What drives lake food webs?

Posted on September 26, 2009


Because of their landlocked status, lakes have often been assumed to support relatively closed ecosystems, with food webs that are driven mostly by internal production – i.e., photosynthesis by aquatic plants within the lake itself – rather than by inputs of carbon from the surrounding land.  This belief has been challenged by recent studies in which lake waters have been labelled with inorganic carbon (13C) to track transfers of carbon through the food web.  InPeterLake, a small lake inWisconsin, estimates of the amount of fish growth supported by externally-sourced carbon were high (51-80%).  Although this contribution fell to 25-55% when nutrients were added to the lake, presumably because they stimulated internal production, the results showed that lake food webs can be heavily subsidized by terrestrial carbon.   This conclusion seems to hold regardless of lake size.   InLake Crompton,Wisconsin, a relatively large lake with a maximum depth of 18.5 m, around half of the growth of fishes (bluegill and yellow perch) was fuelled by external carbon sources.  Bottom-dwelling invertebrates were more important food sources for fish than midwater prey, even though the production of invertebrates was much higher in midwater than on the bottom.  Although somewhat paradoxical, this finding was probably due to the fact that midwater invertebrates tend to be relatively small, and therefore less attractive as prey.

References:  

Carpenter, S.,  Cole,J. Pace,M., Van de Bogert, M.,  Bade, D., Bastviken, D., Gille, C., Hodgson, J., Kitchell, J. &  Kritzberg, E.  2005. Ecosystem subsidies: terrestrial support of aquatic food webs from 13C addition to contrasting lakes. Ecology 86, 2737 –2750. 

Weidel, B., Carpenter, S., Cole, J., Hodgson, J., Kitchell, J., Pace, M. & Solomon, C.  2008.  Carbon sources supporting fish growth in a north temperate lake.  aquatic Sciences 70, 446 – 458.

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