THE PHYTOPLANKTON OF MCGINNIS LAKE

RESULTS

(See tables below for phytoplankton data)

May 11, 1988

Phytoplankton cell densities were low (<210 cells/ml) in the May collections. An unidentified motile, unicellular green alga dominated the McGinnis Lake phytoplankton at the 1 m depth at both Stations A (90%) and B (76%). The diatom Asterionella formosa comprised 45-55% of the phytoplankton at both stations at the 4 m and 7 m depths. Other moderately abundant algae were the blue-greens Anabaena flos-aquae (Station A: 41% at 7 m; Station B: 19% at 1 m, 32% at 7 m) and Anabaena sp. (Station A: 2% at 1 m, 17% at 4 m). The diatoms Fragilaria crotonensis and an unidentified species of Fragilaria composed 11-22% of the phytoplankton in the 7 m samples. Sphaerocystis schroeteri, a treen alga, accounted for 21% of the algae at the 4 m depth at Station A but was not otherwise observed. Several algae made up the remainder of the phytoplankton.

September 28, 1988

Algal cell densities were high (2000-5000 cells/ml) in all of the September collections. The phytoplankton was dominated by a bloom of Aphanothece nidulans. The blue-green alga comprised 89-95% of the algae in samples from 1 m, 4 m, and 7 m at both Stations A and B. Other blue-greens present in all 6 samples were Anabaena flos-aquae, Aphanocapsa cf. elachista and Chroococcus sp. Each represented 6% of the cells counted. They cryptophyte Rhodomonas sp. and Quadrigula sp., a green, were also present in all six samples. Numerous taxa from variouis algal divisions made up the remainder of the phytoplankton.

Discussion

In addition to the unidentified motile green alga, the May, 1988, the phytoplankton of McGinnis Lake contained a high proportion of the diatoms Asterionella formosa and Fragilaria sp. Both organisms are frequently associated with mesotrophic to eutrophic conditions (Taylor, et al. 1981, Reynolds 1984b). High populations of the blue-green Anabaena sp. (especially Anabaena flos-aquae) and the colonial green Sphaerocystis schroeteri are also typical of mesotrophic to eutrophic waters (Taylor, et al. 1981, Hutchinson 1967, Reynolds 1984b).

Large populations of Aphanothece nidulans and Aphanothece sp., as seen in the September, 1988, collections, are frequently observed in autumn in eutrophic and hypertrophic lakes (Reynolds 1984a). Aphanocapsa often accompanies Aphanothece, as it did in this collection.

Small numberes of Anabaena flos-aquae, Rhodomonas and Quadrigula were present. Chroococcus is a common subdominant in the phytoplankton of mesotrophic to hypertrophic waters. It is often associated with nuisance blooms but seldom forms blooms by itseslf (Paerl 1988). Rhodomonas is often abundant (along with Cryptomonas) mesotrophic to hypertrophic lakes (Reynolds 1984a).

The diatoms Asterionella and Fragilaria are all frequently associated with mesotrophic to eutrophic conditions, particularly in spring (Taylor, et al. 1981; Reynolds 1984b). Anabaena flos-aquae, a common constituent of blue-green algal blooms, becomes abundant in eutrophic waters (Taylor, et al. 1981, Reynolds 1984a, Hutchinson 1967). Sphaerocystis schroeteri is considered typical of mesotrophic (Reynolds 1984a) and eutrophic conditions (Taylor, et al. 1981). Populations of both of the latter species are favored by increasing thermal stratification (Reynolds 1984a). The high populations of Asterionella and Fragilaria in McGinnis Lake in May, 1987, and of Anabaena flos-aquae in May, 1988, indicate the presence of readily available nutrients (Reynolds 1984a, Paerl 1988).

Large numberes of Aphanothece and Aphanocapsa, as seen in September, 1988, are typical of hypertrophic lakes and confirm nutrient availability. The phytoplankton assemblages identified in collections from McGinnis Lake from two periods indicate that the lake is mesotrophic to eutrophic.

Literature Cited

McGINNIS LAKE PHYTOPLANKTON FOR SPRING AND AUTUMN 1988
Spring , 11 May 1988
Station A
Sample Depth	Phytoplankton	Algal Cells per ml	Percentage
1 Meter	motile unicellular green alga sp.	3185	90%
	Asterionella formosa	9	5%
	Quadrigula chodatii	5	3%
	Anabaena sp.	3	2%
4 Meter	Asterionella formosa	17	49%
	Sphaerocystis schroeter	7	21%
	Anabaena sp.	6	17%
	Quadrigula chodatii	3	8%
	centric diatoms	1	4%
7 Meters	Asterionella formosa	25	44%
	Anabaena flos-aquae	23	41%
	Fragilaria sp.	6	11%
	Nitzschia sp.	2	4%
Station B
1 Meter	motile unicellular green alga	3146	76%
	Anabaena flos-aquae	36	19%
	Anabaena flos-aquae	6	3%
4 Meters	Asterionella formosa	13	56%
	Fragilaria crotonensis	4	17%
	motile unicellular green alga	4	15%
	Cyclotella sp.	1	6%
	Quadrigula chodatii	1	4%
	Fragilaria sp.	1	3%
	Sphaerocystis schroeteri	24	14%
	Stephanodiscus sp.	18	10%
	Quadrigula chodatii	6	3%
7 Meter	Asterionella formosa	31	45%
	Anabaena flos-aquae	22	32%
	Fragilaria sp.	12	18%
	Fragilaria crotonensis	3	4%
Autumn, 28 September 1988
Station A
Sample Depth	Phytoplankton	Algal Cells per ml	Percentage
1 Meter	Aphanocapsa elachista	4482	90%
	Chroococcus sp.	205	4%
	Anabaena flos-aquae	166	3%
4 Meter	Aphanothece nidulans	2863	92%
	Aphanocapsa cf. elachista	93	3%
	Anabaena flos-aquae	68	2%
	Chroococcus prescottii	68	2%
7 Meter	Aphanothece nidulans	1618	89%
	Anabaena flos-aquae	98	5%
	Mougeotia sp	31	2%
Station B
Sample Depth	Phytoplankton	Algal Cells per ml	Percentage
1 Meter	Aphanothece nidulans	3591	94%
	Chroococcus prescottii	92	2%
	Aphanocapsa cf. elachista	70	2%
4 Meter	Aphanothece nidulans	1900	95%
	Aphanocapsa cf. elachista	36	2%
7 Meter	Aphanothece nidulans	2679	91%
	Anabaena flos-aquae	98	3%
	Chroococcus prescottii	64	2%
	Aphanocapsa cf. elachista	52	2%