Ecology of Peridinium willei and P. volzii (Dinophyceae) in Danish lakes

Abstract

The distribution of Peridinium willei and P. volzii was studied in Danish lakes. Both species were confined to lakes with concentrations of Total P < 0.15 mg 1 ‐1 , with the majority of occurrences at Total P concentration between 0.020–0.040 mg 1 ‐1 and concentrations of PO 4 P between detection limit and 0.040 mg 1 ‐1 . The occurrence of the species in relation to inorganic N compounds (NH 4 N and NO 2 + NO 3 N) was significantly broader for P. willei than for P. volzii: P. willei had an almost even distribution within a wide range of NH 4 N, whereas P. volzii mainly occurred between 0.001 and 0.10 NH 4 N 1 ‐1 . P. willei had an almost even distribution at values beween 0.005 and 0.42 mg NO 2 + NO 3 N 1 ‐1 , whereas P. volzii mainly occurred below 0.050 mg NO 2 + NO 3 N 1 1 . P. willei was found at pH values between 4.2 and 8.5, whereas P. volzii was confined to lakes with a slightly basic pH. The study confirmed the broad limits of P. willei and the much more narrow limits of P. volzii in relation to seasonal occurrence and pH, as well as an affinity of the former to ponds and lakes with a rich bottom vegetation. The study also showed, however, that the species were not as widespread and common in recent Danish lake phytoplankton as generally stated by previous authors. The use of different ecological factors to give weight to species separation is discussed. The inclusion of P. volzii in P. willei proposed by Popovsky & Phiester is not supported by the present study, as the two taxa appear to have different ecological tolerances.