Slice of PLOS: Mesocosms and Climate Change

By 2016, most scientifically literate people have come to accept the inevitability of climate change. But what’s much less clear is how different species will respond to the world-wide shifts in temperature and weather pattern that lie ahead. Studies of natural environments suffer from many and unpredictable variables, and even then the correlative nature of these studies limits our ability to nail cause and effect. On the other hand, lab-based experiments, while offering better control over those variables, are excessively artificial and may not reflect natural conditions.

Mesocosms appear to offer the Goldilocks solution (see Damien Fordham’s excellent primer on this). They recreate a natural environment in a small – often enclosed or semi-enclosed – system, where particular variables can be altered or held constant. Some studies use mesocosms to investigate how warming temperatures will affect the fitness of specific species. For example, in their recent PLOS Biology paper, Elvire Bestion and colleagues used an array of large, semi-natural enclosures called the Metatron. This device allowed them to study how the warmer climate predicted for the year 2100 might affect the life cycle and demography of the common lizard. They found that an increased temperature of 2°C for two years led to accelerated growth, earlier breeding, and decreased adult survival. Extrapolating their data using a matrix population model predicted that a warmer climate will lead to the extinction of some European lizard populations within 20 years.

When by contrast, in a study published in PLOS ONE, Qing-lin Wang and co-workers examined how exposure to warmer temperatures of adult sea cucumbers affects the thermal sensitivity of their offspring, they found that juvenile sea cucumbers whose parents had been acclimatized to warmer water temperatures had a higher thermal resistance than those whose parents were acclimatized to cooler waters, hinting that sea cucumbers could be resilient to warming temperatures.

In addition to studying single species, mesocosms can be used to study how communities respond to warmer temperatures. In another recent PLOS Biology paper, Gabriel Yvon-Durocher and coauthors used outdoor experimental pools which were open and allowed for natural dispersal, to study how the plankton community structure changed with increased temperature. Perhaps surprisingly, they found that 5 years of a 4°C increase in temperature actually enhanced the biodiversity and productivity in a plankton community.

Researchers from Harvard, Yale and Bowling Green State University used mesocosm experiments consisting of 19-litre soil-filled buckets in warming chambers to investigate how increased temperature effects the forest floor food web structure and soil carbon dioxide emissions, as shown in this PLOS ONE article. Also in PLOS ONE, Silvia Pajares and coauthors used mesocosm experiments to assess how bacterial mat communities from an extremely impoverished environment in an oasis in the Mexican Chihauahua desert responded to raised or fluctuating levels of heat or UV irradiation.

Mesocosms can also be used to look for ways to mitigate the effects of climate change. In this PLOS ONE article by Elizabeth Strain and colleagues, the authors explore whether decreasing manmade stressors might increase the resilience of a critical ecosystem member, the seaweed Cytoseira barbata, to increased environmental temperature. Using a mixture of manipulative field experiments and mesocosms, they find that decreasing either sediment load from beach erosion and dredging or exogenous nutrients from sewage and agricultural runoff either sediment or exogenous nutrients enhances the ability of juvenile canopy algae to grow at high temperature.

Given the complexity and context-dependence of the results described here, it’s clear that extensive further research is needed to help predict and prepare for the effects of climate change. Research using mesocosms will be central to understanding how species and communities respond to changes in their environment over extended periods of time, and for identifying human interventions that can help species to cope with the inevitably warmer temperatures that face them.

Credit for Featured image: Elvire Bestion.

For more detailed reading:

[or see this associated PLOS Collection]

Bestion, E., Teyssier, A., Richard, M., Clobert, J., & Cote, J. (2015). Live Fast, Die Young: Experimental Evidence of Population Extinction Risk due to Climate Change PLOS Biology, 13 (10) DOI: 10.1371/journal.pbio.1002281

Fordham DA (2015) Mesocosms Reveal Ecological Surprises from Climate Change. PLoS Biol 13(12): e1002323. doi: 10.1371/journal.pbio.1002323

Wang Q-l, Yu S-s, Dong Y-w (2015) Parental Effect of Long Acclimatization on Thermal Tolerance of Juvenile Sea Cucumber Apostichopus japonicus. PLoS ONE 10(11): e0143372. doi: 10.1371/journal.pone.0143372

Yvon-Durocher G, Allen AP, Cellamare M, Dossena M, Gaston KJ, Leitao M, et al. (2015) Five Years of Experimental Warming Increases the Biodiversity and Productivity of Phytoplankton. PLoS Biol 13(12): e1002324. doi: 10.1371/journal.pbio.1002324

Pelini SL, Maran AM, Chen AR, Kaseman J, Crowther TW (2015) Higher Trophic Levels Overwhelm Climate Change Impacts on Terrestrial Ecosystem Functioning. PLoS ONE 10(8): e0136344. doi: 10.1371/journal.pone.0136344

Pajares S, Souza V, Eguiarte LE (2015) Multivariate and Phylogenetic Analyses Assessing the Response of Bacterial Mat Communities from an Ancient Oligotrophic Aquatic Ecosystem to Different Scenarios of Long-Term Environmental Disturbance. PLoS ONE 10(3): e0119741. doi: 10.1371/journal.pone.0119741

Strain EMA, van Belzen J, van Dalen J, Bouma TJ, Airoldi L (2015) Management of Local Stressors Can Improve the Resilience of Marine Canopy Algae to Global Stressors. PLoS ONE 10(3): e0120837. doi: 10.1371/journal.pone.0120837