COMPARATIVE STUDY OF SOME ASPECTS OF BIOLOGY OF.THREE MANGROVE CRABS FROM THE MANGROVE WETLAND OF LAGOS, NIGERIA.

Abstract

The size composition, growth pattern and feeding habit of 395 crab specimens of the hairy
mangrove crab - S. hurardii, fiddler crab - U. tangeri and land crab - C. armatum collected from
the mangrove swamp of the Lagos Lagoon were examined for six months. The carapace length of
S. huzardii ranged from 1.70 C/J1- 4.60 em (Carapace width from 1.90 em - 3.60 em) whilst that of
U. tangeri ranged from 1.10 cm - 3.60 em (Carapace width from 1.40 em - 4.20 cm) and C.
armatum 4.50 em - 9.50 em (Carapace width from 4.60 cm - 9.80 em). The total weight of S
.huzardii ranged from 8.10 - 23.50 g,from 2.00 g - 27.30 g in U. tangeri, and ranged from 39./0 g
- 131.80 g in C. armatum. The crabs exhibited allometric growth. The condition factor K ranged
from 20.0-1.01 em in S. huzardii, 1.50 - 2.76 em in U. tangeri {UuI14.0 - 67.8 em in C. armatum.
44 out of 150 specimens of S. huzardii had empty stomach, 38 out of the 125 specimens of U.
tangeri had empty stomach while 26 out the 120 specimens of C. armatum had empty stomach.
The stomach content of these three ecological related crustaceans showed S. huzardii fed mainly
on diatoms, detritus, protozoa, filamentous algae; U. tangeri fed mainly on detritus, diatoms,
protozoa, green algae, plant materials and sand grains; while C. armatum fed mainly
phytoplankton, zooplankton, plant materials and sand grains. There was evidence of interspecific
competition amongst this group of crustaceans, although each had been able to survive
adequately. The sex.ratio in S. huzardii was 1:0.4, 1:0.4 in U. tangeri and 1: 1.1 in C. armatum.