanent territories, while others apparently shifted landward during the wet season, possibly due to the wetter conditions created by freshwater runoff and high spring tides Many species showed strong associations with particular mangal zones. Large-billed gerygones, grey whistlers (Pachycephala simplex), shining flycatchers (Myiagra alecto) and mangrove fantails (Rhipidura phasiana) were associated with the Rhizophora zone at the wetter (more frequently inundated) end of the plot; mangrove robins (Eopsaltria pulverulenta) and mangrove gerygones (Gerygone laevigaster), were encountered most in the Ceriops zone; and green-backed gerygones (Gerygone chloronata) strongly favoured the dry landward edge. Four foraging guilds were evident among 13 of the most abundant species, the largest of which was the insectivorous foliage-foraging guild. Species in this group partitioned resources by differential selection of mangrove species, heights and foraging techniques. The tiny (6.4 g) mangrove gerygone was the most specialized species, spending 80% of its time on Avicennia marina. Contrary to the literature, breeding of mangal-dwelling birds peaked during the dry season. The ecology, evolution and biogeography of mangrove-endemic birds is reviewed in the light of this study and recent information from Western Australia.

Root biomass of a mangrove forest in southern Thailand. 1. Estimation by the trench method and the zonal structure of root biomass

ABSTRACTIn a mangrove forest in southern Thailand, the root biomass was estimated for the Sonneratia zone, the Sonneratia-Bruguiera ecotone, the Bruguiera zone and the Rhizophora zone. A 0.2 m (width) × 15.5 m (length) × 1.0 m (depth) trench was dug between two trees of Rhizophora apiculata and the roots in the trench harvested, rinsed, sorted by diameter and weighed. The dry weight of roots collected from the trench was 135.6 kg, equivalent to a total root biomass of 437.5 t ha−1 including 220.5 t ha−1 of fine roots.The root density distribution of a single tree was assumed to be predictable exponentially. Two variables of the equation were determined by iteration using the data from a trench excavation and tree distribution study. This equation was applied to 1.3 ha and the root biomass distribution was analysed. The root biomass in each of the above four zones was estimated at 171.8, 84.8, 242.6 and 509.5 t ha−1, respectively. The proportion of fine roots (<2 mm) ranged from 46.4% to 66.4%.

The genus Rhizophora in Suriname

The peculiar distribution of the species of Rhizophora (Rhizophoraceae) is wellknown. Floras and manuals usually mention one western species — R. mangle L. — that occurs both in the coastal regions of tropical and subtropical America and in the corresponding habitats of west tropical Africa, and an eastern species — R. mucronata Lam. — occurring both in tropical Asia and in east tropical Africa. It is also well-known that a few other species occur in tropical Asia; a recent revision has been given by HOU (1958). G. F. W. MEYER (1818) described from British Guiana a second American species, R. racemosa, differing in the inflorescence which is forked and 2-flowered in R. mangle and much-branched in R. racemosa. ENGLER (1876) regarded this species as a variety of R. mangle; most botanists, however, considered it synonymous with the latter. LEECHMAN (1918) published an investigation of the Rhizophoras of Georgetown, British Guiana. He found not only the two species of Meyer but also a third species, R. harrisonii Leechm., provided with a much-branched inflorescence as in R. racemosa. The hypocotyls (also considered radicles) of both R. mangle and R. harrisonii reach a length of up to 30 cm, that of R. racemosa a length of up to 65 cm. The opinion of most botanists, however, remained unchanged: namely that the material of the genus Rhizophora from both America and West-Africa belongs to one species, R. mangle L. In treating the Rhizophoraceae for the Flora of Suriname I shared this opinion (JONKER, 1942). In 1953, however, KEAY published his revision of the West-African Rhizophoras based on field observations. He concluded that the three species recognized by Leechman also occurred in West-Africa. SAVORY (1953) studied the ecology of Rhizophora in Nigeria and found that the most common species is R. racemosa, a pioneer at the outer border of the Rhizophora zone. R. harrisonii is dominant in the middle region and R. mangle in the interior part of the zone. The latter has the highest salt tolerance and occurs in the habitats with the highest salt concentration in the dry season. The other species obtain, especially in the wet season, more fresh water.