Phytoplankton functional attributes along trophic gradient and season

Abstract

Each of the following phytoplankton functional attributes could be described by significant (P < 0.05) response surfaces defined by trophic status (T) from oligotrophy to hypertrophy and season (S) from early vernal period to late summer: phytoplankton cell volume, growth rate, the ratio between minimum quotas of total N and total P, affinity for P, half-saturation constant for growth with respect to P, and temperature optimum and light optimum for growth. Sinking rate could not be so described. The response surfaces were calculated by multiple regressions, including first-and second-order terms of T and S and the interaction term T. S. Although the data base was rather limited (number of phytoplankton species ranged from 10 to 3 I), the resulting surfaces often reflected a corresponding attribute of the water along T and S (e.g. phytoplankton temperature optimum for growth reflected water temperature). The results support the frequent use of physical factors as explanatory variables for the distribution and abundance of phytoplankton.The abundance of phytoplankton species and the species structure of phytoplankton assemblages vary along trophic and seasonal gradients (Reynolds 1980(Reynolds , 1984b. Because phytoplankton species with similar functional attributes (such as size, maximum growth rate, and optimum temperature for growth) also share similar ecologies (Reynolds 1988), we wanted to find out whether it is possible to give a statistically significant description of the attributes along trophic gradient (T, measured as the level of total P concentration) and season (S, related to day of the year). Discussions of species successions often imply such functional relationships. For example, Sommer (1986, p. 6) wrote that "in eutrophic lakes where P is not limiting during early spring, the higher maximum growth rate makes nanoplanktonic algae such as small Centrales and Rhodomonas dominant." The functional attributes of an alga might also relate directly its position in a seasonal succession of algae. Statement 5 of the PEGmodel of seasonal succession of planktonic events in fresh waters states that "there then (after herbivore grazing) follows a 'clear-water' equilibrium phase which persists until inedible algae species develop in significant numbers" (Sommer et al. 1986, p. 435.) Because inedibility is often related to biovolumes, e.g. volumes > -15 x 1 O3 pm3 (diam, 30 pm, Carpenter et al. 1993), herbivory and not season may be a primary vehicle for the presence of large-size algae or algal colonies. Several more statements about the relationship between algal attributes and species abundance could be listed and some of these would be partly confounding. Our quest, then, is a statistical pattern along trophy and season persisting "through" the web of biotic interactions. Materials and methodsWe use literature values for phytoplankton attributes. Our basic idea is that data should not be screened before the data are included in the analysis; instead, screening should be a consequence of the stati...

Lago Maggiore oligotrophication as seen from the long-term evolution of its phytoplankton taxonomic size structure

“…1). We can see also a high similarity between spectra divided by 5-8 years, e.g., between the years -2001-1995 Fig. 2).…”

“…It is very plausible that the rearrangement of the phytoplankton assemblage towards the growing number of smaller species was a consequence of the ecosystem changes related to nutrient reduction. This reduction could have given a growing advantage to species with a higher S/V ratio, being more efficient in assimilating nutrients (Chisholm 1982;Seip & Reynolds 1995). The decrease of phytoplankton size at lower nutrient levels has been frequently observed in lakes (see, for example, Masson et al 2000).…”

Patterns in phytoplankton taxonomic composition across temperate lakes of differing nutrient status

“…nutrient uptake, division rates, motility, sinking, and grazing losses), interact with both taxon size and morphology (e.g. Seip and Reynolds 1995). Therefore, an algal division with a wide diversity of taxon size and shape might be expected to succeed in a broad range of environments.…”

Total phosphorus–chlorophyll a size fraction relationships in southern Québec lakes

“…Significant shifts in algal species composition and functional attributes typically occur across a lake trophic state gradient (e.g. Smith 1990;Watson et al 1992;Seip and Reynolds 1995). As a result of these shifts in taxonomic composition, pronounced changes in algal size structure also occur with nutrient enrichment.…”