Exploring the environmental context of recentDidymosphenia geminataproliferation in Gaspésie, Quebec, using paleolimnology

Abstract

Management authorities often perceive Didymosphenia geminata (didymo) as an invasive, nuisance diatom species that has been introduced to eastern Canada; however, observations from early 20th century diatom surveys challenge this characterization. We apply paleolimnological techniques to place recent didymo blooms from Gaspésie, Quebec, into historical and environmental context. Sedimentary diatom assemblages were examined from Lac Humqui (a headwater lake) and Lac au Saumon (a lake with an inflowing river currently supporting blooms). The Lac Humqui assemblage experienced a broad-scale shift in their dominant life strategy with declines in fragilarioid taxa and increases in planktonic diatoms (i.e., CyclotellaDiscostella species) that began ϳ1970 and increased to modern abundances ϳ1990. Strong relationships between this diatom shift and increases in regional air temperatures and earlier river ice-out dates are consistent with longer growing seasons and enhanced thermal stability in Lac Humqui. Didymo was observed throughout the Lac au Saumon core, demonstrating that it has been present in the region since at least ϳ1970. Our paleolimnological evidence indicates that blooms likely form in response to regional consequences of climate warming, rather than human introduction. Résumé :Si les instances d'aménagement considèrent souvent Didymosphenia geminata (didymo) comme une espèce de diatomée envahissante (EEE) introduite dans l'est du Canada, des observations dans le cadre d'études de diatomées depuis le début du 20 e siècle remettent en question cette caractérisation. Nous avons appliqué des techniques de paléolimnologie pour remettre des proliférations récentes de didymo en Gaspésie (Québec) dans leur contexte environnemental historique. Des assemblages de diatomées sédimentaires du lac Humqui (un lac d'amont) et du lac au Saumon (dans lequel se jette une rivière qui supporte actuellement des proliférations) ont été examinés. La stratégie biologique dominante de l'assemblage du lac Humqui a subi un changement à grande échelle, dont une baisse d'abondance de taxons de fragilarioïdes et des augmentations des diatomées planctoniques (c.-à -d. espèces de Cyclotella-Discostella), qui ont débuté vers 1970, leurs abondances modernes ayant été atteintes vers 1990. De fortes corrélations entre cette modification des assemblages de diatomées et l'augmentation des températures de l'air régionales et le devancement des dates de dégel des rivières sont compatibles avec de plus longues périodes de végétation et la plus grande stabilité thermique du lac Humqui. Didymo a été observée dans toute la partie centrale du lac au Saumon, ce qui démontre qu'elle est présente dans la région depuis au moins ϳ1970. Nos observations paléolimnologiques indiquent que les proliférations se forment vraisemblablement en réponse aux conséquences régionales du réchauffement climatique plutôt qu'à l'introduction par les humains. [Traduit par la Rédaction]

Rock snot and lake mud: exploring the history of recent blooms of Didymosphenia geminata using information contained in lake sediments

“…Each species has its own environmental preferences, thus the environmental science Science from the Source diatom assemblage (the collection of species) is highly reflective of its surrounding environment. "Introduced" or "invasive" are problematic designations for microorganisms such as diatoms, including didymo 9 . It has been suggested that random dispersal (i.e.…”

“…Thus, the idea of an invasive diatom species is difficult to confirm, as absence of evidence is not evidence of absence 10,11 . Additionally, it is difficult to establish whether a species is truly absent using conventional sampling methods that may underestimate the presence of rare taxa 9,10,11 . Therefore, determining whether didymo (and other diatom species) can truly be considered "introduced" is challenging 9 .…”

“…Additionally, it is difficult to establish whether a species is truly absent using conventional sampling methods that may underestimate the presence of rare taxa 9,10,11 . Therefore, determining whether didymo (and other diatom species) can truly be considered "introduced" is challenging 9 . However, there is some evidence in reports written by diatomists from the early 20th century who observed this species throughout southern Quebec and New Brunswick 12 , suggesting that didymo may indeed be native to the region.…”

“…The impacts of global climate change on recently reported blooms of didymo in the Gaspésie (as well as other regions) are poorly understood, but are suspected as a potential driver of blooms 9,13 . Didymo blooms may become more frequent under warming condiLavery, Kurek, Rühland, Gillis, Pisaric, Smol Rock snot and lake mud tions because of its ecological optima and tolerances 14 ; however, without long-term monitoring data it is difficult to determine whether the recently observed didymo proliferation is extraordinary in the context of the last ~100 years 15 .…”

“…Paleolimnology examines the physical, chemical and biological remains that are preserved in sediments that accumulate in lake basins and can establish what natural conditions were before, during, and after the onset of human activities ~150 years ago 16 . By investigating the diatom taxa that lived in the lake over the past few hundred years and inferring the environmental conditions the assemblages reflect, we can produce important insights into the triggers of didymo blooms 9,17 . Our study, which was recently published with full scientific details 9 and is summarized again here, examined diatom assemblage changes over time in dated sediment cores from two lakes in the Gaspésie region 9 .…”