Trends in body size across an environmental gradient: A differential response in scavenging and non-scavenging demersal deep-sea fish

British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK.
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.05). 11/2005; 272(1576):2051-7. DOI: 10.1098/rspb.2005.3189
Source: PubMed


Body size trends across environmental gradients are widely reported but poorly understood. Here, we investigate contrasting relationships between size (body mass) and depth in the scavenging and predatory demersal ichthyofauna (800-4800 m) of the North-east Atlantic. The mean size of scavenging fish, identified as those regularly attracted to baited cameras, increased significantly with depth, while in non-scavengers there was a significant decline in size. The increase in scavenger size is a consequence of both intra and inter-specific effects. The observation of opposing relationships, in different functional groups, across the same environmental gradient indicates ecological rather than physiological causes. Simple energetic models indicate that the dissimilarity can be explained by different patterns of food distribution. While food availability declines with depth for both groups, the food is likely to be in large, randomly distributed packages for scavengers and as smaller but more evenly distributed items for predators. Larger size in scavengers permits higher swimming speeds, greater endurance as a consequence of larger energy reserves and lower mass specific metabolic rate, factors that are critical to survival on sporadic food items.

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    • "The potential decline in fractional size at particularly deep depths could suggest that there is a depth limit to the benefits of a stable environment. For example, food availability may be too low to support large individuals, which has been found to be the case for certain functional groups (Collins et al. 2005). Accounting for the population fractional size structure by including observed length of individuals as well as their potential length at the species level allows a more accurate description of the function of the assemblage as a whole. "
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