Detecting Heatwave Impacts on Marine Forests

Can depth provide biodiversity refuge against marine heatwaves?

About me

Welcome! My name is Roger Amate, I am a first-year IMBRSea master student. For the Professional Practices I did an 8-week internship at Centro de Ciências do Mar in Faro, Portugal.

I have always been fascinated by marine science, and the more I learn the more convinced I become that I want to dedicate myself researching to improve the sustainability of commercial fisheries, For these reason, I decided to enrol myself in this master programme. Even that, there are many other topics that interest me, as climate change and marine conservation. I applied for these specific professional practices since this is a topic that arouses my interest and having already worked on it previously, I believed that my contribution could be beneficial.

Picture 1. Me during the bibliographical research.

Picture 2. Me working in the database.

Picture 3. Me with my two supervisors, Eliza and Jorge.

The Center

The Centro de Ciências do Mar (CCMAR) is an independent non-profit research organisation within the University of Algarve. Dedicated to R&D in marine sciences, it aims to promote multidisciplinary research and education related to the marine environment, emphasising the processes of environmental change that affect marine ecosystems. Two significant research challenges are conducted at CCMAR:

What are the causes and consequences of environmental changes for marine ecosystems?
How to conserve and reveal the potential of living marine resources, considering the expected environmental changes?

To tackle these two significant challenges, its research strategically follows three thematic lines: global environmental change, ocean management and conservation, and marine products and resources. CCMAR activities extend beyond scientific research to include advanced scientific training, collaborations with industry, meeting societal challenges and building bridges with international partners. CCMAR is composed of multiple research groups. I conducted my Professional Practices in the frame of research of one of them, the BEE, the Biogeographical Ecology and Evolution team, which studies patterns and processes mediating population biology from ecological to evolutionary scales.

I conducted my practices under the supervision of Jorge Assis, whose research is mainly focused on species distribution modelling at multiple scales, seascape ecology and seascape genetics. I also had a second supervisor, Eliza Fragkopoulou, a PhD student working with Jorge. (Picture 3)

The study

These practices aimed to compile available information on marine heatwaves (MHW) impacts on marine forests globally. As MHW mainly impact the shallower regions of the sea, the compilation of such information may enable the detection of a depth-impact gradient across species, identifying refugia of MHW with depth.

What is a Marine Heatwave?

Marine heatwaves (MHW) are defined as detecting at a location a daily sea-surface temperature (SST) above a threshold, for at least five consecutive days. Consecutive events with a maximum gap of 2 days between them are considered as the same event. The threshold is defined as the SST 90th percentile of a 30-year climatological record and is calculated at each grid cell for each calendar day within an 11-day window centred on the calendar day of interest across all years, and then smoothed using a 31-day moving average on each day (Hobday et al, 2016).

This definition is a general definition that must not be taken as the only correct way to define a MHW. It is a standard that can be adapted according to the objectives of the study and context. As recommended in the same study: The definition of MHW must be a flexible system allowing for further development of descriptive indices, for particular ecosystems or species as needed by individual research goals. (Hobday et al, 2016).

But in our project we were studying the effects of MHW at a global scale, we used this proposed definition of MHWs without any modification.

The Problem

During the 20th century and the beginning of the 21st, there was a global warming of + 0.76ºC. Specifically, in the seas and oceans, there has been a warming of + 0.3ºC of the surface from 1950 to 2000 (Levitus et al., 2000).

In recent decades, there has been an increase in the magnitude and frequency of cases of impacts on marine communities. This increase has been related to the increase in water temperature (Crisci et al., 2011; Bensoussan et al. 2019). As a result, many organisms in this sea are being subjected, especially during heat waves, to temperatures approaching or exceeding their tolerance limits. In this sense, exposure to sublethal temperatures can act causing physiological stress that can result in a decrease in available energy due to increased respiration, which can affect numerous biological processes of these organisms (Coma et al., 2002). Likewise, exposure to lethal temperatures acts directly on the body causing metabolic dysfunction (Torrents et al., 2008).

The projections for the s. XXI also show an increase in warming from 1.4 to 5.8ºC depending on the emissions scenario (IPCC, 2015), as well as an increase in the frequency and intensity of heatwaves (Déqué, 2007 ; Frölicher et al., 2018). Analyzing the impact of these events at appropriate scales (spatial and temporal) is crucial to carefully anticipate future changes in marine ecosystems and to propose appropriate management and conservation plans. In particular, understanding how marine ecosystems will respond to climate change is a matter of fundamental interest to science, politics, and management (Linares et al., 2008).

Species with depth ranges larger than the effect of marine heatwaves can survive at the deeper parts of its depth range, those becoming a climatic refugia for the biodiversity

Web of Science and Google Scholar were used to find relevant peer-reviewed literature from 1972 to 2021 for the analysis. The keywords used for our search were: sea surface temperature, heat wave, distribution shift, extreme event, temperature anomaly, heatwave, MHW(MHWs), MME, mortality, habitat compression, deep refugia hypothesis, DRH, mass mortality, and thermal refuge. A first selection of the relevant studies was carried out based on the information contained in the abstracts of all the papers resulting from each of the searches. Then, each of the papers that were selected was read to extract the mortality data with depth because of thermal anomalies. As a result, a total of 63 refereed articles, with data from multiple worldwide locations (Figure 1) were included in the database.

Figure 1. Map with all the localities surveyed in the 63 studies represented by red dots.

Figure 2. Screen capture taken during the creation of the database with Excel.

The Database

63 studies

754 impacts with depth registers

161 different localities sampled

17 Marine Ecoregions of the World

Main information for each register

Species maximum surveyed depth

Shallowest depth affected

Deepest depth affected

Year of the event

Results

Figure 3. Plots of each species' habitat depth range (light grey) and the species impacted depth range (bold grey). The majority of species still have part of their depth range not impacted.

Table 1. Summarizes the number of species impacted each 10m of depth. The second column represents the number of species that have a register of impact between 0 and the corresponding depth. The third column is the % over the total of species between the depth values. The fourth column represents the increase in % for each 10m included in the depth range.

Table 2. Summarizes the number of studies by its maximum depth range. We can observe that more than 80% of the studies have their depth range between 0 and 40, with the almost half of the studies (46,03%) having its maximum depth between 20 and 40m, what could indicate that between these depths we find the most significant depth, the one that represents the transition between affection and non-affection (Linares et al., 2005).

Table 3. Summarizes the number of species’ depth range each 10m. The second column represents the number of species that have a depth range between 0 and the corresponding depth. The third column is the % over the total of species between the depth values. The fourth column represents the increase in % for each 10m included in the depth range.

Only 27.84% of the species have their depth range until 30m (Table 3), and 749,38% of the registers of impact are between 0 and 30m. Below 30m depth we will find 72.16% of the species studied. This means that more than 70% of the species populations analysed in this study can survive at deeper parts (>30m), what support the idea of a climatic refugia with depth.

Check out the presentation that I did to the research group!

Presentation.mp4

The 5 Main Points to Discuss

Depth can provide climatic refugia with depth for those organisms that can not escape MHW.

Photosynthetic organisms have their depth refuge constrained by light availability.

Apart from scuba diving, other methods must be used to survey MHW affection over communities to a greater depth than 40m.

Models from previous years until the present can provide us valuable information about where, when and with what intensity MHW happened.

Prediction models could provide us with information about future MHW and its characteristics.

What I have learned

I have learned to be more flexible with my schedule and objectives. Thanks to this, my capacity to work independently, show initiative, respond to new challenges, and organise the workload have improved notably, especially the latest. Thanks to these practices, I am skilful in bibliographical research and the use of its two main resources, Web of Science and Google Scholar. During these practices, I have learned many new and valuable things, concepts, and ways of thinking. During this experience, I have learnt a lot of exciting stuff about MHW, but working on this project has helped me realise that this is not the field in which I want to make my career. It has made me realise that at this moment, I want to dedicate my time and efforts to conservation but the conservation of species with commercial fishing interests, and I want to learn as much as possible about ecosystem-based management.

Sources

CCMAR -. (2021). - CCMAR -. [online] Available at: https://www.ccmar.ualg.pt/
Bensoussan N, Garrabou J, Chiggiato J, Buongiorno Nardelli B, Pisano A, von Schuckmann K (in press) (2019) Insights on 2017 Marine Heat Waves in the Mediterranean Sea. Copernicus Marine Service Ocean State Report #3 Journal of Oceanography
Coma R, Ribes M, Gili J.M., Zabala M (2002) Seasonality of in situ respiration rate in three temperate benthic suspension feeders. Limnology and Oceanography, 47, 324–331.
Cramer W, Guiot J, Fader M, Garrabou J, Gattuso JP, Iglesias A, Lange MA, Lionello P, Llasat MC, Paz S, Peñuelas J, Snoussi M, Toreti A, Tsimplis MN, Xoplaki E (2018) Climate change and interconnected risks to sustainable development in the Mediterranean. Nature Climate Change ,8 , 972-980.
Crisci C, Bensoussan N, Romano J.C., Garrabou J (2011) Temperature anomalies and mortality events in marine communities: Insight on factors behind differential mortality impacts in the NW Mediterranean. PLoS ONE, 6, e23814.
Déqué M (2007) Frequency of precipitation and temperature extremes over France in an anthropogenic scenario: model results and statistical correction according to observed values. Global and Planetary Change, 57, 16–26.
Frölicher T, Fischer EM, Gruber N (2018). Marine Heatwaves under global warming. Nature, 560, 360-364
Hobday AJ, Oliver CJ, Sen Gupta A, Benthuysen JA, Burrows MT, Donat MG, Holbrook NJ, Moore PJ, Thomsen MS, Wernberg T, and Smale Da (2018) Categorizing and naming marine heatwaves Oceanography 31 2 162 173 https :://doi org/ 10 5670 /oceanog 2018 205
IPCC (2015) Climate change 2015: The Physical Science Basis. Contribution of working group I to the Fourth Assesment Report of the intergovernmental panel on climate change (Cambridge University Press, Cambridge, UK and New York, NY, USA, 996p.
Levitus S, Antonov JI, Boyer TP, Stephens C (2000) Warming of the World Ocean. Science, 5461, 2225–2229.
Linares C, Coma R, Diaz D, Zabala M, Hereu B, Dantart L (2008) Effects of a mass mortality event on gorgonian reproduction. Coral Reefs, 27, 27-34.
Torrents O, Tambutte E, Caminiti N, Garrabou J (2008) Upper thermal thresholds of shallow vs. deep populations of the precious Mediterranean red coral Corallium rubrum (L.): assessing the potential effects of warming in the NW Mediterranean. Journal of Experimental Marine Biology and Ecology, 357, 7–19.

Roger Amate López-Sivera - amatelopezsivera.roger@imbrsea.eu

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