Journal of Threatened Taxa | www.threatenedtaxa.org | 26 January 2022 | 14(1): 20406–20412

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

https://doi.org/10.11609/jott.7719.14.1.20406-20412

#7719 | Received 22 October 2021 | Finally accepted 28 December 2021

New distribution record of globally threatened Ocean Turf Grass Halophila beccarii Ascherson, 1871 from the North Andaman Islands highlights the importance of seagrass exploratory surveys

Swapnali Gole ¹, Prasad Gaidhani ², Srabani Bose ³, Anant Pande ⁴, Jeyaraj Antony Johnson ⁵ & Kuppusamy Sivakumar ⁶

^1–6 Wildlife Institute of India, P.O. Box 18, Chandrabani, Dehradun, Uttarakhand 248001, India.

¹ gole.swapnali@gmail.com, ² prasadgaidhani10@gmail.com, ³ srabanibose11081995@gmail.com, ⁴ anant@wii.gov.in,

⁵ jaj@wii.gov.in, ⁶ ksivakumarwii@gmail.com (corresponding author)

Editor: Anonymity requested. Date of publication: 26 January 2022 (online & print)

Citation: Gole, S., P. Gaidhani, S. Bose, A. Pande, J.A. Johnson & K. Sivakumar (2022). New distribution record of globally threatened Ocean Turf Grass Halophila beccarii Ascherson, 1871 from the North Andaman Islands highlights the importance of seagrass exploratory surveys. Journal of Threatened Taxa 14(1): 20406–20412. https://doi.org/10.11609/jott.7719.14.1.20406-20412

Copyright: © Gole et al. 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: National CAMPA Advisory Council (NCAC), Ministry of Environment, Forest and Climate Change, Government of India (Grant/Award Number: 13-28(01)/2015-CAMPA).

Competing interests: The authors declare no competing interests.

Author details: Swapnali Gole is working on dugongs and seagrasses in the Andaman Islands, as a part of the CAMPA_Dugong Project, Wildlife Institute of India. Her doctoral research is on the ecology of seagrass habitats and associated macro-benthic invertebrates in the Andaman Islands. Prasad Gaidhani worked as an intern with the Wildlife Institute of India’s CAMPA_Dugong Project in the Andaman Islands. His primary research interests encompass species research, community-based conservation with special emphasis on human-wildlife conflict, across different sea/landscapes. Srabani Bose is working on seagrass and its associated microbenthic fauna, as a part of the CAMPA Dugong Project, Wildlife Institute of India. Her research interest in on understanding the role of benthic fauna in the critical dugong habitat and also taxonomical study of microbenthic fauna. Anant Pande’s work is focused on understanding drivers of population decline of marine mammal and seabird populations, developing strategies for their conservation and management. His work involves conducting field assessments of marine megafauna populations to provide evidence-based inputs to policy makers. Jeyaraj Antony Johnson has been working on taxonomy, ecology and biology of Indian fishes. His research included species distribution patterns, community structure, spatio-temporal changes in resource (food and space) partitioning among co-existing species, conservation of rare and threatened species, e-flow assessment and effects of human disturbance on aquatic resources. Currently he is coordinating the freshwater fish monitoring project under MoEFCC’s Long-term Ecological Observation (LTEO) programme. Sivakumar Kuppusamy has been working on conservation and management of aquatic biodiversity especially marine biodiversity of India as well as of Antarctica. His research involves understanding species distribution pattern, species ecology and behavioural ecology. Currently he is coordinating the MoEFCC-CAMPA funded project on the recovery of Dugong and its habitats in India. He has also involved in the developing a detail project report for the Project Dolphin.

Author contributions: SG—conceptualisation and drafting of manuscript, field work, sample collection and post processing, data entry and analysis. PDF—field work, sample collection and post processing. SB—laboratory work of infaunal macrobenthic samples. AP—supervision of the field work, conceptualisation and reviewing the manuscript. JAJ—supervision of the field work, reviewing the manuscript. SK—study design, supervision of the field work and data analysis, reviewing the manuscript.

Acknowledgements: This study was sponsored by National CAMPA Advisory Council (NCAC), Ministry of Environment, Forest and Climate Change, Government of India (Grant/Award Number: 13-28(01)/2015-CAMPA). We acknowledge D.M. Shukla (CWLW, Department of Environment and Forests, Andaman & Nicobar) for granting necessary work permits and assistance provided by K.G. Rassogi, divisional forest officer (Mayabunder Wildlife Division). Our special thanks to the frontline staff of the Mayabunder Wildlife Division; Alagar Gopi (Forest guard), Charlice Kullu (Forest guard), Saw Tubo, Saw Johnson, Saw Immui, Thomas, and Sumra Rao. Lastly, we thank Sohini Dudhat (Wildlife Institute of India), Dr. Himansu Das (Environment Agency, Abu Dhabi), Dr. Nehru Prabhakaran (Wildlife Institute of India), and Sohom Seal (Wildlife Institute of India) for their valuable inputs on the manuscript.

Abstract: Halophila beccarii, listed as ‘Vulnerable’ on the IUCN Red List, aids in seagrass and mangrove succession, acts as a substrate stabilizer and provides feeding grounds for mega-herbivores like dugongs. This species was first recorded from the Andaman & Nicobar Islands in 2015, and its distribution status within the archipelago remains under-investigated. We report a new distribution record of H. beccarii from the North Andamans and shed light on its inter-island distribution. H. beccarii was recorded from a mixed meadow comprising of Cymodocea rotundata (20.5 ± 28.8%, mean seagrass cover), Thalassia hemprichii (16.3 ± 23.3%, mean seagrass cover), and Halodule pinifolia (6.3 ± 12.1%, mean seagrass cover) at Pokkadera, North and Middle Andaman district. H. beccarii had the highest mean seagrass cover (30 ± 34.7%) and shoot density (103.5 ± 68.3 shoots/ m²) among sympatric seagrass species. We also recorded eight seagrass-associated macrofaunal groups (gastropods, bivalves, polychaetes, foraminiferans, nematodes, brachyurans, decapods and asteroids) from the infaunal and epibenthic micro-habitats within the meadow. Infaunal macrobenthos had a much higher density (73.5 ± 129.7 individuals/m²) than the epibenthic macrofauna (0.4 ± 1.5 individuals/m²), possibly influenced by the seagrass canopy structure and biomass. Overall, gastropods were the most dominant macrobenthic faunal group (overall mean 95.0 ± 106.1 individuals/m²). The present findings emphasize the need for more exploratory surveys to understand H. beccarii distribution in the Andaman & Nicobar archipelago to identify priority conservation areas.

Keywords: Andaman & Nicobar Islands, Dugongs, epifauna, habitat conservation, macrobenthos, seagrass associated.

Abbreviations: ANI—Andaman & Nicobar Islands | LIT—Line Intercept Transect.

INTRODUCTION

Seagrasses are ecosystem engineers (Hoegh-Guldberg & Bruno 2010) that stabilize sediments (Ondiviela et al. 2014), modify habitats they colonize (Koch 2001) and contribute to coastal protection (Ondiviela et al. 2014). Seagrass meadows contribute to local carbon sinks (Suchanek et al. 1985), trophic transfer within habitats (Costanza et al. 1997), and primary production (Waycott et al. 2009), and they support a diversity of associated invertebrate fauna (Orth et al. 1984; Lee et al. 2001; Leopardas et al. 2014; Su et al. 2020).

In India, seagrasses are distributed along the coastlines of Gujarat, Maharashtra, Karnataka, Kerala, Tamil Nadu, and Odisha states, and the Lakshadweep and Andaman & Nicobar archipelagos (Thangaradjou et al. 2018). These ecologically valuable and fragile coastal habitats are threatened in Indian waters by high anthropogenic dependency, destructive practices like boat anchorage, extractive fishing, and nutrient enrichment through agricultural run-offs or domestic sewage disposal (Thangaradjou et al. 2008; Sridhar et al. 2010; Nobi & Thangaradjou 2012). Despite being protected under the ‘Coastal Regulation Zone Act’ (Dhiman et al. 2019), seagrasses have received less attention than other marine ecosystems (Jagtap et al. 2003).

Seagrass research in the Andaman & Nicobar Islands (ANI) has been sporadic. Pioneering work by Jagtap (1991, 1992) and Das (1996) collectively reported nine species. Halodule uninervis, Thalassia hemprichii, and Halophila ovata were the first seagrass records from ANI (Jagtap 1991), followed by new regional records of Halophila ovalis, Cymodocea rotundata, Enhalus acoroides, and Syringodium isoetifolium (Jagtap 1992). Pan-Island seagrass exploratory surveys by Das (1996) reported Cymodocea serrulata and Halodule pinifolia, followed by a two decadal gap in investigating species distribution status in ANI. Later, Halophila minor and Halophila decipiens were reported from the island waters (D’Souza et al. 2015).

The most recent addition to the species checklist from Andaman waters is Halophila beccarii reported from the Haddo Bay of South Andaman (Savurirajan et al. 2015). Globally, H. beccarii has a fragmented distribution range in the Indo--Pacific region which extends from the eastern coast of Africa up to southeastern Asia (Green & Short 2003). Although the species was first reported from Indian waters in 1991 (Jagtap 1991), its distribution was not known from the Andaman Islands till 2015. Furthermore, little is known about its inter-island distribution, as records post the first report (Savurirajan et al. 2015) are restricted to South Andaman (Ragavan et al. 2016).

In this study, we report a new distribution site for Halophila beccarii in the Andaman Islands and update its current distribution status for the Andaman group. Our study provides detailed meadow characteristics and associated macrofaunal assemblages, and highlights the habitat importance of seagrass meadows.

STUDY AREA

The Andaman and Nicobar archipelago is situated in the Bay of Bengal (6.750–13.683 ⁰N and 92.2–93.95 ⁰E) and encompasses 836 islands, islets, and rocky outcrops with a total geographical area of 8,249 km² (http://andaman.gov.in) and a 1,962 km long coastline (Census Directorate 2011). The shallow waters of the archipelago support 830 hectares of seagrass cover (Ragavan et al. 2016).

The present study was carried out in May 2019 as a part of a pan-island seagrass mapping survey at Pokkadera (12.902⁰N & 92.910⁰E). Pokkadera is situated on the East coast of Mayabunder (North & Middle Andaman district) in the Andaman archipelago. It’s a large intertidal unprotected area, with a vertical zonation expanse (distance between high to low tide when exposed) in low tide, up to ~ 400 m. The benthic substrate profile is characterized by mixed muddy-sandy sediment in the upper and lower intertidal zones and exposed sand bars in the mid-intertidal area (Figure 1). Pokkadera is an ecologically diverse site, which supports critical coastal ecosystems like seagrass meadows, mangroves, sandy, and rocky intertidal habitats, along with tropical littoral vegetation.

Methods

Field sampling

We carried out on-foot exploration during low tide in the upper intertidal zone of Pokkadera. After locating a seagrass meadow we walked the perimeter and GPS marked the points at the edges (transition of seagrass habitat and adjacent unvegetated sediments). Later, we plotted the coordinates on Google Earth Pro version 7.3 to calculate the total area of the sampled study site. We used systematic line intercept transects (LIT) to assess seagrass meadow characteristics such as species composition, seagrass cover, shoot density, shoot length, total biomass (above and below ground; dry weight), and non-epiphytic algal cover (English et al. 1997). We deployed four 50 m long LITs inside the meadow, spaced apart at a distance of 150–200m. A 50 x 50 cm quadrat was placed after every 5 m interval on the LIT to record meadow characteristics (percentage seagrass cover, species composition, non-epiphytic algal cover). Algal shoots, independent of seagrass blades with distinct substratum penetration, were quantified to estimate non-epiphytic algal cover within the quadrat. We recorded seagrass-associated epibenthic macrofaunal groups within the quadrat to estimate group densities (ind. /m²).

We collected seagrass samples from a 20 X 20 cm quadrat within the larger (50 x 50 cm) quadrat in each transect (n= 3/ transect) to estimate seagrass shoot density, shoot length, and total biomass (above and below ground; dry weight) in the laboratory. To assess the seagrass-associated infaunal (within the sediments) macrobenthic communities, we hand-scooped (up to 10 cm) sediment samples in triplicates from 20 X 20 cm area, randomly from each transect (n= 3/ transect). Seagrass and macrobenthic sediment samples were stored in ziplock bags on the field and transported to the laboratory for further analysis.

We also recorded environmental parameters on the field, like pH and sea surface temperature using a hand-held multi-parameter tester (Eutech Oaklon- PCS Testr 35) and salinity with a handheld refractometer (LABART).

Laboratory analysis

In the laboratory, we rinsed seagrass samples with fresh water to remove sediment particles from the shoots and roots. We discarded any algal shoots within the samples and thoroughly rinsed them again. Later, we counted seagrass shoots (species-specific) present in the samples to estimate shoot density (shoots/ m²). Further, using a measuring scale (cm), we recorded the length of randomly picked ten shoots to give species-specific shoot length. For Halophila beccarii, we noted additional measurements (shoot width, n=9, and internodal length, n=6), species characteristics, and natural history observations. Lastly, we sun-dried the seagrass samples (whole plant, shoots, and roots) and calculated total biomass above and below ground by dry weight (g/m²) on a micro-scale weighing balance (WENSAR PGB-220/ 0.001 to 200 g).

Infaunal macrobenthic analysis

We immediately preserved the macrobenthic sediments in 4% (buffered) formalin-Rose Bengal solution and later sieved them on a 500 micron mesh to retain macrobenthic fauna (0.5mm and above; Ingole et al. 2009). We identified the seagrass associated macrofauna up to group level under a stereoscope (Zeiss discovery V.8) and, groups were validated using standard identification manuals (Fauchald 1977; Keppner & Tarjan 1989; Sturm et al. 2006; Sasaki 2008). Lastly, we counted individuals of each group to estimate their abundances.

RESULTS

We recorded four seagrass species and eight macrobenthic groups associated with seagrass habitats from the present study. We report a new distribution record of globally threatened seagrass species, Halophila beccarii, from the North Andaman region. Pokkadera seagrass meadow spreads across ~8.2 hectares (Figure 1), comprising early-successional species like H. beccarii, Halodule pinifolia, and Cymodocea rotundata; and late-successional species like Thalassia hemprichii (Vonk et al. 2015; Nowicki et al. 2017).

The mean seagrass cover in the meadow was 18.3 ± 24.7 %, with a non-epiphytic algal cover of 18.3 ± 35 %. H. beccarii (30 ± 34.7 %) and H. pinifolia (6.3 ± 12.1 %) contributed to the highest and lowest seagrass cover. H. beccarii had the highest shoot density (103.5 ± 68.3 shoots/ m²), whereas C. rotundata added to maximum total biomass (44.0 ± 56.1 g/ m^--2; Table 1).

Halophila beccarii

Halophila beccarii belongs to the family Hydrocharitaceae in the order Alismatales. The specimen recorded at the Pokkadera meadow had 4–8 lanceolate leaves with no cross venation (Image 1B & C). The mean shoot length was 1.3 ± 0.4 cm (n= 10), mean shoot width was 1.3 ± 0.5 mm (n= 9) with a mean internodal length of 1.7 ± 0.3 cm (n= 6). Rhizomes were smooth as observed for the species (Image 1B).

Habitat

Halophila beccarii was distributed in the upper intertidal zone, either as monospecific strands on sand flats or was found associated with T. hemprichii, C. rotundata, and H. pinifolia in a mixed species meadow (Image 1A). The species was present in intertidal puddles or exposed on sand bars in line with previous observations (Waycott et al. 2004) and here was dominantly distributed at the fringes of the intertidal zone, adjacent to littoral vegetation.

Associated macrobenthic fauna

We recorded a total of eight macrofaunal groups, both epibenthic (n= 5 groups; number of quadrats= 44) and infaunal (n= 5 groups; number of sediment samples = 12) belonging to six phyla, associated with the seagrass beds at Pokkadera viz; gastropods, bivalves, polychaetes, nematodes, brachyuran, decapods, asteroids, and foraminiferans. Gastropods and bivalves were common groups found in both the micro-habitats.

In order of abundance, gastropods (51.4%) dominated the infaunal assemblages, followed by bivalves (35.2%) and polychaetes (7.4%), while the least dominant groups were nematodes (3%) and foraminifera (3%). Gastropods were dominant in epibenthic assemblages (50%), followed by brachyurans (31.3%; Table 2). The total mean density of epibenthic groups (0.4 ± 1.5 ind. /m²) was much lower than infaunal assemblages (73.5 ± 129.7 ind. /m²; Table 2).

DISCUSSION

Halophila beccarii is a euryhaline species found associated with mangrove vegetation (Jagtap 1991) that provides numerous ecosystem services. Studies have highlighted the role of H. beccarii meadows as sediment stabilizers, refugia to macrobenthic and fish diversity (Mathews et al. 2010), and pioneers for seagrass succession (Aye et al. 2014). The species is presently listed as ‘Vulnerable’ in the IUCN Red List (Short et al. 2010) and some of the major threats are coastal infrastructure development, marine pollution, and exploitative fishing practices, leading to modifications of its natural habitat (Short et al. 2010).

In addition to reporting a new distribution record, our study emphasizes the importance of mixed seagrass beds for associated species thus, highlights the value of these coastal ecosystems. Studies have highlighted habitat importance of H. beccarii meadows in supporting macrobenthic diversity (Su et al. 2020). Our findings suggest high numerical dominance of infaunal assemblages which needs further investigation, as epifaunal and infaunal abundance in seagrass meadows is influenced by meadow characteristics like structural complexity, canopy height, leaf morphology, shoot density, and above and below ground biomass (Orth et al. 1984; Lee et al. 2001; Leopardas et al. 2014).

The intertidal region at Pokkadera is an unprotected area, and the seagrass habitats are open ground for shoreline fishing activities and cattle trampling during ebb tide, posing a threat to the existing seagrass beds, and in turn associated fauna. Based on few anecdotal reports by local fishers, Pokkadera is a dugong feeding habitat, which signifies the importance of the site and adds to the necessity for habitat and species conservation.

Scientists have emphasized the need for integrating research with policy-making to conserve H. beccarii habitats (Ramesh et al. 2018). Our work highlights H. beccarii distribution for prioritizing its conservation in the Andaman and Nicobar Islands, in line with recommendations to aid ecological assessments globally (Short et al. 2010). Lastly, we strongly recommend the need for more seagrass exploratory surveys and long-term monitoring of critical meadows to form a robust baseline for seagrass management in the Andaman Islands.

Table 1. Seagrass meadow characteristics of Pokkadera seagrass meadow, Mayabunder, North and Middle Andaman district of Andaman & Nicobar Islands.

Meadow characteristics	Seagrass species
	Halophila beccarii	Cymodocea rotundata	Thalassia hemprichii	Halodule pinifolia
Mean seagrass cover (%)	30 ± 34.7	20.5 ± 28.8	16.3 ± 23.3	6.3 ± 12.1
Shoot density (shoots/ m^2)	103.5 ± 68.3	45.5 ± 24.4	40.6 ± 30	42.5 ± 12
Shoot length (cm; n= 10)	3.2 ± 2.8	6.9 ± 1.7	5.1 ± 3.5	4.3 ± 1.4
Total Biomass (above and below; dry weight) (g/ m^2)	1.3 ± 2.2	44.0 ± 56.1	14.1 ± 25.1	0.6 ± 1.8
Sea surface temperature- (°C) 37.3 ± 0.7		Salinity- (ppt) 29.0 ± 1.0	pH- 8.8 ± 0.1

(Values expressed as mean ± standard deviation).

Table 2. Mean densities of major seagrass-associated macrobenthic taxonomic groups recorded at Pokkadera seagrass meadow.

Faunal groups	Infaunal (ind. / m^2)	Epifaunal (ind. / m^2)
Gastropods	188.9 ± 151.8	1 ± 1.7
Bivalves	129.2 ± 391	0.1 ± 0.7
Polychaetes	27.1 ± 52.2	not recorded
Nematodes	11.1 ± 26	not recorded
Foraminiferans	11.1 ± 27.4	not recorded
Asteroids	not recorded	0.1 ± 0.7
Brachyurans	not recorded	0.6 ± 3.5
Decapods	not recorded	0.1 ± 0.7

For figure & image - - click here

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