Research Articles

Distribution of Mangrove Species within Bhitarkanika National Park in Orissa, India

V. P. Upadhyay, P. K. Mishra and J. R. Sahu

PEER REVIEWED
Mangrove swamps, some of the most productive wetlands on the planet, are under intense pressure from development, population spread and pollution. This report evaluates species density and distribution in a national reserve using standard ecological sampling methodology.
PEER REVIEWED


V. P. Upadhyay1*, P. K. Mishra1 and J. R. Sahu2

1 Ministry of Environment and Forests, Eastern Regional Office, Bhubaneswar, Orissa, India 751 023, 2 Government College, Bhadrak, Orissa, India, *Author to whom correspondence should be directed

Email: vpupadhyay@hotmail.com

Trees for Life Journal 2008, Vol 3:4

The electronic version of this article is the complete one and can be found online at: http://www.tfljournal.org/article.php/20080104111556743

Received: September 8, 2006; Accepted: June 12, 2007; Published: May 19, 2008

Copyright: ©2008 V. P. Upadhyay et al.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.




Mangrove forests are extraordinarily diverse coastal communities anchored by salt-tolerant plants along certain tropical seacoasts. Their distinctive aerial roots help to trap sediment, prevent shoreline erosion, and provide habitat for a variety of sea life. Their unique mode of viviparous reproduction (producing seeds that germinate before becoming detached from the parent plant) allows for the rapid dissemination of viable young plants. Mangrove swamps or forests are among the most productive wetlands on the planet. They are also under intense pressure from development, population spread and pollution. The mangroves of Bhitarkanika National Park, in the Kendrapara district of Orissa, India (located at approximately 20°40’N, 87°00’E) make up about 700 of the 2500 sq. km of mangroves on India’s east coast. This mangrove forest is home to one of the largest nesting colonies of sea birds in India, including a variety of egrets, cormorants and herons, as well as an enormous diversity of fish, shrimp, prawn, crabs and other larger marine animals including saltwater crocodiles and sea turtles. The following report evaluates species density and relative distribution amongst four sites within the Bhitarkanika reserve, using standard ecological sampling methodology.




Mangrove forests are evergreen estuarine and open systems which receive nutrients, fresh water and sediments from terrestrial environments. Mangroves vary both in their salinity tolerance and the degree to which salinity may be necessary to maintain their growth and competitive dominance (6). Mangroves grow throughout the tropics wherever the average monthly minimum temperature is 200C (4). The ecological importance of these ecosystems for maintaining marine life, their high productivity and role in supplying organic material to coastal marine ecosystems have been demonstrated in many studies (12, 14, 17). The mangroves import nutrients, fresh water and sediments from the terrestrial environment and outflow organic matter and water to the marine and estuarine environment. Coastal mangroves perform regulatory functions by reducing coastal erosion and flooding, supplying nutrients, and retarding runoff. They provide vital shelter belts to protect inland homesteads, agriculture, livestock, and other properties located in near-shore environments. Mangroves ensure improved fish catch to coastal communities and thus have great socioeconomic value (1). The mangrove areas provide habitat for spawning and nursery ground for various marine species like fishes, shellfishes, crustaceans and other invertebrates (9, 15, 21). India has deltaic, estuarine, backwater, sheltered and insular bay types of mangrove formations (3). About 56.7% of the total mangrove area of India is found along the east coast, 23.5% on the west coast and 19.8% in the Andaman and Nicobar islands (11). Mangroves are spread over an area of 214 sq. km in Orissa (11). There is an increase of 4 sq. km compared to a 1997 assessment (10, 11) with an increase reported in Bhadrak and Kendrapara districts. However, there is an overall decline in quality and quantity of mangrove cover in Orissa mainly due to shoreline changes, settlements, sediment loading and conversion for agriculture and aquaculture (21).

We carried out a phytosociological study in the Bhitarkanika Mangrove Sanctuary located on the eastern coast of the state of Orissa, India at 4 sites (i.e. Dangmal, Bhitarkanika, Thakurdia and Kakranasi blocks [Figure 1]). At each site, 30 quadrats of 10 m x 10 m were sampled randomly, thus totaling 120 quadrats with a total area of 12,000 m2. Excoecaria agallocha was generally the densest species at all sites (Table 1). In Dangmal Block 20 species from 14 families were recorded. Heritiera fomes had the highest density followed by Excoecaria agallocha and Cynometra ramiflora, with Xylocarpus molluccensis and Brownlowia tersa showing the lowest density. Bhitarkanika Block encompasses a total of 24 tree species belonging to 13 families and has a similar trend of species density. However, Avicennia alba and Thespesia populnea exhibited lowest density at this site. Sixteen species were found from 11 families in Thakurdia Block. Excoecaria agallocha showed the highest density, followed by Ceriops decandra and Lumnitzera racemosa. Xylocarpus granatum and Kandelia candel were observed having the lowest density. In Kakranasi Block 17 tree species from 10 families were recorded. Excoecaria agallocha and C. decandra exhibited highest density. B. gymnorrhiza , R. apiculata, S. apetala and X. mekongensis showed lowest density. These mangrove areas and species provide diverse ecological and socioeconomic services to humans and the coastal environment. Several species are used for fuel wood, fodder, and timber purposes and also have medicinal values. The Heritiera species is known for the durability and strength of its wood. Avicennia is used as fodder. Indigenous medicines are prepared from Bruguiera gymnorrhiza (diarrhea and to control blood pressure), Rhizophora mucronata (angina), Acanthus ilicifolius (asthma, rheumatism), Lumnitzera racemosa (herpes and itches), Cynometra ramiflora and Excoecaria agallocha (Leprosy). Further, these plants are also used to treat various other disorders like headache, abdominal troubles, skin diseases, etc. (21).

Figure 2(Click to enlarge)

Figure 1: Location of study sites (in bold) in Bhitarkanika Mangrove Sanctuary, on the eastern coast of the state of Orissa, India

Among the 4 study sites, the species number is highest in Bhitarkanika block. This block, along with Dangmal, is a core area of wildlife sanctuary. Cerbera manghas is found only in Bhitarkanika and Dangmal forest blocks with a density of 43/ha in Bhitarkanika and 17/ha in Dangmal block. E. agallocha is a dominant species at all sites. This species is a characteristic mangrove associate occurring in the back mangal areas (landward zone) (20) and has highest density at Thakurdia block among all species and sites. This species could be a primary mangrove element at the Thakurdia block due to peculiar topography and a higher elevation. Although tidal amplitude in the nearby Baunsagada River is high (2-5 m) most areas do not get regular tidal inundation. It is possible that this forest block has been through the usual successional stages of early colonizers (Porteresia coarctata, Myriostachya wighitiana) having a characteristic assemblage of associated species such as Salvadora persica, Caesalpinia crista, etc.

Bhitarkanika has the highest species diversity among all study sites (5.33 species per quadrat). Statistical analysis to find the correlation between species diversity and density established that there is a strong positive relationship between the above parameters across all sites with a value of coefficient of determination above 81% (r =0.911-0.932; p<0.001). Species richness is higher (> 30 to 55 species) at latitudes between 0 and 200 (N or S) and at longitudes between 70 and 1350E (7). It is highest in the Indo West Pacific and declines relatively smoothly from the peak species richness of 1000 E longitude (8). No records are available regarding the changes in the species composition in Bhitarkanika areas. The main reason for changes in species composition is reduction in the periodicity and quantity of fresh water reaching the mangrove environment (18). This system is still not much affected by such factors. The floral components, forest structure, and biomass of the mangrove wetlands are governed at the micro level by soil and water salinity and particularly by the salinity of the water that is present in the pores of the soil (5). The presence and luxuriant growth of salt-marsh succulent species such as Suaeda spp. are indicative of an increase in salinity (13) and a degrading mangrove site. However, such luxuriant growth of Suaeda is not reported from all the forest blocks in Bhitarkanika and therefore it could be said that an increase in salinity is not a stress factor in the area.

The Biodiversity Conservation Prioritisation Project (BCPP) India and Zoo Outreach Organisation, India through the CAMP (Conservation Assessment and Management Plan) noted 12 (20%) Indian mangrove species Critically Endangered, 40 Endangered (66%), 5 (8%) Vulnerable, 1 at Lower Risk near Threatened (Salicornia brachiata), 1 under the category of Lower Risk Least Concern (Acrostichum aureum) and 1 species could not be evaluated (16). The IUCN criteria were used for assessing the status of the species. We also categorized the mangrove species of Bhitarkanika following the above criteria.

Species of Bhitarkanika that are Critically Endangered are: A. alba, A. marina, B. gymnorrhiza. Species that are listed as Endangered are: A. ilicifolius, A. rotundifolia, A. corniculatum, A. cucullata, A. officinalis, B. tersa, C. manghas, C. decandra, H. fomes, K. candel, L. racemosa, M. wighitiana, P. paludosa, S. apetala, S. caeseolaris, T. troupii, X. granatum, X. mekongensis, and X. molluccensis. Species that are identified as Vulnerable are: E. agallocha, P. coarctata, and R. mucronata.

The vegetation of Bhitarkanika and the adjacent Mahanadi delta is diverse and seems to be among the richest of the world. The estuarine regions of Bhitarkanika do not have species like Sonneratia griffithii, which is available in the Sundarbans area of west Bengal. H. fomes, S. griffithii and Aegialitis rotundifolia are endemic to the coastal part of South Asia (2). Although the structural attributes of mangrove vegetation of Bhitarkanika studied during the present investigation do not indicate conspicuous signs of degradation, a conservation and management plan should take note of differences in species number and absence of some species from some sites to develop regeneration strategies. Further, the above classification has established that more species are in the Endangered category, thus requiring special management intervention to increase the species population in this mangrove ecosystem. Research on the reproductive life history of these species, including the knowledge of hydrodynamic functions of the ecosystem, is immediately needed and will be useful to develop scientific conservation and management plans for mangroves of Bhitarkanika Sanctuary.

 

Table 1: Number of plants per hectare at the study sites

Species

Dangmal

Bhitarkanika

Thakurdia

Kakranasi

Average for the area

Excoecaria
agallocha

1568

1772

5814

5188

3586

Heritiera
fomes

3267

3080

833

866

2012

Cynometra
ramiflora

1199

759

 

 

979

Phoenix
paludosa

70

23

160

 

84

Hibiscus
tiliaceous

260

83

 

30

124

Pongamia
pinnata

180

67

 

 

124

Avicennia
officinalis

80

196

50

1212

385

Sonneratia
apetala

50

236

13

17

79

Kandelia
candel

27

53

10

 

30

Amoora
cucullata

40

123

 

 

82

Rhizophora
mucronata

40

63

30

40

43

Hertiera
littoralis

47

 

 

 

47

Cerebra
manghas

17

43

 

 

30

Xylocarpus
granatum

37

73

10

13

33

Aegiceras
corniculatum

176

363

1868

150

639

Bruguiera
gymnorrhiza

70

60

 

7

46

Tamarix
troupii

20

 

 

 

20

Ceriops
decandra

30

103

4222

3750

2026

Xylocarpus
molluccensis

3

40

 

 

22

Brownlowia
tersa

7

13

 

 

10

Intsia
bijuga

 

27

 

 

27

Sonneratia
caeseolaris

 

73

17

1012

367

Avicennia
alba

 

10

726

969

568

Thespesia
populnea

 

10

17

7

13

Rhizophora
apiculata

 

20

 

10

15

Xylocarpus
mekongensis

 

33

 

10

22

Aegialitis
rotundifolia

 

 

203

107

155

Lumnitzera
racemosa

 

 

1875

150

1014

Avicennia
marina

 

 

246

 

246

 

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