Spatial distribution and substrate preference pattern of Ilyoplax frater along intertidal areas of Pakistan

Item Type article

Authors Saher, Noor Us; Qureshi, Noureen Aziz; Aziz, Uroj

Download date 29/09/2021 18:37:06

Link to Item http://hdl.handle.net/1834/40786 Pakistan Journal of Marine Sciences, Vol. 23(1&2), 33-43, 2014.

SPATIAL DISTRIBUTION AND SUBSTRATE PREFERENCE PATTERN OF ILYOPLAX FRATER ALONG INTERTIDAL AREAS OF PAKISTAN Noor Us Saher, Noureen Aziz Qureshi and Uroj Aziz Centre of Excellence in Marine Biology, University of Karachi, Karachi-75270, Pakistan (NUS); Department of Zoology, Government College Women University, Faisalabad, Pakistan (NAQ); A.P.W.A. Government College for Women Karimabad, Karachi, Pakistan (UA). email: [email protected]

ABSTRACT: Spatial distribution of dotillid i.e. Ilyoplax frater studied along the intertidal shores of Pakistan using transect and quadrate sampling method. The study revealed a significant correlation between the distribution of Ilyoplax frater and habitat characteristics like tidal level and sediment structure, as these were more abundant in low to mid tide level with high moisture, porosity and mud content. The morphology of feeding appendages i.e showed meral segment is not expended, having plumose to serrate setae which is characteristics of deposit feeding crabs adapted in muddy cum sandy environment having feeding appandages specialized in relation to habitat. Significant spatial variations in crab density was observed among sites, highest density of crabs were reported from Bhambore with low mean size (6.86 ± 1.66) with a size range 2 mm – 11mm of carapace width (CW) .

KEYWORDS: Dotillid crab, spatial distribution, habitat, crab density.

INTRODUCTION

Among the burrowing decapod , crabs are noteworthy for their dominance, abundance and species richness along tropical to subtropical mangrove forest. Along intertidal mangrove ecosystem of Pakistan three species of estuarine dotillid crabs of genus Ilyoplax were reported in previous studies (Alcock, 1900; Tirmizi and Ghani, 1996). Among these the Ilyoplax frater is widely distributed along the shoreline and accounts as an important faunal component which plays an important role in the ecological dynamics of shores. These small sized dotillid crabs construct their burrows in soft sediments and feed upon the drained surface organic deposits (Jones and Clayton, 1983; Al-Khayat, 1996; Saher and Qureshi, 2011a; Saher and Qureshi, 2011b) and are thus responsible for sediment turnover and organic matter recycling. Zonation pattern, distribution and abundance of benthic communities in intertidal zones is imposed by number of biological and ecological factors (Teal, 1958; Ono, 1965; Hartnoll, 1973; Icely and Jones, 1978, Saher and Qureshi, 2011b). Biological factors including recruitment, intra and inter-specific competition and food availability define distributional pattern of on the other hand, sediment sorting, variation in substrate characteristics, tidal regime and shore profile cause environmental gradients and a patchy habitat structure (Attrill and Rundle, 2002). These biological and ecological variables create different niches in intertidal zones thus providing limiting factor for the 34 Pakistan Journal of Marine Sciences, Vol. 23(1&2), 2014. distribution of species in the different zones and may be considered the ultimate cause of broad scale community patterns, both spatially and temporally (Luk and Zajac, 2013). The main purpose of the current study is to examine variations in the spatial distribution and abundance of I. frater along the Pakistan coast and to identify the relationship of their distributional pattern in relation with their feeding habit, morphology of the mouthparts and substrate type.

MATERIALS & METHODS

Study area: The coastal belt of Pakistan situated along Northern border of Arabian Sea. It covers an area of about 1050 km stretches along Sindh and Balochistan coast. Pakistan is located in semi-arid zone, having semidiurnal tide and low rainfall throughout the year. The coastal areas in Pakistan are characterized by mud flats, delta lagoons, bays, plains, cliffs, beaches, and rocky shores which support considerable biodiversity in intertidal areas and offshore waters. The study was conducted at 7 localities (Table 1) along Pakistan coast, including five along Sind coast (Korangi Creek, Bhambore, Ketibunder, Dhabeji, and Sonari) and two on Balochistan coast (Bhaira and Sonmiani).

Table 1. Sampling sites of Ilyoplax frater selected for the studyalong the Pakistan coast .

No Site Abbreviation Substrate Lat / long o o 1. Bhaira Bh Median to very fine sand 25 29’N, 66 33’E o o 2. Bhambore BHM Coarse to very fine sand 24 43N, 67 35’E o o 3 Dhabeji Dh Very fine sand 24 48’N, 67 29’E o o 4. Ketibunder KB Coarse to very fine sand 24 09N, 67 20’E o o 5. Korangi Creek KC Median to fine sand 24 79’N,67 20’E o o 6. Sonari So Median to very fine sand 24 53N, 66 42’E Sonmiani Bay o o 7. SB Median to very fine sand 25 26’N, 66 35’E lagoon

Sampling Procedure : Crab and sediment samples were collected from selected study sites during low tides. To assess the crab density and to minimize the error two transects were selected and samples were collected at three levels, perpendicular to the shoreline which were determined by a tidal range (i. Low water level L ii . Mid-water level M iii . High or upper water level H). Samples were collected through quadrate method (0.25m 2 × 0.25 m 2). Sediments in the quadrates were dug and the crabs were collected by hand from the Saher et. al. : substrate preference pattern of Ilyoplax frater 35 excavated sediment. For grain size analysis PVC core (internal diameter 5.6 cm) digged down upto 20 cm. All samples were placed in airtight bags and brought back to the o laboratory, crabs were washed, identified and preserved at -20 C. Sediment Analysis: In order to characterize the sediment parameters along studied site, i.e., porosity, organic content, grain size and moisture estimated. The sediment organic content was estimated as the percentage of weight loss on ignition into a muffle furnace at 450°C for 3 hours, then each sample was oven dried at 60 ºC to a constant weight. The dried samples (approx. 100 gs) were then sieved through a sieve shaker and each fraction weighed separately and characterized by following (Folk, 1974) (details in Saher and Qureshi, 2010, 2011, 2012). Crab density and distribution: The density of crabs ( ρ) per m 2 was calculated using the formula: ρ= n 0.25 Where n = number of individuals in the quadrat. General linearized Model GLM (ANOVA) performed to compare the density of crabs among sites and within shore levels using MINITAB 17 software (P value < 0.05 was considered as significant). To correlate the environmental parameters with crab density and abundance structure, the data were subjected to Pearson’s correlation and Principal Component Analysis. Student t-test was employed to analyze whether the size of male crab was equal to female crab at each site. To understand the functional morphology related to substrate, 2 nd maxilliped was removed and detailed studies of setation on its inner surface were made using a Scanning Electron Microscope (SEM).

RESULTS & DISCUSSION

The spatial variability in distribution of Ilyoplax frater was observed and was significantly different among all studied sites (F 6 = 6.29, P<0.005). The lowest density was observed at Bhaira (4.0 ± 2) and the highest level of density was observed at

Fig.1. Density distribution of I. frater at three levels and seven selected sites along the coast of Pakistan 1. Low tide level, 2. Mid tide level, 3. High tide level. b. Density of crab along the distribution range of I. frat er. 36 Pakistan Journal of Marine Sciences, Vol. 23(1&2), 2014.

Bhambore (72.6 ± 26.6) during low tide level (Fig. 1, Table 2). Density of crabs varied significantly along each tidal level (F = 3.52, P < 0.005) as density was higher in low and mid tide level than the high tide level. During the study, size of male and female crab was not significantly different. Mean size (CW) of Ilyoplax frater was largest at Sonmiani Bay (8.02 ± 1.39) and smallest at Bhambore (6.84 ± 1.7).

Table 2. Percent abundance, mean sizes of male and female crabs and results of t- test for Ilyoplax frater collected from the study area. (M= male crab, F= female crab, % = percent abundance, CW= carapace width in millimeter, S.D = standard deviation).

Mean size Mean size Percent Density t-test Chi - (Cw) mm, (Cw) mm, No. Site abundance range m -2 square x2 S.D S.D M % F % (mean) T value Pvalue Male Female 0 – 9 8.0 ± 0.10 7.0 ± 0.66 1 Bhaira 16.6 83.3 24.4 0.00 0.60 0.58 (4) (8 - 8.5) ( 6-9.5) 22 – 90 7.0 ± 0.17 6.6 ± 0.16 2 Bhambore 48.5 51.4 0.08 0.77 -1.73 0.08 (70) (2.5 – 11) ( 3 -10) 0 -14 7.0 ± 0.66 9.0 ± 0.16 3 Dhabeji 60 40 2.02 0.15 -1.70 0.23 (3.3) (7 – 9) (7- 9) 14 -74 7.1 ± 0.22 8.4 ± 1.3 4 Keti bunder 41.5 58.4 1.63 0.20 -0.93 0.35 (34.6) (4.5 – 10.5) ( 5.5 – 10.5) Korangi 0– 32 8.0 ± 0.30 7.5 ± 0.28 5 46.1 53.8 0.32 0.57 -0.34 0.73 creek (17.3) (5.5 – 8.5) (6 – 9.5) 1 – 42 7.5 ± 0.42 6.8 ±0.91 6 Sonari 50 50 0.00 1.00 0.66 0.52 (14.6) (6 – 9) (4 – 9) Sonmiani 8 -26 7.8 ± 0.33 8.0 ± 0.25 7 35.7 64.2 4.00 0.04 -0.50 0.62 bay (19.5) (4 – 10.0) (4.5 – 11)

The sediment grain size distributions showed high sand content at SB 99.3% while lowest at KB 83.73%. Mud content was highest at KB (14.9%) and lowest at SB (0.384%). Sediment median grain size was highest at BHM (3.61) and lowest at Dh (1.555). Total Organic matter TOM was highest at Dh (20.35) and was particularly lowest at SB (1.43). Total moisture content was highest at KB (37.07) and lowest at SB (3.20). Porosity highest values at KB (95.85) and was lowest (14.23) at SB. Sediment properties including particle size at different sampling sites were shown in Fig 2. Pearson correlation used to determine the relationship of sediment properties with crab density (Table 3). The mean grain size showed negative correlation with organic matter, sand particles and tidal levels, however It was positively correlated with crab density, mud content, porosity and moisture content of the sediment. Crab density showed positive correlation with median and mud and negatively correlated with organic matter. PCA results showed that PC1 and PC2 account for 70.5% of the total variation (Fig. 3). PC1 accounts for most of the possible variation among sites, evaluated characteristics includes sorting, moisture content, porosity, mud, and sand content were plotted on the first Saher et. al. : substrate preference pattern of Ilyoplax frater 37

principal component, positive values of except sand content, while PC2 showed correlation with median and crab density while negatively correlate with organic matter. The Eigenvalue and ratios of explained variances presented in Table 4.

Fig. 2. The percent distribution of sediment properties along the selected study sites of Pakistan.

Fig. 3. PCA plot representing distribution of sediment variables and crab abundance along coast of Pakistan. 38 Pakistan Journal of Marine Sciences, Vol. 23(1&2), 2014.

Table 3. Pearson Correlations between density of Ilyoplax frater and sediment properties (Med = Median grain size, MC = percent moisture content, Por = percent porosity, TOM = total organic matter, Gra = granule size, SP = sand particles, Den = crab density).

Med MC Por TOM Gra SP Mud

MC 0.233 * * * * * * 0.243 * * * * * *

Por 0.313 0.944 * * * * * 0.112 0.000 * * * * *

TOM -0.358 0.335 0.393 * * * * 0.066 0.088 0.042 * * * *

Gra 0.029 0.293 0.336 0.083 * * * 0.885 0.138 0.087 0.680 * * *

SP -0.282 -0.487 -0.499 -0.114 -0.660 * * 0.154 0.010 0.008 0.572 0.000 * *

Mud 0.422 0.617 0.638 0.034 0.413 -0.831 * 0.028 0.001 0.000 0.865 0.032 0.000 *

Den 0.476 0.261 0.249 -0.419 0.299 -0.279 0.407 0.012 0.188 0.211 0.029 0.130 0.159 0.035

Morphology of second maxilliped: The morphological features of crab mouthparts represent their mode of habitat. The scanning electron micrographs provide detailed pictures of setae present on second maxilliped Fig.4. The ischium and merus long, not expanded bear simple and plumose setae on median margin. The carpus recurved, has long curved plumose setae on medial margin. The dactylus is small and covered with numerous stout comb-like setae, tip of setae not spatulate. Terminal flagellum of exopodite also bears plumose setae. The present study conducted to examine distribution and abundance of estuarine crab I. frater along the coast of Pakistan. Mangal forest provides dynamic ecosystems where physical, geochemical, and biological factors are constantly reshaping the landscape that may regulate fauna response along different shores as well as at different tidal levels. The crab density was significantly different among sites, this finding suggests that variation in crab densities reflect meso-scale differences in the physical factors e.g. beach profile, slope, tidal creeks, sediment compactness, ease of digging, duration of exposure tides time and hydrology of the area (Luke and Zajac, 2013). The highest densities of Ilyoplax frater found within low to mid tide level relative to high tide level areas and consistent with previous report (Saher & Qureshi, 2011). The distribution and abundance Saher et. al. : substrate preference pattern of Ilyoplax frater 39 of crabs depend on their ability to make and maintain their burrows in a respective habitat (Pandya & Vachhrajani, 2010; Saher & Qureshi, 2011a,b) as well as their adaptability to avoid dry condition. Choice of habitat during life cycle of organism is an ontogenic behaviour which change with age and exhibited distinct distribution pattern and substrate preference. Ilyoplax frater juvenile first settled to low tide level which submerged for a longer period of time and act as nursery ground with increase food availability and less thermal stress, as the size increase they move from low to mid tide level. A similar tendency was observed by various authors (Fielder, 1971; Saher & Qureshi, 2011b; Hartnoll, 1975; Frith & Brunenmeister, 1980; Grassle et al. , 1992; Sundberg & Kennedy, 1993).

Table 4. Results of PCA showing Eigenvalues and percentages of explained variability

Variable PC1 PC2 PC3 1 Median 0.258 0.420 0.239 2 Sorting 0.401 -0.144 -0.353 3 %Moisture 0.416 -0.252 0.102 4 %Porosity 0.417 -0.257 0.116 5 %Organics 0.115 -0.636 0.092 6 %Granule 0.269 0.169 -0.748 7 %Sand -0.422 -0.160 0.012 8 %Mud 0.351 0.090 0.464 9 crab density 0.198 0.455 0.109 Eigenvalue 4.474 1.906 1.028 Proportion 0.497 0.212 0.114 Cumulative 0.497 0.709 0.823

Smallest mean size of crabs recovered from Bhambor, number of other brachyurans crab species also reside within a mangrove system use similar habitat as a result intra and interspecific competition for food and space is developed. The availability of food and competition for space, affect the size and growth of organisms in which they survive (Saher & Qureshi, 2011b). Sexual dimorphism was not observed, mean size (CW) of male and female was not significantly different at all studied sites similar to the previous finding (Saher & Qureshi, 2010).The chi square x2test showed that ratio of male and female crabs was similar in all sites except in Bhaira and Sonmiani. In ocypodid crabs sex ratio varies with breeding seasons as female crabs were abundant than male, ratio changes during less reproductive period I. frater breed all year round with peak season are southwest monsoon, present sampling was done during same time period (Saher & Qureshi, 2010). The observed departures from the 1:1 sex ratio can be a result of sex-related capabilities to cope with

40 Pakistan Journal of Marine Sciences, Vol. 23(1&2), 2014.

Fig. 4. Second maxilliped of Ilyoplax frater : a, second maxilliped inner surface; b, short setae on the median margin of propodus; c, setae on distill end of 2nd maxilliped. environmental extremeties and different spatial or temporal utilization of habitat resources (Saher & Qureshi, 2012). Pearson correlation showed a positive correlation of mud content with moisture and porosity, as fine grained sediments have higher capacity to retain intertidal water than sandy substrate. Results showed that crabs density is positively correlated with mud content, median and moisture content these small sized crabs prefer to excavate burrow in relatively soft sediments having high moisture content. Less desiccation supports them to tolerate harsh environmental conditions, results are consistent with previous reports (Pandya & Vachhrajani, 2010; Saher & Qureshi 2011b). The mean surface sediment organic content was highly variable across sampling sites and showed negative correlation with crab density, ecologically sediment with organic matter <5% considered as good, 5–10% represent moderate and > 10% signifies low quality of sediment (Marin et al. , 2008). Reduction in density of I. frater with increasing level of organic matter consistent with previous experimental studies. (Schratzberger & Warwick , 1999). During collection crabs recovered from the open mud flat near the mangrove plantation, which is characteristic behavioral trait, i.e. male crab showed visual signals such as waving of chelipeds during courtship so they preferred open and high shores rather than vegetated to avoid visual restrictions (Crane, 1975; Kosuge et al., 1994; Poovachirano & Minoru, 1994; Bezerra et al. , 2006). The mouthparts modification and feeding behavior of these deposit feeder crabs is related to substrate composition. The positive correlation with mud contents and median property signify the highest occurrence of crab at low and mid tide level and showed their adaptation to avoid the desiccation and importance of substrate texture and feeding in the Saher et. al. : substrate preference pattern of Ilyoplax frater 41 spatial distribution of I. frater . Like other mangrove Ocypodoid crabs feeding method and habitat preference is mainly correlated with the specialization of the mouthpart, I. frater extract detritus food from surrounding sediments through suspension feeding (Altevogt, 1955; Miller, 1961; Ono, 1965; Al- Khayat, 1996). They have setose mouth part especially in second maxillped, I frater have plumose setae in second maxilliped indicated that the species is more specialized to feed on fine sediment which was abundant in low and mid tide level then upper shore level. Previously it was reported that mud dwelling species of genus Uca have similar type of setae (Macintosh, 1988; Bezerra et al, 2006). It can be concluded within the context of the present study, the distribution of crabs and feeding behavior of I. frater is related to substrate composition and as mouthpart modifications allows feeding to deposit feeding crabs at low to mid intertidal areas.

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