Question: In your work in the ocean of the North Pole, I understand you use coding to predict changes in the food web. I believe algae would be producers on the food web. How do you see change in our environment caused by humans affecting primary, secondary and tertiary food webs?

Fabian Grosse answered on 9 Jul 2020: last edited 9 Jul 2020 7:30 am

Hi Daniel,

Yes, you understand correctly and, yes, algae are the primary producers in the marine foodwebs. My own work focuses on algae but close colleagues of mine look into changes in zooplankton, the secondary producers feeding on these algae.
In the Arctic, the most obvious change we can observe is the retreating sea ice: it becomes thinner, its structure changes (for instance, melt ponds on the ice seem to occur more often), forms later in the year and melts earlier–all as a result of increasing temperatures.

These changes in sea ice cause have multiple effects: algae need light and nutrients to grow. The decline in sea ice results in higher light availability, so potentially more growth. It further allows the wind to have a stronger effect on the water column. In other words, it can increase vertical mixing, which is important for nutrient supply, especially in summer, when the algae have used almost all nutrients near the surface. So, again, potentially more growth.
More growth, doesn’t seem to pose much of a problem at first glance, right? The problem then is, however, that the timing of algal blooms may change (because sufficient light becomes available earlier in the year due to earlier ice melt) and that different species of algae start growing more than they used to while others grow less. This can have significant impacts on the upper food web because zooplankton “care” about what they eat. The quality of their food determines their growth and the amount of fats they contain, which in turn is very important for the fish and other animals eating zooplankton. And this is likely to propagate further through the food web. However, we are only starting to better understand what changes in the algal communities occur and how these affect zooplankton. And it becomes even more complex higher up in the food web (and I personally don’t know too much about that).
I hope this answers your question!