Gilbert, Lola, Jeanniard-du-Dot, Tiphaine, Cherel, Yves, Spitz, Jérôme, 2025 Major and trace nutrient concentrations in sub-Antarctic forage fish around the Kerguelen Islands: All are not equal for nutrient recycling by top predators. Journal of Experimental Marine Biology and Ecology. 586. https://doi.org/10.1016/j.jembe.2025.152097
Nutrient Needs
We’re taught at a young age how important it is to have a balanced diet for a healthy lifestyle. A major component of our diets that we should maintain are nutrients. At their most basic level, these are chemical compounds typically required for proper body function. They can be divided into the following seven major groups:
- Carbohydrates
- Proteins
- Fats
- Vitamins
- Minerals
- Dietary fiber
- Water
It can be easy to forget sometimes, but animals need this balance as well.
Fish Nutrients
The Kerguelen Plateau in the Southern Indian Ocean is the center of nutrient studies in the ocean. Its location is perfect to study this topic because the plateau obstructs the flow of a major current in the region (the Antarctic Circumpolar Current). This forces cold, nutrient rich water up to the surface, making it a highly productive place where many marine animals congregate to feed. Past studies have focused on the nutrient cycle as it moves through the food web from primary producers all the way up to the top predators before returning back to the beginning. However, how predators get all their nutrients to maintain a balanced diet is not well understood. Researchers decided to study 34 forage fish species of the Kerguelen Plateau to assess their nutrient content. Their goal was to identify different concentrations between species and then describe groups of fish that would fulfill similar nutrient needs for predators.
Element Composition
In this study, nutrients were broken down to their basic elements and classified as major, essential-trace, and non-essential nutrients.
Fish were found to be heterogeneous for nutrient concentrations. In other words, some fish had higher concentrations of certain nutrients and were lower in others. For example, the Antarctic jonasfish had the highest concentration of magnesium, but one of the lowest concentrations of cobalt. Iron was found to be the most variable major nutrient across the fish sampled. As for non-essential nutrients, cadmium was one of the least variable while silver and lead had a wide range of concentrations.
Four general clusters were found that shared similar nutrient compositions. Cluster 1 was made up by a majority of lanternfish and were best described by low concentrations of salt and zinc. Cluster 2 had eight species all associated with the ocean floor. They had the highest concentrations of phosphorus, potassium, and arsenic. They also had the lowest amounts of lead. Cluster 3 was made up of fish found in the mid-range of the water column. They had the highest concentrations of silver and lowest concentrations of calcium, nickel, and cobalt. Lastly cluster 4 was a mixed bag of fish found in the water column and on the ocean floor. They had the highest concentrations of salt, magnesium, and iron and the lowest concentrations in arsenic and cadmium.
Healthiest Fish Options
This study found that different forage fish meet certain nutrient dietary needs for predators at the Kerguelen Plateau. However, four groups of fish were identified to fill similar nutrient compositions. Clusters 2 and 4 seem to offer some of the best nutrients including at least 2 major essential nutrients. Not only that, but have some of the lowest concentrations of non-essential nutrients. On the other hand, Cluster 1 and 3 seem to offer less dietary value with minimal concentrations of essential nutrients.
Even with these clusters identified, there were significant variations in the concentrations of nutrients between species. This demonstrates that prey aren’t interchangeable. Particular fish are eaten to fill dietary needs. A change in prey could have negative impacts on the health of local predators. Identifying the nutritional value of these fish helps inform us which fish may be more important than others. Monitoring these populations for declines from activities such as over-fishing will help preface possible health declines of predators in the area.
I am a recent MSc graduate in marine biology from Bangor University, where I studied population dynamics of elasmobranchs off the coast of Wales. My interests lie in ecological data analysis to understand environmental processes and identify natural patterns. However, nothing beats being in the field and interacting directly with the marine life.
