K. Kathiresan

Biology of Mangroves and Mangrove Ecosystems

Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions. n nBecause of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules. n nMangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds). n nBecause they are surrounded by loose sediments, the submerged mangroves roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character. n nLiving at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves. n nHabitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged. n nThese impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests. n nMangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the worlds most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

Mosquito Larvicidal Effect of Seaweed Extracts

Fifteen seaweeds, Caulerpa peltata, C. racemosa, C. scalpelliformis, Chaetomorpha linum, Codium decorticatum, Dictyota dichotoma, Enteromorpha clathrata, E. intestinalis, Halimeda opuntia, Hypnea valentiae, Sargassum tenerrimum, S. wightii, Turbinaria conoides, T. oranata and Ulva lactuca were extracted in acetone and evaluated for mosquito larvicidal activity against Aedes aegypti L. Caulerpa scalpelliformis and Dictyota dichotoma were found most effective with LC50 values of 53.70 and 61.65 mg L respectively.

Mosquito Larvicidal Activity of Marine Plant Extracts with Synthetic Insecticides

Two seaweeds, Caulerpa scalpelliformis, Dictyota dichotoma and one mangrove sample, stilt root of Rhizophora apiculata were extracted in acetone and were combined with synthetic insecticides, DDT, BHC and malathion and evaluated for mosquito larvicidal activity against Aedes aegypti. The extracts showed synergism with the insecticides. The stilt root of Rhizophora apiculata exhibited highest synergistic activity with BHC.

Antiviral Evaluation of Some Marine Plants Against Semliki Forest Virus

AbstractExtracts of Seaweeds, seagrasses, and mangroves were screened in vitro against Semliki forest virus (SFV) on Vero cells. Anti-SFV activity was determined on the basis of inhibition of cytopathic effect (CPE). Of the 50 extracts tested, nine were found effective by inhibiting CPE from 55 to 95%. Ceriops decandra (Griff.) W. Theobald leaf showed the higher activity in vitro. The extracts effective in the in vitro assay were tested in vivo and their activity was determined on the basis of mortality and average survival time. Two extracts, Cheilosporum spectabile and Rhizophora mucronata Lam. (Rhizophoraceae), were found to be effective in protecting mice from lethal SFV infection.

Antiviral activity of marine and coastal plants from India

AbstractSeaweeds, seagrasses, and mangroves were studied for their antiviral activity against Encephalomy-ocarditis virus (EMCV). Of 73 extracts, 20 showed in vitro anti-EMCV activity. Of these 20 extracts, seven were prophylactically and three were therapeutically active. Only two extracts, Cheilosporum spectabile and Rhizophora mucronata, were found to be effective with both in vitro and in vivo assay systems.

Note: Repellency of Marine Plant Extracts against the MosquitoAedes aegypti

AbstractFour seaweeds (Caulerpa peltata, C. racemosa, C. scalpelliformis and Diclyota dichotoma) And eleven mangrove plant samples (the leaves of Avicennia marina, A. officinalis, Excoecaria agallocha, Lumnitzera racemosa, Rhizophora apiculata, R. lamarckii, R. mucronata, Salicornia brachiata, Sonneratia apetala, Xylocarpus granatum And the stilt root of Rhizophora apiculata) were extracted in acetone And tested on human skin for repellent activity against the biting of Aedes aegypti. The stilt root of Rhizophora apiculata was found most effective And gave protection for 70 minutes at a dose of 1 mg dry plant extract per cm2 of skin.

Studies on Mosquito Larvicidal Activity of Rhizophora apiculata

AbstractExtracts of stilt root samples of Rhizophora apiculata were studied for mosquito larvicidal activity against Aedes aegypti as influenced by the season of collection, the maturity of sample, method of drying, and solvent used for extraction. The terminal portion of the root sample, collected during summer, dried under shade and extracted in petroleum ether, was found to exhibit the highest activity. The season of plant collection had a marked effect on the level of larvicidal activity rather than the other factors.