Depth-related distribution and abundance of seastars (Echinodermata: Asteroidea) in the Porcupine Seabight and Porcupine Abyssal Plain, N.E. Atlantic

https://doi.org/10.1016/S0967-0637(02)00090-0Get rights and content

Abstract

The depth-related distribution of seastar (Echinodermata: Asteroidea) species between 150 and 4950 m in the Porcupine Seabight and Porcupine Abyssal Plain is described. 47 species of asteroid were identified from ∼14,000 individuals collected. The bathymetric range of each species is recorded. What are considered quantitative data, from an acoustically monitored epibenthic sledge and supplementary data from otter trawls, are used to display the relative abundance of individuals within their bathymetric range. Asteroid species are found to have very narrow centres of distribution in which they are abundant, despite much wider total adult depth ranges. Centres of distribution may be skewed. This might result from competition for resources or be related to the occurrence of favourable habitats at particular depths. The bathymetric distributions of the juveniles of some species extend outside the adult depth ranges. There is a distinct pattern of zonation with two major regions of faunal change and six distinct zones. An upper slope zone ranges from 150 to ∼700 m depth, an upper bathyal zone between 700 and 1100 m, a mid-bathyal zone from 1100 to1700 m and a lower bathyal zone between 1700 and 2500 m. Below 2500 m the lower continental slope and continental rise have a characteristic asteroid fauna. The abyssal zone starts at about 2800 m. Regions of major faunal change are identified at the boundaries of both upper and mid-bathyal zones and at the transition of bathyal to abyssal fauna. Diversity is greatest at ∼1800 m, decreasing with depth to ∼2600 m before increasing again to high levels at ∼4700 m.

Introduction

The zonation of fauna in the deep sea has been documented extensively (for review see Carney et al., 1983). Zones are described as regions of lesser faunal change bounded by regions of greater faunal change. (Menzies et al., 1973; Hecker, 1990; Gage and Tyler, 1991). Previous workers have focused either on general faunal zonation patterns (Le Danois, 1948; Rowe and Menzies, 1969; Haedrich et al., 1975; Ohta, 1983) or on the zonation of specific taxa, e.g. fish (Day and Pearcy, 1968), gastropods (Rex, 1977), echinoderms (Gage, 1986), holothurians (Billett, 1991) and decapod crustaceans (Cartes and Sardà, 1993). These studies have shown, regardless of the taxon examined, that deep-sea fauna undergo a non-repeating sequential change with depth and most species have predictable and restricted depth ranges (Rowe and Menzies, 1969; Carney et al., 1983; Gage and Tyler, 1991).

Previous studies on the zonation of specific taxa have used data on the shallowest and deepest records of a species to recognise critical depths of faunal change. This method is of use in examining major faunal boundaries, but it does not identify more subtle changes that are related to the abundance of species. Use of data on both first and last occurrence and changes in abundance provide a better overall picture of faunal zonation. In terms of species distribution the use of depth of first and last occurrence can reveal only where a species does and does not live. It reveals nothing about how a species occupies the depth range in which it is able to live. Very few studies have examined the depth-related distribution of deep-sea species within their depth ranges in order to elucidate small-scale patterns of zonation (Haedrich et al., 1975; Billett, 1991).

In studies examining general faunal change from the shelf break at 200 m to the abyss, up to seven different faunal zones have been recognised (Menzies et al., 1973; Musick, 1976; Haedrich et al., 1980). Three faunal boundaries have been reported consistently in the literature: (1) the shelf-slope break (200–500 m), (2) a less-pronounced boundary around 1000–1400 m (Day and Pearcy, 1968; Rowe and Menzies, 1969; Sanders and Hessler, 1969; Dayton and Hessler, 1972; Haedrich et al., 1975; Rex, 1977; Carney et al., 1983; Gage et al., 1985; Hecker, 1990), (3) a general boundary at ∼3000 m for megafauna (Vinogradova et al., 1959; Zenkevitch, 1963; Rowe and Menzies, 1969; Haedrich et al., 1980). 3000 m has been proposed as the start of the abyssal fauna (Hansen, 1975; Sibuet, 1979; Billett, 1991). That these depth boundaries occur at many locations worldwide indicates that important controlling variables are present at these depths and that these may occur globally.

There are many logistic problems associated with identifying and measuring factors that may affect zonation and depth related distribution, and as a result, nearly all deep-sea studies have looked at those factors that correlate with changes in the fauna. These factors include temperature (Rowe and Menzies, 1969; Haedrich et al., 1975), pressure (Siebenaller and Somero, 1978; Somero et al., 1983; Young et al., 1996), oxygen minimum (Carney and Carey, 1976; Pearcy et al., 1982; Gage, 1986), sediment type (Day and Pearcy, 1968; Haedrich et al., 1975), water mass structure (Tyler and Zibrowius, 1992), currents, topography and food supply (Rowe and Menzies, 1969; Hecker, 1990; Rice et al., 1990; Cartes and Sardà, 1993), larval dispersal (Rowe and Menzies, 1969; Grassle et al., 1979; Billett, 1991), competition, predation and trophic level (Rex (1976), Rex (1977); Haedrich et al., 1980; Cartes and Sardà, 1993). Identifying specific environmental variables that restrict the depth ranges of deep-sea species and their effects on an organism remains an unresolved problem. However, a more detailed knowledge of the vertical distribution of deep-sea species may help to indicate factors that affect species distribution and large-scale zonation (Young et al., 1996).

This study, based on what are considered quantitative samples and an extensive data set, determines the bathymetric distribution of asteroid species from the shelf break to the abyssal plain and examines the depth-related distribution and abundance of species within their depth ranges. Patterns of asteroid distribution are discussed in terms of what is known of their ecology. Large-scale zonation of the asteroid fauna are also investigated and correlated with available information on the physical environment.

Section snippets

Site description

The Porcupine Seabight and Porcupine Abyssal Plain are located more than 200 km to the southwest of Ireland (Fig. 1). The Porcupine Seabight forms an amphitheatre-shaped embayment in the continental margin, which measures approximately 300 km from north to south and 200 km from east to west. Its sides slope steadily from the edge of the Irish shelf at 200 m down to a depth of ∼3000 m. At the mouth of the Seabight, the seabed slopes away more steeply to a depth of ∼4000 m to join the Porcupine Abyssal

Species distribution

When all the asteroid species are arranged in series based on their depth distribution a non-repeating replacement of species is seen (Fig. 3). Each species shows a discrete depth range with some ranges extending over more than 1000 m. Most species show a patchy distribution through their depth range, often occurring, in any great abundance, only over a very narrow depth range of 200–300 m. The data suggest that although a number of species of asteroid may be present at a particular depth, only 2

Discussion

Many megabenthic animals are known to form aggregations (Pawson, 1976; Nybakken et al., 1998), particularly the echinoderms, such as the ophiuroids (Smith and Hamilton, 1983), holothurians (Billett and Hansen, 1982), and sea urchins (Grassle et al., 1975). Aggregations may be for feeding (Grassle et al., 1975; Billett and Hansen, 1982) or reproduction (Billett and Hansen, 1982; Smith and Hamilton, 1983). They may contain large numbers of individuals. Should any samples encounter such a patch

Acknowledgments

We would like to thank the officers and crew of R.R.V Discovery, Dr. Brian Bett and Dr. Martin Sheader for their statistical advice, Dr. Alex Rogers for advice on the evolution of deep-sea faunas, Ailsa Clark for her expertise in asteroid taxonomy, Dr. Adrian New and Dr. Neil Kenyon for information on the water masses and currents in the N.E. Atlantic and Andrew Whitehouse for his editorial comments. The manuscript benefited from the helpful comments of two anonymous reviews. This project is

References (85)

  • J.M. Huthnance

    Waves and currents near the continental shelf edge

    Progress in Oceanography

    (1981)
  • A.L. New et al.

    Aspects of the circulation in the Rockall Trough

    Continental Shelf Research

    (2001)
  • J. Nybakken et al.

    Distribution density and relative abundance of benthic invertebrate megafauna from three sites at the base of the continental slope off central California as determined by camera sled and beam trawl

    Deep-Sea Research II

    (1998)
  • R.D. Pingree et al.

    Celtic and Armorican slope and shelf residual currents

    Progress in Oceanography

    (1989)
  • R.D. Pingree et al.

    Seasonality of the European slope current (Goban Spur) and ocean margin exchange

    Continental Shelf Research

    (1999)
  • M.A. Rex

    Biological accommodation in the deep-sea benthosComparative evidence on the importance of predation and productivity

    Deep-Sea Research I

    (1976)
  • M.A. Rex

    Zonation in deep-sea gastropodsthe importance of biological interactions to rates of zonation

  • A.L. Rice et al.

    Dense aggregations of a hexactinellid sponge, Pheronema carpenteri, in the Porcupine Seabight (northeast Atlantic Ocean), and possible causes

    Progress in Oceanography

    (1990)
  • A.D. Rogers

    The role of the oceanic oxygen minima in generating biodiversity in the deep-sea

    Deep-Sea Research II

    (2000)
  • G.T. Rowe et al.

    Zonation of large benthic invertebrates in the deep-sea off the Carolinas

    Deep-Sea Research I

    (1969)
  • M. Sibuet

    Distribution and diversity of echinoderms (Holothuroidea-Asteroidea) in the abyssal zone of the Bay of Biscay

    Deep-Sea Research I

    (1977)
  • C.R. Smith et al.

    Epibenthic megafauna of a bathyal basin off southern-California—patterns of abundance, biomass, and dispersion

    Deep-Sea Research I

    (1983)
  • T.C.E. van Weering et al.

    Recent sediments, sediment accumulation and carbon burial at Goban Spur, NW European continental margin (47–50°N)

    Progress in Oceanography

    (1998)
  • Billett, D.S.M., 1987. Benthic results: Echinodermata. In Great Meteor East: a Biological Characterisation. Institute...
  • D.S.M. Billett

    Deep-sea holothurians

    Oceanography and Marine Biology: an Annual Review

    (1991)
  • A.G. Carey

    Food sources of sublittoral, bathyal and abyssal asteroids in the northeast Pacific Ocean

    Ophelia

    (1972)
  • R.S. Carney et al.

    Distribution pattern of holothurians on the north-eastern Pacific (Oregon, USA) continental shelf slope, and abyssal plain

    Thalassia Jugoslavica

    (1976)
  • Carney, R.S., Haedrich, R.L., Rowe, G.T., 1983. Zonation of fauna in the deep sea. In: Rowe, G.T. (Ed.), The Sea, Vol....
  • J.E. Cartes et al.

    Zonation of deep-sea decapod fauna in the Catalan Sea (western Mediterranean)

    Marine Ecology-Progress Series

    (1993)
  • A.M. Christensen

    The feeding biology of the sea star Astropecten irregularis Pennant

    Ophelia

    (1970)
  • Clark, A.M., Downey, M.E., 1992. Starfishes of the Atlantic. Chapman and Hall, London,...
  • Clarke, K.R., Warwick, R.M., 1994. Change in Marine Communities: an Approach to Statistical Analysis and...
  • D.S. Day et al.

    Species associations of benthic fishes on the continental shelf and slope off Oregon

    Journal of the Fish Research Board of Canada

    (1968)
  • T. Fenchel

    Feeding biology of the sea star Luidia sarsi Duben and Koren

    Ophelia

    (1965)
  • J.D. Gage

    The benthic fauna of the Rockall Trough—regional distribution and bathymetric zonation

    Proceedings of the Royal Society of Edinburgh Section B-Biological Sciences

    (1986)
  • J.D. Gage et al.

    Non-viable seasonal settlement of larvae of the upper bathyal brittle star Ophiocten gracilis in the Rockall Trough abyssal

    Marine Biology

    (1981)
  • Gage, J.D., Tyler, P.A., 1991. Deep-Sea Biology: a Natural History of Organisms at the Deep-Sea Floor. Cambridge...
  • J.D. Gage et al.

    Echinoderms of the Rockall Trough and adjacent areas. 1. Crinoidea, Asteroidea and Ophiuroidea

    Bulletin of the British Museum of Natural History (Zoology)

    (1983)
  • J.D. Gage et al.

    Echinoderms of the Rockall Trough and adjacent areas. 1. Crinoidea, Asteroidea and Ophiuroidea

    Bulletin of the British Museum of Natural History (Zoology)

    (1983)
  • J.D. Gage et al.

    Echinoderm zonation in the Rockall Trough (NE Atlantic)

  • J.F. Grassle et al.

    Faunal changes with depth in the deep-sea benthos

    Ambio Special Report

    (1979)
  • R.L. Haedrich et al.

    Zonation and faunal composition of epibenthic populations on the continental slope south of New England

    Journal of Marine Research

    (1975)
  • Cited by (119)

    • Starfish (Asteroidea, Echinodermata) from Iceland; spatial distribution and abundance

      2021, Deep-Sea Research Part I: Oceanographic Research Papers
    • Foraging strategies in four deep-sea benthic species

      2021, Journal of Experimental Marine Biology and Ecology
    View all citing articles on Scopus
    View full text