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Salt Marsh and Seagrass Communities of Bakkhali Estuary, Cox’s Bazar, Bangladesh

M.K. Abu Hena
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh

F.T. Short
Department of Natural Resources, University of New Hampshire, Jackson Estuarine Laboratory, 85 Adams Point Road, Durham, NH 03824, USA

S.M. Sharifuzzaman
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh

M. Hasan
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh

M. Rezowan
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh

M. Ali
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh

Abstract/ Executive Summary:

The species identification, distribution pattern, density and biomass of salt marsh and seagrass plants with some of the ecological parameters were studied in the Bakkhali river estuary, Cox’s Bazar, Bangladesh during the first half of 2006. Two salt marsh species (Spartina sp. and Imperata cylindrica) and one seagrass species (Halophila beccarii) were identified during this investigation, providing the first reports of Spartina sp. and H. beccarii in coastal Bangladesh. Seagrass H. beccarii was found in an accreted area and co-existing with salt marsh, and scattered sparsely in the salt marsh habitat and macroalgae Ulva intestinalis. Flowering and fruiting were recorded from the seagrass H. beccarri during January and February. No flowers and fruits were observed for the salt marsh Spartina sp. during the study period. Results showed that the shoot density of Spartina ranged from 400 to 2875 shoots m² with the highest total biomass (165.80 g dry weight (DW) m²) in March. Shoot density of H. beccarii ranged from 2716 to 14320 shoots m² in this estuarine coastal environment. The total biomass of seagrass was higher (17.56 g DW m² ) in March compared to the other months. The highest H. beccarii above ground (AG) biomass and below ground (BG) biomass were 9.59 g DW m2 and 9.42 g DW m² , respectively. These parameters are comparable with those generally observed for the salt marsh and seagrass species in the other places of the world. 2007 Elsevier Ltd. All rights reserved.

Keywords: Seagrass; Halophila beccarii; Salt marsh; Spartina sp; Biomass; Bangladesh

Location: Cox’s Bazar, Bangladesh

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Plant

Objectives:

This study was conducted with the following objectives: (a) to identify the number of species of salt marsh and seagrass occurring in the vicinity of the Bakkhali river estuary in Bangladesh; (b) to determine the shoot density and biomass as well as ecological status of the existing salt marsh and seagrass meadows.

Methodology:

The study area was situated in the vicinity of the Bakkhali river estuary, Cox’s Bazar (20 850 4000e20 460 9200 N and 91 960 6000e92 340 3700 E; ) which has a maritime climate, and the temperatures are buffered by the nearby ocean (Khan and Karim, 1982). The maximum air temperature attained in summer ranges from 31.1e33.3 C and minimum in winter ranges from 24.8e29.8 C in the estuarine environment of Bangladesh (Mahmood et al., 1978; Mahmood, 1986). Drought conditions prevail during the winter months, i.e. November-February and rainfall is confined to the monsoon period. Normally, 80e90% of the annual rainfall occurs during the monsoon months of June-September. This study was conducted during the period of January to June 2006. Sampling was done monthly at the spring low tide. The Bakkhali estuary is an important river estuary with a harbor and important local fishery. The estuary is approximately 0.5 km wide and >10 m deep at its mid point. The tide in the coastal and estuarine area of Bakkhali is semi-diurnal with two high and two low periods as per day and maximum amplitude of 3 m at spring tide (Mahmood, 1986). 2.1. Salt marsh and seagrass parameters 2.1.1. Species identification Fresh samples of salt marsh and seagrass were collected in plastic bags containing sea water and kept in an ice box. All samples were brought back to the Laboratory of Estuarine, Coastal and Aquaculture Research (LECAR) in the Institute of Marine Sciences and Fisheries (IMSF), University of Chittagong. Salt marsh and seagrass species identification were based on reference keys by Chapman (1977) and den Hartog (1970), respectively. All specimens were stored as herbarium sheets in the museum of the Institute of Marine Sciences and Fisheries for future reference. 2.1.2. Shoot density Shoot density of salt marsh was estimated randomly by using a 20 20 cm quadrat in the intertidal and accreted area at the estuary in a permanent plot of 50 50 m. At least five quadrat samples were collected randomly from the sampling areas every month. For seagrass, the 20 20 cm quadrat was placed in the accreted area where seagrass grows only in association with salt marsh and macroalgae. Shoot density of seagrass was sampled along a 50 m transect, with five quadrats sampled each month following the procedure described by English et al. (1994) and Brower and Zar (1984). The quadrats were placed randomly along the transect. All plants inside the quadrats were collected in plastic bags carefully and brought back to the LECAR for future analysis. The samples were washed and counted manually in the laboratory. The data obtained were converted to shoots m² . 2.1.3. Salt marsh and seagrass biomass Salt marsh and seagrass plants collected for density measures were rinsed briefly under running tap water. Leaves and sheaths for AG biomass were separated from roots and rhizomes for BG biomass. Epiphytes and algal communities were removed carefully from the plants by scraping with a knife (Kemp et al., 1987). Plant material was then dried at 75 C for 48 h to obtain dry weight (DW) following the procedure described by Schubauer and Hopkinson (1984) and Norhadi (1993). The data obtained from this study were expressed as g DW m² . 2.2. Ecological parameters 2.2.1. Collection and analysis of soils As an ecological study of the salt marsh and seagrass, water parameters such as temperature, transparency and salinity were measured in situ by mercury thermometer, Secchi disk (30 cm in diameter) and refractometer (0e100&, OSK, Japan), respectively. Soil pH was detected in situ using a soil pH meter (soil tester, Takemura Electrical Works Ltd). Soil samples were collected using a mud corer, placed in plastic bags and labeled. After collection, all samples were brought back to the laboratory within 2e4 h for analysis. In the laboratory, the samples were dried at 100 C for 24 h and powdered, sieved through a 0.5 mm stainless steel sieve and kept in a desiccator until further analysis. All determinations were in triplicate and the mean value was used to obtain representation of each parameter. The texture of the soil was analyzed following the procedure described by Bouyoucos (1962), soil organic matter by Boyd (1995) and soil carbon by Nelson and Sommers (1982).

Source of Information: Estuarine, Coastal and Shelf Science 75 (2007) 72-78

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Achievement/Findings:

It is likely that several environmental and physical factors, i.e., soil organic matter, water quality, activities of domestic animal and coastal communities probably are important in controlling the shoot density and biomass of coastal and estuarine macrophytes. However, the human interruption and grazing effect of domestic cattle cannot be overlooked, and probably influence the distribution, growth and biomass production of these macrophytes especially taller salt marsh Spartina sp. compared to creeping seagrass H. beccarii

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