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

Abstract

A B S T R A C TBenthesicymus 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.

New record for the deep-sea genus Tripoplax (Mollusca: Polyplacophora) in the eastern Pacific

“…Tripoplax cf. balaenophila is a member of the deep-sea mollusks fauna associated with the lower boundary of the OMZ occurring off western Mexico, an habitat characterized by severe hypoxic conditions and colonized by well-adapted species that are generally abundant (Zamorano et al 2006;Papiol & Hendrickx 2015). Specimens from Chile were collected in shallower depth compared to the Mexican material, but the OMZ off Chile is also much shallower than in the Mexican Pacific (Helly & Levin 2004).…”