Identification of marine heatwaves in the Archipelago Sea and experimental testing of their impacts on the non-indigenous Harris mud crab
Kraufvelin, Lucinda (2021)
Kraufvelin, Lucinda
2021
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2021041210099
https://urn.fi/URN:NBN:fi-fe2021041210099
Tiivistelmä
Seawater temperature is an important variable affecting both the distribution and performance of marine organisms. In conjunction with climate change, marine heatwaves are expected to become more frequent and increase in their intensity and duration, mainly driven by a warming trend in sea surface temperature (SST). The effects of warming on marine organisms are diverse, and arguably the Baltic Sea can be considered particularly prone to marine heatwaves, as it is a comparable shallow enclosed water body. Additionally, the Baltic Sea has low functional redundancy and species diversity, which may further increase the potential impacts of extreme events. Despite the rapid warming rates of SST observed in and projected for the Baltic Sea compared to other large marine waterbodies, not many experimental studies have been conducted on the impact of heatwaves on its coastal marine communities. This is particularly true for the northern parts of the Baltic, such as the northern Baltic Proper and the Finnish Archipelago Sea.
This study consists of a modelling and an experimental part. In the modelling part, the frequency, intensity, and duration of marine heatwaves in the Finnish Archipelago Sea were identified by applying the available software package “heatwaveR”, on two SST datasets from the region (a long-term dataset spanning 52 years and a shorter dataset of high-resolution spanning 12 years). Subsequently, trends in these characteristics of marine heatwaves were examined. For the experimental part of this thesis, the impact of simulated marine heatwaves was tested on the non-indigenous Harris mud crab, Rhithropanopeus harrisii. Experimental treatments were designed based on metrics retrieved from the climatological SST data assessed in the modelling part. The treatments represented three scenarios for SST: a present average marine heatwave in the Archipelago Sea (Present), an event of increased amplitude (Amplitude) and a future heatwave scenario of a high amplitude (Intensified). The study species, R.harrisii recently entered the Finnish Archipelago Sea with an expanding distribution range, which may be driven by its relatively high tolerance to environmental stress in
comparison to the corresponding tolerances of many native species. Thus, I hypothesized that R. harrisii would tolerate benign heatwave treatments of present day intensity but may suffer from intense heat stress experienced in the applied future heatwave scenarios. Measured response variables were feeding on mussel prey and growth of the crab (wet weight and carapace width).
The long-term dataset showed that mean SST (both summer and annual) in the Archipelago Sea has increased over the last 52 years (0.4 and 0.5 °C per decade, respectively), and so has the frequency of marine heatwave events, partly driven by this increase in mean SST in the region. No significant trends were detected over the12-year high-resolution dataset. There was no significant difference in crab feeding rates between the heatwave treatments over the 36-day long experimental period, although crabs showed a tendency to feed more with increasing temperatures (non significant trends). There was, however, a significant time effect on feeding, but this effect was only present when no treatments were taken into consideration. No significant differences in crab growth between the three heatwave treatments could be detected.
Mean SST in the Baltic Sea is increasing and so are the extremes. Since rising SST is one of the main drivers of marine heatwaves worldwide, these are likely to become more common in the future. R. harrisii might benefit in a warmer Baltic Sea as it is indicated from this study: individuals showed intensified feeding with increasing SST and tolerated well the extreme temperatures associated with the applied marine heatwaves. Due to its recent introduction, the role of R. harrisii in the Archipelago Sea food web is still not fully understood. Yet, the combined effects of the temperature tolerance of this introduced secondary consumer and marine heatwaves may have possible consequences for the entire ecosystem, primarily by changing the interaction among species.
This study consists of a modelling and an experimental part. In the modelling part, the frequency, intensity, and duration of marine heatwaves in the Finnish Archipelago Sea were identified by applying the available software package “heatwaveR”, on two SST datasets from the region (a long-term dataset spanning 52 years and a shorter dataset of high-resolution spanning 12 years). Subsequently, trends in these characteristics of marine heatwaves were examined. For the experimental part of this thesis, the impact of simulated marine heatwaves was tested on the non-indigenous Harris mud crab, Rhithropanopeus harrisii. Experimental treatments were designed based on metrics retrieved from the climatological SST data assessed in the modelling part. The treatments represented three scenarios for SST: a present average marine heatwave in the Archipelago Sea (Present), an event of increased amplitude (Amplitude) and a future heatwave scenario of a high amplitude (Intensified). The study species, R.harrisii recently entered the Finnish Archipelago Sea with an expanding distribution range, which may be driven by its relatively high tolerance to environmental stress in
comparison to the corresponding tolerances of many native species. Thus, I hypothesized that R. harrisii would tolerate benign heatwave treatments of present day intensity but may suffer from intense heat stress experienced in the applied future heatwave scenarios. Measured response variables were feeding on mussel prey and growth of the crab (wet weight and carapace width).
The long-term dataset showed that mean SST (both summer and annual) in the Archipelago Sea has increased over the last 52 years (0.4 and 0.5 °C per decade, respectively), and so has the frequency of marine heatwave events, partly driven by this increase in mean SST in the region. No significant trends were detected over the12-year high-resolution dataset. There was no significant difference in crab feeding rates between the heatwave treatments over the 36-day long experimental period, although crabs showed a tendency to feed more with increasing temperatures (non significant trends). There was, however, a significant time effect on feeding, but this effect was only present when no treatments were taken into consideration. No significant differences in crab growth between the three heatwave treatments could be detected.
Mean SST in the Baltic Sea is increasing and so are the extremes. Since rising SST is one of the main drivers of marine heatwaves worldwide, these are likely to become more common in the future. R. harrisii might benefit in a warmer Baltic Sea as it is indicated from this study: individuals showed intensified feeding with increasing SST and tolerated well the extreme temperatures associated with the applied marine heatwaves. Due to its recent introduction, the role of R. harrisii in the Archipelago Sea food web is still not fully understood. Yet, the combined effects of the temperature tolerance of this introduced secondary consumer and marine heatwaves may have possible consequences for the entire ecosystem, primarily by changing the interaction among species.