Journal of Threatened Taxa | www.threatenedtaxa.org | 26 May 2022 | 14(5): 21068–21075

 

ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print) 

https://doi.org/10.11609/jott.6551.14.5.21068-21075

#6551 | Received 09 August 2020 | Final received 10 April 2022 | Finally accepted 01 May 2022

 

 

 

Floristic studies on mangrove vegetation of Kanika Island, Bhadrak District, Odisha, India

 

P. Poornima

 

DFO Residence, Divisional Forest Office, Khordha Main Road, Khordha, Odisha 752055, India.

poornimapandian4@gmail.com

 

 

 

Editor: A.J. Solomon Raju, Andhra University, Visakhapatnam, India.      Date of publication: 26 May 2022 (online & print)

 

Citation: Poornima, P. (2022). Floristic studies on mangrove vegetation of Kanika Island, Bhadrak District, Odisha, India. Journal of Threatened Taxa 14(5): 21068–21075. https://doi.org/10.11609/jott.6551.14.5.21068-21075

 

Copyright: © Poornima 2022. Creative Commons Attribution 4.0 International License.  JoTT allows unrestricted use, reproduction, and distribution of this article in any medium by providing adequate credit to the author(s) and the source of publication.

 

Funding: None.

 

Competing interests: The author declares no competing interests.

 

Author details: P. Poornima—an Indian Forest Service (IFS) Officer, working as Divisional Forest Officer in Odisha, India.

 

Acknowledgements: I thank Shri. Subash Chandra Nayak, Range officer, Chandbali, Shri. Sushanta Mohanty, Dy Ranger, Shri Gadadhar Biswal, Forester, Dhamra and members of Protection Squad, Bhadrak WL Division for helping in data collection.

 

 

 

Abstract: This study pertains to the floristic composition of unexplored mangrove habitats of Kanika Island, Bhadrak District, Odisha, India. Six quadrats each measuring 31.62 x 31.62 m (0.1 ha) were laid at randomly selected sites in the Island between October 2019 and February 2020. Quantitative inventory yielded a total of 12 species across the sampled quadrats. Qualitative floristic inventory of the Island revealed a total of 20 species belonging to 17 genera and 13 families, including four true mangrove species, viz., Avicennia alba, A. marina, A. officinalis, and Lumnitzera littorea were evaluated as ‘Least Concern’ by the IUCN Red List. Out of 20 species, eight species were trees, followed by herbs (8 species), shrubs (3 species), and a climber. The study revealed that four species were true mangroves and 16 species were mangrove associates. Avicennia alba and A. marina were found dominant and have potential for regeneration in the island.

 

Keywords: Basal area, diversity index, importance-value, mangrove-associates, true-mangroves.

 

 

INTRODUCTION

                  

Mangroves are ecologically important coastal vegetation that is globally represented by 70 species (Polidaro et al. 2010), of which, 46 are present in India (Ragavan et al. 2016). The number of reported mangrove species in India varies from 34 to 69 (Untawale 1987; Banerjee 1984; Banerjee et al. 1989; Naskar 1993; Mandal et al. 1995). Such a variation in the number is mainly due to the inclusion of many mangrove associates in the list by various researchers. The mangrove vegetation of the east coast of India differs from that of the west coast. Mangroves of the east coast are larger with high diversity due to the presence of tidal creeks, canals, and brackish water bodies (Ahmed 1972). Mangroves are dynamic and its floristic composition reflects the health of the vegetation. Any changes in the floristic structure alter its functions and services (Alongi 2014; Krauss et al. 2014). Recent studies highlighted the importance of extensive floristic studies in understanding the diversity of true mangroves in different mangrove regions in India (Ragavan 2015; Saenger et al. 2019). Though conservation and management of mangroves have become a global priority, yet many of the mangrove patches within India are lacking baseline information (e.g., species diversity and threats) that are vital for their long-term management. Addressing such knowledge gaps will be imperative to improve our understanding of phytogeography, which can eventually contribute to the better management and conservation of this ecologically and economically important coastal ecosystem. I studied one such unexplored mangrove forests in Kanika Island, Odisha situated on the east coast of India. The objectives of the study were: (i) to quantitatively evaluate and document the species diversity, density, basal area, and IVI in the study area, (ii) to check whether there is any invasion by alien species into the island, (iii) to determine the dominant tree species, (iv) to enumerate the true mangroves and mangrove associates, and (v) to study the natural regeneration potential of dominant mangrove species in the Island.

 

 

MATERIALS AND METHODS

 

Study area

Kanika Island (20.830oN–86.985oE) is situated at the mouth of Dhamra River, which is the confluence of Baitarini and Dhamra rivers, in Bhadrak district of Odisha (Image 1). It has drying mud and sand flats covering an extent of 485 ha. The island has no human habitation. The district covers an area of 2,505 km2 with the human population of c. 15,00,000 (2011 census) and agriculture and fishing are their major occupation. The average annual rainfall of the district is 1,530 mm and the average annual temperature is 26.8 oC

 

METHODS

 

The quantitative data on mangrove vegetation was collected by laying six quadrats (each 31.62 x 31.62 m) (0.6 ha) at sites (I to VI) on the Island by ensuring 300–500 m distance between each quadrat between October 2019 and February 2020. All the plant species were identified using Mandal & Bar (2018), www.plantlist.org, www.indiabiodiversity.org, & www.ipni.org and enumerated according to Manon (2006), such as trees (>1 m height) and juveniles (<1 m height). For trees and shrubs, the girth was measured at breast height using measurement tape and for herbs and climber, the girth was measured close to the ground. Vegetation data was quantitatively analyzed for species richness, density, basal area, and above-ground biomass based on the individual species enumerated in the quadrats. The excel data was used to compute community indices like Fischer’s alpha diversity index, Simpson’s diversity index (Simpson 1949) and importance value index (IVI). Data analysis was carried out using Biodiversity Pro Ver. 2.0. The dominance of species was calculated based on species IVI (Curtis & McIntosh 1950; Cintron & Novelli 1984). Above ground biomass (AGB) calculation was restricted only for trees and shrubs using diameter (D), height (H), and wood specific density (ρ) (species-specific) and using allometric equation of Chave et al. (2005). Study sites were determined using a Garmin Etrex 20x GPS device. Photography and videography was done using a Nikon P1000 digital camera. The collected data was tabulated, analyzed, and represented graphically.

 

 

RESULTS AND DISCUSSION

 

Qualitative diversity inventory yielded a total of 20 species belonging to 17 genera and 13 families in Kanika Island. Among 20 species, eight were trees, three were shrubs, eight were herbs and one was a climber. According to the classification of Barik and Choudhury (2014), four species were true mangroves and the remaining 16 species were mangrove associates. Fabaceae, with four species was the most species-rich family. Avicenniaceae was represented by three species, whereas families such as Malvaceae and Convolvulaceae had two species each. The remaining nine families were represented by only one species each. The genus Avicennia had contributed three species, Ipomoea represented two species and other 15 genera had contributed one species each. The study revealed that Kanika Island harbors only five mangrove species probably due to the small land cover (Table 1).

 

Species diversity

In the study area, sites V and VI with seven species each were the species-rich plots. The dry sandy elevated area of these plots supported more species of herbs and shrubs than the other plots that are primarily established on marshy areas. The probable reason is that true mangrove species grow in saline marshy areas, whereas sandy elevated areas support mangrove as well as associated species. Acanthus ilicifolius was found along the borders of creeks, canals, and marshes whereas the creeper Ipomoea pes-caprae and the herb Sesuvium portulacastrum were observed on the exposed elevated sand bars. Individuals of Pongamia pinnata, Thespesia populnea, and Hibiscus tiliaceus have grown on dry sandy areas in sites V–VI. Derris scandens was observed under the vegetations of E. agallocha. The remaining quadrats (I–IV) were laid in the marshy regions having creeks and canals, which naturally had homogeneous vegetation containing dominant species such as A. alba and A. marina. Blasco (1975) considered A. marina as the most salt tolerant mangrove species. The occurrence of A. marina as a dominant species on the island has corroborated the views of Blasco (1975).

 

Density

Maximum density of 4,750 individuals/ha was found in site-IV, followed by site-III with 1,670 /ha due to the predominant representation of juveniles of A. marina and A. alba. Avicennia marina had contributed to density of 246 individuals/ha in Bhitarkanika Wildlife Sanctuary (Upadhyay & Mishra 2014), 884 individuals/ha in Godavari delta mangroves (Venkatana & Rao 1993), 1,107 individuals /ha in south-west coast of India (Sreelakshmi et al. 2018), and density of 1,731 individuals/ha in Coringa Wildlife Sanctuary (Satyanarayan et al. 2002). It indicates that the density of A. marina (662 individuals/ha) is lesser in Kanika Island than the other mangroves studied by Venkatana & Rao (1993), Sreelakshmi et al. (2018), and Satyanarayan et al. (2002). 

 

Basal area

Basal area is an indicator for measuring forest-stand development, biomass, and productivity (Twilley 1998). The mean basal area of all the six plots was 3.137 (0.52±0.41). The maximum basal area (11.63 m2/ha) was observed in site-I and the minimum basal area (0.14m2/ha) was recorded in site-V. Site-I had more basal area than the other sites due to the occurrence of A. marina and A. alba. Out of 12 species enumerated, A. marina (0.993 m2/0.6 ha), A. alba (0.889 m2/0.6 ha), and A. ilicifolius (0.403 m2/0.6 ha) had contributed to maximum basal area. Upadhyay & Mishra (2014) had recorded the basal area of A. marina (0.89 m2/ha), A. alba (1.23 m2/ha) in Bhitarkanika, whereas Venkatana & Rao (1993) had observed 3 m2/ha for the same two species in Godavari delta. George et al. (2017) had observed that the total stand basal area of mangroves of Kerala state was 20.33 m2/ha. In the present study, the average stand basal area measured was 31.37 m2/ha. It indicates that the mangrove stand density, biomass, regeneration capacity, and productivity of mangrove forest in Kanika Island is higher than the mangrove ecosystems studied by Upadhyay & Mishra (2014), Venkatana & Rao (1993), and George et al. (2017) and hence this basal area work is important for the present study.

 

Above-ground biomass

The present study on the mean above ground biomass (AGB) of true mangrove in Kanika Island reveals that the highest AGB of 3.757 tons/0.6 ha was recorded in A. alba, while the lowest AGB value of 0.032 tons/0.6 ha was found in A. officinalis (Table 2). But in Sunderbans, the AGB of Avicennia spp. was 101.9–118.7 tons/ha in 1991 (Choudhry 1991), whereas in 2014 it was 8.9 to 50.9 tons/ha (Joshi & Ghose 2014) and 104.1 tons/ha in Australia (Woodroffe 1985). The AGB of Thane creek, Maharashtra was estimated as 54.9 tons/ha (Pachpande & Pejaver 2015). Authors such as Chmura et al. (2003), Bouillon et al. (2008), Duarte et al. (2009), Murdiyarso et al. (2009), Kennesy et al. (2010), Chen et al. (2012), and Kauffman & Donato (2012) have highlighted that though mangroves represent small geographical areas, they are capable of high potential carbon sequestration. The average AGB of Kanika Island was 8.261 tons/ha which is less than the above said mangroves.

 

Diversity indices

Alpha diversity index was highest for site-VI (2.113) due to the occurrence of seven different species and site-II had the lowest value of 0.198 due to the homogeneous vegetation consisting of A. marina. Simpson’s Index shows the highest value of 1.000 in site-II due to occurrence of large woody trees consisting of A. marina. Site-V had the lowest index value 0.297 due to presence of large number of herbs with less girth. Diversity indices revealed that the vegetation of all the study sites was varied and hence the vegetation is heterogeneous in nature (Table 2).

 

Importance Value Index (IVI)

Out of 12 species enumerated, A. marina had the highest IVI of 126.91, followed by A. alba (45.59), A. ilicifolius (26.69), and P. pinnata (17.89) while the remaining eight species had IVI of less than 15.58. Avicennia officinalis had the lowest IVI of 5.63. The IVI depicts the ecological importance of a species in a given ecosystem and also helps give conservation priority to the species (Malimbwi et al. 2005; Kacholi 2013). In the present study, A. marina and A. alba showed high IVI due to their higher relative frequency, relative density, and relative basal area. The IVI of A. marina and A. alba in Thakurdia mangroves in Odisha were 8.2 and 19.73, respectively (Mishra et al. 2005), whereas the IVI of A. marina and A. alba were found to be 126.91 and 45.59 on Kanika Island, respectively. It indicates that A. marina and A. alba enjoy pre-dominance in Kanika island and the reasons for their dominance needs further study.

The analysis of community structure of mangroves at six study sites (0.6 ha) revealed that the relative density of A. marina and A. alba were higher than the remaining 10 species. It clearly indicates that the mangrove vegetation in Kanika island is characterized by the dominance of A. marina and A. alba. Eight mangrove associate species were recorded in addition to the species recorded in all six quadrats. Derris scandens was observed in close association with mangroves. Ipoemea pes-caprae, H. tiliaceus, C. inerme, P. pinnata, T. populnea, S. bacciformis, S. maritima, S. portulacastrum, C. rosea, and L. sarmentosa occurred on the sand dunes and sand bars in the elevated region of the island. Individuals with stunted growth of P. pinnata and T. populnea were found in the elevated areas. Sauropus bacciformis was found in the dried muddy regions of the island. Only one species of grass A. lagopoides (Poaceae) was found in the dried muddy areas (Table 2).

 

True Mangrove vs. Mangrove Associates

Ragavan et al. (2016) had stated that there are 35 true mangrove species in Sunderbans, 35 species in Odisha, 16 species in Karnataka, 19 species in Kerala, 22 species in Andhra Pradesh (Swain et al. 2008), 17 species in Pichavaram, Tamil Nadu (Salachandran et al. 2009), and 16 species in Goa (Sanjappa et al. 2011). But in the present study, out of 20 species counted, only four species—A. alba, A. marina, A. officinalis, and L. littorea—were found to be true mangroves and the remaining 16 species were only mangrove associates (Table 1). The occurrence of less number (4) of true mangrove species may be due to the small extent of Kanika Island. In the present study, P. juliflora trees also occur in the elevated sandy beach (site-VI). Since there is no human habitation in Kanika Island, the possibility of introduction of these species by humans is very less. Hence, there might be possibility of dispersal of seeds from inland to this island by river water. The impact of P. juliflora on the mangrove ecosystem in the study area requires sustained monitoring and further studies (Image 2).

 

Regeneration of mangroves

The study on the mature (≥1 m height) and juvenile (≤1 m height) individuals of A. marina and A. alba revealed that A. marina had the highest percentage of juveniles than A. alba. No juveniles of A. officinalis were found in the study sites. Most of the juveniles were found in the exposed areas adjacent to dense mangroves. This may be due to the fact that the seedlings found in open areas grow faster than those under canopy (Ellison & Farnsworth 1993, 1996). If the number of seedlings/saplings of a particular mangrove species is greater than 50% of their mature trees/ha, it is considered to possess good regeneration potential (Gan 1995). In the present study, 92% (n= 609) individuals of A. marina and 58.1% (n= 18) individuals of A. alba were found to be juveniles. It indicates that these two species were found dominant and have potential for regeneration in the Island as stated by Gan (1995). Apart from natural regeneration some seedlings also found washed into the shore by waves. Seedlings found in open areas grow faster than those under canopy (Ellison & Farnsworth 1993, 1996). In the present observations of seedlings found in the exposed areas corroborate the findings of Ellison & Farnsworth (1993, 1996).

The regeneration potentials of such seeds in inter tidal zones require further studies. It was observed that 13 matured A. marina trees were found damaged due to erosion of waves and of them, four were found dead. Since there is no anthropogenic pressure in the Island, the sea erosion related threats to the mangrove may pose a major management challenge in the near future (Image 3).

 

IUCN status

The IUCN Red List of Threatened Species has classified the status of A. alba, A. officinalis, A. marina, and L. littorea as ‘Least Concern’. These four mangroves are a common occurrence in all the mangrove vegetations of eastern and western coasts and Andaman & Nicobar Islands. Apart from India, A. marina is distributed in Australia, Indonesia, Thailand, Malaysia, Singapore, Philippines, and China. Avicennia alba is found in all the above said countries except China (Ragavan et al. 2016). Seven species were not evaluated and P. juliflora is an invasive alien species. Kanika Island has been considered ecologically sensitive as it provides habitat for several  mangrove species (Table 1).

 

 

CONCLUSION

 

My study provides an overview of mangrove species diversity in Kanika Island, Odisha. This Island harbors four true mangroves and 16 mangrove associates. The dominance of A. marina and A. alba is indicative of species robustness where other species have failed to colonize. The status and species composition of mangrove forest is a basic requirement and a pre-requisite for effective long-term monitoring, management and conservation of mangrove resources. It is suggested that immediate attention should be given for strengthening research activities to build database on true mangrove and mangrove associates. Since the island is uninhabited and free from cattle, there is no anthropogenic pressure on this mangrove vegetation. However, the fishing activities around the island should be regulated without causing any harm to the fragile mangrove ecosystem.

 

 

Table 1. List of plant species enumerated by qualitative survey in Kanika Island and their IUCN Red List Status

 

Binomial

Family

Life forms

True mangrove (TM) or mangrove associate (MA)

IUCN Red List status

Native / Non-native

01

Excoecaria agallocha L.

Euphorbiaceae

Tree

MA

Least Concern

Native

02

Avicennia alba Blume.

Avicenniaceae

Tree

TM

Least Concern

Native

03

Avicennia marina (Forsk.) Vierh.

Avicenniaceae

Tree

TM

Least Concern

Native

04

Avicennia officinalis L.

Avicenniaceae

Tree

TM

Least Concern

Native

05

Lumnitzera littorea (Jack) Voigt.

Combretaceae

Tree

TM

Least Concern

Native

06

Acanthus ilicifolius L.

Acanthaceae

Shrub

MA

Least Concern

Native

07

Thespesia populnea L.

Solander ex Correa

Malvaceae

Tree

MA

Least Concern

Native

08

Hibiscus tiliaceus L.

Malvaceae

Shrub

MA

Least Concern

Native

09

Suaeda maritima (L.) Dumort.

Chenopodiaceae

Herb

MA

Not assessed

Native

10

Clerodendrum inerme Gaertn

Verbenaceae

Shrub

MA

Not assessed

Native

11

Ipomea pes-caprae (L.) Sweet

Convolvulaceae

Herb

MA

Not Evaluated

Native

12

Ipomea tuba (Schl.) G. Don

Convolvulaceae

Herb

MA

Not assessed

Native

13

Sesuvium portulacastrum L.

Aizoaceae

Herb

MA

Least Concern

Native

14

Pongamia pinnata (L.) Pierre

Fabaceae

Tree

MA

Least Concern

Native

15

Sauropus bacciformis (L.) Airy Shaw

Phyllanthaceae

Herb

MA

Not assessed

Native

16

Prosopis juliflora (SW.) DC.

Fabaceae

Tree

MA

Invasive alien species

Non-native

17

Derris scandens Benth

Fabaceae

Climber

MA

Not assessed

Native

18

Launea sarmentosa (Willd.) Sch. Bip.

Asteraceae

Herb

MA

Not assessed

Native

19

Canavalia rosea (Sw.) DC.

Fabaceae

Herb

MA

Least Concern

Native

20

Aeluropus lagopoides (L.) Thwaites

Poaceae

Herb

MA

Invasive alien species

Non-native

 

 

Table 2. Basal area, importance value index, and above ground biomass of mangroves on Kanika Island.

 

Name of the species

Total BA (m2)

IVI

Total AGB (Kg)

1

Acanthus ilicifolius

0.403

26.69

0

2

Avicennia alba

0.889

45.59

3757.53

3

Avicennia marina

0.993

126.91

3331.78

4

Avicennia officinalis

0.027

05.63

32.81

5

Derris scandens

0.011

11.53

0

6

Excoecaria agallocha

0.101

12.78

89.66

7

Hibiscus tiliaceus

0.080

12.78

59.23

8

Ipomoea pes-caprae

0.001

12.21

0

9

Pongamia pinnata

0.254

17.89

302.23

10

Prosopis juliflora

0.196

11.03

446.46

11

Sesuvium portulacastrum

0.002

07.16

0

12

Thespesia populnea

0.182

15.58

241.36

Total

3.139

-

8261.06

 

For images - - click here

 

 

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