THE INFLUENCE OF SUBMERGED MACROPHYTES ON SEDIMENTARY DIATOM ASSEMBLAGES 1 Jesse C. Vermaire 2,3 Department of Biology, McGill University, Montreal, Quebec, Canada, H3A 1B1 Yves T. Prairie De ´partement des Sciences Biologiques, Universite ´ du Que ´bec a ` Montre ´al, Montre ´al Que ´bec, Canada H3C 3P8 and Irene Gregory-Eaves Department of Biology, McGill University, Montreal, Quebec, Canada, H3A 1B1 Submerged macrophytes are a central component of lake ecosystems; however, little is known regard- ing their long-term response to environmental change. We have examined the potential of diatoms as indicators of past macrophyte biomass. We first sampled periphyton to determine whether habitat was a predictor of diatom assemblage. We then sam- pled 41 lakes in Quebec, Canada, to evaluate whether whole-lake submerged macrophyte biomass (BiomEpiV) influenced surface sediment diatom assemblages. A multivariate regression tree (MRT) was used to construct a semiquantitative model to reconstruct past macrophyte biomass. We deter- mined that periphytic diatom assemblages on macro- phytes were significantly different from those on wood and rocks (ANOSIM R = 0.63, P < 0.01). A redundancy analysis (RDA) of the 41-lake data set identified BiomEpiV as a significant (P < 0.05) vari- able in structuring sedimentary diatom assemblages. The MRT analysis classified the lakes into three groups. These groups were (A) high-macrophyte, nutrient-limited lakes (BiomEpiV ‡525 lg Æ L )1 ; total phosphorus [TP] <35 lg Æ L )1 ; 23 lakes); (B) low- macrophyte, nutrient-limited lakes (BiomEpiV <525 lg Æ L )1 ; TP <35 lg Æ L )1 ; 12 lakes); and (C) eutrophic lakes (TP ‡35 lg Æ L )1 ; six lakes). A semi- quantitative model correctly predicted the MRT group of the lake 71% of the time (P < 0.001). These results suggest that submerged macrophytes have a significant influence on diatom community structure and that sedimentary diatom assemblages can be used to infer past macrophyte abundance. Key index words: diatoms; eutrophication; paleo- limnology; shallow lakes; submerged macrophytes Abbreviations: ANOSIM, analysis of similarities; BiomEpiV, whole-lake submerged macrophyte biomass; color, colored dissolved organic matter; DOC, dissolved organic carbon; MRT, multivariate regression tree; PCA, principal components analy- sis; RDA, redundancy analysis; TN, total nitrogen; TP, total phosphorus The littoral zone is often considered the most productive and biologically diverse region of a lake. Littoral benthic production provides an important energy subsidy to pelagic organisms and may act to stabilize aquatic food webs (Schindler et al. 1996, Vadeboncoeur et al. 2002, Vander Zanden and Vadeboncoeur 2002, Rooney et al. 2006). This phe- nomenon is particularly true for the numerous small and shallow lakes that occupy the landscape (Downing et al. 2006), but even in larger and dee- per systems, littoral benthic production has been shown to be a substantial component of lake food webs (Vadeboncoeur et al. 2008). Yet, the close proximity of the littoral zone to human activities within the terrestrial environment commonly makes it the first region of a lake to be disturbed (Lambert et al. 2008). Furthermore, the littoral zone is often the habitat most affected by human activities because the benthic and rooted organisms that occupy this zone are very sensitive to reductions in light availability, a normal consequence of cultural eutrophication (Sand-Jensen and Borum 1991, Vadeboncoeur et al. 2003). Submerged macrophytes (referred to from here on as macrophytes) are a central component of lake ecosystems and frequently dominate the littoral zone of temperate lakes. They are known to be involved in many important ecosystem feedback loops that regulate the physical, chemical, and bio- logical features of lakes (Carpenter 1981, Scheffer et al. 1993, Jeppesen et al. 1998, Tan and O ¨ zesmi 1 Received 28 January 2010. Accepted 9 March 2011. 2 Author for correspondence: e-mail jvermaire@gmail.com. 3 Present address: Department of Geography and Environmental Studies, Carleton University, Ottawa, Ontario, Canada, K1S 5B6. J. Phycol. 47, 1230–1240 (2011) Ó 2011 Phycological Society of America DOI: 10.1111/j.1529-8817.2011.01069.x 1230