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Recovery Strategy for the Seaside Centipede Lichen (Heterodermia sitchensis) in Canada (Proposed)


1 Background

1.1 Species Description

Seaside Centipede Lichen is a semi-erect, cushion-forming, foliose lichen to about 2 cm across. The lobes are short to elongate, 1–2 mm wide, and furnished with long thin "eyelashes" (cilia). The upper surface is pale greenish and often bears scattered whitish "spots". Mature specimens usually have urn-shaped apothecia near the lobe tips, these with prominent rims bearing ring-shaped soralia on their inner surface. The thallus is white and cottony (noncorticate) below and bears long, blackish marginal cilia. A more detailed description is given in Goward (1984).

1.1.1 Distribution1

Seaside Centipede Lichen is endemic to the Pacific Northwest of North America. At the time of its description in the mid 1980s, it was known from only two sites on the west coast of Vancouver Island. The first of these was Schooner Cove in Pacific Rim National Park Reserve and the second was near Ucluelet on the Ucluth Peninsula. Unfortunately, it disappeared from the latter locality in the early 1990s as a result of clearcut logging for subdivision development (Goward, personal observation). Since then intensive surveys have located it at a number of locations in Canada (Table 1) and two specimens have been reported from Cape Lookout in Oregon (McHenry and Tønsberg 2002). Seaside Centipede Lichen is ranked S2S3 (imperilled to vulnerable) in BC and G2G3 globally (NatureServe 2005).

After four years of search effort (2001–2004) the known population in Canada numbers 212 thalli (based on the most recent counts at each site; Goward and Wright 2003, Wright 2004). Almost 90 percent of these are restricted to five localities: Florencia Island, Wouwer Island, Folger Island, Lawrence Islets, and the Spring Island area. Elsewhere the occurrence of this species is highly localized.

Table 1 : Seaside Centipede Lichen (Heterodermia sitchensis) occurrences in Canada
(PRNPR = Pacific Rim National Park Reserve, BC = Province of British Columbia Crown land). Table is organized by observation year.
Site descriptionObservation yearJurisdictionStatus, if knownThalli #
Schooner Cove – Holotype Locality1983PRNPR 15
Ucluth Peninsula A1983Town of Ucluelet 5
Total Observed Thalli – 198320
Schooner Cove – Holotype Locality1991PRNPRStable15
Total Observed Thalli – 1991
(Status Report prepared in 1994 based on this data)
15
Ucluth Peninsula ANATown of UclueletExtirpated in early 1990’s
Schooner Cove - Holotype Locality2001PRNPRDeclining1
Florencia Bay North2001PRNPR 3
Wickaninnish South2001PRNPR 2
Wickaninnish S - Village2001PRNPR 1
Florencia Island2001PRNPR 60
Ucluth Peninsula B2001BC 2
Wouwer Island2001PRNPR 42
Small Islet near Wouwer Island2001PRNPR 2
Dicebox Island2001PRNPR 1
Lawrence Islets2001BC 1
Total Observed Thalli - 2001115
Florencia Island2002PRNPR 27
Lawrence Islets2002BC  21 
Schooner Cove - Holotype locality2002PRNPRDeclining1 thallus dying
East of Schooner Cove Holotype locality2002PRNPRDeclining3 (2 thalli dying)
Wouwer Island2002PRNPRDeclining12
Folger Island2002BC 18
Benson Island2002PRNPR 1
Total Observed Thalli - 200283
Spring Island (Kyuquot Sound)2004BC 6
Unnamed Island (Kyuquot Sound)2004BC 48
Total Observed Thalli - 200454
Global range

Seaside Centipede Lichen is only known from the west coast of Vancouver Island in British Columbia, Canada and from one site on the Oregon coast. The latter site, Cape Lookout in Coastal Oregon (McHenry and Tønsberg 2002), is a narrow peninsula jutting 2 km into the Pacific Ocean.

Canadian range

Approximately 20 locations on the west coast of Vancouver Island are currently known. The majority of these occur within Pacific Rim National Park Reserve (Table 1). In 2002, new occurrences located outside the park were on Folger Island and Lawrence Islets. Folger Island is located near Bamfield between the Broken Group Island Unit and the West Coast Trail Unit of Pacific Rim National Park Reserve. Lawrence Islets are located north of Pacific Rim National Park Reserve between Vargas and Bartlett islands in Clayoquot Sound. The Canadian range was extended approximately 130 km to the northwest in 2004 when two sites were found in Kyuquot Sound.

Percent of Global Distribution in Canada

Almost 100% of the global distribution occurs in Canada. Seaside Centipede Lichen is known from only one site outside Canada.

1.1.2 Population Sizes and Trends

Some previously known sites, including the holotype locality at Schooner Cove in Pacific Rim National Park Reserve, have been resurveyed (Table 1). The holotype locality has been in decline for several years, in 2002 significantly fewer thalli were observed and the remaining thalli were noted to be in poor condition. Other sites resurveyed in 2002 showed a similar trend of declining thalli numbers and health from the previous year. It is believed that inordinately severe winter storms during the winter of 2001/2002 resulted in the loss of specimens and reduced vigour at many sites. Longer-term comparisons from the holotype locality suggest that Seaside Centipede Lichen is short-lived and must frequently colonize new sites. It is not known whether Seaside Centipede Lichen has been significantly affected by human activities or whether its abundance is similar to historic levels.

1.1.3 Description of the species' needs

Biological needs and limiting factors

Seaside Centipede Lichen is a pioneer lichen largely confined to small twigs. It reproduces asexually. As with other pioneer lichens it tends to be short-lived, enduring perhaps 10 to 15 years until such time as it is out-competed by more aggressive lichens and bryophytes. This observation may be key to understanding its status as a rare species; while Seaside Centipede Lichen has adopted a life strategy based on a requirement for frequent dispersal and colonization, it also appears to be a poor disperser. The life history of Seaside Centipede Lichen suggests a particular sensitivity to habitat modification and a strong dependence on the maintenance of robust coastal ecosystems.

Seaside Centipede Lichen appears to lead a very precarious existence as a site must satisfy many peculiar conditions for successful colonization and growth. For instance, the frequent association of Seaside Centipede Lichenwith the perch branches of birds suggests this species is not stable at most sites; though the host trees themselves may be long-lived, the branches supporting Seaside Centipede Lichenare likely to be relatively ephemeral.

Ecological Role

Seaside Centipede Lichen is not known to serve a critical or keystone ecological function, no other species are known to be dependant upon it. It appears to have a very complex life history, but this does not translate into important ecological function for other species or ecosystem processes. It does play a role in trapping marine-derived nutrients in a terrestrial system. We anticipate that further research into nutrient cycles on the Pacific coast will reveal more species and processes which demonstrate sea to shore cycling to be a very important function in coastal terrestrial environments.

It is well known that lichens are important sentinels of environmental change. Seaside Centipede Lichen and associated lichen species may fit well into environmental monitoring strategies as indicators of environmental change and/or degradation.

Habitat needs

Seaside Centipede Lichen is a tree-dwelling lichen found to date only on Sitka Spruce (Picea sitchensis). Seaside Centipede Lichen is not distributed at random, rather this species exhibits several clear and to a large extent predictable patterns of distribution. Some of the important habitat features required by Seaside Centipede Licheninclude the following (Goward 2001, Goward and Wright 2002):

  • It is known only from Sitka Spruce branches within several metres of the high tide zone. Existing evidence suggests that Seaside Centipede Lichen may be more abundant in the lower portions of the Sitka Spruce canopy (however, see Section 1.5). A majority of Seaside Centipede Lichen finds were made on old trees having a more or less cylindrical canopy structure (young regenerating trees with more conical canopies rarely support this species). Seaside Centipede Lichen is found on bark in defoliated portions of young branches.
  • It is only found in regions of very high moisture such as those exposed to frequent fog banks or spindrift.
  • It may be limited to sites offering some protection from full exposure to maritime conditions such as leeward sides of bays, inlets, islands, and islets and the sheltered portions of capes, headlands, spits, and peninsulas.
  • It is benefited by and requires secondary nutrient enrichment at most sites where it occurs. Key factors associated with the requirement for nutrient enrichment include basic bedrock geology (calcium rich rock: limestone, dolomites, etc.) and/or secondary nutrient enrichment. Observed sources of this nutrient enrichment include--
    • wildlife attracted to certain shoreline sites (islands, capes, headlands, spits, and peninsulas),
    • bird droppings beneath frequently used bird perches,
    • aerosols from breath and scat of sea lions on haul-outs and wintering grounds,
    • fecal bombing from seabirds flying to or from a colony,
    • aboriginal midden sites.

In general four broad factors largely predict the presence of this species: ocean proximity, old or slow growing Sitka Spruce, partly defoliated branches, and nutrient enrichment (Goward and Wright 2002). The specific habitat requirements of Seaside Centipede Lichen result in a limited supply of suitable habitat.

In addition, suitable habitat may be further restricted to old-growth forests. Few ecologically and geographically restricted epiphytic lichens are known to occur in second-growth forests (Goward 1994b). By virtue of their structural homogeneity and especially their environmental instability, second-growth forests are unsuited to colonization by most lichens growing at or near the ecological limits of their range (Goward 1994a). In contrast, old-growth forests are structurally much more heterogeneous and environmentally more stable (Franklin et al. 1981), and so permit colonization by a much wider assortment of species including those with poor dispersal abilities (Goward 1993, 1994 a and b).

It is perhaps useful to also describe habitats that tend not to support Seaside Centipede Lichen. Localities lacking a fringe of Sitka Spruce are one such habitat. The general scarcity of Sitka Spruce in the inner islands of the Broken Group reduce the chances that Seaside Centipede Lichen will be found there at any level of abundance. Sites supporting only young spruce trees usually lack Seaside Centipede Lichen. Young trees generally have a conical growth form not conducive to enrichment by perching birds or dripzone effects. Finally, as already suggested, mainland localities support Seaside Centipede Lichen at much lower levels of abundance than their island counterparts.

1.2 Threats

The following points are the primary natural or human-induced threats that have been observed to impact Seaside Centipede Lichen population and habitat.

1.2.1 Habitat loss

Much of the known information on the biology of this species indicates that it would be extremely vulnerable to elimination of a portion of its range. Its suspected vulnerability is based on an apparently short lifespan, poor dispersal ability, highly specific habitat requirements, the ephemeral nature of its preferred habitat, and limited suitable habitat availability (details in Section 1.1.3).

Habitat loss through activities such as foreshore development, forest harvesting, pruning, branch collection, or other disturbance are a major threat to Seaside Centipede Lichen. One of two Seaside Centipede Lichen sites discovered in 1983 has been lost due to site clearing for subdivision development. This effect is site-specific. Site restoration after host tree loss would take at least 50 years and probably much longer for a suitably sized Sitka Spruce tree to develop.

Significant populations of Seaside Centipede Lichen occur mostly in the lower branches of Sitka Spruce trees. Site clearing by homeowners or other land stewards to gain better access to the coast or improve the view of the ocean can involve removal of these lower branches and loss of Seaside Centipede Lichen and/or its habitat. Furthermore, collection of the easily accessible lower branches for firewood could lead to significant habitat loss.

Forest harvesting is a threat if harvesting occurs near sites with Seaside Centipede Lichen. Harris (1984) suggests that a buffer strip of trees would have to be at least 60 metres wide to preserve the highly specific microclimatic conditions required by more sensitive epiphytic lichens.

1.2.2 Disruption of natural patterns of nutrient distribution

This species depends on localized nutrient enrichment, often mediated by local wildlife. Any change in patterns of use on sea lion haul-outs, a reduction in raptor or seabird populations, or seabird colony disruption poses a threat to existing Seaside Centipede Lichen populations. Many factors including foreshore development, loss of bird perches, and food availability can influence numbers of seabirds, raptors, and marine mammals. Other activities or effects that can potentially alter ecosystem processes, degrade Seaside Centipede Lichen habitat, and impact the ability of Seaside Centipede Lichen to maintain a self-sustaining population include pollution, climate change, human population growth, urbanization, logging, and tourism.

It is unknown what impacts coastal development may have on the distribution of raptors, seabirds, and marine mammals which all appear to play a critical role in the nutrient enrichment requirements of Seaside Centipede Lichen.

1.2.3 Increased severity of weather patterns

Some of the warmest years recorded since weather records have been kept occurred in the last decade or two; this pattern of warming seems to be accompanied by an increase in the frequency and severity of storm events. An increased severity of winter storms can result in branches hosting Seaside Centipede Lichen to be repeatedly sprayed with salt water and violently washed by breaking waves. All populations would be expected to suffer to some degree by deteriorating winter weather conditions. However, due to specific geography of the coast and predominant fetch, specific populations may be devastatingly impacted by storm events. Some Seaside Centipede Lichen populations will be afforded a relatively high degree of protection from severe winter storm events due to their occurrence on the leeward side of islands. The effects of severe winter weather patterns were apparent during the field study conducted in June 2002 (Goward and Wright 2003). The effects of wave action were clearly evidenced on affected branches, and several specimens had died or were in poor vigour.

1.2.4 Natural or anthropogenic climate changes

Natural or human-influenced drying conditions could be precipitated if global warming trends prove to be a longer-term phenomenon. This could adversely affect all populations of Seaside Centipede Lichen.

1.3 Critical Habitat

1.3.1 Identification of the species' critical habitat

No critical habitat, as defined under the federal Species at Risk Act [s2], is proposed for identification at this time.

While much has been learned about the habitat of the Seaside Centipede Lichen, more definitive work must be completed before any specific sites can be formally proposed as critical habitat. It is expected that critical habitat will be proposed within one or more recovery action plans following consultation and development of stewardship options with affected landowners and organizations and completion of outstanding work required to quantify specific habitat and area requirements for the species.

Notwithstanding the above, information on the current state of knowledge regarding habitat needs and sites of occupation are included in this recovery strategy. This section describes, to the extent possible, the occupied and potential habitat, examples of activities which are likely to destroy critical habitat, and a schedule of studies required to define critical habitat.

Occupied Habitat

Habitat © Parks Canada Agency/Brian Reader
Habitat © Parks Canada Agency/Brian Reader

All known sites (Table 1), as well as sufficient dispersal habitat, and important ecosystem functions should be considered during the process of critical habitat identification--it is likely that critical habitat identification will need to occur on a site by site basis and consider metapopulation2 dynamics.

Potential Habitat

This recovery strategy endorses the retention of existing habitat for the survival of Seaside Centipede Lichenand is not suggesting recovery of degraded habitat where the species was present historically.

1.3.2 Examples of activities likely to result in destruction of critical habitat

  • Foreshore development, forest harvest, branch collection for firewood, branch pruning or tree clearing, and logging of old- or older-growth coastal fringe forests all have the potential to directly affect individuals and habitat by removal of Sitka Spruce trees or lower branches.
  • Human induced changes in nutrient distribution patterns which are often mediated by local wildlife could be caused by pollution, human population growth, urbanization, and tourism and would impact the species by altering, reducing, or eliminating nutrient enrichment in otherwise suitable habitats.
  • Human induced atmospheric modifications resulting in climate change could have a variety of effects including a drying trend and increased storm severity both of which would degrade or eliminate current habitat.

1.3.3 Existing and recommended approaches to habitat protection

The core of the known range of Seaside Centipede Lichen is within Pacific Rim National Park Reserve (10 of 15 extant sites) where it is afforded protection under the regulations of the Canada National Parks Act and the Species at Risk Act. Regulations under the Canada National Parks Act prohibit collection of plant material including tree branches: National Park General Regulations state, “No person shall remove, deface, damage or destroy any flora or natural objects in a Park except in accordance with a permit issued under subsection 11(1) or 12(1).” Habitat availability should remain relatively constant within Pacific Rim National Park Reserve.

The land tenure of the remainder of the known Seaside Centipede Lichen range (5 of 15 sites) is uncertain. Locations on Provincial Crown land can be protected by the Province of British Columbia through existing statutes such as designation as a Wildlife Habitat Area under the Forest and Range Practices Act or Old Growth Management Areas under the Land Act.

1.3.4 Schedule of studies to identify critical habitat

Survey Requirements
  • Identify and field survey suitable habitat for Seaside Centipede Lichenon the west coast of Vancouver Island between Tofino and Nootka Island. Assess the size of any discovered populations and record their coordinates. Completion date: 2007.
  • Survey the central British Columbia coast for Seaside Centipede Lichen. Completion date: 2008
  • Continue to survey Pacific Rim National Park Reserve and environs for new Seaside Centipede Lichen occurrences and other rare lichen species. Through 2006--2010.
Biological/Ecological Research Requirements
  • Continue research on pH and microelement requirements of Seaside Centipede Lichen and associated lichen species. This research should include an analysis of lichen communities occurring under environmental conditions dissimilar to those required by Seaside Centipede Lichen. Completion date: 2007.
  • Investigate dispersal and recruitment in order to estimate the amount and configuration of occupied and unoccupied habitat needed to achieve the recovery program objective of a self-sustaining healthy population of Seaside Centipede Lichen. Completion date dependant on the outcome of studies.

1.4 Actions Already Completed or Underway

  • In 2001 and 2002 research was undertaken by Parks Canada to improve knowledge about Seaside Centipede Lichen and other rare lichens in the Pacific Rim National Park Reserve region (Goward 2001, Goward and Wright 2003). Results have increased the known occurrences from one site to more than 20 and indicate a need for nitrogen enrichment. Also, it appears that Seaside Centipede Lichenis intolerant to heavy salt water spray and that unusually intense storms can cause high mortality. This research provided valuable information and should be continued.
  • In 2003 the Queen Charlotte Islands were surveyed for the presence of Seaside Centipede Lichen, butno thalli were found (Goward 2004). The majority of habitat surveyed was inappropriate and appropriate habitat didn’t appear to support Seaside Centipede Lichen. The investigators postulate that the severe climate is unsuitable for the species. Future surveys should focus on other areas.
  • Kyuquot Sound and the Broughton Archipelago off Vancouver Island were investigated (Wright 2004). Seaside Centipede Lichen was found on Spring Island and an adjacent unnamed island in Kyuquot Sound. No Seaside Centipede Lichen thalli were found in the Broughton Archipelago. Surveys in British Columbia should continue because this species is likely to have a wider range and larger population than currently known.

1.5 Knowledge Gaps

This initial recovery strategy for Seaside Centipede Lichen focuses on conservation of identified Seaside Centipede Lichen sites while research improves our understanding of the range, distribution, life history, and ecology of the species. This section lists several knowledge gaps that must be filled in order to further refine recovery strategy goals in the next planning iteration and improve Seaside Centipede Lichen conservation.

  • It will take several years of further study before the amount of habitat needed to maintain the current population size can be determined.
  • It is not known whether Seaside Centipede Lichen has been significantly affected by human activities or whether its abundance is similar to historic levels.
  • How widespread is Seaside Centipede Lichen in coastal British Columbia? A survey of pre-selected sites on the central mainland coast should be undertaken, including localities used by ground-nesting and tree-nesting birds. Unsurveyed sections of Vancouver Island between Tofino and Nootka Island should also be investigated for Seaside Centipede Lichen occurrences.
  • In order to reassess its endangered status additional study is needed on phenology and ecology of Seaside Centipede Lichen.
  • Can Seaside Centipede Lichen be supported in the long term by localized nodes of enrichment created by perching birds?
  • Several questions basic to the life history of Seaside Centipede Lichen remain unanswered. For example, is nutrient-enrichment required only for the establishment phase of this species, or must an elevated pH be maintained throughout its life? Again, is endogenous nutrient enrichment (nutrient transfer mediated through the roots of trees) sufficient to promote colonization by Seaside Centipede Lichen, or is exogenous enrichment (nutrient transfer from defecating birds, etc.) also required?
  • Further study of Seaside Centipede Lichendistribution within spruce canopies is needed. While recent research indicates that Seaside Centipede Lichen tends to preferentially occupy the lower branches of Sitka Spruce trees, this may be an artifact of sampling. Field studies in 2002 did find occurrences of Seaside Centipede Lichen much higher in the canopy than previously known.
  • Propagating Seaside Centipede Lichen has not been tried.
  • More information is required to determine the relative risk that threats such as severe winter storms, increased frequency and severity of warming and drying events, and human-caused impacts such as firewood collection have on Seaside Centipede Lichen populations.

1 In the discussion on distribution, the term "site" is used to refer to occurrences of H. sitchensis on the scale of a single tree or a few adjacent trees. "Locality" designates an assemblage of more or less neighbouring sites.
2 The assemblage of discrete local populations in an area connected by dispersal or migration.