Ecology of Benthesicymus tanneri Faxon, 1893 (Dendrobranchiata: Benthesicymidae) from the Mexican Pacific slope

Benthesicymus tanneri Faxon, 1893 (Benthesicymidae) is a poorly known benthopelagic shrimp dominant in the lower oxygen minimum zone (OMZ) boundary in the Mexican Pacific. Its bathymetric distribution and diet were studied off the Mexican Pacific continental slope at depths of 710-2309 m, and the potential environmental drivers were analyzed. A total of 187 specimens were collected between 772 and 2010 m, although most were found between 1008 and 1620 m. This represents a wide bathymetric distribution compared to other species inhabiting lower OMZ boundaries. The size of individuals (carapace length, CL) ranged from 11.2 to 53.3 mm with no clear bathymetric patterns in the size distribution of the species. The sex ratio (males:females, M:F) changed with depth from M:F = 1:1 at 700-1000 m to M:F = 1:5 at 1300-1600 m. The main prey of B. tanneri in all the samples analyzed was the pelagic red crab Pleuroncodes planipes (Munididae Ahyong, Baba, Macpherson and Poore, 2010), and secondary preys were benthopelagic and bathypelagic fishes and shrimp-like decapod crustaceans. Only 15% of the stomachs were empty. Specimens of P. planipes captured simultaneously to B. tanneri were measured as an indicator of the size of available prey and 90% of individuals measured 11.1-14.8 mm CL. Benthesicymus tanneri was collected within wide ranges of values of the different environmental variables considered, and statistical analyses did not provide solid relationships between the patterns of distribution and the environmental factors (Spearman R and Generalized Linear Models). We hypothesize that B. tanneri is a eurytopic species whose swimming capacity allows for temporal vertical migrations into the water column.