Disappearing Kilimanjaro snow—Are we the last generation to explore equatorial glacier biodiversity?

Abstract Glaciation accompanied our human ancestors in Africa throughout the Pleistocene. Regrettably, equatorial glaciers and snow are disappearing rapidly, and we are likely the last generation who will get to know these peculiar places. Despite the permanently harsh conditions of glacier/snow habitats, they support a remarkable diversity of life ranging from bacteria to animals. Numerous papers have been devoted to microbial communities and unique animals on polar glaciers and high mountains, but only two reports relate to glacial biodiversity in equatorial regions, which are destined to melt completely within the next few decades. Equatorial glaciers constitute “cold islands” in tropics, and discovering their diversity might shed light on the biogeography, dispersal, and history of psychrophiles. Thus, an opportunity to protect biota of equatorial glaciers hinges on ex situ conservation. It is timely and crucial that we should investigate the glacial biodiversity of the few remaining equatorial glaciers.

Historically, glaciers have been considered sophisticated parts of our natural landscape, space for explorers, recreation, and a symbol of the wilderness (Carey, 2007). Currently, however, glaciers and ice sheets are considered natural hazards as contributors to sea-level rise and an economic threat due to shrinking of frozen freshwater reservoirs (Beniston, Stoffel, & Hill, 2011). For biologists, glaciers were once considered unproductive and sterile, but in the last few decades, this view has been fully reversed with discoveries of extremophilic glacier organisms across the domains of life (Edwards et al., 2014;Shain et al., 2016;Takeuchi, Kohshima, Yoshimura, Sekto, & Fujita, 2000;Zawierucha et al., 2015). Although glacial organisms (e.g., algae, invertebrates) were first observed in the 19th century (Drygalski, 1897), glaciers as an important ecological habitat remained forgotten since that time (Hodson et al., 2008). Abiotic views of glaciers as simply water in a frozen state have evolved into peculiar biomes, differing from polar and high mountain ecosystems by unique organism assemblages, topographic features, and climate (Anesio & Laybourn-Parry, 2012). Although glaciers have been a particular focus of polar biologists, ecologists, and biochemists over the past two decades (Bagshaw et al., 2013;Cook et al., 2016;Dial, Ganey, & Skiles, 2018;Takeuchi et al., 2000), we emphasize that equatorial glacier habitats, biodiversity, and ecosystems remain mostly unexplored (Uetake et al., 2014;Zawierucha, Gąsiorek, et al., 2018). We identified marginal knowledge on equatorial glacier biodiversity using search engines such as Scopus, Web of Science, and literature published herein. We supported our investigation using Google scholar. Using a set of keywords related to glacial ecosystems (Table 1), we revealed that this knowledge is almost nonexistent in comparison with tropical, mountain, and polar glaciers. Even though some data on equatorial ice are hidden under the term tropical (Kuja et al., 2018;Zawierucha, Gąsiorek et al., 2018), still knowledge of equatorial glaciers is limited. Certainly, as shown in Table 1, a number of published studies correlate with the area of glaciation.
Even though equatorial glaciers are small (i.e., playing marginal roles in global cycles in comparison with polar ice caps, perhabs influencing small scientfic interests), due to their high speed of melting and their unique location, they should be studied urgently. Nonetheless, it seems their existence was and still is forgotten. Jan Carstenszoon, a Dutch explorer who visited New Guinea in 1623, reported on the existence of Puncak Jaya snow to citizens of the old continent, which was ridiculed by those who were skeptical about glaciers in the tropics. Since then, equatorial glaciers have been mostly neglected in the biological sciences and are mostly within the scope of glaciologists (Kaser et al., 2010;Milner et al., 2017;Thompson, Brecher, Mosley-Thompson, Hardy, & Mark, 2009;Thompson et al., 2011). Importantly, these aggregations are home to numerous microorganisms, and the inevitatble loss these glaciers (located at Rwenzori Mountains) will lead to the loss of this unique habitat. Subsequently, Zawierucha, Gąsiorek, et al. (2018) discovered rotifers and tardigrades in GMGA and described a new tardigrade species, Adropion afroglacialis (and another identified to the genus level, Figure 2), emphasizing the need for equatorial glacial biodiversity conservation.
Additionally, Kuja et al. (2018) and Nedbálova & Sklenár (2008) studied snow packs on Mount Kenya and Ecuador respectively, emphasizing the extinction threat of cold-adapted microbes. However, as on glaciers of polar, alpine and third pole regions, scientists should expect more species of metazoans on and in the vicinity of equatorial glaciers, together with novel species of primary producers and bacteria. Glaciers worldwide as supraglacial ecosystems encompass habitats like streams, lakes, cryoconite holes (water-filled reservoirs on glacier surfaces), weathering crusts, glacier mice (moss balls), dirt cones, and tills (Cook et al., 2016;Coulson & Midgley, 2012;Franzetti et al., 2017;Hodson et al., 2008; Figure 3). Parts of equatorial glaciers covered by perennial snow also may constitute viable habitats based on recently discovered distinct TA B L E 1 Results of search in scientific browsers Scopus and WoS (Web of Science) using titles, abstracts, keywords, and topic of papers in relation to ecosystems on glaciers (Accessed on 09. a Alpine refers to the type of polar and high mountain glaciers. b Cryoconite is dark sediment on the glacier surface (from ancient Greek "kryos"-cold and "konis"-dust, Nordenskiöld (1875)) comprising mineral particulate matter of local and remote origin, including organic compounds, bacteria, algae, fungi, which in turn support protozoans and invertebrates.

F I G U R E 2 Water bears (Tardigrada)
found on disappearing Ugandan glacier.
(scale bar given in micrometers)
Moreover, glacial ecosystems include not only supraglacial environments, but also englacial and subglacial channels which, despite much research in polar regions, remains enigmatic, yet inhabited by diverse microbial communities (Achberger et al., 2017). In equatorial zones, these habitats are more speculatory than empirically recognized. To date, only GMGA and snow have been described, while other potential habitats remain undiscovered.
Knowledge Unfortunately, the story of equatorial glaciers is quickly coming to an end before its scientific inquiry has really begun-important scientific data are literally melting away. Melting ice and snow packs in Antropocene is not only triggered by temperature, but in tropical regions is more complex due to the effects of deforestation, influencing rain, and atmospheric humidity (Basantes-Serrano et al., 2016;Kaser et al., 2010;Klein & Kincaid, 2006;Mölg, Rott, Kaser, Fischer & Cullen, 2006;Thompson et al., 2009). Most of glaciers on Kilimanjaro (Figure 4 A-B) will most likely disappear within 25 years, while small glaciers in New Guinea near the Puncak Jaya peak will last only a few more decades (Thompson et al., 2009(Thompson et al., , 2011; the Ugandan glacier probably will be gone in <5 years (Mölg et al., 2006;Taylor, Mileham, Tindimugaya, Majugu, Muwanga, & Nakileza, 2006). Fairing slightly better are South American glaciers, although those proximal to the Equator are melting very quickly (Thompson et al., 2011). For example, the glaciers on Antisana volcano in Ecuador, a few degrees south of the Equator, will survive <50 years (Basantes-Serrano et al., 2016).
Strong fluctuations in equatorial ice cover occurred during the late Pleistocene and early Holocene (Downie, 1964;Kaser et al., 2010;Mark & Osmaston, 2008;Thompson et al., 2009) these glaciers before mass extinctions. As keystone species, these glaciers support the existence of cold streams, which are home for unique assemblages of plants and animals, and also plants and animals on glaciers (Milner et al., 2017;Zawierucha, Gąsiorek, et al., 2018). Finally, as flagship species, these glaciers increase awareness about the loss of ice ecosystems, the most visible changes of natural ecosystems on Earth and their unknown biodiversity at the Equator; thus, equatorial glaciers serve as a last endangered endemic species.
The prediction of a changing global climate mobilized world leaders in 1992 to reverse these warming trends, leading to an international environmental treaty "United Nations Framework GBO 1 highlights the opportunity of ex situ conservation. Such examples include seed banks (in glacial communities the equivalent are ice core banks) as well as organizations which store biological materials for analysis. Taking into account that the species extincton rate is 100-1,000 higher than before human existence (Pimm, Russel, Gitleman, & Brooks, 1995), it is undisputable that propa-  (Martin & McMinn, 2018), but it is alarming that we forget about the last glaciers which we can explore in our home, on Earth.

ACK N OWLED G M ENTS
We thank two anonymous reviewers for their valuable comments that improved the manuscript. Studies on glacial biota were supported by National Science Center grant no. NCN 2013/11/N/ NZ8/00597 to K.Z. We would like to thanks Jun Uetake and Elżbieta Wiejaczka for sharing of picture of Rwenzori and Kilimanjaro glaciers, and Witold Szczuciński for discussion on equatorial glaciers.

CO N FLI C T O F I NTE R E S T
None declared.

AU TH O R CO NTR IB U TI O N S
KZ conceived the study, wrote the manuscript, and revised and edited the manuscript. DS contributed to the text and revisions.

DATA ACC E S S I B I L I T Y
Data sharing is not applicable to this article as no new data were created or analyzed in this study.