Depth-specific patterns of benthic secondary production in an oligotrophic lake

Benthic secondary production plays an important role in the population, community, and ecosystem dynamics of lakes. However, whole-lake estimates of benthic secondary production are rare, and very little is known about intralake patterns in production. We measured benthic secondary production for the dominant macroinvertebrate taxa in Crampton Lake, a 26-ha north-temperate lake at the border of Wisconsin and Michigan, USA. Production was estimated by the size-frequency method for each taxon at each depth where it occurred. Confidence intervals for production estimates were determined by bootstrapping. A small number of taxa were responsible for most benthic secondary production, and most taxa were not highly productive. Thus, we observed a log-normal rank-production relationship. This relationship might be common in other lakes. However, production was not strongly related to abundance, a result that suggests that even rare taxa might contribute substantially to secondary production. Whole-lake benthic secondary production averaged 4.4 g dry mass m(-2) y(-1). Across depths, confidence intervals for area-specific rates of production generally overlapped, although point estimates were somewhat higher in the littoral zone (4.8-6.5) than in the profundal zone (3.2-4.5). Despite this similarity in rates, >65% of whole-lake benthic secondary production occurred in the littoral zone because of lake morphometry. A synthesis of limited published data revealed multiple patterns in the relationship between depth and benthic secondary production in other lakes. In most lakes, area-specific rates of production either declined or remained constant as depth increased. This observation, combined with the fact that most lakes are small and predominantly littoral, suggests that littoral dominance of whole-lake benthic secondary production might be widespread, and might help explain recent findings that lake fishes rely heavily on littoral production.