Events characterized by high temperatures in the oceans have become increasingly common, including in the Southern Ocean.
This Ocean, where numerous species live, most of which are endemic to this region, due to the dynamics and interaction of water currents in this part of the planet, and which end up being much more sensitive to these events. One of the most important currents for prey and predators in the Southern Ocean is the Polar Front. However, with the progressive increase in ocean temperature, it is expected that the Polar Front will contract towards the south, towards the Antarctic continent. Thus, these spatial changes in the Polar Front may cause difficulties for predators that forage for their prey in that area.
Interestingly, these climate changes in the ocean, contrary to what we usually think, can have different consequences in the same species.
Such case is the King Penguins. Among the various colonies that exist scattered around the South Pole, two of them are found on the Kerguelen Islands and the Crozet Islands, which are 1400km away. However, in recent years it has taken different directions, with the Kerguelen penguin population growing and in the Crozet Islands significantly decreasing.
So, to understand the influence of these events with high temperatures in the ocean on these populations and to find out if they would be complicit in this outcome, a team analysed 25 years of data. They analysed where the penguins foraged for food and how long it took, the number and success of the chicks, including their weight.
The results are interesting, and completely different. Overall, they confirmed that the reproductive success of king penguins varies dramatically from year to year, mainly due to climatic differences. However, distinctly on the two islands. In Kerguelen, the position of the front is much closer to the island, and changes in its position in the ocean do not significantly affect the capture of prey for chicks by penguin couples. The researchers even suggest that it is possible that these higher temperatures are having a positive effect on the abundance and growth of prey and consequently greater reproductive success in the penguin population. At the same time, during the winter, these warmer conditions will increase the probability of survival of the hatchlings. On the Crozet Islands, the king penguin population has been declining. On this island position on the Polar Front, it has varied between 217 and 642km to the island, 10x more when compared to Kerguelen. Due to the characteristics of each region, the position of the Polar Front is much more mobile in Crozet, being even more accentuated during these high ocean temperature events. Thus, king penguins are forced to travel greater distances to find prey, when compared to Kerguelen. Consequently, this increase in expenditure of time and energy, and sometimes failure to capture prey, is reflected in a greater probability of death for the offspring.
In the future, with the continuation of these changes and climatic events, the Polar Front will also continue to move towards the south. As we can see, the same process will have completely different results in king penguins from two subantarctic islands. Hoping that the population on Kerguelen will continue to grow and will eventually replace the Crozet colony which continues to see numbers dwindle.
Therefore, it is always important to evaluate and consider not only large-scale processes but also local and regional characteristics to obtain more reliable results from which we can act correctly.
Source: Brisson‐Curadeau, É., Elliott, K., & Bost, C. A. (2022). Contrasting bottom‐up effects of warming ocean on two king penguin populations. Global Change Biology https://doi.org/10.1111/gcb.16519
Author: José Abreu