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Abstract: We used a quiet, deep-diving remotely operated vehicle (ROV) to conduct oblique, quantitative video transects of the bathypelagic fauna at depths between 1000 and 3500m at a site over the Monterey Submarine Canyon, in the eastern North Pacific off central California. Fifteen such dives were made over a two-year period. Analyses of the video data revealed a rich and diverse fauna dominated by gelatinous animals. In particular, the holopelagic polychaete Poeobius meseres was an important detritivore in the upper half of this depth range. As Poeobius abundance eventually declined with increasing depth, larvacean abundance increased. In contrast, the relative numbers of crustacean grazers, principally copepods and mysids, remained relatively constant with depth. Medusae were most abundant and most diverse among the gelatinous predators, which also included ctenophores, and siphonophores. Chaetognaths occurred chiefly in the upper half of the depth range. While there is considerable overlap, the bathypelagic fauna can be separated into upper (1000 to 2300m) and lower (2400 to 3300m) zones, as well as a distinct and populous benthic boundary layer. Within the overall bathypelagic community is a complex web of trophic links involving gelatinous predators that feed on both gelatinous and hard-bodied particle feeders, as well as on each other. The amount of organic carbon contained in this jelly web is substantial but its ecological fate is uncertain. The assessment of bathypelagic communities will be important for establishing baselines to conserve deep pelagic biodiversity within high-seas protected areas. [Copyright &y& Elsevier]

The opisthoproctid fish Macropinna microstoma occupies lower mesopelagic depths in Monterey Bay and elsewhere in the subarctic and temperate North Pacific. Like several other species in the family, Macropinna has upward-directed tubular eyes and a tiny, terminal mouth. This arrangement is such that in their upright position, the visual field of these highly specialized eyes does not include the mouth, which makes it difficult to understand how feeding takes place. In situ observations and laboratory studies reveal that the eyes of Macropinna can change position from dorsally-directed to rostrally-directed, which resolves the apparent paradox. The eyes are contained within a transparent shield that covers the top of the head and may provide protection for the eyes from the tentacles of cnidarians, one of the apparent sources of the food of Macropinna. [ABSTRACT FROM AUTHOR]

The archaic, deep-sea cephalopod Vampyroteuthis infernalis occurs in dark, oxygen-poor waters below 600 m off Monterey Bay, California. Living specimens, collected gently with a remotely operated vehicle (ROV) and quickly transported to a laboratory ashore, have revealed two hitherto undescribed means of bioluminescent expression for the species. In the first, light is produced by a new type of organ located at the tips of all eight arms. In the second, a viscous fluid containing microscopic luminous particles is released from the arm tips to form a glowing cloud around the animal. Both modes of light production are apparently linked to anti-predation strategies. Use of the tip-lights is readily educed by contact stimuli, while fluid expulsion has a much higher triggering threshold. Coelenterazine and luciferase are the chemical precursors of light production. This paper presents observations on the structure and operation of the arm-tip light organs, the character of the luminous cloud, and how the light they produce is incorporated into behavioral patterns. [ABSTRACT FROM AUTHOR]

A new species in the genus Mesochordaeus is described from 25 specimens collected by a remotely operated vehicle at mesopelagic depths in Monterey Bay, California. Mesochordaeus erythrocephalus is a large species (tail length up to 50 mm, trunk length up to 7 mm) characterized by large crescent-shaped spiracles, digitate lips, a bifurcate tail and bright red pigmentation of the digestive system. The filtering 'house' is large, 4-5 times the tail length of the animal, and its structure is most similar to that of another large mesopelagic larvacean, Bathochordaeus. This description confirms the distinctness of this recently erected genus, but raises questions as to its taxonomic affiliation. [ABSTRACT FROM PUBLISHER]

Provides information on a study which addressed the seasonal changes in the abundance of Nanomia bijuga in Monterey Bay, California. How the study was conducted; Results; Discussion of the results.

An unresolved issue in ocean science is the discrepancy betweenthe food requirements of the animals living on the deep sea floor andtheir food supply, as measured by sediment traps. A 10-year time-seriesstudy of the water column off Monterey Bay, California, revealed thatthe discarded mucus feeding structures of giant larvaceans carry asubstantial portion of the upper ocean's productivity to the deepseabed. These abundant, rapidly sinking, carbon-rich vectors are notdetected by conventional sampling methods and thus have not beenincluded in calculations of vertical nutrient flux or in oceanic carbonbudgets. [ABSTRACT FROM AUTHOR]

Pelagic crustaceans are arguably the most abundant group of metazoans on Earth, yet little is known about their natural behavior. The deep pelagic shrimp Hymenopenaeus doris is a common decapod that thrives in low oxygen layers of the eastern Pacific Ocean. When first observed in situ using a remotely operated vehicle, most specimens of H. doris appeared dead due to inactivity and inverted orientation. Closer inspection revealed that these animals were utilizing small, subtle shifts in appendage position to control their orientation and sink rate. In this mode, they resembled molted shrimp exoskeletons. We hypothesize that these shrimp may avoid capture by visually-cued predators with this characteristic behavior. The low metabolic rates of H. doris (0.55-0.81 mg O2 kg-1 min-1) are similar to other deep-living shrimp, and also align with their high hypoxia tolerance and reduced activity. We observed similar behavior in another deep pelagic decapod, Petalidium suspiriosum, which transiently inhabited Monterey Canyon, California, during a period of anomalously warm ocean conditions., Competing Interests: The authors have declared that no competing interests exist.

Little is known about the reproductive habits of deep-living squids. Using remotely operated vehicles in the deep waters of the Monterey Submarine Canyon, we have found evidence of mating, i.e. implanted sperm packages, on similar body locations in males and females of the rarely seen mesopelagic squid Octopoteuthis deletron. Equivalent numbers of both sexes were found to have mated, indicating that male squid routinely and indiscriminately mate with both males and females. Most squid species are short-lived, semelparous (i.e. with a single, brief reproductive period) and promiscuous. In the deep, dark habitat where O. deletron lives, potential mates are few and far between. We suggest that same-sex mating behaviour by O. deletron is part of a reproductive strategy that maximizes success by inducing males to indiscriminately and swiftly inseminate every conspecific that they encounter.

A unique 16-year time series of deep video surveys in Monterey Bay reveals that the Humboldt squid, Dosidicus gigas, has substantially expanded its perennial geographic range in the eastern North Pacific by invading the waters off central California. This sustained range expansion coincides with changes in climate-linked oceanographic conditions and a reduction in competing top predators. It is also coincident with a decline in the abundance of Pacific hake, the most important commercial groundfish species off western North America. Recognizing the interactive effects of multiple changes in the environment is an issue of growing concern in ocean conservation and sustainability research.

An extraordinary new species, Chaetopterus pugaporcinus, is described from eight specimens collected from deep mesopelagic waters off Monterey Bay, California, by remotely operated vehicles. All specimens exhibit a consistent combination of both adult and larval characteristics, leaving in question the maturity of the specimens. All specimens lack ciliated larval bands and the stout, modified chaetae (cutting spines) typically found in segment A4 of chaetopterids. If the specimens described here are larvae, they are remarkable for their size, which ranged from 10 to 21 mm total length, nearly twice the length of the largest polychaete larvae previously reported and 5 to 10 times larger than known chaetopterid larvae. Then too, their lack of segment addition prior to settlement would be atypical. If adult, they are particularly unusual in their habitat choice and body form. Morphology of the uncini and comparison to larval morphology indicated a close relationship to either Chaetopterus or Mesochaetopterus. However, the lack of cutting spines and typical adult morphology made it impossible to determine to what genus this species should be allied. Thus, we carried out the first molecular phylogenetic analysis of the Chaetopteridae in order to appropriately place and name the new species. Three partial genes were sequenced for 21 annelid species. The sequencing also provides the first molecular evidence that Chaetopterus variopedatus sensu Hartman (1959) is not a single cosmopolitan species. The question of C. pugaporcinus being a delayed larva or a genuine holopelagic chaetopterid is discussed.