Depth-dependence in stable isotope ratio dN of benthic POM consumers: The role of particle dynamics and organism trophic guild
نویسندگان
چکیده
The stable nitrogen isotope ratio (dN) is an established indicator of trophic hierarchy in marine food-web studies. Most of these studies presume that spatial variation in the primary food source is negligible, although a water-depthrelated increase in dN of particulate organic matter (POM) has been found in many systems. We used the high-Antarctic Weddell Sea shelf and slope ecosystem to test whether such a depth-related change in dN is reflected at higher trophic levels, i.e., benthic consumers of POM. In suspension feeders (SF) we found a significant increase in dN with water depth of up to 9.8%, whereas in deposit feeders (DF) a depth effect was barely detectable. Particle-size preferences of the two feeding guilds combined with particle-size-dependent sinking velocities and biogeochemical reworking of POM are discussed as the major causes of these differences. It is essential to marine food-web studies to take into account the general depth effect on POM dN as well as potential feeding-guild-specific differences in the response of POM consumer tissue dN to avoid serious bias and misinterpretation of stable-isotope-based trophic information. r 2007 Elsevier Ltd. All rights reserved.
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