Prototype quillwort (Isoetes prototypus) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Search effort

Plants of the genus Isoetes have been collected throughout much of Nova Scotia during the past 100 plus years. Determination to species for most of these collections was unlikely to have been made at the time of collection as most collections are identified post fieldwork; thus the plants collected might well represent a relative abundance of various Isoetes species in that province. Although I. prototypus had been collected in Nova Scotia in the past, along with other species of Isoetes, the number of pre-1990 collections of this species is by far the lowest of any species of Isoetes known to occur in the province. This seems more likely to indicate a genuine rarity, and not just undercollection of the species. 

In an attempt to find I. prototypus and other species of Isoetes, D.M. Britton had checked 43 lakes, 1 river and 1 creek in Nova Scotia during fieldwork conducted between 1989 and 2000. His fieldwork uncovered two previously unknown sites for I. prototypus, sites 3 and 7. I. prototypus was independently discovered at site 7 by D.F. Brunton and Dr. Karen McIntosh around the same time it was found there by D.M. Britton. Brunton and McIntosh have checked at least 50 lakes in New Brunswick and Nova Scotia for I. prototypus, other Isoetes species and various Isoetes hybrids, and more than 20 additional lakes in Maine, New Hampshire and Massachusetts. The fact that these very targeted searches resulted in so few populations of I. prototypus being found attests to the rarity and selective nature of this species (Brunton pers. com. 2004).

A total of 50 lakes (1 in Maine, 25 in New Brunswick, 24 in Nova Scotia) were searched for I.prototypus during survey work conducted for this status report in 2003 and additional field work in 2004. Excluding travel time, at least 46 hours were spent investigating lakes having I. prototypus populations, while at least 56 hours were spent investigating lakes where I. prototypus was not found. Twenty days were spent conducting fieldwork, and approximately 5075 km were travelled. A total of 170 collections were made in 2003, 124 from the genus Isoetes, 27 representing I. prototypus; numbers of collections made in 2004 have not yet been tallied.

No reference sources (e.g., maps, databases, etc.) enabling the identification of lakes that may have suitable habitat characteristics for I.prototypus are readily available. Attempts to identify potential candidate lakes were made by consulting provincial government agencies that record lake survey data (mainly for fisheries); by consulting biologists and ecologists who have a good knowledge of lakes in New Brunswick and Nova Scotia, and/or have reviewed aerial photos and topographic (elevation) maps or viewed potential sites by air; by consulting local fishermen; and by consultation with Dr. D.M. Britton. Very little effort was made to survey lakes that were not oligotrophic or nutrient poor.

The discovery of I. prototypus at sites 2 and 5 was a result of D.M. Britton’s encouragement that these lakes had high potential for this species. Its discovery at sites 8 and 9 came from discussions with Sean Doucette, a local fisherman, who suggested that several lakes in this part of Nova Scotia were good for trout fishing and were spring-fed. It was discovered in flotsam at site 12 by Dwayne L. and Mary E.J. Sabine during a late spring fishing expedition. Its discovery at site 11 was a result of systematic checking of high elevation, clear water lakes that seemed to be good candidates when viewed from the air by Dedreic Grecian.

As a result of the fieldwork in 2003 and 2004, it seems likely to expect populations of I. prototypus in more lakes than the 13 known to date. Nova Scotia offers the greatest potential, especially in the small ‘kettle’ ponds near Digby (Brunton, pers. com.), and perhaps in the lakes near site 3. Consultation with fisheries biologists and trout fishermen may provide helpful guidance for discovering new sites. The lakes in southwestern New Brunswick and those within 30 km of the Maine coast certainly have not been extensively explored for this species and offer numerous high potential sites. The recent discovery of the species in a lake in central New Brunswick indicates a large new region of potential habitat in the province.

Given its predilection for clear water, boreal-type ponds and lakes and scattered occurrence within its known range, I. prototypus could be expected to occur elsewhere over a wide area of northeastern North America including northern New Brunswick, eastern Maine and the Gaspé Peninsula in eastern Quebec (D.F. Brunton pers. com. with E. Haber, May, 2005).

Since I. prototypus was first described in 1991, considerable time, effort and resources have been expended in intentional searches for this and other Isoetes species (Britton pers. com. 2003, Brunton pers. com. 2004). Part of the elusiveness of I. prototypus has been its preference for deep water (1.5 m or more). In many lakes, visibility from the water’s surface is rarely greater than 2 m, and more frequently less. Site 3 has tea-coloured water, obscuring visibility beyond 0.5 m. Searching using a glass-bottomed bucket can be successful in lakes with clearer water on sunny days; however, I. prototypus is often covered with algae, making it extremely difficult to see or definitively recognize from the surface. Populations of I. prototypus can readily be confused with or obscured by other species of deep water Isoetes (e.g., I. lacustris) or mat-forming aquatics such as Eriocaulon aquaticum and Myriophyllum tenellum.

In the past, combing shoreline flotsam for plants dislodged through natural processes was mainly how specimens of I. prototypus were collected, and how most site occurrences were detected. According to D.M. Britton (pers. com. 2003), wracks of I prototypus are most commonly seen in July, while Brunton (pers. com. 2004) has observed that these are most abundant later in the season, in August and September. Floaters have been seen at site 10 at all times of the year when there is no ice (Goltz, pers. observation). However, in 2003, only one floating clump of I. prototypus was found at site 10; none of ten I. prototypus lakes had any floaters. Low numbers of floating plants of this species were found at site 12 in June and September of 2004, but none was seen there in the spring of 2003. Thus surveying flotsam is an unreliable survey method, though convenient when plants are found.

The following search techniques were employed while doing fieldwork for this status report:

• examining flotsam along lake shores
• dragging of anchor or paddle
• surface viewing from air mattress and from canoe
• use of glass bottom bucket from canoe
• wading
• swimming with mask (and snorkel), and
• scuba diving (sites 10 and 12 only)

Techniques such as dragging a boat anchor to dislodge plants, which then float to the surface, have had success in several lakes (Britton 2002, pers. com.). Swimming and scuba diving proved to be the most reliable methods for the detection of I. prototypus. These allow increased visibility of the lake’s bottom, with easy access to vegetation to verify potential populations. Except for a few plants in site 4 and site 10, all plants were found in 1.5 metres of water or deeper. The greatest depth of water that plants of the genus Isoetes were collected from was 5 m, which is challenging even for a swimmer wearing a wet suit. However, the majority of I. prototypus plants were located in water 1.5 to 2.5 m deep, within reach of a surface swimmer. Surveying with scuba equipment allows greater detail and exploration at greater depths, but is also considerably more expensive and cumbersome.

At the depths preferred by I. prototypus, a swimmer can often do a preliminary survey with his feet while bobbing in the water, for even with water slippers on, it is possible to discern between Eriocaulon mats and Isoetes, as one can feel the stiff quill tips breaking off, as well as the prickly texture of I. prototypus, I. lacustris, and other straight-quilled Isoetes that may possibly be of hybrid origin. Some dense mats of robust Myriophyllum tenellum had a similar texture to straight-quilled populations of Isoetes, necessitating retrieval of plants from the bottom to be certain of their identification. In two lakes (site 8 and 9), I. prototypus was almost completely obscured by a tremendous abundance of Utricularia purpurea, and was only detected by palpating (by hand or foot) the lake bottom beneath these other plants.

In most of the lakes where I. prototypus was known to occur or was discovered during fieldwork in 2003 and 2004, it seldom took more than five minutes to find the species in situ, except for at sites 1 and 3, where many hours were spent before this species was seen.

Abundance

Prior to 2003, I. prototypus had been seen in situ in only four Canadian lakes (sites 1, 4, 6, 10) and the single locality in Maine (site 13). There had been no quantitative studies on the sizes of Isoetes prototypus populations in any of the Canadian lakes, nor had the populations been studied over time at any site where this species occurs. The occurrence of I. prototypus in most lakes had mainly been documented by collections of plants that had been uprooted and found floating near the lakeshore or washed up on shore.

Gradually more is becoming known of the size of I. prototypus populations. In situ populations typically occur in large uniform swards, measuring up to 200 X 50 m, at depths of ± 2 m. Comprehensive population studies on I. prototypus were made in 2000 at site 13, in Maine, where plants were estimated to grow at a density of 50 per square metre, and covered a total area of about 134 sq. m (Weber 2003, pers. com.). Since sampling was insufficient to get a firm estimate of the number of plants per sq. m, Weber suggested that a conservative estimate of the population size at the Maine site is 8775 to 10,000 plants.

Within one of the dense swards of I. prototypus at site 10, a 0.25 m² quadrat area was found to contain 30 plants. This count was made in 2003 without the aid of scuba gear. Based on this count, it was estimated that 120 plants would occur within an area of 1 m². The crown of one of the largest I. prototypus plants from site 10 measured 20 by 8.5 cm or 0.20 by 0.085 m, and therefore would cover an area of 0.017 sq. m; this means that there could be about 59 plants of this size in an area of 1 m². As this plant was roughly double the size of most plants of this species, our estimate of about 120 plants per m²seemed realistic. However, Brunton (pers. com. 2004) believes that our estimate of the density of plants of this species within the mats is far too conservative and suggests that the average density figure should be at least doubled, since it is typical for the leaves of adjacent plants of aquatic Isoetes to overlap considerably, and the density calculation does not make allowance for such overlap.

At site 12, counts of I. prototypus within the 0.25 m² quadrat area were done while using scuba gear in 2004. Counts made in one of the swards of I.prototypus ranged from 54 to 98 (mean 80.3) per 0.25 m², or 216 to 392/m². It would be interesting to determine how counts at all sites might differ if done consistently with the assistance of scuba gear.

It had been hoped that more accurate population estimates could be determined for all sites, and that a GPS reading could be made for all populations in each lake. However this proved to be impossible. Populations of I. prototypus often grew intermixed with other Isoetes sp. and it was often not feasible to determine identity in situ under water, since the morphology and colour of the other quillwort species were superficially so similar. More precise counts might have been achieved through uprooting large numbers of plants but such practice would be unethical for a species that is potentially at risk. At site 3, the strongly pigmented water made it extremely difficult to find populations in situ. At sites 8 and 9 plants were almost completely obscured by Utricularia purpurea. Since most populations were ultimately detected by swimming, the use of GPS equipment was prohibited.

Table 1 has been compiled from 2003 and 2004 fieldwork and Weber’s estimate for the Maine locality. The estimates provided in Table 1 do not purport to reflect total I. prototypus populations in any of the lakes. A thorough survey to record all populations of I. prototypus at the lakes where this species is known to occur would have required considerably more time than was available, especially given the dual objective of trying to find new sites for this species. The most thorough population survey was done at site 10; otherwise, the total area surveyed in the other lakes seldom exceeded one-fourth of the area of any lake. Some lakes (sites 2, 8, 9 and 11) were only surveyed until plants morphologically resembling I. prototypus were discovered. Sites 6 and 7 were only briefly surveyed to confirm that I. prototypus populations were still extant and to locate the species in situ. Plant density, and the length and width of I. prototypus populations were estimated while swimming. Actual populations in all lakes are most likely considerably higher than reported here. According to D.F. Brunton (pers. com. 2004), who has considerable field experience with many species of Isoetes, “counting aquatic quillworts is notoriously difficult and inaccurate” and “numbers are undoubtedly larger in virtually all cases”.

Brunton (pers. com. 2004) considers our population estimates to be extremely low, except perhaps at site 4, where he suggests that our population estimate may be a bit high based on his personal observations. He believes that “there are tens of thousands of plants at site 7 alone, for instance”, based on his “observations in 1998 of I. prototypus leaves piled up in 5-20 cm deep 'drifts' that extended along several hundredmetres of shoreline”. He found similar wracks of plants along shorter stretches of shoreline at site 1 in the mid to late 1990s. At the bottom of site 13 in Maine, he observed that “it forms a dense, virtually pure lawn of plants extending over a large area”.

In summary, our attempts to quantify the sizes of I. prototypus populations at all locations were woefully inadequate and the numbers in Table 1 should be regarded as only best estimates, despite our concerted efforts. Brunton (pers. com. 2004) suggested that population estimates for aquaticIsoetes might best be described within a numerical range (e.g., 12 million ±2 million estimate forI. bolanderi, an Alberta species) rather than trying to provide more precise totals, since the latter could well prove to be inadequate, inaccurate and totally misleading.

Fluctuations and trends

Isoetes prototypus populations are still extant in all lakes where this species has been found. In many lakes it seems to be abundant. D.M. Britton (pers. com. 2003) is concerned that populations may have declined at sites 1, 4 and 6, but good populations were still found there in 2003. D.F. Brunton (pers. com. 2004) suggests that the populations at site 7 have plummeted if our 2003 population estimate is compared to the shoreline drifts that were found there in 1998. Since none of the I.prototypus populations has been studied over time, it is impossible to ascertain any trend. Even though the population at site 10 has been monitored more than others, with submerged plants it is very difficult to determine whether or not populations are increasing or decreasing without monitoring permanent quadrats over time. Brunton (pers. com. 2004) cautions that further speculation could be dangerous because “it could encourage a false sense of security in regards to the long-term stability of these very fragile and sensitive populations”.

Unlike many of the other lakes, populations of I. prototypus at sites 5, 8, 9 and 11 appeared to be much lower. Plants of I. prototypus at site 5 were extremely difficult to discover among the swards of other Isoetes species and hybrids. Further study of these four lakes is warranted.

Rescue effect

Isoetes prototypus is still extant and locally abundant at the single known location in the United States. It is possible that spores of this species from plants growing in situ or from dislodged plants washed up along shorelines could be ingested by migratory waterfowl, shorebirds or songbirds and transported to a suitable lake in Atlantic Canada. It is also plausible that spores from dislodged plants might be inadvertently transported in mud and organic material caked on boats, footwear (boots) or tires of vehicles used to launch boats, although Brunton (pers. com. 2004) cautions that “there is no documented incident (or suggestion) anywhere of an aquatic Isoetes being successfully transported by the unintentional actions of humans”. Spores of I. prototypus from the Maine site (site 13) are evidently being preserved in a seed bank (Greene, Weber and Rooney 2002).

Since most of the globally known sites for this species occur in Canada, it is more likely that the Canadian sites and populations could serve as a source of distribution for I. prototypus to expand further into the United States, rather than vice versa.

All known populations of I.prototypus are present within lakes that do not drain into one another and are therefore discontinuous and fragmented. Most of the lakes have cottages and most have been stocked with trout. The lakes are used for fishing and boating occurs on most lakes. Spores could spread by clinging to boats or through waterfowl movements but such events are presumed to occur infrequently. Brunton (pers. com. 2004) believes that I. prototypus has an extremely “tough time getting around and everything points to local populations being ancient and only rarely moved beyond where the water currents can take them”. He considers that the potential for dispersal by the agents suggested above would be “extremely rare”, as evidenced by the fact that sub-populations of more wide-ranging Isoetes taxa (e.g., I. engelmannii and I.appalachiana) are strikingly genetically dis-similar.