Flooded jellyskin (Leptogium rivulare) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

What populations might have been, or might still be, at the sites of two of the old records (at Lake Temagami and Wawa) are not known. Such records (herbarium specimens) indicate only the presence of the species there at the time of collection (1946 and 1965, respectively). These sites were too vaguely recorded to facilitate a renewed search for them.

The finding, in 2001, of a substantial population of the lichen in the area of the original Ottawa collection, made in 1972, suggests that they are one and the same, although it has not been possible to verify that it coincides with the exact same site (I.M. Brodo, personal communication).

Apart from the recently discovered occurrence in Manitoba, Leptogium rivulare is therefore currently known from only three circumscribed localities 15 to 35 km apart, which are treated here as separate populations. At this point, long-term trends can only be inferred from what is currently observable.

Examination of every tree and rock in all but one of the flood zones, together with rough but thorough measurement of the amount of lichen on each one, has provided a good basis for estimating the remainder. There is a total of about 40 square metres of the lichen (plus or minus 15%), with 70% being in the Ottawa location, and 30% in Darling Township. The six thalli in the Pakenham Township population account for only 0.03% of the total.

Within the two main populations, there is a similar range of distribution from pond to pond, with about 70 to 85% being in one main pond in each case, and lesser to quite minute amounts in the associated ponds. The detailed notes that have been taken will allow these populations to be tracked in the future.

In these two localities, Ottawa and Darling Township, the lichen occurs almost exclusively on tree bases around seasonal ponds. It forms irregular growths on dozens to many hundreds of trees in these places. On some trees, it is barely present; on others, it forms large, encrusting patches about 50 cm across. The great numbers of small thalli often scattered over the bark indicate that successful reproduction is occuring, while the large patches show persistence over many years. Almost all individuals are fertile, and are capable of reproducing when only a few years old. There is no general sign of decline, but on one pond it appears senescent and may have been stranded above the floodwaters for too many years. In another pond, heavy and extensive growths of moss seem to be rapidly covering the lichen on a significant number of trees.

The lichen has sometimes been reported from sluggish waterways, so the third locality, being on a quite turbulent section of Indian Creek in Pakenham Township, raises some interesting questions. Could Leptogium rivulare exist on rocks in similar watercourses elsewhere? Careful checking upstream from this site, and examination of similarly placed rocks in other creeks and rivers, has failed to reveal any.

It is also questionable whether the Indian Creek site is a natural population. There is reason to think it may be the inadvertent result of a unique and accidental introduction. Thorough checking of all known habitat that might feed into Indian Creek failed to reveal the lichen anywhere but in the creekbed, and there, it has been found only downstream from a certain point.

All six thalli that came to light in three hours of intense searching among hundreds of boulders were at the same level in the dry creekbed, at the top of the zone occupied by the semi-aquatic lichen, Dermatocarpon luridum. In 2002, four of the six thalli were the same size (about 6 cm across), and two were about half that size. The growth rate inferred elsewhere indicates that the larger specimens might all be about 10 years old. These observations suggested a single point introduction, at a time when the water stood at one particular level.

Review of RobertLee’s notes reveals that on June 23, 1994, during a heat wave that followed heavy rainstorms, he and some fellow naturalists went wading, fully clothed, for an hour in the Ottawa pond where Leptogium rivulare has subsequently been found to grow most abundantly. On yet another very hot day about a week later, he and one of these same people sat for a long time with their pant legs in the cool, turbulent water just upstream of the Indian Creek site.  The floodwaters were just beginning to subside. If, as is discussed below, the spores are dispersed in water, they could have accumulated on clothing at the first site, and been washed out at the second. The spores would have landed on the tops of flat rocks where the lichen is now found, just as the water was falling away from them for the season. The timeline and the spatial distribution seem to allow for this interpretation.

Whether or not the lichen reached Indian Creek by accidental transfer, perhaps the important point is that it has established itself there. The discovery of Leptogium rivulare on a stony beach in Manitoba, also in close association with Dermatocarpon luridum, suggests that these apparently anomalous habitats are at least viable possibilities.

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