Spatial Distribution and Substratum Preference of the Brachyuran Crab, Macrophthalmus Depressus (Decapoda, Ocypodidae) along the Lower Estuarine Mudflat of Mahi River, Gujarat, India

• Published in: Crustaceana 2010-01, Vol.83 (9), p.1055-1067
• Main Authors: Pandya, Pranav, Vachhrajani, Kauresh
• Format: Article
• Language: English
• Subjects: Aquatic habitats; Beaches; Benthic zone; Brackish; Coasts; Crabs; Decapoda; Estuaries; Freshwater; Gulfs; Macrophthalmus depressus; Marine; Mud flats; Ocypodidae; Sediments; Zoning
• ISSN: 0011-216X; 1568-5403
• DOI: 10.1163/001121610X521235

The distribution of the ocypodid crab, Macrophthalmus depressus Rüppell, 1830, was studied on the lower intertidal mudflats of the Mahi River estuary of the Gulf of Khambhat, Gujarat, India. Zoning of the study area was done based on coastal morphology and sediment composition. Distribution pattern and density were studied using transect and quadrate sampling methods. Five zones with variable sand, silt, and clay composition could be distinguished perpendicular to the shore line. Zones 1 and 2 represented the upper inter tidal area (≥60% sand), Zones 3 and 4 the mid-inter tidal area (70-80% silt + clay) and Zone 5 the lower inter tidal area (≥50% sand). Quadrant analysis showed the density of M. depressus burrows as follows: Zone 1, no animals present (hence not further included in the study); Zone 2, 28.66 ± 9.86; Zone 3, 83.20 ± 33.87; Zone 4, 62.00 ± 9.16; and Zone 5, 52.50 ± 24.74 individuals per m². The mean density of the crab varied from 0 to 83 individuals per linear metre along the transect all over the above mentioned zones. The densier distribution in, and thus presumed preference for, Zones 3 and 4 can be attributed to the sediment composition as well as to the slope, which together make the substrate firm and suitable for easy burrow construction. The study revealed a significant correlation between the distribution of Macrophthalmus depressus and these habitat characteristics, thus describing the microhabitat preferences of the species. La distribution du crabe ocypodidé Macrophthalmus depressus Rüppell, 1830, a été étudiée dans les zones intertidales de l'estuaire de la rivière Mahi dans le golfe de Khambhat, Gujarat, Inde. La zonation de l'aire étudiée a été faite sur la base de la morphologie de la côte et de la composition du Sédiment. La distribution et la densité ont été étudiées en utilisant des transects et des quadrats pour l'échantillonnage. Cinq zones avec une composition variable en sable, vase et argile ont pu être distinguées perpendiculairement à la côte. Les Zones 1 et 2 représented l'aire haute intertidale (70-80% vase + argile), Zones 3 et 4 l'aire moyenne intertidale (≥60% sable), et la Zone 5 l'aire basse intertidale (≥50% sable). Les analyses des quadrats montrent la densité de terriers de M. depressus comme : Zone 1, pas d'animal present (done plus inclus dans cette étude) ; Zone 2, 28.66 ± 9.86 ; Zone 3, 83.20 ± 33.87 ; Zone 4, 62.00 ± 9.16 ; et Zone 5, 52.50 ± 24.74 individus par m². La densité moyenne des crabes varie