Toyonobu Fujii

Hadal trenches: the ecology of the deepest places on Earth

Hadal trenches account for the deepest 45% of the oceanic depth range and host active and diverse biological communities. Advances in our understanding of hadal community structure and function have, until recently, relied on technologies that were unable to document ecological information. Renewed international interest in exploring the deepest marine environment on Earth provides impetus to re-evaluate hadal community ecology. We review the abiotic and biotic characteristics of trenches and offer a contemporary perspective of trench ecology. The application of existing, rather than the generation of novel, ecological theory offers the best prospect of understanding deep ocean ecology.

Liparid and macrourid fishes of the hadal zone: in situ observations of activity and feeding behaviour

Using baited camera landers, the first images of living fishes were recorded in the hadal zone (6000–11 000 m) in the Pacific Ocean. The widespread abyssal macrourid Coryphaenoides yaquinae was observed at a new depth record of approximately 7000 m in the Japan Trench. Two endemic species of liparid were observed at similar depths: Pseudoliparis amblystomopsis in the Japan Trench and Notoliparis kermadecensis in the Kermadec Trench. From these observations, we have documented swimming and feeding behaviour of these species and derived the first estimates of hadal fish abundance. The liparids intercepted bait within 100–200 min but were observed to preferentially feed on scavenging amphipods. Notoliparis kermadecensis act as top predators in the hadal food web, exhibiting up to nine suction-feeding events per minute. Both species showed distinctive swimming gaits: P. amblystomopsis (mean length 22.5 cm) displayed a mean tail-beat frequency of 0.47 Hz and mean caudal : pectoral frequency ratio of 0.76, whereas N. kermadecensis (mean length 31.5 cm) displayed respective values of 1.04 and 2.08 Hz. Despite living at extreme depths, these endemic liparids exhibit similar activity levels compared with shallow-water liparids.

Bioaccumulation of persistent organic pollutants in the deepest ocean fauna

The legacy and reach of anthropogenic influence is most clearly evidenced by its impact on the most remote and inaccessible habitats on Earth. Here we identify extraordinary levels of persistent organic pollutants in the endemic amphipod fauna from two of the deepest ocean trenches (>10,000 metres). Contaminant levels were considerably higher than documented for nearby regions of heavy industrialization, indicating bioaccumulation of anthropogenic contamination and inferring that these pollutants are pervasive across the world’s oceans and to full ocean depth.

A Large Aggregation of Liparids at 7703 meters and a Reappraisal of the Abundance and Diversity of Hadal Fish

Few biological studies have investigated the hadal depths within oceanic trenches that plummet from 6000 meters (m) to the full ocean depth of almost 11,000 m. Here we present the deepest known in situ observations of fish: a hadal snailfish, Pseudoliparis amblystomopsis (Andriashev 1955), from 7703-m deep in the Japan Trench, which was obtained using a baited video lander. The maximum number of fish we observed was unexpectedly higher than trawl catch records of any known hadal fish. We describe changes in fish abundance and associated behaviors over time, including feeding, resting, and swimming. In light of these new observations, we reappraise the occurrence and diversity records of hadal fishes that have been constructed from fragmentary and often misleading information derived from historical explorations and global data sets. This reappraisal suggests that hadal fish diversity may be lower—although some hadal fish species may attain much larger populations—than previously thought.

In situ observations of trophic behaviour and locomotion of Princaxelia amphipods (Crustacea: Pardaliscidae) at hadal depths in four West Pacific Trenches

The genus Princaxelia, Pardaliscidae, is a rarely recorded, infrequently collected and hitherto observed benthic amphipod, typically found at hadal depths (.6000 m) in the Pacific Ocean trenches. Little is known about the behaviour or physiology of this genus. Using a baited camera lander, observations of Princaxelia jamiesoni were made in the Japan Trench (7703 m) and Izu–Ogasawara Trench (9316 m) and of Princaxelia aff. abyssalis in the Kermadec Trench (7966 m) and Tonga Trench (8798 m). These amphipods rapidly intercepted the bait and preyed upon smaller lysianassoid amphipods. Mean absolute swimming speeds for P. jamiesoni and P. aff. abyssalis were 4.16 cm.s + 1.8 SD and 4.02 cm.s + 0.87 SD respectively. These amphipods have the capacity for long range swimming, high manoeuvrability in close range, and efficient predatory behaviour. Burst swimming speeds for P. aff. abyssalis were 9 and 10 cm.s with accelerations up to 22–25 cm.s.

Temporal variation in environmental conditions and the structure of fish assemblages around an offshore oil platform in the North Sea

This study reports temporal variations in the environmental conditions and the structure of fish assemblages observed in the vicinity of an offshore oil platform and the surrounding seafloor in the North Sea. Multi-seasonal sampling was conducted at a typical large steel jacketed facility, using mid-water fish traps at three different depths (i.e., 10, 50 & 100 m). Commercially important gadoids such as saithe Pollachius virens, haddock Melanogrammus aeglefinus and cod Gadus morhua were the most abundant species, however, the species composition and the relative abundances of the species varied with depth, season and between years. Comparisons with a large-scale bottom trawl survey data suggested highly dynamic and species-specific interactions between fish movements, changing environmental conditions and the physical presence of an offshore platform. Given the number of platforms currently installed across the North Sea, there is a need to identify biological mechanisms behind such dynamic interactions.

Climate Change, Sea-Level Rise and Implications for Coastal and Estuarine Shoreline Management with Particular Reference to the Ecology of Intertidal Benthic Macrofauna in NW Europe.

In many European estuaries, extensive areas of intertidal habitats consist of bare mudflats and sandflats that harbour a very high abundance and biomass of macrobenthic invertebrates. The high stocks of macrobenthos in turn provide important food sources for the higher trophic levels such as fish and shorebirds. Climate change and associated sea-level rise will have potential to cause changes in coastal and estuarine physical properties in a number of ways and thereby influence the ecology of estuarine dependent organisms. Although the mechanisms involved in biological responses resulting from such environmental changes are complex, the ecological effects are likely to be significant for the estuarine benthic macrofauna and hence the consumers they support. This paper reviews the utilisation patterns of estuarine intertidal habitats by shorebirds, fish and crustaceans, as well as factors affecting the distribution, abundance and biomass of estuarine macrobenthos that is known to be important food source for these estuarine predators. This study also provides simple conceptual models of the likely impacts of sea-level rise on the physical and biological elements of estuarine intertidal habitats, and implications of these results are discussed in the context of sustainable long term flood and coastal management in estuarine environments.

Scavenging interactions between the arrow tooth eel Synaphobranchus kaupii and the Portuguese dogfish Centroscymnus coelolepis

A scavenging interaction between the arrow tooth eel Synaphobranchus kaupii and the Portuguese dogfish Centroscymnus coelolepis, both ubiquitous components of fish assemblages at bathyal depths, was observed. Using a baited camera between 1297 and 2453 m in the eastern Atlantic Ocean continental slope, it was shown that despite consistently rapid arrival times of S. kaupii (<5 min), their feeding bouts (indicated by acute peak in numbers) did not take place until shortly after C. coelolepis arrived and removed the exterior surface of the bait (skipjack tuna Katsuwonus pelamis carcass). Change in the numbers of S. kaupii was hence dependent on the arrival of a more powerful scavenger throughout the study site, and at the deeper stations where the population of C. coelolepis declined, S. kaupii was observed to be present but waited for >2 h before feeding, thus contradicting conventional scavenging assumptions in the presence of a food fall.

Locomotory activity and feeding strategy of the hadal munnopsid isopod Rectisura cf. herculea (Crustacea: Asellota) in the Japan Trench

SUMMARY Benthic fauna in the hadal zone (6500-11,000 m) rely on maintaining sufficient locomotory activity to exploit a low, patchy and uniquely distributed food supply while exposed to high pressure, low temperatures and responding to predator-prey interactions. Very little is currently known about the locomotory capabilities of hadal fauna. In situ video footage of the isopod Rectisura cf. herculea (Birstein 1957) (Asellota, Munnopsidae) was obtained from 6945 and 7703 m deep in the Japan Trench (NW Pacific Ocean). Measurements of locomotion revealed routine walking speeds of 0.19±0.04 BL s-1 (mean ± s.d.), increasing to 0.33±0.04 BL s-1 if naturally perturbed by larger organisms. When immediately threatened by the presence of predators (decapod crustaceans), the isopods are capable of eliciting backward escape jumps and burst swimming escape responses of 2.6±1.5 BL s-1 and 4.63±0.9 BL s-1, respectively. These data suggest no significant reduction in locomotory capability despite the extreme depths in which they inhabit. These observations also revealed the isopod to be a bait-attending and aggregative species and suggest that it may not be obligatorily selecting infaunal food sources as previously thought.