AGOSTA, A*; WILDEY, HC; VUTURO, SA; SHUSTER, SM: The Distribution of the Mud Shrimp, Neotrypaea uncinata, on Horizontal, Vertical and Geographic Scales within Estero Morua, Sonora, Mexico

Mud shrimp (Decapoda: Thallassinidea) are among the most abundant infaunal animals inhabiting estuaries and mud flats in temperate and tropical waters. We examined the vertical and horizontal distributions of the mud shrimp, Neotrypaea uncinata and Upogebia pugettensis in two locations within Estero Morua, near Puerto Pe�asco, Sonora, M�xico. We collected substrate cores every meter along 30 meter transects using a 10 x 97cm PCV tube. Two transects were taken from each of two study sites, located at the estero mouth and at its interior. In each core, we recorded the depth, sex, carapace length, dominant chela, reproductive condition, and species of each mud shrimp found. The number of individuals found between sites differed significantly. Shrimp were over-dispersed on a horizontal scale within one transect from each location. We identified four reproductive classes of animals: juvenile, male, female, and gravid female. Carapace length among these classes differed significantly, with males and gravid females larger than non-gravid female and juveniles. Increases in carapace length accurately predicted female reproductive condition using logistic regression. Mud shrimp showed significant stratification within the substrate by sex and reproductive condition. A post-hoc test revealed that gravid females were significantly deeper within the substrate than all other classes. These results suggest that the distribution and abundance of N. uncinata vary on vertical, horizontal, and geographic scales in their natural habitat.