Impact of Marine Heatwaves on Red Gorgonian Corals

Extreme climate events linked to climate change, like heatwaves, are becoming more common and are harming biodiversity. These events can lead to mass mortality events where many species die off and can cause a decline in the number of individuals in various species. This raises serious concerns about the future of different forms of life on our planet.

Scientists have studied how different species respond to these extreme events, and they have found that responses can vary greatly depending on the species, location, and time period. However, most research so far has focused on single events, which gives only a limited view of the problem. To better understand how species cope with these challenges, it's important to look at multiple events over time.

Our approach focuses on understanding how extreme climate events, specifically Marine Heatwaves, affect the red gorgonian, a coral species living in the Mediterranean Sea. This species plays a key role in its habitat, but it has been shown to be sensitive to rising temperatures caused by heatwaves. By looking at multiple heatwave events and how they impact this coral, we can gain insights into the broader issue of biodiversity loss due to climate change.

#The Importance of Marine Heatwaves

Marine heatwaves are periods of unusually warm water, and they pose a significant threat to marine ecosystems. These heatwaves can disrupt the growth and survival of various marine species. Over the past two decades, the Mediterranean Sea has experienced a rise in marine heatwaves, leading to significant mortality events affecting many types of marine life, including corals and other invertebrates.

The red gorgonian, a type of coral that forms important habitats in the Mediterranean, has faced severe impacts from these heatwaves. Research has shown that these events can lead to high levels of tissue damage and mortality in coral populations. Understanding how the red gorgonian and similar species respond to these events will be crucial for conservation efforts.

#Research Focus

Our study aims to assess the impacts of recurrent marine heatwaves on the red gorgonian and to investigate the factors that shape its ecological responses. We will look at three main components of response: genetic, environmental, and plastic (adaptive) responses.

The genetic component refers to the inherited traits of the organism that can influence its ability to survive under stressful conditions. The environmental component takes into account the surroundings of the organism, such as the temperature and interactions with other species. The plastic component involves how individuals can adjust their behavior or physiology based on their environment.

To do this, we will perform a series of experiments and field surveys over multiple years. Our goal is to see how the red gorgonian’s responses vary with environmental conditions and whether its genetic makeup plays a role in its survival.

#Overview of the Research Methodology

#Sampling Locations

We selected three sites in the Mediterranean Sea to study the red gorgonian: Pota del Llop, La Vaca, and Tascons. These sites were chosen because they are relatively close to each other and have similar environmental conditions. We marked and collected samples from adult colonies of the red gorgonian in these locations for our experiments.

#Common Garden Experiments

We conducted common garden experiments over three consecutive years to evaluate how the red gorgonian responds to temperature stress. In these experiments, we brought the marked colonies to a controlled environment where we could manipulate the water temperature.

Each colony was separated into two groups-one group was exposed to normal temperature, while the other group was subjected to elevated temperatures. Throughout the experiment, we monitored the health of the colonies by measuring the extent of tissue necrosis (damage) over time. This allowed us to assess how well different colonies could tolerate the heat stress.

#Genetic Analysis

To understand the genetic diversity among the colonies, we conducted DNA analysis on samples collected from different sites. By examining the genetic variation within and between populations, we can gain insights into how genetic factors influence the species' responses to heatwaves.

#Environmental Monitoring

We also monitored the environmental conditions at our sampling sites, particularly focusing on sea temperature during the summer months before our experiments. This helped us to connect the observed biological responses to the thermal stress experienced by the corals.

#Results from the Experiments

#Tissue Necrosis Observations

Throughout our experiments, we observed signs of tissue necrosis in all populations of the red gorgonian. In the first two years, the levels of injury were moderate, with about 30-60% damage recorded. However, in the third year, the heat stress was particularly severe, leading to higher mortality rates. Most colonies not only showed extensive tissue damage but ultimately failed to survive the extended exposure to elevated temperatures.

#Individual Fitness and Response to Stress

Using statistical models, we evaluated how different factors contributed to the overall responses of the colonies. Our findings indicated that the year had a significant impact on the health of the colonies, and individual variability in response was also significant. However, the population or genetic factors had little effect on the overall outcomes.

#Genetic Diversity Findings

From our genetic analysis, we detected distinct genetic clusters corresponding to the different populations. While there was genetic differentiation among the sites, the overall genetic diversity was low. This lack of genetic variability may limit the potential for adaptation to climate-induced stress, making the populations more vulnerable to ongoing environmental change.

#Environmental Temperature History

The environmental monitoring revealed that the summers leading up to our experiments were marked by extreme heat days. The highest temperatures recorded in 2017 corresponded with the most significant damage observed in the colonies. This correlation highlights the influence of local temperature conditions on the health of the red gorgonian.

#Sensitivity to Environmental Changes

Through sensitivity analyses, we found that the degree of response to thermal stress among individuals varied greatly. Some genotypes showed a higher tolerance to heat stress, while others were highly susceptible. However, the overall trend indicated a limited ability for the populations to adapt to increasing temperatures due to the high environmental sensitivity observed.

#Field Survey Findings

After experiencing marine heatwaves in 2018 and 2022, we conducted field surveys to evaluate tissue necrosis in the previously marked colonies. Our findings revealed that a significant number of colonies exhibited high levels of necrosis, indicating that the effects of heatwaves persisted over time. The results from the field surveys aligned with our experimental findings, further confirming the vulnerability of these populations.

#Implications for Conservation

The results from our study raise important questions about the future of the red gorgonian and similar species in the Mediterranean. Given the high levels of mortality and limited potential for adaptation, these populations may face imminent threats due to ongoing climate change.

While local conservation efforts may help to some extent, immediate action to address greenhouse gas emissions is vital for the long-term survival of these species and the health of marine ecosystems.

#Conclusion

Our research highlights the intricate relationship between extreme climate events and biodiversity loss, particularly in vulnerable marine species such as the red gorgonian. By adopting a multi-event perspective, we can better understand the impacts of recurrent heatwaves and the factors that shape ecological responses.

The findings suggest that the red gorgonian populations are experiencing declining health due to a combination of high environmental sensitivity, limited genetic diversity, and an inability to adapt to rapidly changing conditions. This calls for urgent attention and action to protect marine biodiversity in the face of climate change.

#Future Directions

Further investigations that incorporate population genomics, environmental data, and mortality trends will be crucial in understanding the adaptive potential of marine species. As extreme climate events become more frequent, ongoing research and proactive measures will be essential in preserving the delicate balance of marine ecosystems and their inhabitants.