Effect of Salinity Change on Marine Plankton: A Review
Research Question
We aimed to assess our current knowledge of salinity effects on plankton in marine, brackish, or estuarine waters. What is the state of current knowledge on this topic?
Why study salinity?
Due to climate change some parts of the world's ocean are getting saltier while others less so. As weather patterns shift, increased rainfall can cause freshening events, while drought conditions have the opposite effect. In this way, ocean salinity is closely tied to the water cycle. Changes in salinity also alters the density of seawater thereby effecting circulation patterns. Ocean circulation is responsible for the distribution of heat in the ocean. Therefore, changes to circulation patterns can further contribute to our changing climate. Understanding how organisms respond to changes in salinity is important to inform predictions and conservation efforts as climate change persists.
Why Study Plankton?
Despite their small size, plankton play an enormous role in the health of our oceans. For one, they form the base of the oceanic food web. Phytoplankton act as the trees of the ocean, producing more than half the planets oxygen, and bacterioplankton recycle and remineralize material and energy within the food web. Plankton are also great indicators of change. Timing and production of these small organisms are tightly linked with environmental factors such as temperature, nutrient availability, circulation patterns, and more. Environmental change, often as a result of climate change, has consequences for plankton communities and therefore cascading effects up the food chain.
Methods
A literature review was conducted to answer our research question following these steps:
1. Web of Science search for papers fitting specific search criteria: (salinity OR saltiness OR freshening OR haline) AND *plankton AND (marine OR brackish OR estuar*). The result was over 4000 papers!!
2. Divide the 4,417 papers of the search results equally amongst 5 team members. Allow for some overlap in the distribution so some papers are randomly vetted twice. This ensures human error and differences in individual judgment are accounted for. The R-package, Metagear is the tool we used for this step (example R-codes can be seen in the photo above).
3. Develop a screening quiz to identify and extract information from papers applicable to our research questions, eliminate those that are not applicable, and group papers that may be interesting for some other reason.
4. Read LOTS of abstracts! And then read a few more.
Some interesting results to date... after vetting 1,036 papers as a team
Manipulated Variable: Salinity
Of the papers found to be applicable to our research question, more than half quantified the effect of salinity change on plankton over a natural gradient.
Location
Most commonly, experiments took place in estuaries, followed by labs.
Response Variables
Papers measured a variety of response variables, however, abundance and community composition were most common.
Plankton Classification
Papers dealt most commonly with phytoplankton and no applicable papers were found to date studying icthyoplankton.
Importance of Review papers
Review papers, such as meta-analyses, provide a summary of what is known on a subject to date. They help identify gaps in knowledge, inform future research and identify contradictions or establish consensus. Overall, they assess the current state of knowledge on a given topic.
About the Pelagic Biodiversity Lab
I worked with the Pelagic Biodiversity Lab of the Tvärminne Zoological Station and the University of Helsinki. This lab, led by Aleksandra Lewandowska, conducts research focused on climate change and its effect on biodiversity of pelagic food webs. Current research includes the application of a trait-based approach to the effect of salinity on phytoplankton communities by Iris Orizar. In addition, Clio hall is currently working on quantifying the effect of salinity change on planktonic diversity and community composition as well as the combined effect of salinity change and temperature on food web interactions. As a whole the lab's research includes lots of field and laboratory work including as part of the EU network of mesocosm facilities for research on marine and freshwater ecosystems (AQUACOSM).
Views around Tvärminne Zoological Station. Photo courtersy of Justin Tierney.
Lessons Learnt
The scientific process requires a large amount of adaptability to changing circumstances and challenges.
"Time to put plan Z into effect" -Plankton (Spongebob)
Working from home is great for endless coffee but brings with it it's own set of challenges (and missed opportunities for great views).