Species assemblages of Alpheus of similar morphology occur along the tropical and subtropical margins of all world oceans. We studied sympatric populations of Alpheus belonging to three color morphs recognized along an intertidal gradient at Cabo Branco beach, State of Paraíba, Brazil. Morphological measurements of populations sampled monthly during a year were used to obtain indexes of size and fluctuating asymmetry. Standard statistical analyses were used in order to verify if the stress gradient established along the intertidal region affects spatial distribution, size and body symmetry in these three sympatric populations. Alpheus armillatus sensu stricto, the most frequent species, was predominant in the upper meso-littoral zone, being significantly smaller in the lower zone. A. cf. angulosus was predominant in the middle zone, while A. cf. heterochaelis was restricted to the upper zone. Individuals of A. cf. angulosus were significantly smaller than those of the other two morphs. Males were larger than females in all morphotypes, while cheliped dimensions show allometric growth. Couples invariably belong to a same morph. We obtained indications that competition between morphs are favoring the establishment of larger individuals in the most disputed zones of the middle and upper meso-littoral, although we were not able to confirm whether wave action was the main environmental factor responsible for these gradients in body size and symmetry along the intertidal region. Our data provide further ecological and biological evidence for the three color morphs representing distinct species, whose sympatric populations may be further recognized by additional morphological criteria. However, we are unsure about the constancy of these auxiliary distinguishing characters for allopatric populations from throughout their full western Atlantic ranges.
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Vol. 29 • No. 3