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.

INTRODUCTION

This 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 m2 ring-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 m2 Rectangular Mid-water Trawl (RMT 1) hauls. Thurston (1976b) has discussed the limitations of the sampling techniques as they affect the present results.

First reports of the association between Exspina typica and three species of abyssal holothurian are presented. These records suggest that the association is a real one, and not an artefact of sampling, but throw no light on the nature of the association. The geographic and bathymetric distributions of E. typica are summarized, and the species is shown to be a widely distributed cold water stenotherm.

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.

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).

Objectives: Although the importance of economic evaluations is recognized, research suggests the ways in which studies are summarized may not be optimal for a busy decision maker with little training in economics methodology. Therefore, the objective of this study was to seek decision makers' views on different summary formats, including a score, short summary, and structured abstracts of different degrees of detail.

Methods: We contacted 2,400 people, of which 84 decision makers volunteered and were presented, cumulatively, with different formats and asked whether these provided sufficient detail on the methodology and results of an economic study.

Results: From the fifty decision makers who responded to the questionnaire, it was found that the preferred combination was a very short summary, plus a more detailed structured abstract. It was also found that decision makers with economics training preferred the most detailed format, partly reflecting their reasons for consulting economic evaluations.

Conclusions: Decision makers require both an initial screen of study content, plus more detail should they find the study relevant or interesting.

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 (<300 m), but 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 (<250 m). Among the incirrate octopods, 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.