MANGROVE SURVEY

GEER Foundation, using LISS-III data of November 1998, mapped mangrove forests of Gujarat on a scale of 1:50,000. This was a significant improvement over the Forest Survey of India assessment at that tune that was at the scale of 1:250,000 till then. The study simultaneously identified mudflats that hold promise as potential mangrove area. It reported dense mangrove over 455.6 km2 sparse mangrove 482.8 km2 totaling to 938.4 km2 of mangrove cover in Gujarat. This was lower than reported by FSI in FSR 1999 as 1031 km2 FSI too, in its SFR 2001 report based on changes in scale and technology, found the mangrove cover in Gujarat as 911km2 that is close to the estimates of GEER. It simultaneously estimated potential mangrove area as 637.2 km2 with other mud flats estimated at 2094.4 km2.

These reports generated interest in mangroves of Gujarat at various fora. It stimulated policy inputs, investment for research, survey, and regeneration. Protective role of mangroves got further highlighted by the observation that mangroves played a significant role in mitigating damage due to the 2004 Tsunami that impacted Andaman Nicobar Islands and eastern coast of South India. It also gave recognition to the concept bio-shield at the highest policy level.

10.8.1 THE IUCNSPONSORED PROJECT UNDER MANGROVE FOR FUTURE PROGRAM

In 2009, the mangrove areas of south Gujarat were surveyed for their floristic diversity and natural regeneration under a project funded by Mangrove for Future (MFF) program sponsored by International Union for Conservation of Nature (IUCN) at Gujarat Ecological Education and Research (GEER) Foundation.

Detailed mapping of the mudflats was performed in south Gujarat and Gulf of Cambay to identify and locate potential mangrove afforestation areas. The study identified areas that are larger than 100 ha. It identified 70 such potential areas totaling 79155.17 ha. This study categorized these potential areas into A, B, and C zones. The zone A included intertidal areas adjacent to creeks/water sources, which have either clay or clay dominated mixed soils receiving tidal inundation for 7-15 days in the tidal cycle of 15 days. Zone A areas are ideal for mangrove afforestation. The area of Zone A was reported to be 20129.68 ha. The zone В included areas that are generally behind zone A areas and receive tidal inundation for 4-6 days in the tidal cycle of 15 days. This is inadequate inundation for mangroves. These areas required intervention to facilitate frequent marine water movement for raising mangrove species. Zone В area was estimated to be 37483.41 ha. The zone C areas are further inland with inundation limited to 1-3 days are suited for mangrove associates. Zone C area was estimated to be 21542.08 ha. Each area with its zone was mapped and maps have been made available to field units to plan afforestation/regeneration program.

The detailed study of the floristic diversity of the mangrove forests of Gulf of Cambay included mangrove areas of Valsad, Navsari, Surat, Bhaiuch, Vadodara, Anand, Kheda, Ahmedabad, and Bhavnagar districts. The study surveyed the diversity of mangroves, mangrove associates, species richness, and natural recruitment in various zones of the study region. It also studied preferred substrata for various mangrove species occurring in the region. The study revealed interesting community usage and dependency on mangrove and vegetation in intertidal regions.

The study identified occurrence of 14 mangrove species that included 12 of earlier reported species and two species that were not reported earlier. It identified 122 mangrove associates that included 21 monocots.

Mangrove species of Gulf of Cambay:

  • 1. Avicennia marina (Forsk.) Vierh
  • 2. Avicennia officinalis L.
  • 3. Avicennia alba Bl.
  • 4. Ceriops tagal (Perr.) Robinson
  • 5. Cerops dec an dr a
  • 6. Aegiceras cornicnlata (L.) Blanco
  • 7. Exoecaria agallocah L.
  • 8. Sonneratia apetala Buch.- Ham.
  • 9. Rliizophora nincoronata Lamk.
  • 10. Brugniera cylinderica (L.) Bl.
  • 11. Acanthus ilicifolins L.
  • 12. Brugniera gymnorhiza (L.) Savingny.
  • 13. Kandelia candel (L.) Diuce
  • 14. Lunmitzera racemosa Willd.

Common mangrove associates of Gulf of Cambay:

  • 1. Aeluropus lagopoides (L.) Trin. Ex Thw.
  • 2. Cress a cretica L.
  • 3. Porteresia coarctata (Roxb.) Tateoka
  • 4. Sesuvium potidacastrum (L) L
  • 5. Salvadorapersica L
  • 6. Saclicornia brachiate Roxb
  • 7. Salicornia nudiflora Roxb
  • 8. Clerodendrutn inerme (L.) Gaertn. F.

The study reported some of the lesser known mangrove areas in the estuaries of Purna River.

Direct dependence of local community on mangroves was observed for fodder and fuel. Village women were seen going for fodder collection to smaller islands near the village on a shared boat. Villagers also reaped benefits of fish collection and at least in one of the villages, there is a tradition of protecting mangroves; for their protection, they offer to the village from natural calamities. It may be inferred that there were local traditions in the region for protection of mangrove but have fallen in disuse with time.

10.8.2 RESEARCH ON REPRODUCTIVE ECOLOGY OF MANGROVE OF GUJARAT

The GEER Foundation undertook research on pollination biology and reproductive ecology of three major mangrove species with the funding from Ministry of Environment and Forest, Government of India, (2005-2008), viz.,

  • 1. Aegiceras comiculatum (L.) Blanco,
  • 2. Ceriops tagal (Perr.) C.B. Robinson
  • 3. Rhizophora mucronata Lamk

The study was conducted in the Gulf of Kutch. It studied flower production, flowering synchrony, pollinators, and their visitation and developmental biology. The study explored relationship of different environmental parameters with breeding success and integrated data on these aspects to arrive at logical conclusions that are useful to develop conservation plans for the selected species of mangroves.

The study of floral biology detailed the periods and processes of transformation from matured bud to seed setting stage. Pollen production and viability with identification and visitation pattern of pollinators for the three species have been detailed in the report. The detailed sequence extent of anther dehiscence, pollen dispersal, stigma receptivity, nectar secretion, and pollinator visits when placed on a time axis that divided the total life of flower from anthesis to completion of fertilization into 10 sequential floral stages revealed interesting observations regarding the reproductive strategy of these species.

10.8.2.1 AEGICERAS CORNICULATUM

The study inferred that for A. comiculatum anther dehiscence and stigma receptivity are broadly out of phase except during a small period of overlap during stage-4 and stage-5 when the level of receptivity for stigma is veiy low. Further, the period of high-stigma receptivity is during the later stages when anther dehiscence has already completed and pollen grains are not available. This implies that the species favors cross-breeding through protandiy. However, during stage-4 and stage-5, weak presence of anther dehiscence and stigma receptivity was observed that indicates a the small possibility of self-breeding also, usually found in mangrove species to help propagate in isolated populations. It is also indicated that there is a possibility of pollination by pollen of other flowers of the same inflorescence or the same tree (geitonogamy), which helps the propagation of species as an isolated population.

10.8.2.2 CERIOPSTAGAL

Anther dehiscence and stigma receptivity are found to be broadly out of phase for C. tagal except during a small period during stage-4 when the level of stigma receptivity is very low. Further, the period of high stigma receptivity is during later stages when anther dehiscence has already been completed and pollen grains are not available. This implies that the species favors cross-breeding through protandiy. However, during stage-4, weak presence of anther dehiscence and stigma receptivity is observed indicating that the species holds a small possibility of self-breeding also. Like A. connculatum in the case of C. tagal to there are conditions wherein there is possibility of pollination by pollen of other flowers of the same inflorescence or the same tree (geitonogmay) that helps propagation of species as an isolated population.

10.8.2.3 RHIZOPHORA MUCRONATA

Anther dehiscence and stigma receptivity are widely out of phase for R. mucronata. The anther dehiscence is completed during stage-2, whereas the significant stigma receptivity is observed during stage-6 onwards. Hence, anther dehiscence and stigma receptivity are widely separated overtime without any overlap unlike in the case of A. connculatum and Ceriops tagal However, this tune gap is bridged by the function of petal corona that effectively increases the pollen presentation time and makes some pollen available up to stage-7 when the stigma receptivity is considerably high. Therefore, petal performs an extra reproductive function keeping alive some possibility of self-breeding in a flower, which otherwise strongly favors cross-breeding, through very pronounced protandry. The presence of corona on lateral margins of petals regulates the pollen dispersal and effectively increases the pollen presentation period. Thus, corona plays the role of holding some pollen grains, though a very small proportion of the total, until the period of stigma receptivity just starts. Therefore, there are very small chances that some pollen grains held by corona may remain viable until stigma receptivity just starts. It is inferred that the possibility of self-breeding is extremely low for R. mucronata though not ruled out. This small possibility of self-breeding helps R. mucronata to propagate even as isolated populations.

It is also interesting to note that the pollinator’s visits are in two distinct phases, that is, stage-3 to stage-5 and stage-7 to stage-9. The visit during the first phase is prompted by pollen as a reward (bees, ants, and beetles). The reward of pollen during the first phase facilitates cross-breeding because the stigma is not receptive and the pollinators may carry the pollen grains outside the flower. The reward during the second phase also favors crossbreeding because, during this phase, pollen grains from the same flower are not available and the pollinators seeking the reward may bring in the pollen grains from other flowers.

The study of breeding mechanism of indicated occurrence of autogamy, geitonogamy, and xenogamy in all the three species, that is, Aegiceras comiculatum, Ceriops tagal, and Rhizophora mucronata. None of these species are purely self-breeding or purely cross-breeding.

REGENERATION

The research work also documented the species ’ preference for site conditions (such as the type of substratum and the inundation) in natural regeneration of major mangrove species and their associates. It was species increases as the clay component in soil increases. As the sand increases in soil mangrove associates appear to have greater success.

The overall status of natural recruitment of different mangrove species and mangrove associates was found as follows:

Aviccennia marina 68%

Aegiceras corniculatum 04%

Ceriops tagal 17%

Rhizophora mucronata 01%

Mangrove associates 10%

The research work on the three species indicated reproductive success as A. comicuJatum (42%) C. tagaJ (3%), and R. mucronata (1%) (Pandey and Pandey, 2009). In case of A. comicuJatum, despite a better breeding success, the natural recruitment has been found to be low indicating that the availability of matured propagule may be there but the chances of establishment are relatively less. This may be due to preference of crabs for the propagules of A. comicuJatum as it has less fiber and tannin content. Though Ceriops tagaJ has lower reproductive success there is better recruitment as its propagules are not preferred by herbivores as it has relatively high-fiber and tannin content.

SUBSTRATUM REQUIREMENT

The substratum preference by different species for natural recruitment was studied. The study reported that the substrata with sand being its predominant content supported non-mangrove species and Avicennia marina. The area with substrata having some clay and more sand was found to be occupied by A. marina and R. mucronata. The substrata with higher clay content than sand in the region is occupied by A. marina, R. mucronate, and C. tagaJ. Substrata having clay as its predominant content is occupied by Ceriops tagaJ and A. comicuJatum. The hard clay was found to be the place for A. marina, Ceriops tagaJ, and non-mangroves.

CARBON SEQUESTRATION IN MANGROVES FORESTS OF GUJARAT

The detailed biometric exercise was conducted to study carbon sequestration in the mangrove forests of Gujarat. The tree numbers were estimated for nine major mangrove species in girth classes. Biometric exercise was conducted to estimate biomass for each species in various girth classes for below ground and above-ground biomass and soil carbon was also estimated. The coast of Gujarat was divided into four regions, viz., Kutch, Gulf of Kutch, Saurashtra, and South Gujarat. In each region, the mangrove areas were categorized to dense, moderately dense, and sparse mangrove areas. Thus, the mangrove area of Gujarat was divided into 12 categories. In Kutch region, the carbon sequestration ranged between 41.65 ton per ha and 91.47 ton per ha averaging to 67.73 ton per ha. In Gulf of Kutch, the carbon sequestration is higher ranging from 19.66 to 118.83 ton per ha averaging to 82.90 Ton per ha.

Mangroves of South Gujarat region have the highest carbon sequestration per unit area with an average of 180.24 ton per ha. The total carbon sequestration in mangrove forests of Gujarat is estimated to be 5.874 million ton in soils and 2.242 million ton in plants totaling to 8.116 million ton.

CONCLUSION AND RESEARCH NEEDS

Research interest in mangroves has been only a few decades old. Most of the research reports are empirical observations that need to be pursued and confirmed. Some of the research areas are detailed below that may be considered priority concerns.

  • 1. Growth pattern: Initial research on growth pattern has thrown many interesting observations. Pandey et al. (2012) observed two growth seasons for Avecinia spp. in the Gulf of Kutch. It may be explored if there are two growth periods in other regions and for other species. How the growth periods relate to local climate with the variation in growth rate. It may also have a relation with underground growth of the root system and so the establishment of the new recruits. This may help optimize the planting season.
  • 2. Mangrove ecosystem functioning: The variations in coastal environment call for long-term research to have adequate understanding of cause-effect phenomena in mangrove ecosystems. The nutrient cycling in mangroves needs to be better understood. It will help appreciate their role in regulating water quality, thereby, learning how mangroves maintain nutritional homeostasis while being subjected to high rates of water turn over (ocean and freshwater) that certainly must leach large amounts of nutrients.
  • 3. Reproductive biology: The research on reproductive biology of few species have enlightened on the misconceptions about mangrove reproduction. The details of role of local biodiversity in the reproduction of mangroves and symbiotic relationship between large diversity of fauna with mangrove vegetation have been observed. The research on reproductive biology is fundamental to understanding the mangrove species need to be pursued with greater inputs.
  • 4. The ecological role of mangroves: Almost all the reports on mangroves have highlighted the ecological role of mangrove in the marine ecosystem. The contribution of mangrove in sustaining the diversity of marine life, enhancing fish catches, stabilizing coasts, arresting silt is reported. Some authors have reported on contribution of mangroves to sustaining corals by reducing silt load and eutrophication in the region. The mangrove ecosystems have been observed to be highly productive; however, they need scientific investigation to establish cause-effect relationship.
  • 5. Role of mangroves in recycling heavy metal: There are studies indicating the ability of mangroves to address ecotoxic waste containing heavy metal. A valid question that may be researched - Can mangroves recycle heavy metals in an environmentally safe and scientifically sound manner?
  • 6. Economic valuation of the ecological services by mangroves: In modern world discussions often continue on the importance, need and future hidden in the rich biodiversity, ecological stability, and environmental conservation. But hard economic considerations with often narrow national and even regional biases guide the decisions. It is, therefore, of immense importance that the economic contribution of mangroves is evaluated and quantified as in local, regional, and global categories.

KEYWORDS

  • mangrove forests
  • ecological services
  • mangrove mapping
  • potential areas
  • carbon sequestration

REFERENCES

Anon. The State of Forest Report, Forest Survey of India, Deliradun, 1987, p 84.

Anon. The State of Forest Report, Forest Survey of India, Deliradun, 1989, p 50.

Anon. India's Wetlands, Mangroves and Coral Reefs. World Wide Fund for Nature India for Ministry of Environment & Forests Governement of India, New Delhi, 1992, p 61.

Anon. India State of Forest Report, Forest Survey of India. Deliradun, 1997, p 72.

Anon. India State of Forest Report, Forest Survey of India. Deliradun, 2001, p 130.

Anon. India State of Forest Report, Forest Survey of India. Deliradun, 2013, p 252.

Anon. India State of Forest Report, Forest Survey of India. Deliradun, 2015, p 300.

Anon. India State of Forest Report, Forest Survey of India. Dehradun, 2017, p 363.

Biswas, N. The Gulf of Kutch Marine National Park and Sanctuary’: A Case Study. International Collective in Support of Fishworkers, Chennai, 2006, p 46.

Ong, J. E.; Gong, W. K. Structure, Function and Management of Mangrove Ecosystems. ISME Mangrove Educational Book Series No. 2. International Society for Mangrove Ecosystems (ISME): Okinawa, Japan, and International Tropical Timber Organization (ITTO): Yokohama, Japan, 2013; p 81.

Pandey, C. N.; Pandey R. Study of Floristic Diversity’ and Natural Recruitment of Mangrove Species in Selected Mangrove Habitats of South Gujarat. GEER Foundation, Gandhinagar, 2009, p 92.

Pandey C. N.; Pandey R. Pollination Biology> and Reproductive Ecology> of Major Mangrove species of Gujarat. GEER Foundation: Gandhinagar, 2009; p 918.

Pandey, C. N.; Pandey, R.: Mali M. Carbon Sequestration by Mangroves of Gujarat. GEER Foundation: Gandhinagar, 2012; p 159.

Pandey, C. N.; Pandey, R.. Khokhariya, B. Potential Area Mapping for Mangrove Restoration in South Gujarat. GEER Foundation: Gandhinagar, 2012; p 248.

Singh, H. S. Mangroves in Gujarat (Current status and strategy'for conseivation). GEER Foundation: Gandhinagar, 1999; p 127.

Sigh.H. S.;Yennawar,P.;Asari,R. J.;Tatu,K.;Raval, B.R .An Ecological and Socio-Economic Study in Marine National Park and Sanctuaiy in the Gulf of Kutch (A Comprehensive Study on Biodiversity and Management Issues). GEER Foundation: Gandhinagar, 2006.

Spalding, M. D.; Blasco, F.; Field, C. D., Eds.; World Mangrove Atlas. The International Society for Mangrove Ecosystems: Okinawa, Japan, 1997; p 178.

 
Source
< Prev   CONTENTS   Source   Next >