DOI: 10.5061/dryad.tmpg4f569
title: When resilience is not enough: 2022 extreme marine heatwave threatens climatic refugia for a habitat-forming Mediterranean octocoral

description: Climate change is impacting ecosystems worldwide, and the Mediterranean
 Sea is no exception. Extreme climatic events, such as marine heat waves
 (MHWs), are increasing in frequency, extent, and intensity during the last
 decades, which has been associated with an increase in mass mortality
 events for multiple species. Coralligenous assemblages, where the
 octocoral Paramuricea clavata lives, are strongly affected by
 MHWs. The Medes Islands Marine Reserve (NW Mediterranean) was considered a
 climate refugia for P. clavata, as their populations were showing some
 resilience to these changing conditions. In this study, we
 assessed the impacts of the MHWs that occurred between 2016 and 2022 in
 seven shallow populations of the octocoral P. clavata from a
 Mediterranean Marine Protected Area. The years that the mortality
 rates increased significantly were associated with the ones with strong
 MHWs, 2022 being the one with higher mortalities. In 2022, with 50 MHW
 days, the proportion of total affected colonies was almost 70%, with a
 proportion of the injured surface of almost 40%, reaching levels never
 attained in our study site since the monitoring was started. We
 also found spatial variability between the monitored populations. Whereas
 few of them showed low levels of mortality, others lost around 75% of
 their biomass. The significant impacts documented here raise
 concerns about the future of shallow P. clavata populations
 across the Mediterranean, suggesting that the resilience of this species
 may not be maintained to sustain these populations face the ongoing
 warming trends.
description: # When resilience is not enough: 2022 extreme marine heatwave threatens
 climatic refugia for a habitat-forming Mediterranean octocoral
 [https://doi.org/10.5061/dryad.tmpg4f569](https://doi.org/10.5061/dryad.tmpg4f569) ## Description of the data and file structure The data set contains 3 documents: 1\) "QuadratsMedesTot.csv" is the collected data of each gorgonian, each year in each location. Any cells without information count as NA values. The variables are: Data: date in which the data was collected. Any: year of the sampling. Observador: name of the observer. Proteccio: protection degree of the location. Parc: name of the natural parc where the data was collected. Lloc: name of the site/location. Fondaria: depth. Quadrat: number of the quadrat. Talla: size of the colony (cm). Necrosi: proportion (%) of early mortality/necrosis of the tissue of each colony. Epibiosi: proportion (%) of late mortality/epibiosis of the tissue of each colony. Observacions: any other additional observations. 2\) "6-Stat_Report_Medes_200207-202210_2022-12-07.csv" is the collected data of the water temperature in the location of the study. The data is collected by a HOBO every 5 m depth, until 40 m, each day since 2002. This data set is available through the repository [www.t-mednet.org](http://www.t-mednet.org), a collaborative initiative which conducts large-scale and long-term monitoring throughout the Mediterrabeab Sea. To ask for the data set write to [www.t-mednet.org](http://www.t-mednet.org). The variables are: date: date in which the data was collected. depth(m): depth. N: number of temperature detecions per day and depth. mean: mean of the temperature of each day and depth. std: standard error. max: maximum temprature detected each day and depth (ºC). min: minimum temprature detected each day and depth (ºC). 3\) "MHW_classification.csv" is the termotolerance curve data set, where we will add, through R Studio, some additional data: Temp: each temperature of the curve. Species: name of the species. Site: location of the study. MHWDays, Year, Size and Impacted will be filled with the calculations through the RStudio scripts; everything is explained there In this paper we calculate the mortality of the red gorgonian Paramuricea clavata. We make two approximations: 1\) Temporal evolution of the mortality, from 2016 to 2022. Here we will use the "Temporal evolution + MHWs" script, and the 3 data frames (6-Stat_Report_Medes_200207-202210_2022-12-07.csv, MHW_classification.csv and QuadratsMedesTot.csv). We did 3 plots:     a) MHWs: We calculated the Marine Heat Waves of each year.     b) Affected colonies: We calculated the proportion of affected colonies of each year.     c) Injured surface: We calculated the proportion of dead tissue of each year. 2\) Spatial analyses. Here we used the "Mortality per site" script, and the "QuadratsMedesTot.csv) data frame. We did 2 plots to show how different is the mortality in each site of the monitoring:     a) Proportion of affected/not affected colonies per site in the year 2022.     b) Biomass change from 2016 to 2022 in each site. ## Code/Software All code instructions are outlined within the R scripts.