K. Iken et al., Food web structure of the benthic community at the Porcupine Abyssal Plain(NE Atlantic): a stable isotope analysis, PROG OCEAN, 50(1-4), 2001, pp. 383-405
The deep-sea benthic community at the Porcupine Abyssal Plain (NE Atlantic)
is a highly food limited system. The annual input of sedimenting phytodetr
itus, which reaches the sea floor around May/June, is the major input of en
ergy. The relative trophic position of the most abundant components of the
benthos (90 species or higher taxonomic groups), including meiofaunal, macr
ofaunal, and megafaunal organisms, was evaluated by :stable isotope analysi
s. The majority of the macro- and megafaunal organisms investigated were de
posit feeders (N=35), less numerous were suspension feeders (N=17) and pred
ators/scavengers (N=29). Stable nitrogen values overlap and cover a large r
ange within feeding types, indicating a strong overlap in food sources and
a high degree of competition for food. Suspension feeders, mainly cnidarian
s, have a broad trophic spectrum through feeding on resuspended material as
well as capturing pelagic prey; thus during the greater part of the year t
hey can compensate for any shortage in sedimenting fresh POM. Benthic depos
it feeders use a variety of feeding strategies to exploit their common food
resource. The holothurians, the dominant megabenthic group at PAP, include
d some highly mobile species, which seem to be quite efficient in tracing a
nd exploiting localised patches of nutritious phytodetritus. Other holothur
ian species, however, forage successfully on more refractory material, poss
ibly assisted by enteric bacteria. Predators/scavengers fall into two group
s, representing two major trophic pathways. Firstly, several of the inverte
brate predators prey on deposit-feeding organisms and so are the end consum
ers of an exclusively benthic food web. Secondly, there are highly mobile b
enthopelagic predators/scavengers, which are a major link with the benthope
lagic food web through their feeding on pelagic prey.
Generally, within the benthic community at PAP competition for food is redu
ced by two alternative evolutionary adaptations: (1) specialization on slig
htly different food sources and (2) vertical expansion of the trophic spect
rum. This leads to a rather complex food web, covering a total delta N-15 r
ange of at least 10%o. (C) 2001 Elsevier Science Ltd. All rights reserved.