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Shore to Landward Transect Burrow Diversity of Fiddler Crab in a Tropical Intertidal Coast of Chittagong in Bangladesh

Nafisa Khatun
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Mostt Tajnova Islam
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Nishat Sultana
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Sonya Mrong
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Md. Azizul Huq
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

Burrows indicate the abundance and distribution of fiddler crab in an intertidal coast that varies with structure and morphology within intertidal habitats. We observed fiddler crab burrow density and characters (burrow length, depth, diameter and volume) within randomly selected six 1m² quadrate from three intertidal habitats: higher saltmarsh, mangrove pool (a small ditch distributed within mangrove) and mangrove land through field surveys in a coast of Chittagong, Bangladesh. Burrows were observed and counted for density estimation, and burrow characteristics were studied through excavating 10 representative burrows from each quadrate of each habitat. Spearman correlation was used to relate between the distances (from shore towards land) and burrow characters. Transect starting from saltmarsh as base towards mangrove land showed burrow density decreased from shore to higher intertidal habitat. Simultaneously, higher burrow length and diameter were observed landward and contrariwise shoreward. Burrow prevalence in mangrove pools represents fiddler crabs are abundant within land and shore interface presumably due to the dual privilege of easy burrowing and moist condition required for gill ventilation.

Keywords: Burrow characters, Saltmarsh, Mangrove, Mangrove pool

Location: Dakshin Kattoly sea beach, Salimpur, Chittagong

Start Date: 00-11-2015

End Date: 00-02-2016

Program Area: Animal Health and Management

Commodity: Crab

Objectives:

To understanding burrow distribution pattern in intertidal habitats of Bangladesh

Methodology:

Sampling took place in a tropical intertidal coast during low tide at South Kattoly sea beach, locally known as Dakshin Kattoly sea beach, Salimpur, Chittagong (Latitude 22035’50” N, Longitude 91075’40” E) along the Bay of Bengal. This coast was planted by mangrove forest under the Asian Development Bank green belt project on 1997-1998 and characterized by a long intertidal salt marsh merged with mudflat and mangroves stretches about 200 m from the shore line. Tides are semi-diurnal with high tide and low tides in every 6 hours interval. The characteristic of the coast is muddy or sandy coast dominated by saltmarsh Porteresia coarctata (Aysha et al., 2015), and mangrove was dominated by Avicennia spp. Fiddler crab was found in higher marsh but not in lower saltmarsh. A special feature of around 1 ft deep irregular shaped ditch (round or oval or L- shaped,), mangrove pool was observed within mangrove land adjacent to salt marsh. Pools remain water logged as it receives water during spring tide, but usually get dry when normal tidal water cannot reach. Sampling was followed by transect from saltmarsh towards mangrove by selecting three habitats (saltmarsh, mangrove pool and mangrove) and data were collected from November 2015 to February 2016. As burrow count provide quick and reliable estimate (Warren, 1990), burrow abundance and burrow characteristics (diameter, length, depth, volume and shapes) were determined in three intertidal habitats from shore towards land viz. higher saltmarsh, mangrove pools and mangrove higher intertidal land. In each habitat, we selected six 1 m² (1 m ×1 m) quadrates randomly to count burrows visually. But three quadrates in saltmarsh were chosen intentionally along the same line to consider them as base point to measure landward distance of other quadrates. Burrow length, depth and shape were measured with measuring tape after excavating 10 representative burrows from each quadrate using soil corer up to 30 cm depth. Burrow diameter was measured by digital venire calipers. Burrow volume was calculated using the formula (πr²h, where π = 3.1416, r = radius, h = length) assuming a cylindrical hole. The distance of each quadrate was measured from the first three quadrates which were situated in saltmarsh. In order to find correlations between distances (shores to landward) and burrow characters, each quadrate distance was measured from the quadrate positioned in salt marsh considering as the base point (0 m) towards mangrove, so that we can understand sea to landward burrow characters. Data were checked for homogeneity with Levine’s test and for normality with Shapiro-Wilk test. We compared means of burrow characters among three habitats using one-way ANOVA through SPSS version-16.0. Significance was assigned at the 0.05% level. Bivariate Pearson correlation analysis (2-tailed) was used to find correlation between shore to landward distance and burrow characters.

Source of Information: Res. Agric. Livest. Fish. Vol. 4, No. 2, August 2017: 131-140

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Fiddler crab burrow distribution and characters differed in different habitats of the intertidal coast of Bangladesh with more burrow density in shoreward and contrariwise towards landward. The number of burrows reduced towards higher intertidal zone but burrows of this area had higher burrow depth and diameter which represents water availability, substrate characteristics and size of burrowing individuals determine the burrow characters. Contrarily, smaller and temporary burrows were denser in saltmarsh towards shore. Highest burrows in mangrove pool indicated crabs prefer to stay in moist condition, where water availability support burrowing and gill activity. Fiddler crabs are ecologically important bio-turbator contribute in nutrient replenishment and support for nutrient enrichment in the intertidal habitat. The current study focused on fiddler crab burrows at the scale of 1 m² sampling plots. For better understanding of burrow characters, a more detailed study with a finer sampling design and massive burrow observation along with more intensive ecological study is required.

Knowledge Management: Journal