Invertebrate diversity in Icelandic freshwater springs

Freshwater springs are thermally stable environments which are largely unaffected by changes in air temperature. They could thus have the potential to buffer rising temperatures and serve as small-scale refugia for aquatic invertebrates in a warming world. To better understand what environmental variables drive invertebrate diversity and community composition, I conducted an extensive field survey on springs in Iceland. Due to rifts in the tectonic plates, large parts of Iceland are of volcanic origin and geothermally active. Thus, a high number of freshwater springs can be found along the edges of the porous lava fields, ranging in temperature from 2°C to boiling hot. Springs also differ in other characteristics, e.g., altitude, spring type, substrate, and vegetation density. I studied the invertebrate community of 49 springs on a spatial scale and followed one of them throughout a year to analyse temporal variability. The most abundant invertebrate groups in Icelandic springs were Chironomidae (Diptera), followed by Ostracoda and Copepoda. One of the main drivers of community composition was temperature, resulting in a distinct species group characteristic for hot springs. Additionally, spring type and geographical position influenced communities. Community composition also differed on a temporal scale within the same spring, with distinctions between summer and winter community. This seasonality in the invertebrate community was unaffected by temperature changes but had implications on the apex predator in the system, Arctic charr. The results of this thesis give some insight into Icelandic spring ecosystems and will contribute to conservation of these unique habitats.Fjölbreytileiki ferskvatnslinda er mikill t.d. hvað hita varðar, allt frá því að vera mjög kaldar og sjóðandi heitar. Þrátt fyrir þennan fjölbreytileika er þó hiti í hverjum og einstökum lindum mjög stöðugur og hafa breytingar í lofthita lítil áhrif á hitastig þeirra. Lindir gætu þannig dregið úr áhrifum af hækkandi hita og þannig myndað skjól, á smáum skala, fyrir ferskvatnshryggleysingja í hlýnandi loftslagi. Til þess að skilja betur hvaða umhverfisbreytur hafa áhrif á fjölbreytileika og samfélagsgerðir hryggleysingja þá framkvæmdi ég umfangsmikla rannsókn á lindum víðsvegar á Íslandi. Vegna flekahreyfinga og mikillar eldvirkni eru stórir hlutar landsins nýlegar bergmyndanir þar sem jarðhiti er algengur. Á jöðrum gegndræpra hrauna má finna mikinn fjölda ferskvatnslinda. Lindir eru einnig breytilegar m.t.t. annarra þátta, t.d. hæðar yfir sjávarmáli, lindargerð, botngerð og þéttleika gróðurs. Ég rannsakaði smádýrasamfélög í 49 lindum víðsvegar um landinu. Einnig fylgdi ég eftir breytingum yfir árið í einni lind, til að rannsaka stöðugleika smádýrasamfélags. Algengasti hópur smádýra í íslenskum lindum voru rykmý (Chironomidae, Diptera), þar næst skelkrabbar (Ostracoda) og árfætlur (Copepoda). Einn mikilvægasti þáttur í að skýra uppbyggingu dýrasamfélaga í lindum var hiti og var sérstakur dýrahópur einkennandi fyrir heitar lindir. Einnig skýrðu lindargerð og landfræðileg staðsetning þeirra mikið af þeim breytileika sem sást í samfélagsgerðum hinna ýmsu linda. Greinilegur breytileiki í samfélagsgerð var að finna milli sumars og veturs og var hann ótengdur breytingum í umhverfishitastigi. Hinsvegar hafði árstíðamunurinn áhrif á mikilvægan afræningja í þeim samfélögum, dvergbleikjuna. Niðurstöður rannsóknarinnar gefa upplýsingar um vistkerfi linda. Auk þess bæta niðurstöður rannsóknarinnar við þekkingu okkar á vistkerfum ferskvatnslinda sem m.a. verður hægt að nýta við hverskyns nýtingu og þ.m.t. verndun þessara einstöku búsvæða

Chironomidae fauna of springs in Iceland: Assessing the ecological relevance behind Tuxen’s spring classification

In 1937, S.L. Tuxen studied the animal community of hot springs in Iceland, and classified springs according to their relative temperature into cold, tepid, and hot. Eighty years after Tuxen’s study, we revisited some of the hot springs in Skagafjörður, Northern Iceland. Our aim was to compare the invertebrate community of 1937 and today, and to assess the stability of hot spring habitats over the years. To test Tuxen’s spring classification on an ecological basis, we furthermore collected chironomid larvae from 24 springs of a broad range of temperature, with samples taken both at the surface area of the spring and at the groundwater level. The chironomid species composition of hot springs differed from that of cold and tepid springs. Whereas Cricotopus sylvestris, Arctopelopia sp., and Procladius sp. characterised the chironomid community in Icelandic hot springs, cold and tepid springs were dominated by Eukiefferiella minor, Orthocladius frigidus and Diamesa spp. Community composition analyses and the exclusive occurrence of taxa in one of the temperature classes validated the ecological relevance of Tuxen’s spring classification for the chironomid species community. Both environmental parameters and invertebrate community of Icelandic hot springs seem to be the same as 80 years ago. Although springs have the potential to provide stable habitats, they are currently under high anthropogenic pressure, and should be increasingly considered in nature conservation.

Chironomidae fauna of springs in Iceland – assessing the ecological relevance behind Tuxen’s spring classification

Publisher's version (útgefin grein)In 1937, S.L. Tuxen studied the animal community of hot springs in Iceland, and classified springs according to their relative temperature into cold, tepid, and hot. Eighty years after Tuxen’s study, we revisited some of the hot springs in Skagafjörður, Northern Iceland. Our aim was to compare the invertebrate community of 1937 and today, and to assess the stability of hot spring habitats over the years. To test Tuxen’s spring classification on an ecological basis, we furthermore collected chironomid larvae from 24 springs of a broad range of temperature, with samples taken both at the surface area of the spring and at the groundwater level. The chironomid species composition of hot springs differed from that of cold and tepid springs. Whereas Cricotopus sylvestris, Arctopelopia sp., and Procladius sp. characterised the chironomid community in Icelandic hot springs, cold and tepid springs were dominated by Eukiefferiella minor, Orthocladius frigidus and Diamesa spp. Community composition analyses and the exclusive occurrence of taxa in one of the temperature classes validated the ecological relevance of Tuxen’s spring classification for the chironomid species community. Both environmental parameters and invertebrate community of Icelandic hot springs seem to be the same as 80 years ago. Although springs have the potential to provide stable habitats, they are currently under high anthropogenic pressure, and should be increasingly considered in nature conservation.Icelandic Research Fund (RANNÍS), grant nr. 141863-051Peer Reviewe

Bacterial diversity in Icelandic cold spring sources and in relation to the groundwater amphipod Crangonyx islandicus

Publisher's version (útgefin grein)Crangonyx islandicus is a groundwater amphipod endemic to Iceland, considered to have survived the Ice Ages in subglacial refugia. Currently the species is found in spring sources in lava fields along the tectonic plate boundary of the country. The discovery of a groundwater species in this inaccessible habitat indicates a hidden ecosystem possibly based on chemoautotrophic microorganisms as primary producers. To explore this spring ecosystem, we assessed its microbial diversity and analysed whether and how the diversity varied between the amphipods and the spring water, and if was dependent on environmental factors and geological settings. Isolated DNA from spring water and from amphipods was analysed using metabarcoding methods, targeting the 16S rRNA gene. Two genera of bacteria, Halomonas and Shewanella were dominating in the amphipod samples in terms of relative abundance, but not in the groundwater samples where Flavobacterium, Pseudomonas and Alkanindiges among others were dominating. The richness of the bacteria taxa in the microbial community of the groundwater spring sources was shaped by pH level and the beta diversity was shaped by geographic locations.This work was supported by the Icelandic Research Council [grant number: 130244-051 to SP and 141863-051 to BKK] and by the doctoral fund at the University of Iceland. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer Reviewe

Distribution of Recent non-marine ostracods in Icelandic lakes, springs, and cave pools

Publisher's version (útgefin grein)Ostracods in Icelandic freshwaters have seldom been researched, with the most comprehensive record from the 1930s. There is a need to update our knowledge of the distribution of ostracods in Iceland as they are an important link in these ecosystems as well as good candidates for biomonitoring. We analysed 25,005 ostracods from 44 lakes, 14 springs, and 10 cave pools. A total of 16 taxa were found, of which seven are new to Iceland. Candona candida (Müller, 1776) is the most widespread species, whereas Cytherissa lacustris (Sars, 1863) and Cypria ophtalmica (Jurine, 1820) are the most abundant, showing great numbers in lakes. Potamocypris fulva (Brady, 1868) is the dominant species in springs. While the fauna of lakes and springs are relatively distinct from each other, cave pools host species that are common in both lakes and springs. Icelandic non-marine ostracods include mostly generalist species, as well as species adapted to cold climates and resemble those of other north European countries while sharing very few species with the North American Arctic. Iceland is experiencing impacts from climate change and a booming tourism. It is possible to use selected freshwater ostracods as biomonitoring tools by constructing a detailed database of these species.Many thanks to the University of Iceland Research Fund and Watanabe Trust Fund for providing financial assistance that made this project possible. We thank Doriane Combot for kindly providing the ostracod samples from cave pools, and all the staff at the Natural History Museum of Kópavogur that provided assistance with the sampling over the years. We are also thankful to the reviewers for their valuable insight and comments that helped this research reach a higher quality. The authors declare no competing financial interests.Peer Reviewe

Seasonal variation in the invertebrate community and diet of a top fish predator in a thermally stable spring

Many life-history events in aquatic invertebrates are triggered by seasonal changes in water temperature, but other ecological factors may be important as well. To rule out the confounding effects of changing water temperature, we studied the seasonal dynamics of an aquatic invertebrate community and their effect on a top fish predator in a thermally stable freshwater spring in South Iceland. We sampled benthic invertebrates five times over a year and conducted a mark-recapture study on the top predator in the system, small benthic Arctic charr, Salvelinus alpinus (L.). We assessed variation in diet composition and feeding preferences by calculating the electivity and individual specialisation of each fish at each sampling time. There was a clear separation of winter and summer communities for the benthic invertebrates. The variation in prey availability was also reflected in the fish diet, with higher feeding selectivity in summer than in winter for the highly abundant Chironomidae larvae. In contrast, individual specialisation as a measure of intrapopulation niche variation was higher in winter when prey availability was lower. We furthermore found that groundwater amphipods might play an important role in the winter diet of spring-dwelling Arctic charr. In conclusion, seasonal variation in the invertebrate community is an important factor to consider and has the potential to alter the phenotype (e.g. growth rates) and behaviour (e.g. feeding preferences) of higher trophic levels

Small Islands, Small Ponds, Small Communities—Water Beetles and Water Boatmen in the Faroe Islands

Water beetles of the families Dytiscidae and Haliplidae (Coleoptera) as well as water boatmen (Heteroptera: Corixidae) are well-studied groups in Northern Europe. In the Faroe Islands, their diversity is much lower than in the British Isles and Fennoscandia. Here, we first describe the communities of water beetles and water boatmen in Faroese ponds and, secondly, assess whether community compositions are driven by habitat characteristics or dispersal abilities of species. To this end, we sampled 57 ponds, ranging between <50 m2 and >50,000 m2. Environmental variables such as pond size, temperature, pH, and depth were measured, and distance to nearest neighboring pond was calculated as a measure of isolation. The sampling yielded 1522 individuals of eight species, with species richness of the ponds ranging between zero and six. Pond size (shoreline length) did explain differences in community composition, whereas water depth explained differences in diversity indices with lower diversity in deeper ponds. We found species-specific relations between abundance and shoreline length, e.g., H. fulvus and H. palustris being restricted to larger ponds. Lastly, water beetle and water boatmen communities in Faroese ponds are discussed in the light of island biogeography and species distributions in the North Atlantic islands