An Uncertain Future for Phytoplankton Spring Blooms
Earlier this week, on my daily commute to class, I caught myself appreciating the nature that surrounded me, an aspect that Canadians across the nation pride themselves on. I also began noticing the oddly warm weather. It was early February and the temperature in London, Ontario varied between 3° to 5°C. My appreciation hardly lasted a minute as I realized that these irregular temperatures at strange times are a prime example that there is a greater issue at hand.
Current Global Crisis
On average, the expected temperature around this time in Ontario is meant to be -2° to -7°C (Aladin, n.d.). However, due to the anthropogenic threats imposed on our ecosystem such as an increase in greenhouse gas emissions and burning of fossil fuels, our planet earth responds by increasing temperature (Environment and Climate Change Canada, 2009). Such factors tend to disrupt the dynamics between organisms as well as organisms and their environment. Therefore, it is essential for climate-driven changes to be further studied for scientists to come up with restoration efforts and solutions that allow Canadians to continue to enjoy such pleasures.
Looking at past studies that have succeeded in understanding how environmental variables affect climate-driven changes, perhaps will help Canadians to adopt similar mechanisms. Referring to a journal article by Hjerne et al., (2019), scientists analyzed long-term phytoplankton data in the Baltic Sea to uncover trends in timing, composition, and size of the spring bloom, and its correlations to environmental variables.
Phytoplankton Spring Bloom
Phytoplankton spring blooms are an important ecological feature that accounts for part of the annual production in many temperate marine freshwater systems, supports the growth of heterotrophic species in the water column and seafloor, while also influencing the pathways circulating living and non-living components of Earth. It is also important to note that high light levels and low water levels result in larger spring blooms whereas cloudy temperatures result in smaller spring blooms. Understanding the natural aspects of spring blooms can help us better understand them when they undergo unnatural conditions. As stated above, the timing, composition, and size of the spring bloom were investigated since they can have significant effects on the dynamics of our ecosystem. For example, bloom timing can affect carbon recycling, energy transfer to higher trophic levels, and sedimentation to the benthos.
As a hotspot for various studies, the Baltic Sea contains a spring bloom that is dominated by diatoms, dinoflagellates, and an autotrophic ciliate Mesodinium ruburm (Lohmann). Typically nitrogen-limited, the Baltic Sea finds itself in an unusual state with increased energy input into the system due to eutrophication and under hypoxic and anoxic conditions due to increased sedimentation. This has consequently been linked to climate warming, a result of human impact.
Lots of Data
Scientists collected phytoplankton and hydrochemical data, specifically temperature, salinity, and nutrient concentration during the daytime over the span of about 30 years at a coastal station and about 20 years from an offshore station. They were interested in analyzing the relationships between spring bloom dynamics and possible environmental predictor variables.
Since the data collected included phytoplankton data, hydrochemical data, and climate data, scientists used statistical analyses to help them draw conclusions. An analysis test was used to investigate monotonic trends in spring bloom dynamics and environmental variables. Another statistical technique used to predict an outcome of a dependent variable while comparing independent variables was used to evaluate the ability of environmental variables to explain the spring bloom dynamics. Predictor variables such as the average water temperature, wind speed, and global irradiance were used to analyze the timing, relative contribution, and magnitude of the bloom. Scientists found that earlier phytoplankton blooms are associated with more sunshine, less windy conditions, and high water temperatures. Also, the blooming time was buffered by a temperature shift in composition from early-blooming diatoms to later blooming dinoflagellates and M. rubrum.
What Did They Find?
Overall, scientists found that the total phytoplankton spring blooms appear earlier by 1 to 2 weeks over the years, from 1990 to 2011, under high water temperatures. This can be credited to the idea that sea temperature levels have risen over the years, resulting in earlier blooms. More so, a positive correlation was seen between mixed layer depths and the total phytoplankton blooming at the offshore station but not at the coastal station. This observation is reasonable since stratification is more important for bloom initiation in deep offshore areas than in shallow coastal areas.
In terms of composition, scientists found that the proportion of dinoflagellates was higher at the offshore station and the proportion of diatoms was lower at the coastal station. This suggests that bloom initiation is dependent on resting stages in shallow areas, but the motility of dinoflagellates allows them to reach deep offshore areas by horizontal transportation than sedimenting diatoms. Additionally, the relationship between ice cover and the proportion of the 3 types of phytoplankton varied. Diatoms favoured cold and icy winters since ice provides a habitat for diatom species that can grow near the ice, resulting in a large seed population after ice break-up, whereas dinoflagellates favoured intermediate temperatures. The proportion of M. rubrum remained relatively unaffected.
Finally, in terms of bloom magnitude, scientists found no consistent trends in spring bloom magnitudes of total phytoplankton but a change in the composition of the total phytoplankton, which was detailed above.
The Future of Spring Blooms
Many ecological features, similar to spring phytoplankton blooms, are being impacted by climate change. This study done in the northern Baltic Proper provides us with an insight into how our actions lead to climate change and ultimately hurt the ecosystem that scientists are trying so hard to protect.
The results of this study have raised many questions: How will marine life react to earlier spring blooms? Are there ways to prevent earlier spring blooms? More importantly, what can we do, as a society, to lessen detrimental impacts on our beautiful natural resources?
Glossary
Benthos: the community of organisms that live, near, in, or at the bottom of the sea. This research discovered the significance of benthos as a key group impacted by bloom timing.
Eutrophication: the enrichment of a body of water with nutrients, specifically nitrogen and phosphorus. This research discovered the significance of eutrophication as a key factor in energy input within spring phytoplankton blooms.
Global Irradiance (GHI): the total solar radiation incident on a horizontal surface. This research discovered the significance of GHI as an environmental variable used to understand the dynamics of spring phytoplankton blooms.
Mixed layer depth (MLD): the measure of the depth to which mixing occurs over a period of time. This research discovered the significance of MLD as an environmental variable that affects spring phytoplankton blooms.
Resting stages: a stage in a process or life cycle in which there is no growth or activity. This research discovered the significance of resting stages as a biological factor that affects spring phytoplankton blooms.
Stratification: a term used to describe when two distinct layers occupy the vertical water column in the sea. This research discovered the significance of stratification as a driver for bloom initiation in shallow waters.
