Inferring the occurrence of regime shifts in a shallow lake during the last 250 years based on multiple indicators

Regime shifts are ecosystem-scale phenomena. In lake studies, most supporting evidence is frequently based on a single state variable. We examined the sediment record of the shallow lake Blanca Chica (Argentina) to explore the response of multiple proxies belonging to different trophic levels (nutrients, chlorophyll and carotenoid pigments, diatoms, Cladocera remains, and Rotifera resting eggs) over the last 250 yr. We explored different ecological indicators to assess changes consistent with regime shifts. To do so, first we identified the timing of transitional periods on multiple-proxies. Then, we explored (1) the nature of the change (linear versus non-linear dynamics), (2) different indicators of a shift across the food web: multimodality and resilience indicators (standard deviation and autocorrelation), and (3) examined the synchronicity of the detected indicators at multiple-trophic levels. Generalized additive models fitted to the ordination scores of the assemblages analyzed revealed two transitions: ca. 1860–1900, and 1915–1990. Ecological indicators of regime shifts revealed that the first transition is consistent with a threshold state response (change in the ecosystem state manifest as a jump when the driver exceeds a state threshold), and the second one with a critical transition (hysteretic transition in which the system change to an alternate stable state). After the first transition lake structure shifted from littoral to pelagic species dominance (evidenced by Cladocera and diatom assemblages), and turbidity increased, indicating a rise in lake water level. This transition was non-linear, showed multimodality, and is most likely driven by an increase in precipitation registered in the region since 1870. During the second transition, nutrient levels rose, all indicators showed multimodality, non-linear dynamics and an increase in standard deviation prior to the regime shift. These dynamics are consistent with a critical transition in response to eutrophication, and coincides with a post-1920 change in land use. Our results show that several ecological indicators of regime shifts need to be examined to perform an accurate diagnosis. We highlight the relevance of a multi-proxy approach including multiple-trophic level responses as the appropriate scale of analysis to determine the occurrence, type and dynamics of regime shifts. We also show that resilience indicators and critical transitions can be detectable in the whole food web and that shallow lakes can undergo different types of regime shifts.Fil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Musazzi, Simona. Consiglio Nazionale delle Ricerche; ItaliaFil: Cordoba, Francisco Elizalde. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mendiolar, Manuela. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Lami, Andrea. Consiglio Nazionale delle Ricerche; Itali

Changes in planktivory and herbivory regimes in a shallow South American lake (Lake Blanca Chica, Argentina) over the last 250 years

Shallow lakes are vulnerable ecosystems impacted by human activities and climate change. The Cladocera occupy a central role in food webs and are an excellent paleoecological indicator of food web structure and trophic status. We conducted a paleolimnological study in Lake Blanca Chica (Argentina) to detect changes on the planktivory and herbivory regimes over the last 250 years. Generalized additive models were fitted to the time series of fish predation indicators (ephippial abundance and size, mucrone size, fish scales, and the planktivory index) and pheophorbide a concentration. The cladoceran assemblage changed from littoral-benthic to pelagic species dominance and zooplankton switched from large-bodied (Daphnia) to small-bodied grazers (Bosmina) ca. 1900 due to increased predation. The shift in planktivory regime (ca. 1920-1930), indicated by fish scales and the planktivory index, as well as herbivory (ca. 1920-1950), was triggered by eutrophication. Changes in planktivory affected the size structure of Bosmina, reducing its body size. This study describes the baseline for the lake as well as the profound changes in the composition and size structure of the zooplankton community due to increased predation and the shift in the planktivory regime. These findings will provide a reference status for future management strategies of this ecosystem.Fil: Carrozzo, David Ricardo. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología; ArgentinaFil: Musazzi, Simona. Consiglio Nazionale delle Ricerche; Italia. Water Research Institute; ItaliaFil: Lami, Andrea. Consiglio Nazionale delle Ricerche; Italia. Water Research Institute; ItaliaFil: Cordoba, Francisco Elizalde. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Cambios en el patrón de herbivoría y en la talla corporal de cladóceros en la Laguna Blanca Chica (Olavarría) en los últimos 200 años

La estructura y dinámica de las comunidades y poblaciones de los lagos se ven afectadas por procesos como la depredación y la herbivoría. En la Laguna Blanca Chica (Olavarría) se llevó a cabo un estudio paleolimnológico cuyo objetivo fue establecer la ocurrencia de cambios en la talla media de restos subfósiles de cladóceros y en la concentración del feofórbido a en los últimos 200 años. La concentración del feofórbido a aumentó entre A. D. 1903-1953; en consecuencia, se infiere un cambio en el patrón de herbivoría. La disminución del tamaño del mucrón en Bosmina huaronensis (Cladocera) (A. D. 1910-1940) indica un cambio en la presión de depredación en el sistema o de tipo de depredador. Los cambios en la talla de los efipios no reflejarían cambios en la presión de depredación, por lo tanto no constituirían un buen indicador en la reconstrucción de la planctivoría en este ambiente.Fil: Carrozzo, David Ricardo. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Musazzi, Simona. Centre National de la Recherche Scientifique; FranciaFil: Lami, Andrea. Centre National de la Recherche Scientifique; FranciaFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaX Congreso de Ecología y Manejo de Ecosistemas Acuáticos PampeanosTandilArgentinaInstituto de Hidrología de Llanuras "Dr. Eduardo Jorge UsunoffInstituto Multidisciplinario Sobre Ecosistemas y Desarrollo Sustentabl

Increases in Picocyanobacteria Abundance in Agriculturally Eutrophic Pampean Lakes Inferred from Historical Records of Secchi Depth and Chlorophyll-a

Phytoplankton size structure has profound consequences on food-web organization and energy transfer. Presently, picocyanobacteria (size < 2µm) represent a major fraction of the autotrophic plankton of Pampean lakes. Glyphosate is known to stimulate the development of picocyanobacteria capable of degrading the herbicide. Due to the worldwide adoption of glyphosate-resistant crops, herbicide usage has increased sharply since the mid-1990s. Unfortunately, there are very few studies (none for the Pampa region) reporting picocyanobacteria abundance before 2000. The proliferation of µm sized particles should decrease Secchi disc depth (ZSD). Therefore ZSD, conditional to chlorophyll-a, may serve as an indicator of picocyanobacteria abundance. We use generalized additive models (GAMs) to analyze a "validation" dataset consisting of 82 records of ZSD, chlorophyll-a, and picocyanobacteria abundance from two Pampean lakes surveys (2009 and 2015). In support of the hypothesis, ZSD was negatively related to picocyanobacteria after accounting for the effect of chlorophyll-a. We then fitted a "historical" dataset using hierarchical GAMs to compare ZSD conditional to chlorophyll-a, before and after 2000. We estimated that ZSD levels during 2000-2021 were, on average, only about half as deep as those during 1980-1999. We conclude that the adoption of glyphosate-resistant crops has stimulated outbreaks of picocyanobacteria populations, resulting in lower water transparency.Fil: Zagarese, Horacio Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Diovisalvi, Nadia Rosalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Izaguirre, Irina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Fermani, Paulina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Unrein, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Castro Berman, Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Pérez, Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin

Habitat complexity in shallow lakes and ponds: importance, threats, and potential for restoration

In this review we describe patterns and mechanisms by which habitat complexity is crucial for the functioning of shallow lakes and ponds, and for the abundance and diversity of biological communities in these ecosystems. Habitat complexity is affected by processes acting at different spatial scales, from the landscape to the ecosystem level (i.e., morphometric attributes) that generate different complexities, determining the potential for organisms to succeed and processes to occur, such as energy and nutrient transfer, and fluxes of greenhouse gases, among others. At the local scale, the three major habitats, pelagic, littoral, and benthic, are characterised by different degrees of structural complexity and a particular set of organisms and processes. Direct and indirect effects of changes in within-lake habitat complexity can either hinder or promote regime shifts in these systems. We also review several anthropogenic pressures (eutrophication, urbanisation, introduction of exotic species, and climate change) that decrease lake resilience through changes in habitat complexity and strategies for habitat complexity restoration. Overall, we emphasize the need to preserve and/or restore habitat complexity as key challenges to account for ecosystem integrity, maintenance of local/regional biodiversity, and for the provision of crucial ecosystem services (e.g., biodiversity, self-purification, and carbon sequestration).Fil: Meerhoff, Mariana. Universidad de la Republica; UruguayFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

The trophic role of Cyphocharax voga (Hensel 1869) according to foraging area and diet analysis in turbid shallow lakes

Detritivory is a widespread strategy that has been associated with shallow, warm and productive systems. Eutrophic and hypereutrophic lakes can be dominated by an assemblage of detritivorous fish species. The trophic role of the pelagic fish Cyphocharax voga in two temperate turbid shallow lakes was analyzed through the study of its diet and foraging area. The results showed that C. voga consumed detritus, zoobenthos and zooplankton (95.77 %, 4.11 % and 0.12 % of total ash free dry mass ingested, respectively). Benthic invertebrates were the most abundant organisms ingested, representing 93 % of the total biomass. In particular, Leydigia louisi, ostracods and harpacticoid copepods contributed most in abundance and biomass. Pelagic prey, represented mainly by Bosmina (Neobosmina) huaronensis, constituted 7 % of the total biomass consumed by fish. Prey availability was determined in the open and littoral areas and in the lake bottom. C. voga showed a selectivity for crustaceans from the lake bottom. This evidence and the high consumption of detritus indicate that C. voga is exploiting the benthic food web. Thus, this fish can be considered a detritivorous species. This strategy seems suitable in turbid lakes (20 – 30 cm Secchi disc depth) where prey detection for visual predators is constrained. Moreover, as C. voga attains a high biomass in warm temperate eutrophic shallow lakes of South America, it might be contributing to the linkage of benthic and pelagic pathways, and detritus and benthic invertebrates may provide a subsidy for the pelagic food web.Fil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Ferrero, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Eutrofización por exeso de nutrinetes en lagos de zonas agrícolas: de la limitación por luz a la limitación por CO2

La eutrofización de lagos y ríos representa un problema global, particularmente intenso en zonas agrícolas. El aumento de la carga de nutrientes (nitrógeno y fósforo) es un proceso constante y generalizado. Las altas tasas de crecimiento de fitoplancton provocan aumento de la biomasa, limitación por luz por autosombreado, disminución de la concentración de CO2, y eventualmente limitación por carbono inorgánico (Flynn and Raven, 2016). Hasta hace unas pocas décadas, la limitación de la biomasa fitoplanctónica por CO2 se consideraba una situación extremadamente inusual. Hoy se sabe que los lagos eutróficos de zonas agrícolas a menudo presentan concentraciones de CO2 inferiores a las de equilibrio(sub-saturación) (Balmer and Downing, 2011). Pero no se cuenta con un criterio que permita identificar la limitación de la biomasa fitoplanctónica por carbono inorgánico. En este trabajo evaluamos (1) en primer lugar, la frecuencia de sub-saturación en lagunas pampeanas. Encontramos que la sub-saturación es mucho más frecuente(anual 34%, verano 44%) que lo reportado para el promedio mundial (fuertemente sesgado hacia lagos templados, profundos de zonas boscosas); (2) en segundo lugar, analizamos bases de datos de largo término de 8 lagos hiper-eutróficos de Europa, América del Norte y del Sur, Asia y Nueva Zelanda, utilizando Modelos Aditivos Generalizados (GAMs) para describir las tendencias de [CO2] alo largo de tres variables forzantes: radiación solar incidente, profundidad del lago, y concentración de clorofila. En general se observó que [CO2]disminuye con la irradiancia incidente y la clorofila, y aumenta con la profundidad del lago; (3) finalmente, el análisis de los patrones de clorofila vs irradiancia y de [CO2] vs irradiancia nos permitió desarrollar un criterio de diagnóstico y, por primera vez, obtener evidencia de limitación de la biomasa fitoplanctónica por carbono a partir de observaciones de campo.Fil: Zagarese, Horacio Ernesto. Universidad Nacional de San Martin. Instituto Tecnologico de Chascomus. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - la Plata. Instituto Tecnologico de Chascomus.; ArgentinaFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaV Reunión del Grupo Argentino de FotobiologíaLa PlataArgentinaGrupo Argentino de Fotobiologí

Species- and community-level responses combine to drive phenology of lake phytoplankton

Global change is leading to shifts in the seasonal timing of growth and maturation for primary producers. Remote sensing is increasingly used to measure the timing of primary production in both aquatic and terrestrial ecosystems, but there is often a poor correlation between these results and direct observations of life-history responses of individual species. One explanation may be that, in addition to phenological shifts, global change is also causing shifts in community composition among species with different seasonal timing of growth and maturation. We quantified how shifts in species phenology and in community composition translated into phenological change in a diverse phytoplankton community from 1962 to 2000. During this time, the aggregate community spring–summer phytoplankton peak has shifted 63 days earlier. The mean taxon shift was only 3 days earlier, and shifts in taxa phenology explained only 40% of the observed community phenological shift. The remaining community shift was attributed to dominant early-season taxa increasing in abundance while a dominant late-season taxon decreased in abundance. In diverse producer communities experiencing multiple stressors, changes in species composition must be considered to fully understand and predict shifts in the seasonal timing of primary production.Fil: Walters, Annika W.. United States Geological Survey; Estados UnidosFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Schindler, Daniel E.. University of Washington; Estados Unido

Unravelling chironomid biodiversity response to climate change in subarctic lakes across temporal and spatial scales

We combined paleolimnological reconstructions and space-for-time substitutions to unravel chironomid biodiversity responses to climate change in subarctic mountains across temporal and spatial scales. Using sediment records, we found that long-term temporal changes in chironomid taxonomic diversity were mainly induced by the temperature tolerance/optimum of species, while little changes in functional diversity were found due to the replacement of similar functional-type taxa within the community. Overall, paleolimnological reconstructions suggested the selection of larger chironomid species by long-term climate cooling and little changes in trophic guilds. Space-for-time substitutions showed, however that low-elevation lakes with forested have more sediment-feeding taxa and larger larvae than high-elevation lakes, thus, suggesting the selection of large chironomid morphotypes with a sediment-feeding mode under warmer climate. Space-for-time substitutions and paleolimnological reconstructions, therefore, gave contrasting results for the link between climate and functional diversity of chironomid communities, likely because space-for-time substitutions failed to match the extent of both spatial and temporal climatic gradients. We suggest that future studies must address biodiversity issues across both temporal and spatial scales as an improved understanding of biodiversity responses to climate change may help us to understand how biodiversity will be affected by ongoing and future change

Carryover effects of predation risk on postembryonic life-history stages in a freshwater shrimp

For organisms with complex life histories it is well known that risk experienced early in life, as embryos or larvae, may have effects throughout the life cycle. Although carryover effects have been well documented in invertebrates with different levels of parental care, there are few examples of predator-induced responses in externally brooded embryos. Here, we studied the effects of nonlethal predation risk throughout the embryonic development of newly spawned eggs carried by female shrimp on the timing of egg hatching, hatchling morphology, larval development and juvenile morphology. We also determined maternal body mass at the end of the embryonic period. Exposure to predation risk cues during embryonic development led to larger larvae which also had longer rostra but reached the juvenile stage sooner, at a smaller size and with shorter rostra. There was no difference in hatching timing, but changes in larval morphology and developmental timing showed that the embryos had perceived waterborne substances indicative of predation risk. In addition to carryover effects on larval and juvenile stages, predation threat provoked a decrease of body mass in mothers exposed to predator cues while brooding. Our results suggest that risk-exposed embryos were able to recognize the same infochemicals as their mothers, manifesting a response in the free-living larval stage. Thus, future studies assessing anti-predator phenotypes should include embryonic development, which seems to determine the morphology and developmental time of subsequent life-history stages according to perceived environmental conditions.Fil: Ituarte, Romina Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Vázquez, María Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Spivak, Eduardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin