The Role of Recovery Phases in Mitigating the Negative Impacts of Marine Heatwaves on the Sea Star Asterias rubens

During recent years, experimental ecology started to focus on regional to local environmental fluctuations in the context of global climate change. Among these, marine heatwaves can pose significant threats to marine organisms. Yet, experimental studies that include fluctuating thermal stress are rare, and if available often fail to base experimental treatments on available long-term environmental data. We evaluated 22-year high-resolution sea surface temperature data on the occurrence of heatwaves and cold-spells in a temperate coastal marine environment. The absence of a general warming trend in the data may in parts be responsible for a lack of changes in heatwave occurrences (frequency) and their traits (intensity, duration, and rate of change) over time. Yet, the retrieved traits for present-day heatwaves ensured most-natural treatment scenarios, enabling an experimental examination of the impacts of marine heatwaves and phases of recovery on an important temperate predator, the common sea star Asterias rubens. In a 68-days long experiment, we compared a 37- and a 28-days long heatwave with a treatment that consisted of three consecutive 12-days long heatwaves with 4 days of recovery in between. The heatwaves had an intensity of 4.6°C above climatological records, resulting in a maximum temperature of 23.25°C. We demonstrate that heatwaves decrease feeding and activity of A. rubens, with longer heatwaves having a more severe and lasting impact on overall feeding pressure (up to 99.7% decrease in feeding rate) and growth (up to 87% reduction in growth rate). Furthermore, heatwaves of similar overall mean temperature, but interrupted, had a minor impact compared to continuous heatwaves, and the impact diminished with repeated heatwave events. We experimentally demonstrated that mild heatwaves of today’s strength decrease the performance of A. rubens. However, this echinoderm may use naturally occurring short interruptions of thermal stress as recovery to persist in a changing and variable ocean. Thus, our results emphasize the significance of thermal fluctuations and especially, the succession and timing of heat-stress event

Experimental study on the impacts of heatwaves with different duration and frequency on the common starfish Asterias rubens: abiotics handheld measurements

Experimental study on the performance of the common sea star Asterias rubens subjected to heatwaves of different duration and frequency (No, Interrupted, Present-day, and Extended). Treatments are based on the climatological analysis of 22-year long temperature data. The study was conducted at GEOMAR, Helmholtz-Centre for Ocean Research Kiel (54.329979 N, 10.148013 E) in the Kiel Indoor Benthocosms (Pansch and Hiebenthal 2019) over 68 days from July 5th to September 10th, 2019. The temperature was measured with a handheld thermometer at least every three days (TTX 110 type T, Ebro, Ingolstadt, Germany). Salinity, pH, and oxygen concentration were also measured over the experimental period (Multi 3630 IDS, WTW, Kaiserslautern, Germany)

Experimental study on the impacts of heatwaves with different duration and frequency on the common starfish Asterias rubens: abiotics logger

Experimental study on the performance of the common sea star Asterias rubens subjected to heatwaves of different duration and frequency (No, Interrupted, Present-day, and Extended). Treatments are based on the climatological analysis of 22-year long temperature data. The study was conducted at GEOMAR, Helmholtz-Centre for Ocean Research Kiel (54.329979 N, 10.148013 E) in the Kiel Indoor Benthocosms (Pansch and Hiebenthal 2019) over 68 days from July 5th to September 10th, 2019. The temperature was logged over the entire experimental period (EnvLogger, ElectricBlue, Vairão, Portugal)

Experimental study on the impacts of heatwaves with different duration and frequency on the common starfish Asterias rubens: treatments

Experimental study on the performance of the common sea star Asterias rubens subjected to heatwaves of different duration and frequency (No, Interrupted, Present-day, and Extended). Treatments are based on the climatological analysis of 22-year long temperature data. The study was conducted at GEOMAR, Helmholtz-Centre for Ocean Research Kiel (54.329979 N, 10.148013 E) in the Kiel Indoor Benthocosms (Pansch and Hiebenthal 2019) over 68 days from July 5th to September 10th, 2019

Experimental study on the impacts of heatwaves with different duration and frequency on the common starfish Asterias rubens: response variables

Experimental study on the performance of the common sea star Asterias rubens subjected to heatwaves of different duration and frequency (No, Interrupted, Present-day, and Extended). Treatments are based on the climatological analysis of 22-year long temperature data. The study was conducted at GEOMAR, Helmholtz-Centre for Ocean Research Kiel (54.329979 N, 10.148013 E) in the Kiel Indoor Benthocosms (Pansch and Hiebenthal 2019) over 68 days from July 5th to September 10th, 2019. Sea star feeding rate was quantified by measuring the shell length of consumed blue mussels (Dial Caliper DialMax Metric, Wiha Division KWB Switzerland). Based on a previously described relationship between shell size and tissue dry weight for mussels in the study area (Morón Lugo et al. 2020), the dry weight of consumed mussels was estimated. Sea star individuals were weighed at the start of the experiment, right before the heatwaves started, before the Present day heatwave started to decline, before the Extended heatwave started to decline, and at the end of the experiment. Sea star activity was measured as the time an individual needed to fully turn back to their oral side after being placed on its aboral side (i.e., righting time). These measurements were taken at the start of the experiment, right before the heatwaves started, before the Present day heatwave started to decline, before the Extended heatwave started to decline, and at the end of the experiment

Experimental study on the impacts of heatwaves with different duration and frequency on the common starfish Asterias rubens

Experimental study on the performance of the common sea star Asterias rubens subjected to heatwaves of different duration and frequency (No, Interrupted, Present-day, and Extended). Treatments are based on the climatological analysis of 22-year long temperature data. The study was conducted at GEOMAR, Helmholtz-Centre for Ocean Research Kiel (54.329979 N, 10.148013 E) in the Kiel Indoor Benthocosms (Pansch and Hiebenthal 2019) over 68 days from July 5th to September 10th, 2019. The temperature was logged over the entire experimental period (EnvLogger, ElectricBlue, Vairão, Portugal) and measured with a handheld thermometer at least every three days (TTX 110 type T, Ebro, Ingolstadt, Germany). Salinity, pH, and oxygen concentration were also measured over the experimental period (Multi 3630 IDS, WTW, Kaiserslautern, Germany). Sea star feeding rate was quantified by measuring the shell length of consumed blue mussels (Dial Caliper DialMax Metric, Wiha Division KWB Switzerland). Based on a previously described relationship between shell size and tissue dry weight for mussels in the study area (Morón Lugo et al. 2020), the dry weight of consumed mussels was estimated. Sea star individuals were weighed at the start of the experiment, right before the heatwaves started, before the Present day heatwave started to decline, before the Extended heatwave started to decline, and at the end of the experiment. Sea star activity was measured as the time an individual needed to fully turn back to their oral side after being placed on its aboral side (i.e., righting time). These measurements were taken at the start of the experiment, right before the heatwaves started, before the Present day heatwave started to decline, before the Extended heatwave started to decline, and at the end of the experiment