Fig 1.
Geographic, depth, and oxygen distribution of Hymenopenaeus doris.
Geographic, depth, and oxygen distribution of Hymenopenaeus doris observed by MBARI ROV Doc Ricketts in the Gulf of California, Mexico, during 2012 (a and c) and 2015 (b and d). Points on maps represent ROV dives where H. doris were encountered. Dashed red lines indicate approximate oxygen survey lines represented by filled contour plots of linearly interpolated ROV CTD-O data (c and d). Contour plots are overlaid with H. doris observations distinguished by time period (UTC-7): dark grey 7:00–10:00 (n = 7), light grey 10:00–14:00 (n = 3), and red 14:00–17:00 (n = 35). Most H. doris were encountered at oxygen concentrations below 0.5 ml L-1. S1 Fig contains analogous plots of temperature.
Fig 2.
Midwater animals associated with mucous feeding webs.
Examples of midwater animals that have been observed in the Monterey Canyon, California, and Gulf of California, Mexico, associated with mucous feeding webs include: amphipods (a, 2553 m), Chaetopterus pugaporcinus (Polychaeta) (b, 1096 m), Tuscarantha braueri (Phaeodaria) (c, 2388 m), Poeobius meseres (Polychaeta) (d, 305 m), and an undescribed pseudothecosome pteropod (e, 993 m). Hymenopenaeus doris has been observed three times (out of 45 total sightings) apparently situated just below a characteristically bi-lobed mucous web (f-h). However, two-dimensional imaging prevented the determination of specific animal locations with respect to webs. In (g), the orange arrow points to H. doris and the two white arrows to the associated mucous web lobes.
Fig 3.
The inverted, motionless sinking behavior of two deep pelagic decapod species.
The head-down, motionless sinking behavior, frequently displayed by the midwater decapod Hymenopenaeus doris in the Gulf of California, Mexico (a-d) and Petalidium suspiriosum in the Monterey Canyon, California (e), may confer visual similarity to molted shrimp exoskeletons (f). Oxygen concentration during respiration experiments of H. doris (g) declined irregularly because we relied on animal movements to mix water. In (g), blue points represent the beginning and end of periods when water was well-mixed by the animal; the slope of linear regressions (black lines) fit to these points calculated routine metabolic rates.