Global warming due to greenhouse gasses emissions already has significant impacts on Earth’s climate system. In addition to changes in the mean air and sea temperature leading to sea ice melting and sea level rise, it will affect atmospheric and oceanic circulation and, consequently, precipitation patterns, including the frequency and duration of extreme climatic events (ECE) like heatwaves, strong winds, storms and hurricanes. ECE are considered any climatic events with a magnitude that deviates significantly from the local recorded average. Winter storm intensity, increased strength and number of days of winds and increased frequency of heatwaves leading to severe droughts and dessication stress are expected to increase. Coastal environments, where a large fraction of world population is concentrated, will be increasingly exposed to natural hazards, making urgent the need to understand how these changes affect the ecosystem structure and functioning to gain a better scientific understanding of long term impacts. This session will explore the effects of ECE on the shallow coastal communities from the micro to the macroorganisms and from the micro to the macroscale in a multidisciplinary approach.
Lead Organizer: Sokratis Papaspyrou, University of Cadiz (sokratis.papaspyrou@uca.es)
Co-organizers:
Alfonso Corzo, University of Cádiz (alfonso.corzo@uca.es)
Presentations
05:00 PM
Subtropical coastal microbiome changes due to massive river run-off after a cyclonic event (5433)
Primary Presenter: Mathisse Meyneng, Ifremer (mathisse.meyneng@ifremer.fr)
Subtropical climate is marked by a wet season during which intense precipitations have significant consequences on the ecological equilibrium of the land-sea continuum. River run-off effect after a cyclonic rainy event was studied in a coastal oligotrophic lagoon of New Caledonia (SW Pacific). Using environmental DNA (eDNA) metabarcoding, the short-term dynamic of water surface coastal microbiome (protist and bacterial communities) was studied both during a dry season, used as a baseline ecological condition, and after the cyclone passage. Community composition was mainly influenced by temperature, organic matter and hydrodynamic processes. During the dry season a coastal-off-shore microbial diversity and biogeochemical gradient was highlighted. This spatial pattern was destructured by the river plume which extended about 20 km, reaching the coral barrier reef of the lagoon. The first day after the cyclone, coastal microbiome decreased in diversity and eDNA microbiological signatures of terrestrial and riverine origins were identified, expecially in coincidence with an increase in terrigenous matter concentration. After the run-off disturbance, particulate matter indicators and community composition were not reestablished to baseline ecological conditions during the 6 days of following monitoring. This study suggests that subtropical lagoons require longer resilience time after an intense run-off impact and that the potential increase in extreme rainy events due to the on-going climate deregulation might cause long-term coastal ecological disequilibrium.
05:15 PM
IMPACTS OF REGIONAL DROUGHT ON APALACHICOLA BAY, FL, USA, A SHALLOW MICROTIDAL ESTUARY (5007)
Primary Presenter: Steven Morey, Florida A & M University (steven.morey@famu.edu)
Apalachicola Bay a shallow, microtidal, multiple inlet estuary along Florida’s coastline in the northeastern Gulf of Mexico, is an economically and ecologically important estuary. Historically, the bay has provided 90% of the oyster harvest for the state of Florida and 10% of the oyster harvest for the United States, and also serves as nursery habitat for commercially and recreationally important finfish. A series of droughts in recent decades, combined with overharvest of oysters, has led to a serious decline in the oyster population with potential ramifications to the ecosystem health and regional fisheries. To support ongoing and future activities aimed at restoring oyster populations within the bay, a high-resolution hydrodynamic model of the bay and surrounding northeastern Gulf of Mexico coastal waters has been developed using the Finite Volume Coastal Ocean Model (FVCOM). The model is run for historical and altered climate and water management scenarios, with particular focus on low-flow periods. Comparisons of the simulated salinity to observations show that, although the model simulates well the salinity variability during years of normal rainfall, the model tends to have a low bias in its simulated salinity during drought years. Analysis of model experiments reveals that reducing the freshwater input from the Apalachicola River based on its measured discharge at the observing station closest to the bay alone is not sufficient to raise the bay’s salinity to the observed range. As the hydrodynamic model output is used to drive individual-based oyster larvae simulations, the low salinity bias results in erroneous estimates of larval survival with the model not reproducing the larval mortality that likely leads to the decline in oyster populations. Thus, additional physical mechanisms are found to be of increased importance for accurate simulation of the bay’s salinity during drought regimes compared to times of normal hydrological conditions. Model experiments reveal three such factors whose importance is enhanced during low-flow conditions are: high-frequency (diurnal) wind variability, local evaporation and precipitation deficit, and newly understood and measured diversions of the Apalachicola River flow downstream of its closest measurement gauge. Including these factors results in a dramatic improvement of the hydrodynamic simulation and corresponding larval simulation.
05:30 PM
The impacts of wind-induced sediment resuspension on light availability and seagrass growth in a shallow coastal lagoon degraded by severe drought (5586)
Primary Presenter: Daniel Chilton, The University of Adelaide (daniel.chilton@adelaide.edu.au)
The ecological structure and function of shallow coastal lagoons is susceptible to droughts through reductions in freshwater inputs and increases to evaporation rates which increase salinity. This can reduce submerged aquatic macrophyte (SAM) distribution and abundance through osmotic stress. Wind-induced sediment resuspension can further impact SAM growth through increased light attenuation. The aim of this study was to investigate the role of wind-induced sediment resuspension on light attenuation and its implications for SAM growth in the Coorong, a shallow coastal lagoon of both regional and international importance which has been degraded by prolonged drought. Two intensive field sampling campaigns were conducted to measure wind speed and direction, wave height and period, water velocity, suspended particle concentration and water column light penetration during diel wind cycles within the shallow (~ 0.5 m) littoral mudflats over the depth range (0.2–1m) of the SAM community. Wind was the primary driver of wave and current-induced benthic shear stresses which surpassed the estimated critical shear stress of the sediment. Particles were increasingly resuspended with sustained shear stresses above estimated particle thresholds and their concentrations peaked several hours after wind and shear stress subsided, likely the result of wind-mediated transport and circulation. Suspended particles increased light attenuation, impacting SAM growth over the reproductive cycle (spring-summer) when winds are strongest. This study highlights the prolonged negative consequences of drought on shallow coastal lagoon ecosystem health.
05:45 PM
Effect of a short-term heatwave on intertidal sediment metabolism (6537)
Primary Presenter: SANDRA RIZZO CALDERON, University of Cadiz (sandra.rizzo@gm.uca.es)
Coastal ecosystems are areas of high ecological value and play a vital role in global biogeochemical cycling. However, they are particularly vulnerable to an increase in intensity and frequency of heat waves. To investigate the impact of heatwaves on benthic metabolism of the intertidal zone of the Guadalquivir Estuary (SW Spain), sediment cores were subjected to a range of temperatures (10ºC to 42ºC) for 4 days followed by a 7-day recovery period. Oxygen microprofiles and whole core incubations were performed daily to measure benthic metabolism (O<sub>2</sub> and CO<sub>2</sub>) and nutrients fluxes (NH<sub>4</sub><sup>+</sup>, NO<sub>2</sub><sup>-</sup>, NO<sub>3</sub><sup>-</sup>). At the end of each phase, solid phase and porewater variables were also recorded. Oxygen uptake increased exponentially with temperature with maximum values on Day 2. However, at the highest temperatures, O<sub>2</sub> consumption decreased 40% within two days, probably due to an exhaustion of the available labile organic matter, being lower than background rates after the recovery period. Nutrient fluxes also increased with the temperature, followed by a decrease back to minimal fluxes during the recovery period. In the sediment, porewater NH<sub>4</sub><sup>+</sup> and Fe<sup>2+</sup> accumulated between 2.5 and 3.5 cm depth, more so at the highest temperatures. This buildup of solutes remained until the end of the recovery period. These data show that heatwaves can have longer lasting effects on the biogeochemistry and community metabolism and composition of intertidal sediments.
06:00 PM
Effects of diurnal temperature fluctuations and heatwaves on intertidal sediment metabolism (7011)
Primary Presenter: Marika Mecca, Universidad de Cadiz (marika.mecca@uca.es)
Heatwaves are periods of anomalous temperature increases lasting more than 3 days and producing significant human and environmental alterations. Coastal wetlands are vulnerable to these changes due to their low thermal inertia. In these areas, microphytobenthos (MPB) contributes significantly to primary production, being an important carbon source for the higher trophic levels. The aim of this study was to determine the effects of diurnal temperature fluctuations and heatwaves on the abundance and productivity of MPB. Sediment cores sampled in the Guadalquivir River salt marshes (SW Spain) were exposed for 7 days to different thermal regimes in the laboratory, i.e. constant (20 deg), low (20-28 deg) and high daily fluctuation (20-34 deg). O2 microprofiles and light reflectance were measured every 30 minutes and used to estimate the net community production (NCP) and the MPB migration patterns, respectively. Our results show that even at constant temperatures, NCP and reflectance vary during the day, with no relevant changes over the course of a week. Under temperature fluctuations, NCP increases with increasing temperature during the day, but decreases overall after three days exposed to a simulated heatwave. Similarly, the migration pattern of MPB remained constant at constant temperature, whereas higher temperatures decreased the surface reflectance, suggesting that the MPB community moved away from the surface. Heat waves could therefore have a major impact on the metabolism and functioning of intertidal areas, decreasing productivity, and altering MPB migration patterns
06:15 PM
IS SEA LEVEL RISE DRIVING MANGROVE DIEBACK IN THE MALDIVES? INSIGHTS FROM REMOTE SENSING AND DENDROGEOCHEMISTRY (6256)
Primary Presenter: Lucy Carruthers, Northumbria University (lucy2.carruthers@northumbria.ac.uk)
During 2020, mangrove die-back occurred on at least 11 islands in the Maldives which is the lowest elevated nation on Earth and where mangroves provide crucial shoreline protection. Here, we use remote sensing and data from wood and sediment cores from dead and living mangrove areas to test the hypothesis that sea level rise is driving mangrove loss. Mangrove health and areal cover were examined from 2014 - 2022 using Landsat satellite images (30 m resolution) and normalized difference vegetation index (NDVI). The relationship between mangrove health, sea level and precipitation was assessed by linear regression, which showed that mangrove die-back corresponds to an increase in sea level rise. Results from NDVI analysis revealed that mangrove health has decreased significantly since 2020, on all islands, resulting in the complete loss of mangroves in some islands. Affected areas are low-lying within the intertidal zone and dominated by the species Bruguiera cylindrica, which has a low tolerance to salinity and waterlogging. Wood cores were sampled for 14C dating and δ13C to calculate temporal changes in water use efficiency, combined with ITRAX elemental scanning to identify changes in water source and availability. Sediment cores were analysed using 210Pb dating and δ13C to identify changes in sediment redox conditions. This research is crucial to the understanding of tipping points for mangrove ecosystems on low-lying islands under climate change and is essential to guide conservation and rehabilitation strategies.
SS068 Extreme Climatic Events: A Challenge for Shallow Coastal Ecosystems
Description
Time: 5:00 PM
Date: 5/6/2023
Room: Auditorium Mallorca