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Response of grazing snails to phosphorus enrichment of modern stromatolitic microbial communities
Author(s) -
ELSER JAMES J.,
SCHAMPEL JOHN H.,
KYLE MARCIA,
WATTS JAMES,
CARSON EVAN W.,
DOWLING THOMAS E.,
TANG CAROL,
ROOPNARINE PETER D.
Publication year - 2005
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.2005.01453.x
Subject(s) - snail , biology , phosphorus , biomass (ecology) , zoology , stromatolite , ecology , ecological stoichiometry , grazing , botany , nutrient , chemistry , carbonate , organic chemistry
Summary 1. The effects of added phosphorus (P) on the growth, P and RNA : DNA contents, and survivorship of snails grazing on laminated microbial mats (living ‘stromatolites’) were examined in the Rio Mesquites at Cuatro Ciénegas, Mexico (total P, c. 0.60 μ mol L −1 ) to test the hypothesis that strong P‐limitation of microautotroph growth produces a stoichiometric constraint on herbivores because of mineral P‐limitation. 2. In a 3‐week experiment performed in summer 2001, addition of phosphorus (+15 μ mol L −1 ) resulted in a strong decline in stromatolite biomass C : P ratio from very high levels ( c. 2300 : 1 by atoms) to moderate levels ( c. 550 : 1). The endemic hydrobiid snail Mexithauma quadripaludium responded to P‐enrichment with elevated body P content and higher RNA : DNA ratios, especially for small animals likely to be actively growing. This positive response is consistent with the existence of a stoichiometric constraint on snail growth. 3. In a longer experiment (8 weeks) involving a more moderate P enrichment (+5 μ mol L −1 ) in summer 2002, P enrichment reduced stromatolite C : P ratio from moderate values in control treatments ( c. 750) to very low values (<100 : 1). Snails responded to stromatolite P‐enrichment with increased body P content but, in contrast to the first experiment, with lower RNA : DNA ratio, lower growth rates, and higher mortality. 4. These contrasting results suggest that both very high and very low biomass C : P ratios in stromatolites are detrimental to M. quadripaludium performance, leading us to hypothesise that these herbivores live on a ‘stoichiometric knife edge’.