Search

Scavenging amphipods are a numerically dominant and taxonomically diverse group that are key necrophages in deep-sea environments. They contribute to the detrital food web by scavenging large food-falls and provide a food source for other organisms, at bathyal and abyssal depths. Samples of this assemblage have been collected at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) in the North Atlantic (48°50′N 16°30′W, 4850 m) for > 30 years. They were collected by means of baited traps between 1985 and 2016, covering a period of well-characterised changes in the upper ocean. From the 19 samples analysed, a total of 16 taxa were identified from 106,261 specimens. Four taxa, Abyssorchomene chevreuxi (Stebbing, 1906), Paralicella tenuipes Chevreux, 1908, P. caperesca Shulenberger & Barnard, 1976, and Eurythenes spp., dominated catches and were present in all samples. The dominant species varied in time with P. tenuipes typically dominant early in the time series (1985–1997) and its congener, P. caperesca, typically dominant later (2011–2016). Amphipod faunal composition exhibited a significant correlation with the Atlantic Multi-decadal Oscillation (AMO). Amphipod diversity was significantly lower in years with higher estimated volumetric particle flux at 3000 m. Species richness varied significantly between AMO phases, with higher values during ‘cool’ phase. Our results suggest a ‘regime shift’ in scavenging amphipod communities following a ‘regime shift’ in surface ocean conditions driven by a phase shift in Atlantic climate (from cool to warm AMO). This shift manifests itself in a remarkable change in dominant species, from obligate necrophages such as Paralicella spp., with semelparous reproduction to Abyssorchomene spp. which have a more varied diet and iteroparous reproduction, and are thus potentially more able to take advantage of greater or varied food availability from increased organic matter flux to the abyssal seafloor.

The genus Eurythenes S. I. Smith in Scudder, 1882, has been the focus of integrated molecular and morphological taxonomy studies in recent years, resulting in the number of species in the genus increasing from three to eight. Samples of Eurythenes spp. collected using free-fall baited traps from the Porcupine Abyssal Plain (PAP), North East Atlantic Ocean, at 4850 m were examined in this study to investigate the identity of the species found using molecular barcoding methods. Mitochondrial COI analysis confirms the presence of E. maldoror at PAP and data from the nuclear 28S rDNA gene provides independent confirmation of this observation. A new, undescribed species that is clearly divergent from all other known species and molecular lineages was identified, which can be distinguished morphologically from known species. A specimen within the E. magellanicus lineage was also found at the site. We discuss the presence of these three Eurythenes species at the Porcupine Abyssal Plain.

Existing population studies of deep-sea amphipods have focused on species that inhabit deep-sea vent or trench environments but few cosmopolitan species have been studied. Here we provide new insight into the life history and population ecology of the pan-oceanic scavenging amphipod Paralicella caperesca and discuss the influence of nutrient-rich submarine canyon environments on the growth and reproduction of this species. Data were collected through the dissection and measurement of 2997 P. caperesca from 14 samples taken from abyssal plains, continental slopes and submarine canyons in the North-East Atlantic. Sexual dimorphism was less pronounced than observed for other scavenging amphipod species but females were significantly larger and had shorter antennae than males. The size of oostegites in female P. caperesca varied considerably within size classes, ovaries contained a relatively large number of oocytes, and no empty ovaries were observed. These factors, in combination with absence of mature females, suggest that P. caperesca practices semelparity, a reproductive strategy that complements the feeding strategy of this obligate necrophage. Five male and seven female size-grouped cohorts were identified for P. caperesca. Cohorts from deep-sea submarine canyon populations showed consistently larger mean total body lengths than non-canyon cohorts. Individuals from canyon samples also expressed sexual characteristics at smaller sizes than non-canyon individuals. We hypothesize that these trends are indicative of nutrient-mediated growth, maturation, and reproduction in P. caperesca. The species is able to grow and reproduce relatively quickly in response to increased nutrient input in canyon environments and therefore dominates scavenging amphipod assemblages.

A new species of the deep-sea scavenging genus Hirondellea (Crustacea: Amphipoda) is described from bathyal depths in the Azores region and on the Mid-Atlantic Ridge. The new species belongs to a group of Hirondellea species which possess an incised inner ramus of uropod 2 and an anteriorly directed spine on epimeron 1. It can be distinguished from other members of this group by a combination of characters: the gnathopod 1 and 2 palm shape; the broadly rounded epimeron 3; the longer telson and broadly rounded head lobe; and the broadly rounded epistome. The species most closely resembles H. wolfendeni, from which it can be distinguished by the shape of the propod of gnathopod 2 and the length of the pereopod 7 propodus. An updated key to the genus Hirondellea is provided.

The distribution, total length (LT) frequency and diet of Patagonotothen guntheri are described from 14 bottom trawl surveys conducted on the Shag Rocks and South Georgia shelves in the austral summers from 1986 to 2006. Patagonotothen guntheri (80–265 mm LT) were caught on the Shag Rocks shelf from depths of 111 to 470 m, but no specimens were caught on the South Georgia shelf. Multiple cohorts were present during each survey and LT-frequency analysis of these cohorts suggests that growth was slow (von Bertalanffy K = 0·133). Evidence from stomach contents and acoustic data (2005 and 2006) showed that P. guntheri is primarily a pelagic feeder, migrating from the sea floor towards the surface to feed during daylight. The diet of smaller fish (

Baited traps deployed at 7800 m in the Atacama Trench off northern Chile, captured over 400 specimens of Eurythenes gryllus. This is the greatest depth of occurrence reported for the species. Of the 398 specimens available for study, all but three were female, giving a sex ratio very different from any reported previously. Female specimens measured 29–76 mm in length, and all were immature. Length/frequency distributions based on total length, peraeonite 1 length, and coxa 4 oostegite length were unimodal. Relationships between total length, and peraeonite 1 length, oostegite length, and wet weight were established. Oostegite development appeared to be precocious compared with published data. Subtle differences in peraeon, urosome, gnathopods, coxa 4, peraeopod 7, and epimeron 3 morphology, and the growth of oostegites separate Atacama Trench specimens from previously described material. The morphology exhibited by these specimens lies outside the known variability of E. gryllus, and suggests that this pan-oceanic entity may be undergoing incipient speciation.

The distribution of deep-water (150–4850 m) benthic and bentho–pelagic cephalopods in the north-east Atlantic is described, based on 592 specimens collected from commercial and research trawling. Thirty-six different species of cephalopod belonging to 14 families were identified, though problems remain with the taxonomy of some of the octopod genera. At the shallower depths (150–500 m) sepiolids were the most abundant group with five species identified. Sepiola atlantica, Sepietta oweniana and Rondeletiola minor were restricted to the shallow depths (Neorossia caroli (400–1535 m) and Rossia macrosoma (205–515 m) extended into deeper water. The squids Todaropsis eblanae and Loligo forbesi were also common in shallow areas (Eledone cirrhosa was found at depths of 208–490 m. Three putative species of Benthoctopus and two of Bathypolypus were identified occupying depths of 250–2700 m. Graneledoneverrucosa was caught at depths of 1785–2095 m. Cirrate octopods dominated the cephalopod catch from the deeper areas, with Opisthoteuthis massyae occurring from 877 to 1398 m, O. grimaldii from 2165 to 2287 m, Stauroteuthissyrtensis from 1425 to 3100 m, Cirroteuthismuelleri from 700 to 4854 m, Cirrothauma murrayi from 2430 to 4850 m and Grimpoteuthis (five putative species) from 1775 to 4877 m. Abundance estimates of the more frequently caught species were calculated from swept areas of trawls and sledges in the Porcupine Seabight and on the Porcupine Abyssal Plain.

A photographic survey of the seafloor was conducted during RRS Discovery cruise 204 in September/October 1993 at the oligotrophic site of the French EUMELI programme at c. 21° N: 31° W (4650 m) on the Cape Verde Abyssal Plain. Two systems were used, a wide angle system (WASP) obtaining usable photographs covering 10 to 30m2, and an epibenthic sledge mounted system obtaining photographs of about 2 m2. A total of more than 3000 usable frames were obtained, covering about 64000 m2 of seafloor. The photographs indicated an epibenthic invertebrate megafaunal density of 5.2 hectare−1 and a demersal fish density of 1.8 hectare −1. In contrast, the photographs were dominated by lebensspuren, particularly of the ‘spoke-burrow’ type usually attributed to echiurans. Spoke-burrow density, where related burrows and other features such as sediment mounds are considered unitary, is estimated at 871 hectare −1. We describe and quantify the five principal types of spoke burrow encountered in this study and, on the basis of these observations and some morphometric studies of the lebensspuren, discuss the possible behaviour of their producers. We have no direct knowledge of the production rate of, or longevity of, lebensspuren in the study area. However, based on a number of assumptions and limited data from other areas we suggest that trace producer (mainly echiurans) density is on the order of tens of individuals per hectare. These trace producers probably greatly outnumber the rest of the invertebrate megabenthos, and we can only guess at the role this potential large population of hidden benthos might have in the overall structure and function of the deep-sea floor ecosystem.

Records attributed to Eurythenes gryllus are discussed in the light of described morphological variation, and the existence of a third species in the genus is postulated. The presence of five pairs of oostegites in E. gryllus, a character almost unique among the Amphipoda, is confirmed. Brooding females of E. gryllus and E. obesus, captured in deep midwater hauls in the eastern North Atlantic Ocean, are reported for the first time. The 120 mm E. gryllus female carried 237 hatchlings (mean length 11.13 mm) and the 48 mm E. obesus female 47 hatchlings (mean length 7.99 mm). Hatchlings showed variability in size and bodily proportion, and measurements of individual body segments could not be used to predict overall length. Despite this variability, no evidence for more than one instar was found. The hatchlings of E. gryllus are established as a hitherto unrecognized instar in this species. Egg size for E. gryllus and E. obesus is predicted. The biological consequences of the absolute and relative size of hatchling in the two species, and the depths of capture of the E. gryllus female, are discussed.

A pop-up time-lapse camera system (BATHYSNACK) was used to study megafaunal organisms attracted to bait at three abyssal localities in the eastern North Atlantic Ocean, a northern site on the Porcupine Abyssal Plain and two sub-tropical sites on the Madeira Abyssal Plain. Fish and decapod crustaceans appeared on 47% of photographs taken during deployments of up to seven days duration. The fishes Coryphaenoides (Nematonurus) armatus and Pachycara bulbiceps and the decapod Munidopsis spp. dominated appearances at the northern locality whereas over 95% of records at the two subtropical localities were of the decapod Plesiopenaeus armatus. Cyclical variations in necrophage abundance did not correlate with tidal cycles of near-bottom currents, although high P. armatus numbers were inversely related to current speed. Most of the frequently recorded entities showed contagious intraspecific distributions. In contrast, many of the interspecies relationships were non-random, with co-occurrences lower than expected, probably as a result of physical disturbance or potential predation. Population densities based on times of first arrival were calculated. Assemblages dominated by fish at higher latitudes and crustaceans at lower latitudes are discussed in terms of organic carbon supply to the deep sea and pelagic community structures.

Epibenthic sledge and otter trawl samples of invertebrate megabenthos were collected from the abyss of the northeastern Atlantic Ocean. Stations were selected to have contrasting overlying water column structure. Strong seasonal pulses of phytodetritus on the sea floor have been recorded on the Porcupine Abyssal Plain (PAP) but not on the Madeira Abyssal Plain (MAP). Sledge-and trawl-derived abundances of 13.73 and 8.13 individuals 103 m−2 were found at PAP, with corresponding wet biomass values of 169.4 and 189.2 g 103 m−2. Data from sledge hauls taken at MAP gave an abundance of 7.48 individuals and 5.15g 103 m−2. Sledge and trawl abundances at Great Meteor East (GME) were 2.91 and 2.19 individuals 103 m−2 and 4.31 and 11.30 g 103 m−2. Holothurians dominated the invertebrate biomass at PAP while Astoroidea and Decapoda Natantia were important taxa at MAP and GME. Otter trawl samples demonstrated fish to be the major component of total megadaunal biomass and suggest that small fixed-frame trawls give gross underestimates of fish abundance and biomass. Size spectra based on abundance and biomass data indicated the megafauna to be a functional group at PAP stationl only. Here peak invertebrate biomass occurred in the 40–80 g wet wt size class. In contrast, no large invertebrates (>20 g wet wt) were found at MAP of GME. Concurrent photographic records indicate higher faunal densities than do net catches. Faunal differences between stations were examined, and a weak relationship between surface productivity and megafaunal abundance was established. Data are inadequate to detect a similar relationship with biomass. Biomass values at PAP of 16–39 times those of MAP and GME appear to be explained by the deposition of phytodetritus at PAP but not at MAP or, probably, at GME. Among invertebrates, detritivores form the dominant feeding guild at all localities, but carnivores are important at MAP and GME. Phytodetritus appears to support the abundant surface-grazing holothurians at PAP.

The Pycnogonida are a group regularly recorded in deep-sea benthic samples, although normally in low numbers. Most analyses from such surveys record new species, and many of these remain known only from a few specimens, often only the types. However, the amount of deep sea-bed sampled is necessarily proportionately so small that it may be argued that any species taken are probably common, owing to their having been sampled at all. It is evident from the gaps in the (often world-wide) distribution of these known species and their limited occurrence that deeper water pycnogonid faunas are still at best poorly known (q.v.Child, 1982).

An intensive investigation of the benthic biology of the Porcupine Seabight, to the south-west of Ireland, was carried out by biologists from the Institute of Oceanographic Sciences Deacon Laboratory (IOSDL) between 1977 and 1986. More than 400 benthic samples were obtained during the study using towed gears and corersover the depth range 200 to 4500 m. Transect and time-lapse photography was used extensively. This paper summarises the techniques employed and provides an analysis of the depth and seasonal coverage. In addition a review is provided of available data on the physical, chemical and geological characteristics of the Porcupine Seabight area, including information collected during the IOSDL study. Finally, existing publications based on the study are listed.

The horizontal and vertical distributions of 15 species of necrophagous amphipods from 44 benthic trapsets at 3144–5940m in the northeast and tropical Atlantic Ocean have been analysed. There is little evidence to suggest that species are endemic to particular abyssal plains and it is probable that the whole area studied, between latitudes 8°N and 50°N is a single faunal entity. Most abyssal necrophages are capable of extensive excursions up into the water column where they overlap with closely related meso-, bathy- and abyssopelagic species. The necrophage/carnivore guild occurs throughout the deep oceans of the world, and consists largely of species of panoceanic distribution.

Two new gammaridean amphipods, Crybelocephalus birsteini sp.nov. and Halicoides discoveryi sp.nov., and a new subspecies of hyperiid amphipod, Scina wagleri atlantis subsp.nov. are described from oceanic plankton samples taken off Fuertaventura, Canary Islands.

INTRODUCTIONThis paper forms the second and last part of a study of the vertical distribution and migration of pelagic Amphipoda based on material collected off Fuertaventura, Canary Islands, during the SOND Cruise in 1965. The first part (Thurston, 1976b) dealt with the Gammaridea. The data presented herein deal with the Hyperiidea, to which is added a general discussion.The background to the cruise has been given by Currie, Boden & Kampa (1969), and Foxton (1969) has described the gear and methods used. This analysis is based primarily on samples obtained from a series of 1 m2ring-net (N 113) hauls, but has been supplemented by selected materials from modified 3 m Isaacs-Kidd Mid-water Trawl (IKMT), neuston net and 1 m2Rectangular Mid-water Trawl (RMT 1) hauls. Thurston (1976b) has discussed the limitations of the sampling techniques as they affect the present results.

Cheus annae, new genus, new species, is described and figured. Comparisons with the Phoxocephalidae, Urothoidae, Platyischnopidae, Haustoriidae, and Pontoporeiidae show many characters in common, particularly with the first three families. The combination of a hoodlike rostrum with a presumed glandular apex, and low morphological diversification of peraeopods 5-7 requires the erection of a new family, the Cheidae.

Vinogradov (1957: 197, 1962: 5) has pointed out the very close agreement in the form of the appendages between L. aestiva and Scypholanceola vanhoeffeni Woltereck, 1909, and suggested tentatively that the two species might be identical. Lanceola and Scypholanceola are distinguished by the structure of the eyes. In the former, the eyes are small and located laterally in convex tubercles, while in the latter the optical elements are proliferated, and form ribbons, the ends of which lie at the bottom of a pair of pits on each side of the head. As both of the speci mens of Lanceola aestiva examined by Stebbing (1888) were in poor condition when they reached him, he was unable to make out the eyes with any certainty and described them as "doubtful, seemingly minute, prominent". In view of the possible identity of S. vanhoeffeni with L. aestiva, the type material from the "Challenger" collections has, by courtesy of Dr. A. L. Rice of the British Museum (Natural History), been re-examined. Stebbing based his original description on the larger of the two specimens in his possession. He dissected this specimen, and the head, mouth parts, urosome and most of the peraeopods were mounted on six microscope slides. The mounted organs were not stained in any way, and this fact coupled with a deterioration of the mounting medium, necessitated their removal from the slides in order that details of the anatomy could be studied. Prior to the mounting of the head, all of the mouth parts, antennae 1 and 2 and most of the integument of the left side, and part of the frontal wall were removed (fig. la). After 90 years, the integument of the head is completely flattened and rather brittle but it has been possible to make out the structure of the right eye and surrounding areas. The ribbon-like mass of optical tissue, widened at each end, and remains of reflecting pigment adjacent to it indicate that the specimen is a Scypholanceola. With gentle manipulation it is also possible to make out the positions of the lips of the eye pits, and a small rostrum. These features are characteristic of S. vanhoeffeni and preclude the only other currently accepted species in the genus, S. agassizi Woltereck, 1909. As S. vanhoeffeni is identical with the "Challenger" species, Woltereck's name must fall as a junior synonym to the latter which should be known as Scypholan