Prototype quillwort (Isoetes prototypus) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

All available data on lakes where I. prototypus is known to occur have been compiled in an attempt to identify common habitat parameters. This information has been provided to COSEWIC as supplementary data that are briefly summarized here.

Isoetes prototypus is a true submerged aquatic of small, oligotrophic, usually cold, spring-fed sterile lakes. Summer temperature stratification was noted at most lakes surveyed and underwater springs were occasionally observed. The pH of the lakes ranged from 5.7 to 7.2, based on measurements obtained from provincial government databases. Although Secchi measurements are not available for most lakes, it was noted that the water was clear to fairly clear at all but one lake (site 3). Lakes with I. prototypus were typically quite shallow, ranging from 3.5 to 12.2 m in maximum depth.

Estimates of water depths suggest that Isoetes prototypus most often occurs in 1.5 to 2.5 metres of water. This depth frequently coincided with the point where the lake’s bottom dropped quickly off from 2 metres to greater depths. A very few plants were found growing in water as shallow as 0.4 m (at sites 4 and 10), but this is very atypical for the species. It has never been found as a rooted emergent. At site 10, some plants were found as deep as 4 m. The solid mats at sites 10 and 12 often abruptly end at just over 2 m depths of water while scattered plants could be found to 2.5 m.

Isoetes prototypus is most often found in soft, flocculent oozy sediment where a swimmer’s foot or hand could easily sink 5 to 30 cm or even more. This sediment was usually found overlying a sandy, gravelly, or rocky bottom, sometimes interrupted by rocky shoals and ridges (e.g., sites 1, 2, 3, 5 and 9). At site 6, some populations were extensively covered with a layer of deciduous leaves at the time of the survey (late August). Brunton’s herbarium label data indicates that he found I. prototypus growing “in sand and silty-sand over clay in an extensive sand plain” at site 4 and “in sand over clay amongst granite boulders” at site 3. At site 4, we found a few plants rooted directly in sand unaccompanied by flocculent sediment but, in our experience, this was an atypical habitat for this species.

According to Brunton (pers. com. 2004), I. prototypus is “quite strongly tied to ponds on small sand plain deposits [e.g., sites 4, 6, 7 and 13] and most probably in post-glacial outwash systems”. However, such landscape features do not appear on provincial maps depicting the geology and surficial geology, presumably because the maps are generally not at a fine enough scale. At the level of detail depicted in these available maps, no relationship of this species with bedrock geology or soil type could be identified.

Isoetes prototypus grows either in pure swards, or mixed with I. lacustris and/or Eriocaulon aquaticum. It is also frequently found in small (<10 sq m) patches of 20 or less plants. In the mats of aquatic vegetation at specific locations where in situ populations of I. prototypus locally occurred, it typically accounted for at least 50% of the vegetation mass, except at sites 7 and 11, where it comprised up to 20% (the remainder being almost exclusively Eriocaulon aquaticum).

Isoetes prototypus falls in the category of isoetids -- a group of small, rosette forming plants associated with poor nutrient conditions in wetlands or water. The only plant species found with I. prototypus in all lakes was Eriocaulon aquaticum. Other frequent associates growing within 5 m of I. prototypus populations included Isoetes lacustris, Lobelia dortmanna and Myriophyllum tenellum.  Additional non-emergent aquatic species often found nearby included I. tuckermanii, Subularia aquatica, Nymphoides cordata, Pontederia cordata, Elatine minima and Sagittaria sp. I. prototypus plants were commonly covered with unidentified algae. At site 4, Brunton (pers. com.) found Subularia aquatica growing among plants of I. prototypus.

Some of the more frequent shoreline species found at lakes where I. prototypus occurs were: Calamagrostis canadensis, Juncus militaris, Lysimachia terrestis, Myrica gale, Sium suave and Triadenum fraseri. Lakes with a very prolific shallow water emergent vegetation rim or extensive boggy margins were thought to be poor candidates for I. prototypus because of their more eutrophic nature.

There was no consistent pattern in forest cover around the lakes. Sites 6 and 7 have a predominance of hardwoods, while sites 3, 10 and 12 are mainly surrounded by Acadian softwood forest. The forest cover around most lakes is mixed (e.g., Abies, Acer rubrum, Acer saccharum, Betula, Picea).

Lakes with I. prototypus are typically good for trout and often have been stocked with Brook Trout, or rarely Rainbow Trout.  Many lakes also contain Banded Killifish.

Freshwater sponges were found in almost all I. prototypus lakes, rarely even growing on I.prototypus plants. Freshwater mussels were also sometimes found near I. prototypus populations. 

The Isoetes prototypus lakes located close to the Bay of Fundy (e.g., sites 3, 4, 5, 6 and 7) often occur on plateaus at elevations over 200 m. Except for sites 1 and 2, the other lakes were all over 100 m in elevation. At sites 10 and 11, a steep rocky cliff face or tall hills border the shoreline at one or more locations.

Habitat trends

There is little information available on habitat trends. Isoetes prototypus is still extant at all lakes where it has been found.

Of the three sites in New Brunswick, one is on a landscape that has recently been subject to intensive forestry except for a mandatory buffer strip that was left around the margins of the lake. The other two New Brunswick sites currently have restricted access. One of these sites (site 11) is surrounded by a fairly intact forest, while the other site (site 10) has been maintained as an open field for many years and recently had a permanent residential dwelling built in this field.

In Nova Scotia, cottage development and associated shoreline deforestation were extensive around two sites (4 and 8) and at one end of each of an additional two sites (sites 6 and 7). At three sites, roads and/or causeways border or encroach upon the shoreline at one or more locations. It is not clear what impact these may or may not have had on the populations of Isoetes prototypus at these lakes.

Habitat protection/ownership

None of the Canadian lakes where I. prototypus has been found is within a protected area. However, site 1 is a source of water supply for a nearby community and is posted against certain activities that might have a negative impact on water quality. No disruptive activities are foreseen for the three sites in New Brunswick.

Sites 3 and 5 occur on Crown land in Nova Scotia, and site 11 occurs on federal (Dept. of National Defence) land in New Brunswick, but the other nine known Canadian lakes where I. prototypus is known to occur are on private land. However, in Nova Scotia, the bottom of almost all lakes is considered to be Crown land, even though the shoreline and land around the lake may be privately owned.  Hence, all known locations for I. prototypus in Nova Scotia are on Crown (public) land.  The ownership of the bottom of lakes in New Brunswick is more complicated since the lake bottom (along with fishing rights) was once granted along with the surrounding land grant, and this ownership of the lake bottom transfers with the deed when a property changes hands. This practice evidently changed in 1863, so lands granted after that year did not include ownership of the lake bottom and fishing rights. Without searching the deeds of New Brunswick properties surrounding a lake back to the original grant, it is impossible to ascertain the ownership of the lake bottom for any lake in the province where I. prototypus has been found (D.L. Sabine pers. com. 2005).

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