Caloplaca maculata – Collected from type locality, south of Waitangi Wharf, Chatham Islands. Image: Allison Knight

The unexpected near demise of Caloplaca maculata from the Chatham Islands

The Chathams Islands group are the eastern-most expression of the New Zealand archipelago. Opinions vary as to the age of the current islands; geological evidence suggests that the current surface expression is anywhere from 2–3 million years old (Holt 2008) but the DNA evidence, based on molecular clock inferences indicates that some of the island groups biota is much older than this (Heenan et al. 2010). Some biologists, favour an island hoping theory, namely that there has always been land in the approximate location of the current islands for at least six million years, meaning that past islands as they eroded away have been augmented or replaced by new land resulting from fresh uplift and / or ongoing volcanic activity. On this issue though the jury is still out.

What is clear is that the isolation of the Chathams group has resulted in the usual features of remote island biota, low species diversity coupled with high endemicity. For example, of the 460 or so plants regarded as indigenous to the islands, over 40 are endemic, including, at least for now, one monotypic genus, Myosotidium, known to the world as the ‘Chatham Island forget-me-not’ (de Lange et al. 2011). That species, along with the endemic black robin (Petroica traversi) are widely regarded as the quintessential international icons of Chatham Island biodiversity.

While our knowledge of the macro-fauna (birds, fish and reptiles especially) and flora (clubmosses, ferns, flowering plants, and bryophytes (hornworts, liverworts and mosses) is fairly good, little is known about the islands fungi (mycobiota) diversity. Literally a handful of fungi (five taxa) have been described as endemic to the island (de Lange 2012), and one lichenized mycobiont, Lecanora kohu described in 2017 ‘maybe’ endemic (Printzen et al. 2017).

While a comprehensive account of the mycobiota of the Chathams is lacking, since 2007, I have been collating a checklist of the lichens of the island group. In this endeavour I was encouraged by the late Dr David Galloway (1942–2014), who was in effect the ‘Father of New Zealand Lichenology’ and his friend, Dr Peter Johnson, who collected Chatham lichens for David during his time on the Chatham Island Conservation Board, and then as a tour group leader. One of Peter’s early Chatham lichen discoveries, Caloplaca maculata was made from the main island, Rekohu (Chatham) ‘just W[est] of Waitangi wharf, Ellice Point, on coastal rock, on [a] ledge of tuff on headland’ (Galloway 2004). At the time it was described David cautiously suggested C. maculata might be endemic to the islands.

Caloplaca maculata near Ellice Point
Fig. 1. Caloplaca maculata as seen in November 2008. The white cracked thallus and bright orange fruiting bodies enable easy field recognition of this species on the Chatham Islands.

Keen to see this lichen and to ascertain its conservation status, I, accompanied by Department of Conservation officer Ben Horne visited the type locality near Ellice Point on 2 December 2008. The lichen was easy to find as it is a distinctive species with a cracked white thallus and orange apothecia (dish-shaped fruiting bodies) located in a remarkably well defined, singular habitat. Namely a shelf of palagonitic tuffaceous rock known as the ‘Red Bluff tuff’ which is about 3 m above sea level and which juts out from a shore platform beneath a large sea cliff. There within an estimated area of 6m2 of more or less exposed palagonitic tuff that forms a narrow shelf we found that Caloplaca maculata was abundant. Sparse associates included a range of buelloid lichens (Amandinea, Buellia spp.), other Caloplaca species and Dufourea ligulata. Above the exposed tuff is a colluvial apron derived from erosion of the cliff face which is comprised of friable, loose tephra sequences, that continually erode and slide down to partially envelope the tuff shelf. In 2008 that apron was densely covered in a thick turf of Chatham Island ice plant (Disphyma papillatum), Dichondra brevifolia, with patches of Chatham Island sow thistle (Sonchus (Embergeria) grandifolius), Chatham Island geranium (Geranium traversii) and tussocks of Festuca coxii. As noted, the habitat is ‘remarkably singular’ by which I mean I could not find comparable habitat along the coastline for about one kilometre either way but being pressed for time I didn’t do then, and still haven’t done since a more comprehensive survey. From a conservation view point, based on the then known extent of the lichen population, well below one hectare, the species easily qualified as ‘Threatened / Nationally Critical’ (Townsend et al. 2008) and it was initially rated as such when the New Zealand Lichen Threat Listing Panel met in November 2009 to undertake New Zealand’s first ever lichen threat assessment (de Lange et al. 2012). However, in an interesting twist in early 2012 Caloplaca expert Dr Ulrik Søchting from Copenhagen, Denmark, accompanied by Dunedin-based lichenologist Dr Allison Knight discovered C. maculata on a coastal rock outcrop at the mouth of Akatore River, south of Dunedin, South Island (de Lange 2012). This late discovery, bolstered by the assumption that the Chatham and Akatore locations of Caloplaca maculata were ‘secure’ prompted the lichen panel to change the threat assessment for this species to ‘At Risk / Naturally Uncommon’ qualified DP [Data Poor], RR [Range Restricted], Sp [Sparse] (de Lange et al. 2012). That is where the story stopped until 15 November 2018, nearly 10 years after I had last seen Caloplaca maculata at Ellice Point, Rekohu (Chatham Island). On that day having just flown in to the island for a Conservation Board meeting the next day, I decided I would visit the Caloplaca site to see how it was faring. What I saw shocked me.

The type locality was still recognisable on the basis of the distinctive geology, and that the colluvial apron was still covered in the thick turf and coastal herb field of Chatham Island endemics that I had noted in 2008. However, the lichen had declined by an estimated 98%. Why I am still not clear but I speculate that the decline may have been caused by storm damage / wave wash, as the location is only 3 metres above a very active and exposed coastline. When this decline happened and whether it is was still ongoing are critical issues for which I don’t have answers. Irrespective, the situation, at least based on what is known of this species on the Chatham Islands is now serious. As such I made another visit to the site on 5 May 2019. The situation was even worse. The previous dense coastal turf and herb field that kept the colluvium above the lichen habitat in check had completely vanished. The reason I assume, was that one or more sheep (Ovis aries) had fallen off the unfenced cliff tops above the site, and being trapped on the ledge forced to eat every scrap of vegetation – whether the animal (animals) were rescued or eventually died I don’t know, what I do know is that during this enforcement entrapment the entire ledge was drowned in an avalanche of sheep droppings. Patient searching found two patches of Caloplaca maculata, the largest of which was 15 mm diameter. Based on what we know of this lichen it is now nearly extinct on the Chatham Islands.

As a post-script to that, during a week-long August 2019 field trip to Rekohu (Chatham Island) with the University of Waikato and Unitec Institute of Technology, School of Environment & Animal Sciences, I made another visit to the Caloplaca type locality. Mercifully the situation had not changed since May 2019, patient searching found the same two lichen patches. Regeneration of the coastal turf and herb field had not as yet commenced.

These discoveries highlight a range of issues. Obviously, the near extinction of Caloplaca maculata on Rekohu (Chatham Island) remained unknown, until a series of unplanned for events came into play, namely I, who knew the lichen, was appointed to the Chatham Island Conservation Board in July 2018, and in November of that year I had the time to visit the type locality. Prior to November last year it would seem that nobody who knew the lichen existed had done so, or if they had, reported on its status. That this happened should not surprise people. Very few people in New Zealand proper let-alone the Chatham Islands know how to identify lichens. Further the discovery came too late for the current threat assessment of New Zealand lichens which was completed in August 2018, and where the previous threat assessment of Caloplaca maculata (‘At Risk / Naturally’ DP, RR, Sp) was confirmed in the absence of any more recent information than the 2008 assessment (de Lange et al. 2018). This highlights the importance of obtaining trend and population data; data that one could argue should have been obtained by monitoring. Again, it is easy to blame those responsible for managing New Zealand indigenous biodiversity but who honestly has ever conducted a species-specific long-term lichen monitoring programme in this country and published on it?

 Caloplaca maculata as seen in November 2018. Note deeply cracked weather thallus and paucity of fruiting bodies (apothecia) – not a happy lichen colony anymore!
Caloplaca maculata as seen in November 2018. Note deeply cracked weather thallus and paucity of fruiting bodies (apothecia) – not a happy lichen colony anymore!

This story also highlights the ongoing problem of providing accurate threat assessments for cryptic taxa. Just focusing on lichens, beyond the obvious question of how do you define an individual, the lack of population and trend data is a serious impediment to accurate threat assessments. This in part explains why just 16 (0.7%) New Zealand lichens out of a possible 2026 have been assessed as ‘Threatened’ and why 1108 (54%) of our lichen mycobiota remains assessed as ‘Data Deficient’. Critically if one looks at the 16 ‘Threatened” lichens, only one Ramalina pollinaria is not qualified ‘Dp’ [Data Poor] which means that the panel has some population trend data on which to base its claim of ‘Threatened’. In this case Ramalina pollinaria does seem to be a very uncommon lichen, known (to the best of New Zealand lichenologists abilities) from just two sites, one in serious, though still only opportunistically monitored decline.

On the positive, two threat assessments for New Zealand lichens have now been completed (de Lange et al. 2012; de Lange et al. 2018). These lists provide a reference point for conservation effort and research, as well as the best statement to the world of the extent of our nations lichen diversity. That we can do better is obvious but it is pleasing to see more people taking note of lichens and actively trying to put names on what they see. This is a critical step toward initiating targeted research into lichen ecology, their use as bioindicators, economic and cultural values and designing realistic conservation programmes.

However, for Caloplaca maculata, least ways on the Chatham Islands, all we can do is hope that further populations will be found, and that the one at Ellice Point recovers. In favour of further discoveries is that the substrate the lichen occupies is widespread, though much of it is inaccessible without a boat, a kind tide or without abseiling. So, we really don’t know if the Ellice Point site is the only Chatham Island occurrence. I doubt it. because, with few exceptions, Chatham Island endemic plants if the habitat is present, will be there; they have also proved to be remarkable resilient. If sites are fenced and adequate possum and weed control is undertaken, they tend to thrive. While lichens are not plants the same situation seems to apply if our experience of Lecanora kohu, the other tentative lichen endemic, is anything to go by. That species was initially known from two specimens collected in 2015 from Hokorereoro / Rangatira / South East Island (Printzen et al. 2017) but since 2018 it has been found in a further seven locations on Rekohu (Chatham Island) at all of which it is locally common. Hopefully, someone will find the same good news for Caloplaca maculata on the islands and perhaps also in New Zealand.

References

de Lange, P.J. 2012: Sole Chatham Islands endemic lichen discovered on south Otago Coastline – Natural Heritage. Chatham Islands, New Zealand. https://chathams.co.nz/ (website accessed: 4 September 2019)

de Lange, P.J.; Heenan, P.B.; Rolfe, J.R. 2011: Checklist of vascular plants recorded from the Chatham Island Islands. Department of Conservation, Wellington. 57pp.

de Lange, P.J.; Galloway, D.J.; Blanchon, D.J.; Knight, A.; Rolfe, J.R.; Crowcroft, G.M.; Hitchmough, R. 2012: Conservation status of New Zealand lichens. New Zealand Journal of Botany 50: 303–363.

de Lange, P.J.; Blanchon, D.J.; Knight, A.; Elix, J.; Lücking, R.; Frogley, K.M.; Harris, A.; Cooper, J.A.; Rolfe, J.R. 2018: Conservation status of New Zealand lichens and lichenicolous fungi, 2018. New Zealand Threat Classification Series 27: 1–64.

Galloway, D.J. 2004: New lichen taxa and names in the New Zealand mycobiota. New Zealand Journal of Botany 42: 105–120.

Heenan, P.B.; Mitchell, A.D.; de Lange, P.J.; Keeling, J.; Paterson, A.M. 2010: Late Cenozoic origin and diversification of Chatham Islands endemic plant species revealed by analyses of DNA sequence data. New Zealand Journal of Botany 48: 83–136.

Holt, K.A. 2008: The Quaternary History of Chatham Island, New Zealand. Unpublished PhD. Massey University, New Zealand. 243p.

Printzen, C.; Blanchon, D.J.; Fryday, A.M.; de Lange, P.J.; Houston, D.M.; Rolfe, J.R. 2017: Lecanora kohu, a new species of Lecanora (Lichenized Ascomycota: Lecanoraceae) from the Chatham Islands, New Zealand. Submitted: New Zealand Journal of Botany 55: 439–451.

Townsend, A.J.; de Lange, P.J.; Norton, D.A.; Molloy, J.; Miskelly, C.; Duffy, C. 2008: The New Zealand Threat Classification System manual. Wellington, Department of Conservation.