Recent studies have correlated dinoflagellate resting cyst morphology to salinity and density variations in the water column, suggesting that morphology can be used for paleoceanographic reconstructions. However, the univariate statistics used by these studies are appropriate only where morphology is related to a single variable. Density is a function of salinity and temperature, so more advanced statistical methods are needed to understand which parameters affect morphology. In this study based on surface (coretop) sediments, a set of environmental variables (sea-surface salinity, temperature, nitrate, and phosphate) was simultaneously correlated to morphological variations seen in resting cysts produced by the dinoflagellate Protoceratium reticulatum (=Operculodinium centrocarpum sensu Wall and Dale). Approximately 3200 measurements were obtained from the North Atlantic Ocean and used to generate a working model based on the Akaike information criterion. Hierarchical partitioning was then applied to establish the independent and joint effects for each predictor variable. Results from these analyses showed that while salinity constitutes the dominant variable affecting process length in the cysts of P. reticulatum in the North Atlantic, it is not the sole explanatory variable and that multicollinearity exists. Temperature and nutrients also showed a significant relationship to the morphology, requiring multiple regression to construct a representative model. The applicability of the North Atlantic working model was finally evaluated by comparing the results to data from the Mediterranean, Marmara, and Black seas, and Baltic-Kattegat-Skagerrak estuarine system. This comparison showed regional differences in morphological-environmental correlation. While salinity constitutes the most important explanatory factor in both the North Atlantic and Baltic-Skagerrak system, this is not so for the Mediterranean-Black Sea region where temperature is the dominant variable. It is concluded that a predictive salinity model based on P. reticulatum cyst morphology has at best a regional application.
Bibliographical noteFunding Information:
This research was supported by a University of Toronto studentship and scholarship and Ontario Graduate Scholarship to I.-M.J., and an NSERC Discovery Grant to M.J.H. K.N.M. is a postdoctoral fellow of FWO Belgium. Marie-Josée Fortin (University of Toronto) is warmly thanked for her generous advice on numerical ecology. We are grateful to Rehab Elshanawany, Kari Grøsfjeld, Rex Harland, Ulrich Kotthoff, Peta Mudie, Speranta Popescu, Vera Pospelova, and Sofia Ribeiro, for the loan of microscope slides. Sample material from the Malangen fjord was provided by the National Lacustrine Core Repository (LacCore). Elisabeth Levac provided samples from Nova Scotia, and Simon Troelstra provided information on Greenland cores and samples from the Mediterranean. Michal Kucera and an anonymous reviewer provided very helpful comments on the manuscript.
Copyright 2014 Elsevier B.V., All rights reserved.
- Hierarchical partitioning
- Model development
- North Atlantic
- Operculodinium centrocarpum