Basis for Listing

In Minnesota, suitable habitat for Najas marina is limited to prairie lakes in a relatively small portion of the state. The species has been recorded a total of 35 times, although recent searches in seemingly ideal habitat have revealed N. marina to be very rare. Efforts to keep lakes in that area healthy and free from pollution have been less than successful. The predominance of agriculture in that region, and the concomitant chemicals and animal waste products are a recurring source of problems. It must be remembered that contaminants released into the air, land, and ditches eventually find their way into lakes. Given its rarity, N. marina was listed as a special concern species in Minnesota in 1996.

  Description

Najas marina is a submerged aquatic plant (macrophyte). The stems are 6-45 cm (2.4-17.7 in.) long and branched on the distal portion. The internodes are 0.3-11 cm (0.1-4.3 in.) long and usually have prickles. The leaves are 0.5-3.9 cm (0.3-1.5 in.) long, and the blade portion is 0.4-4.5 mm (0.02-0.18 in.) wide. The margins of the blade are coarsely serrate with 8-13 teeth per side, and the abaxial surface of the midvein has prickles. There is 1 flower per leaf axil, and the male flowers are on different plants than the female flowers. The reddish brown seeds are ovoid in shape, 2.2-4.5 mm (0.09-0.18 in.) long, and 1.2-2.2 mm (0.05-0.09 in.) wide. The seed is not recurved and the style is situated at the center of the apex. The surface of the seeds is dull and pitted. With its prickly internodes and prickles along the abaxial surface of the leaves, N. marina is the easiest of our Najas to recognize.

  Habitat

In Minnesota, N. marina appears to be limited to a small number of alkaline lakes in the west central prairie counties. The lakes are typically located in shallow basins in calcareous glacial deposits. Analyses of 10 lakes known to support populations of N. marina revealed them to have a total alkalinity ranging from 136 to 481 ppm, with a mean of 246 ppm. The pH of the lakes ranged from 8.3 to 9.4 with a mean of 8.8. The smallest lake included in the analysis was 17 ha (43 ac.) and the largest was 991 ha (2,450 ac.); the average size (excluding the two extremes) was 139 ha (343 ac.). Most of the lakes had a maximum depth less than 4.6 m (15 ft.). The most common aquatic species found to be associated with N. marina in the 10 lakes included Stuckenia pectinata (sago pondweed), Ceratophyllum demersum (coons tail), Schoenoplectus acutus var. acutus (hardstem bulrush), Myriophyllum sibiricum (northern watermilfoil), Lemna trisulca (star duckweed), Potamogeton friesii (Fries pondweed), P. richardsonii (Richardsons pondweed), Najas flexilis (flexuous naiad), Ruppia cirrhosa (spiral ditchgrass), and Zannichellia palustris (horned pondweed).

  Biology / Life History

Najas marina is a submerged annual that reproduces primarily or entirely by seed. Seeds are normally produced in great abundance and appear to be dispersed by waterfowl, which also utilize the seeds for food. Most of the lakes with N. marina are strongly alkaline, a condition that develops when a high rate of evaporation concentrates calcium and magnesium salts. Such conditions are limiting, in an ecological sense, and may explain the characteristic flora of such lakes.

It is known that N. marina exhibits a certain tolerance for poor water quality; sometimes surviving in highly eutrophic lakes where annual algae blooms greatly reduce water clarity. In these situations, N. marina may be one of only a few aquatic macrophytes able to survive. In fact, when competition is reduced in this way, N. marina can become quite abundant, even dominant. However, most occurrences of N. marina are in lakes where the water is clearer and the aquatic plant community is intact and stable. In these situations, N. marina will not become overly abundant or dominant.

  Conservation / Management

Najas marina may survive, and for a period of time actually thrive, in highly eutrophic lakes where the competition has been reduced by deteriorating water quality. Yet it seems very unlikely that N. marina can sustain a viable presence under such conditions in the long-term. Water quality can usually be improved by watershed management practices that attempt to filter pollutants before they reach a lake or eliminate pollutants at their source. If restoration of water quality in an impaired lake is successful, a more diverse community of plants will likely become reestablished. Conditions would then be suitable for N. marina to assume a more sustainable ecological role. Lakes where water quality is already high, and where N. marina occurs in an already stable community, should be vigorously protected from pollution, especially nutrient inputs.

Many resources and tools regarding shoreland management, including lakescaping and restoration, are available for landowners and land managers, and any opportunity to incorporate these concepts would benefit N. marina as well as many other aquatic species.

  Best Time to Search

The best time to search for N. marina is from early July through August.

  References and Additional Information

Clausen, R. T. 1936. Studies in the genus Najas in the northern United States. Rhodora 38:333-345.

Haynes, R. R. 1979. Revision of North and Central American Najas (Najadaceae). Sida 8:34-56.

Haynes, R. R. 2000. Najadaceae. Pages 77-83 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 22. Oxford University Press, New York, New York.

Rosendahl, C. O. 1939. Additional notes on Najas in Minnesota. Rhodora 41:187-189.

Rosendahl, C. O., and F. K. Butters. 1935. The genus Najas in Minnesota. Rhodora 37:345-348.

Stuckey, R. L. 1984. Distributional history of Najas flexilis, N. gracillima, and N. marina (Najadaceae) in eastern North America. The Ohio Journal of Science 84(2):4-5.

Triest, L., J. Van Geyt, and V. Ranson. 1986. Isozyme polymorphism in several populations of Najas marina L. Aquatic Botany 24:373-384.

Wentz, W. A., and R. L. Stuckey. 1971. The changing distribution of the genus Najas (Najadaceae) in Ohio. The Ohio Journal of Science 71(5):292-302.