What is cooking in our Lab?

Our group, in the Department of Marine Biology and Oceanography at the Institute of Marine Sciences, CSIC, Barcelona (Spain), has been conducting research on the ecology of marine zooplankton for several decades. Over the years, we have explored diverse topics, both in the field and in the laboratory. For instance, we have characterized planktonic food web dynamics in various regions, including the North Western Mediterranean and remote areas such as the Arctic and Antarctic. In the lab, we have studied specific groups like marine cladocerans and particular species of copepods, as well as broader topics such as the impacts of diet on aging copepods, and the effects of sea turbulence, pollutants, light cycles, and other factors on zooplankton.

Recently, recognizing the crucial role of climate change on our planet, we have dedicated several research projects to studying the effects of temperature on plankton. Our approach is pioneering as we go beyond simple short-term effects of temperature, and instead, we have adapted copepod, algae, and protozoa populations to different temperatures over the years. This has required a monumental effort, especially during the COVID-19 pandemic when access to laboratories was restricted, considering that certain planktonic organisms require daily attention. Despite the challenges, we are now seeing the results of our hard work.

Our research takes a dual perspective, examining similar questions for copepods and protozoa, but with different approaches. For instance, copepods have a generation time of about a month, whereas protozoa can double in population almost every day.

In our current project, we are asking the following questions, always focusing on species that have been previously adapted to different temperatures:

1. What effect does temperature have on the metabolic rates of marine zooplankton? This question revolves around the concept that metabolic rates speed up with temperature (measured by the Q₁₀ coefficient). However, we have observed that copepods adapted to different temperatures in our study maintain their metabolic rates practically unchanged, regardless of warming. This finding has significant implications for predictive models of climate change, which often rely on data from organisms that have not been adapted. As for protozoa, the response is not as clear and requires further investigation. Preliminary data, however, suggests that protozoa may have a more limited ability to adapt to temperature compared to copepods.
2. What effects does temperature have on the thermal windows of organisms and their survival ability? We have also observed, with copepods, that the range of temperatures in which organisms can survive shifts towards warmer areas of the thermal window in populations adapted to higher temperatures. Although the difference in thermal optimum or tolerance range is small, one or two degrees, it has significant implications for population dynamics under global warming scenarios.
3. What effects does temperature have on the size of organisms? It is well known that most organisms follow Bergmann’s law, which states that larger species are found in colder climates compared to warmer ones. Plankton are no exception, and we have observed copepods, algae, and protozoa conforming to this rule. However, while our results have confirmed this trend in copepods, we have observed that factors such as nutrient availability and culture aging may have a more significant impact on the size of algae than temperature. Regarding protozoa, we have proposed a new hypothesis, as we have observed that much of the existing literature is based on experiments that may not be well-designed. Many marine protozoa, particularly those that consume algae, can ingest prey equivalent to several times their volume, and this ingestion is strongly linked to temperature. Bearing this in mind, it is surprising that most studies on the effects of temperature on the size of protozoa are done under saturating food conditions. Imagine if someone conducted a study to determine the effects of temperature on humans, but did so immediately after the individuals had just eaten an excessive amount of food, like half a cow (if that were even possible). The results of such a study would be misleading. Therefore, we are now trying to demonstrate that when protozoan size is measured accurately and after proper thermal adaptation, the effects of temperature on cell size are negligible.

Soon, we plan to investigate the synergistic effects of temperature with other global change variables, such as nutrient availability and pollutant exposure. However, to obtain conclusive results, some patience will be required as further research is underway. Whish us luck!

To learn more:

• Albert Calbet, Enric Saiz. Thermal acclimation and adaptation in marine protozooplankton and mixoplankton (2022). Frontiers in Microbiology. 13:832810. doi.org/10.3389/fmicb.2022.832810.
• Enric Saiz, Kaiene Griffell, Manuel Olivares, Montserrat Solé, Iason Theodorou, Albert Calbet. Reduction in thermal stress of marine copepods after physiological acclimation (2022). Journal of Plankton Research. 44(3):427-442. doi.org/10.1093/plankt/fbac017.
• Albert Calbet, Rodrigo Andrés Martínez, Enric Saiz, Miquel Alcaraz (2022). Effects of temperature on the bioenergetics of the marine protozoans Gyrodinium dominans and Oxyrrhis marina. Frontiers in Marine Sciences. Volume 9, Article 901096. Doi: 10.3389/fmars.2022.901096.
• Guilherme D. Ferreira, Afroditi Grigoropoulou, Enric Saiz, Albert Calbet (2022). The effect of short-term temperature exposure on vital physiological processes of mixoplankton and protozooplankton. Marine Environmental Research. Volume 179, July 2022, 105693. DOI:10.1016/j.marenvres.2022.105693. Editor’s Choice article 2020-2022.
• Carlos de Juan, Kaiene Griffell, Albert Calbet, Enric Saiz. (2023). Multigenerational response to warming in copepods is influenced by physiological compensation and body size reduction. Limnology and Oceanography. https://doi.org/10.1002/lno.12327.
• Albert Calbet and Enric Saiz (submitted). Does the temperature-size rule apply to marine protozoans after proper acclimation? Functional Ecology.
• Albert Calbet, Minerva García-Martínez, Claudia Traboni, Enric Saiz (submitted) The importance of the growth phase to understand the temperature-size rule in marine phytoplankton. Journal of Phycology.