Mangrove Production Research Articles

Short-circuit in the mangrove food chain

Crabs of the subfamily Sesarminae are important components of mangrove ecosystems in the Indo-west Pacific, Africa, the Caribbean and South America. By retaining a large proportion of mangrove leaf-litter within mangrove forests, they profoundly influence the functioning of mangrove ecosystems. Despite obvious importance to ecosystem functioning, little is known about predation on sesarmid crabs. Three large, predatory fishes of tropical Indo-Pacific estuaries, the groupers Epinephelus coioides and E. malabaricus and the snapper Lutjanus argentimaculatus are known to feed on brachyuran crabs. However, the contribution of sesarmids to the brachyuran component of the diets of these fishes is unknown. To determine the extent to which these fishes prey on sesarmid crabs, the gut contents and stable isotope values (δ13C and δ15N) of E. coioides, E. malabaricus, and L. argentimaculatus from 3 mangrove estuary systems on the northeast coast of tropical Australia were investigated. All 3 species fed extensively on sesarmid crabs. Sesarmid crabs were the dominant food items for E. malabaricus and L. argentimaculatus, occurring in 50% of the stomachs that contained prey, and being the most common prey in terms of overall numbers. Although still the dominant prey, sesarmids occurred in only 30% of E. coioides stomachs. As well as being numerically dominant, sesarmids were large relative to other prey types. The 3 species also had stable isotope values enriched by about +0.75 to +2 δ13C and +1.5 to +2.5 δ15N, which were also consistent with extensive feeding on these crabs. Most other sympatric species had quite different diets and stable isotope profiles. Extensive feeding on sesarmid crabs by these fishes has a range of implications for the ecology of tropical mangrove ecosystems. Food webs are apparently more complex, and food chains leading from mangroves to top predators may be shorter than previously thought. Furthermore, a substantial part of the mangrove productivity sequestered by sesarmid crabs may be exported from mangrove ecosystems as a result of offshore migration by these fishes. The low incidence of piscivory in these fishes adds support to theories that reduced predation pressure may enhance the nursery ground value of tropical mangrove systems for fishes.

A simulation model of organic matter and nutrient accumulation in mangrove wetland soils

The distribution and accumulation of organic matter, nitrogen (N) and phosphorus (P) in mangrove soils at four sites along the Shark River estuary of south Florida were investigated with empirical measures and a process-based model. The mangrove nutrient model (NUMAN) was developed from the SEMIDEC marsh organic matter model and parameterized with data from mangrove wetlands. The soil characteristics in the four mangrove sites varied greatly in both concentrations and profiles of soil carbon, N and P. Organic matter decreased from 82% in the upstream locations to 30% in the marine sites. Comparisons of simulated and observed results demonstrated that landscape gradients of soil characteristics along the estuary can be adequately modeled by accounting for plant production, litter decomposition and export, and allochthonous input of mineral sediments. Model sensitivity analyses suggest that root production has a more significant effect on soil composition than litter fall. Model simulations showed that the greatest change in organic matter, N, and P occurred from the soil surface to 5 cm depth. The rapid decomposition of labile organic matter was responsible for this decrease in organic matter. Simulated N mineralization rates decreased quickly with depth, which corresponded with the decrease of labile organic matter. The increase in organic matter content and decrease in soil bulk density from mangrove sites at downstream locations compared to those at upstream locations was controlled mainly by variation in allochthonous inputs of mineral matter at the mouth of the estuary, along with gradients in mangrove root production. Research on allochthonouns sediment input and in situ root production of mangroves is limited compared to their significance to understanding nutrient biogeochemistry of these wetlands. More accurate simulations of temporal patterns of nutrient characteristics with depth will depend on including the effects of disturbance such as hurricanes on sediment redistribution and biomass production.

Sources, sinks, and export of organic carbon through a tropical, semi‐enclosed delta (Hinchinbrook Channel, Australia)

A mass balance for organic carbon in Hinchinbrook Channel was constructed to identify major sources, sinks, and the magnitude of organic matter available for export to the adjacent coastal zone. Total organic carbon input from the Herbert River and from net production of mangroves, phytoplankton, seagrasses, and benthic microalgae is 8.94 ×109 M Corg yr−1 (moles organic carbon per year). Mangroves and river inputs are the largest carbon sources, accounting for 56% and 27% of the total annual input, respectively. Benthic respiration and burial in sediments are the major sinks, accounting for 46% and 41% respectively of total losses (3.09 ×109 M Corg yr−1). This mangrove‐dominated coastal ecosystem is net autotrophic, with 5.85×109 M Corg yr−1 (65% of total Corg input) available for export to the adjacent nearshore zone. Total export of organic carbon from the region (adding carbon export from Missionary Bay mangroves on the northern end of Hinchinbrook Island) amounts to 82,800 metric tons of organic carbon per year. These results confirm earlier evidence indicating that much of the particulate sediment carbon in the adjacent coastal zone is of mangrove origin. This mass balance, although preliminary, demonstrates the importance of Hinchinbrook Channel as a source of organic matter for the Great Barrier Reef lagoon.

Mangroves of China: a brief review

The distribution, ecology, conservation and management of Chinese mangroves are reviewed. Mangroves naturally occur along the southeast Chinese coast and traverse the provinces of Hainan, Guangdong, Guangxi, Fujian and Taiwan, intermittently extending from 18°N. Thirty-seven mangrove tree species, representing 20 families and 25 genera, have been documented, with thermophilic eurytopic species being the dominant components. A remarkable decrease of species richness is evident from Hainan (18–20°N) to Fujian (23.5–27°N) (35 vs. 9 species). The existing mangrove area is ≈ 17 800 ha, accounting for slightly more than 0.1% of the world's total. Nearly two-thirds of China's mangroves have been lost during the past 40 years, largely due to conversion for rice-farming, embankment for aquaculture ponds and, recently, rapid urban development. A total of 201 papers on Chinese mangroves was published between 1950 and 1995, 178 of which are in Chinese; thus, they are not easily accessible to the international scientific community. Most of the work was conducted after 1985 (91% of the papers published) and research emphasized floristics with little attention to managementrelated issues. The net primary production of the Chinese mangroves shows a latitudinal trend, also significant deviations from predictions on models generated using non-Chinese data. Although 28 Chinese institutions have dealt with mangrove research, only five maintain long-term projects. The bulk of research has been carried out in six mangrove reserves: Qinglan, Dongzhai (Hainan), Mai Po (Hong Kong), Futian (Guangdong), Shankou (Guangxi) and Jiulongjiang (Fujian). Twelve mangrove reserves have been established so far in mainland China, one in Hong Kong (Mai Po) and one in Taiwan (Tanshui). These reserves cover an area of over 19000 ha, of which 8445 ha are mangroves (47% of existing mangrove area). Six measures that can facilitate mangrove conservation and management are recommended: (a) declare more mangrove areas as nature reserves; (b) set up a national mangrove committee and mangrove research centre to foster research and management; (c) develop concrete management guidelines; (d) enact protective legislation and ensure its strict enforcement; (e) launch education programmes in the major mangrove reserves; and (f) stop further nonsustainable exploitation of mangroves and their habitats.

Litter Fall and Energy Flux in a Mangrove Ecosystem

Production, elemental composition andin situdecomposition of litter ofRhizophora apiculata,R. mucronata,Sonneratia albaandAvicenna officinaliswere studied in a mangrove ecosystem fringing Madovi–Zuari Estuaries on the Central West Coast of India. Litter yield ranged from 10.2 tonnes ha-1year-1inA. officinalisthrough 11.8 (R. apiculataandR. mucronata) to 17 tonnes ha-1year-1inS. alba. Seasonally maximum litter fall was in pre- and post-monsoon monthe, with the lowest production in the monsoon. Modelling of litter fall as a function of Julian day and six environmental parameters showed that the observed changes can be explained in terms of dry/wet season and wind speed, with a <10% fifference between calculated and observed annual changes. C, N and P contents of 13 litter fractions in the four species were 41.9–43.4, 0.66–1.15 and 0.054–0.105%. N:P, C:N and C:P ratios were <30, 30–100 and >1000. Total decomposition (98–100% loss in dry weight and C, and >90% loss in N and P) of yellow leaves was within 15 weeks in the twoRhizosporaspp. andS. alba, and within 8 weeks inA. officinalis. In all four species, mass changes during decomposition obeyed first-order kinetics. Comparison of C, N and P fluxes from the decomposing mangrove litter with phytoplankton, bacterial and secondary production in the estuarine waters showed that mangrove production is important mainly for the C budget of the Estuaries and in sustaining the microbial food chain and nutrient regeneration, rather than the particulate food chain directly.

Structure and production in neotropical mangroves

Research on the extensive mangrove communities of neotropical shorelines has generated several hypotheses concerning the factors leading to the zonation of mangrove species from shore to land. Zonation has been thought of as an expression of successional processes that occur as coastlines extend seaward due to land building by mangroves, as an expression of the different physiological requirements of different species, as a function of propagule size, or as the result of the geophysical forces that continually reshape the coastline. This article reviews the evidence for the various hypotheses, and comments on the production of mangroves and their importance in shoreline management.

Litter production and seasonality of mangroves in Papua New Guinea

Productivity, as measured by litter trapping, of a mangrove dominated by Rhizophora stylosa Griff. at Motupore Island (lat. 9° 31′34′́S; long. 147° 17 $ ́ 02‘ E) was 1430 g dry weight m −2 year −1. This is a high figure when compared with other studied mangrove sites. Phenological data were obtained for R. stylosa, R. apiculata Blume and Sonneratia alba Smith. All species have a major leaf fall in the wet season. Flowering in both Rhizophora species is greatest during the wet season, but S. alba peaks during the dry season. Leaf emergence data were only available for R. stylosa and these appeared to be trimodal. Correlations were calculated for each component with rainfall, wind run, maximum temperature and minimum temperature. Some significant correlations were obtained with rainfall and maximum temperature. These correlations are discussed and it is suggested that the seasonality of mangrove phenologies needs to be considered in terms of whole tree physiology rather than isolated environmental factors.

Management of mangrove exploitation in Indonesia

In Indonesia mangrove vegetation covers an area of about 3.8 million hectares. The export value of charcoal, logs. woodchips and other mangrove products was US$4.1 million in 1978. Until 1970 the allocation of mangrove resources was handled by provincial authorities. Since 1970 concessions for areas greater than 100 ha have been controlled by the central government. The sites under central government concession cover an area of 455 000 ha. This area is divided between 13 major concessions permitting a total maximum annual allowable cut of 599 200m 3. In areas under concession, regulation requires that a system of selective cutting combined with seed-tree-based natural regeneration should be applied. A clear-cutting system has been recommended to increase log production. Preliminary studies in different regions show considerable differences in the regeneration process. In Kalimantan it has been shown that. following clear-cutting in alternative strips, regeneration consisted primarily of Rhizophora whilst that of Bruguiera was minimal. Preliminary observations in Sulawesi have shown that no mangrove of commercial value has regenerated. Instead a succession of undergrowth comprising Acanthus ilicifolius and Acrostichum aureum has appeared. The Directorate General of Fisheries of the Indonesian government has recently recommended the establishment of a 400 m-wide ‘green belt’ of mangrove along all shores where mangrove should normally be found and where conditions are still favourable for mangrove growth. The Directorate General of Forestry is also seeking to re-establish former mangrove areas for production forest. Conflicts have arisen in the implementation of these policies, particularly in locations occupied by brackish water fishponds. A compromise in the form of mangrove cum fish culture was introduced. However, the success of this type of culture is questionable.

Relics habitat of mangrove vegetation in south coast of Java

Mangrove vegetation is one of the most richness ecosystems in tropical forest. It has high value economically and ecologically. Mangrove product can be used directly as timber, firewood, charcoal, tannin, dyes, food, medicine, raw material of industries, etc. It also can be used indirectly as fisheries, wastes processing, seashore protection, ecoturisms, educations, etc. In the past time, river estuaries in south coast of Java was mangrove habitat. However, anthropogenic activities had been reduced mangrove vegetation into relix habitat. The aim of the research was to know (1) sites of mangrove vegetation in river estuaries in south coast of Java, (2) diversity of mangrove vegetation, (3) density of Sonneratia alba J.E. Smith, and (4) physical and chemical properties of these sites. The research was conducted in March-April 2002, at 20 river estuaries from Pacitan until Cilacap, south coast of Java. The results indicated that mangrove remnant could be met in 10 river estuaries, namely Grindulu, Teleng, Bogowonto, Cakrayasan, Lukulo, Cincingguling, Ijo, Bengawan, Serayu, and Jeruk Legi-Donan. There were 29 mangrove species in estuaries, consist of major components (9 sp.), minor components (2 sp.), and mangrove associated (18 sp.). The density of Sonneratia alba J.E. Smith varied from 0 till &gt; 250 individual per hectare. The soil sediment could be grouped into sand, silt, and clay, where silt and clay could support mangrove growth finely. The average of environmental parameters as follows: temperature of water and sediment respectively were 32.0oC and 31.4oC, pH of water and sediment respectively were 7.29 and 6.96, total dissolved solid of water was ~ 2000 ppm, dissolved oxygen of water was 9.29 ppm, and water salinity was 16 ppt.© 2002 Jurusan Biologi FMIPA UNS SurakartaKey words: mangrove remnant, Sonneratia alba, diversity, density