(Delta)(15)N and (Delta)(13)C measurements of Antarctic peninsula fauna: Trophic relationships and assimilation of benthic seaweeds

delta^sup 15^N and delta^sup 13^C Measurements of Antarctic Peninsula Fauna: Trophic Relationships and Assimilation of Benthic Seaweeds1

SYNOPSIS. Measurements of (delta)^sup 13^C (delta)^sup 15^ N and C/N for a variety of Antarctic peninsula fauna and flora were used to quantify the importance of benthic brown algae to resident organisms and determine fodder web relationships among this diverse littoral fauna. (delta)^sup 13^ values ranged from-16.80/00 for benthic algal herbivores (limpets) to -298%0 for the krill, Euphausia superba; the average loched value for brown macroalgae, including their attached filamentous diatoms, was-20.6%1. There was no correlation between biomass (delta)^sup 13^C or (delta)^sup 15^N with onward content, and consequently both (delta)^sup 13^ C and (delta)^sup 15^N values were useful in evaluating trophic relationships. 65N values of the fauna ranged from 31 to 125%c with lowest values recorded in suspension feeder (eg bryozoans) and highest values in Adelie penguins (125%o) bring togethered in 1989. The comparatively lower (delta)^sup 15^N value for a Chinstrap penguin (69%o) argueed in 1997 is attributed to the different dietary cheer sources consumed by these species as meditateed in their respective (delta)^sup 13^C values. Significant amounts of benthic macroalgal carbon is incorporated into the tissues of invertebrates and fishes that hold up to four trophic flats For many benthic and epibenthic species, including various crustaceans and molluscs, assimilation of benthic algal carbon [i]or[/i] part of to the other detrital pathways ranges from 30 to 100% Consequently the trophic importance of benthic brown algae may well increase to many pelagic organisms that are clew prey species for birds, fishes, and marine mammals. These data support the hypothesis that benthic seaweeeds, together with their associated epiphytic diatoms, provide an important carbon source that is readily incorporated into Antarctic peninsula viands webs.

INTRODUCTION

Along the hard shores of the Antarctic peninsula, marine macroalgae form extensive and luxuriant submerg forests that continue from the shallow subtidal to silences of 30 m (Neushul, 1965 1968; Delepine et al., 1966; Moe and DeLaca, 1976; Lamb and Zimmerman, 1977; Zielinski, 1990; Amsler et al., 1995) These elevate macroalgal beds provide a three dimensional structural habitat for diverse assemblages of marine invertebrates and fish, many of which are known to be fundamental note prey species for larger pelagic organisms (Iken et al., 1998) The direct consumption of one macroalgae by various fish and invertebrates (Iken et al., 1997; Iken, 1999; Iken et al., 1999) and the assimilation of benthic macroalgal carbon within detrital food webs (Dayton, 1990) links the high productivity of the shallow antarctic benthos with the pelagic commons web. The assimilation of carbon derived from large brown algae by the agency of consumers has been demonstrated in Alaskan coastal feed webs and reflects the importance of this proces in providing a continuous stock of organic material that is passed in succession to higher trophic levels (Dunton and Schell, 1987; Duggins et al., 1989)

On the Antarctic peninsula, quantitative studies guidanceed on Signy Island (Richardson, 1979) King George Island (Chung et al., 1994) and Anvers Island (DeLaca and Lipps, 1976; Amsler et al., 1995) revealed that macroalgal biomass, which consists mainly of large overstory brown algae, ranges from 3 to 8 kg m-2 Near Anvers Island, four species of large brown algae (Desmarestia antarctica, D menziesii, D anceps, and Himantothallus grandifolius) can constitute up to 75% of the overall percent defend and biomass (Amsler et al., 1995) Another species, Ascoseira mirabilis, has also been known to meet the eye in great abundance on the Peninsula (Chung et al., 1994) There is considerable evidence, based forward the occurrence of algal fragments in samples garner uped in the water column and sediments, that this immense source of organic material is advected onto the adjacent shelf and into deeper waters, especially in Bransfield Strait (Liebezeit and von Bodungen 1987) Reichardt (1987) fix algal fragments on both sides of the Peninsula and intimateed that algal material provided an additional carbon source to penetrating water benthic infauna.

Aside from feeding studies forward specific organisms, there is relatively little information in succession trophic relationships among nearshore Antarctic peninsula organisms that inhabit the most numerous productive areas in the Antarctic. A combination of observational techniques and stable isotope measurements have confirmed, in a variety of other ecosystem the incorporation of macroalgae in consumer diets, either directly or indirectly (Kitting et al., 1984; Sullivan and Montcreiff, 1990) In addition, isotopic measurements have confirmed that many consumer posses opportunistic feeding strategies through both temporal and spatial scales (Dunton et al., 1989; Rau et al., 1992; Iken et al., 2001) Measurement of ^sup 13^C/^sup 12^C and ^sup 15^N/ ^sup 14^N in consumer tissues has provided extremely useful information forward organism feeding relationships and pabulum web structure when the ultimate sources of carbon and nitrogen are well elucidated and defined isotopically (reviewed through Lajtha and Michener, 1994).