Species Abundance, Spatial and Vertical Distributionsof Large Heteropods (Pterotracheidae and Carinariidae)in the Northern Gulf of Mexico

• Main Author: Clark, Kristine A.
• Format: Others
• Published: Scholar Commons 2019
• Subjects: biogeography; DEEPEND; diversity; eye size; pelagic; snails; Biology; Oceanography; Other Oceanography and Atmospheric Sciences and Meteorology
• Online Access: https://scholarcommons.usf.edu/etd/7767; https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=8964&context=etd

A description of species abundance, richness and distribution, and eye size of heteropod molluscs from the families Pterotracheidae and Carinariidae in the oligotrophic ecosystem of the northern Gulf of Mexico (GOM) is described based on discrete-depth sampling protocols. The collections were comprised from two midwater sampling programs conducted sequentially after the 2010 Deepwater Horizon oil spill (DWHOS): the Offshore Nekton Sampling and Analysis Program (ONSAP, 2011) and the Deep Pelagic Nekton Dynamics of the Gulf of Mexico (DEEPEND, 2015-2018). Study materials from DEEPEND were collected during the initial five cruises of 2015-2017. These programs collected over 3,495 heteropods in two target families from 46 sampling stations in the northern GOM. We studied five species from the superfamily Pterotracheoidea (the families Carinariidae and Pterotracheidae). The family Pterotracheidae (Pterotrachea coronata, P. hippocampus and P. scutata) were the most abundant and largest specimens examined. The zone along the northeastern GOM continental slope had the greatest species richness and abundances. The study found evidence of diel migration in P. coronata and P. scutata. We compared body size with depth of occurrence to evaluate possible ontogenic habitat shifts. The largest Cardiapoda placenta (>30 mm) and Pterotrachea coronata (>150 mm) were found only in the upper 600 m. No significant ontogenic patterns were obvious in the other four species. We evaluated eye size at capture depth for each species. There was no evidence of eye size increasing with depth among the five species. We compared eye diameter with body length and found that heteropods have consistent and similar eye sizes per species throughout the depth of the measured water column and relative eye size is species-specific. We identified that pterotracheids have smaller eyes than carinariids relative to their total body size. This finding was opposing to our expectation of eye size differences among migrators and non- migrators. This is the first comprehensive large heteropod study in the northern GOM.