Search

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Twenty lakes recovering from a century of atmospheric acid deposition over Northeastern Ontario were resurveyed for phytoplankton following a 20-year period and were compared with a 23-year study of an experimentally acidified lake, L302S (Experimental Lakes Area, ON, Canada). Phytoplankton species significantly tracked abiotic changes during both acidification and chemical recovery in all lakes based on concordance testing. However, ordination analyses showed that many phytoplankton communities had not returned to their preacidification state. Significant explanatory variables of taxonomic responses were pH, dissolved organic carbon (DOC), and inorganic nutrients (N, P), based on canonical correspondence analysis (CCA). Increases in DOC and pH influenced a significant taxonomic shift from acid-tolerant dinoflagellates to a diverse assemblage of cyanobacteria, chlorophytes, and diatoms. Declining nitrogen levels defined a secondary environmental gradient, which was characterized by a decrease in filamentous green algal abundance. L302S remained remote in ordination space from the more chronically and heavily polluted lakes in Northeastern Ontario, indicating that experimental acidification provided a conservative estimate of the true damage to atmospherically polluted lakes. However, L302S did increasingly resemble lakes in Northeastern Ontario, suggesting that experimental acidification simulated the impacts of moderate levels of atmospheric pollution. Our findings demonstrate the importance of ecological history in understanding the responses by boreal lake ecosystems to environmental change. [ABSTRACT FROM AUTHOR]

Three new species and one new variety of Mallomonas (Mallomonadaceae, Chrysophyceae) were discovered in Ontario, Canada. Descriptions based on electron microscopy of silica scale structure are provided for Mallomonas inornata sp. nov., Mallomonas perfossa sp. nov., Mallomonas sexangularis sp. nov., and Mallomonas gutata var. simplex var. nov. The relationships of the scale structures of the new taxa with those known for other similar species are discussed. About 80 Mallomonas species and subspecies now are known from North America. [ABSTRACT FROM AUTHOR]

Chrysochromulina breviturrita sp. Nov. is described as a new haptonema-bearing member of the freshwater Prymnesiophycear. It is ca. three times larger than the only other known freshwater member of the genus (C. parva Lackey) and possesses a haptonema only ca. 0.2-0.3 as long as the haptonema of C. parva. Two equal flagella (1.5-2 × as long as the haptonema), a large contractile incuole, two parietal plastids, a single pyrenoid, nucleus, chrysolaminarin-like droplets and a food vacuole are features readily observed with the light imcroscope. Dried and shadowcast whole mounts examined with the clectron microscope reveal the cell surface covered with two types of small, delicate scales: outer spined scales with a club-shaped terminus and with the spine anchored to a circular to oval base-plate by 2-6 (7) branching arms; and, spineless oval plate seales with concentric lines and radiating ridges on one face and parallel ridges on the other. C. breviturrita has been found in nine lakes in Ontario (Canada). Preliminary observations suggest that it is an important component of lake plankton and has probably not been detected in previous work, more because of its fragility than because of its scarcity. Living specimens are a prerequisite for initial identification, since cells frequently supture and haptonemata are often lost when the organisms are killed with the commonly used fixatives. [ABSTRACT FROM AUTHOR]