Abstract
A major attribute of the Earth’s climate that may be affected by global warming is the amplitude of variability in teleconnections. These global-scale processes involve links between oceanic conditions in one locale and weather in another, often distant, locale. An example is the El Niño Southern Oscillation (ENSO), which can affect rainfall and then the properties of lakes in Europe, Africa, North and South America. It affects rainfall, droughts and the depth of lakes in Florida, USA. It is predicted that the amplitude of variation in the ENSO will increase with global warming and, therefore, droughts will become more severe and periods of rain more intense. We investigated possible effects of climate on the zooplankton in shallow subtropical lakes by studying 16 years of monthly data from six shallow eutrophic lakes located north of Orlando, Florida. Results indicate that water depth and lake volume are tightly coupled with rainfall, as expected. During droughts, when lake depth and volume were greatly reduced, there were intensified cyanobacterial blooms, and the zooplankton shifted towards greater relative biomass of copepods compared to cladocerans. The change of zooplankton was likely due to the intensified selective fish predation in the reduced water volume, and/or selective adverse effects of cyanobacteria on cladocerans. The greatly reduced volume might lead to a ‘perfect storm’ of top-down and bottom-up factors that favor copepods over cladocerans. The mechanism needs further study. Regardless, this study documents a direct link between climate variability and zooplankton composition, and suggests how future changes in climate might affect plankton communities.
Highlights
Zooplankton dynamics in subtropical lakes are affected, as in other geographic regions, by a myriad of factors, including fish and invertebrate predation, food resource quantity and quality, temperature, stratification, abiotic seston and other attributes of water quality [1,2,3,4]
We examined the degree to which the ratio of cladocerans to copepods was influenced by mean depth and cyanobacteria using regression analysis, and again this led to fitting non-linear models
A redundancy analysis (RDA) was performed using the annual mean data to identify the power of independent environmental variables (TP, total nitrogendominated (TN), soluble reactive phosphorus (SRP), DIN, temperature, chlorophyll a (Chl-a), dissolved organic color, flushing rate, mean depth, SD, rainfall and cyanobacteria biovolume) on explaining the variation in the dependent zooplankton variables
Summary
Zooplankton dynamics in subtropical lakes are affected, as in other geographic regions, by a myriad of factors, including fish and invertebrate predation, food resource quantity and quality, temperature, stratification, abiotic seston and other attributes of water quality [1,2,3,4]. We recognize that the temporal dynamics of zooplankton and phytoplankton are affected by factors occurring at multiple temporal scales These include: (1) year-to-year variations in attributes such as depth and flushing that are affected by climate; (2) seasonal variations driven by attributes such as incident solar radiation and temperature; and (3) short-term variations driven by stochastic factors such as periods of intense rainfall, cloud cover, water inflow and calm or windy conditions. 1. Conceptual diagram of the predicted effects of variation in climate and rainfall on drought and water depth in the shallow study lakes; the concentration of fish and nutrients in reduced lake and water depth in thebiomass shallowofstudy lakes; theinconcentration of fish and nutrients in reduced lake volumes; the increased cyanobacteria shallower nutrient-enriched water; and the increase volumes; increasedrelative biomass cyanobacteria shallower nutrient-enriched water; and the in biomassthe of copepods to of cladocerans.
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