Ogden's Pondweed (Potamogeton ogdenii) COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

Potential threats to Ogden’s pondweed are habitat destruction, such as loss of beaver ponds, and competition from invasive plants, such as Eurasian water-milfoil. The extent of such impacts may be minimal at present. At Davis Lock, little impact from invasive plants was evident on the diverse aquatic communities in the quiet bays where Ogden’s pondweed is assumed to have been found. There was also little evidence for invasive plant impact in Black Creek at Murphys Point. However, Eurasian water-milfoil is common in bays of Big Rideau Lake adjacent to and within Murphys Point Provincial Park; extensive areas with good aquatic plant diversity and only a limited presence of the water-milfoil are also present. Curly pondweed (Potamogeton crispus) is an invasive aquatic but it was not seen at Davis Lock and is present in only small numbers in the Murphys Point area. Another invasive aquatic that is common in eastern Ontario is European Frog’s-bit (Hydrocharis morsus-ranae). This species was not seen in the vicinity of Davis Lock, and was rare along Black Creek and in Hoggs Bay.

Although beaver ponds are ephemeral by nature, if a rare species does not spread easily, a population in a pond could be eliminated from an area when the pond was drained. Ogden’s pondweed is also at risk across its range due to its low population numbers. Hellquist & Mertinooke-Jongkind (2003) report a global population of only ten extant sites (only one of the two recent Ontario sites is listed).

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