Four Years into Reef Systems research
ZMT Reef Systems
Four years after the establishment of the Reef Systems worksgroup, group leader Sonia Bejarano presents an overview of the past research pathway of her group and an outlook into the future directions. Past research projects fall into five overarching themes, namely i) Reef biodiversity and ecosystem functioning: current and future drivers, ii) Climate change impacts on reef organisms, functions and services, iii) Local human impacts, uses, and management of reefs, iv) Persistence of reef building corals in the Anthropocene, v) New tools and automation in quantitative reef ecology. Key research highlights per theme are presented. The window for coordinated and decisive action to curb reef degradation is between now and 2050. In the coming years, Reef Systems will thus lead both research and concrete actions that support global strategic action plans to sustain coral reefs through the 21st century. Both research and action will be guided by the principle of balancing the urgency of conserving coral-dominated systems and the need to embrace and understand the functioning of emerging novel systems.
Interaction between Caribbean Sea and Pacific Ocean using climate information of the last 30 years from coral cores of Costa Rica
Sahra Greve1,2, Henry C. Wu2, Henning Kuhnert3, Marie Harbott2, Carlos Jimenez4
1) Faculty of Geosciences, University of Bremen; 2)Leibniz Centre for Tropical Marine Research (ZMT); 3) MARUM – Center for Marine Environmental Sciences; 4) The Cyprus Institute
The importance of climate variability has been intensely studied for the last 30 years and it is clear that the interactions between ocean basins are vital information for climate models and have to be considered when predicting future climate. Sea surface temperature (SST) variability can provide important predictive information about hydrological variability. SST variations over the tropical Pacific exert great impacts on global climate and recent evidence suggests that there is a close connection between the tropical Atlantic and ENSO events originating from the Pacific, to provide more insight on climate variability and interactions across these two basins one massive coral colony each from the eastern Pacific Ocean and the western Caribbean Sea of Costa Rica were analysed for trace elements and stable isotopes. Coral-based SST proxies of Sr/Ca and δ18O demonstrate a close relationship to instrumental SST. Coral δ13C was found to be varying with precipitation record at both localities likely due to metabolic fractionation from photosynthesis. A coherence between coral δ13C in the Caribbean with the NAO index (r=0.15; p<0.01) was detected and in the eastern Pacific, enhanced nutrient transport during La Niña events can be inferred with the increase of Ba/Ca. Correlation between Caribbean and eastern Pacific SST shows a lag of ca. 5 months (r= 0.57; p<0.01) indicating either different controls on the SST in these areas or the atmospheric interaction between the two basins. One striking result found in the eastern Pacific coral was the extensive microboring infestation during the 1997-98 ENSO event possibly due to SST warming-related bleaching resulting in slower coral growth rate. Our replicated results across different regions within the dark growth banding revealed varying degree of secondary skeletal alteration and trace element offsets affecting the ability of coral archives to record accurate climate or environmental signals during these climate extremes.
Multi-coral reconstruction of the South Pacific response to modern climate change
Sara Todorovic1, Henry C. Wu1, Braddock K. Linsley2, Henning Kuhnert3, Albert Benthien4, Klaus-Uwe Richter4, Markus Raitzsch3, Jelle Bijma4, Delphine Dissard5
1) Leibniz Centre for Tropical Marine Research, Bremen, Germany; 2) Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA; MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany; 4) Alfred Wegener Institute – Helmholz Centre for Polar and Marine Research (AWI), Bremerhaven, Germany; 5) IRD-Sorbonne Universités, UPMC, Univ Paris 06-CNRS-MNHN, LOCEAN, Paris, France
Recent increase in anthropogenic CO2 emissions induced a fast and accelerating acidification of our oceans, unique in Earth’s history. Since the beginning of the industrial era the surface seawater pH dropped by 0.1 units. The South Pacific Convergence Zone (SPCZ), the largest persistent precipitation band in the Southern Hemisphere with an associated salinity front modulated by large-scale ocean-atmospheric interactions (El Niño/Southern Oscillation, Interdecadal Pacific Oscillation), shows a strong connection with regional seawater CO2 absorption and pH variability. Here we present paleoclimatic reconstructions generated by the analysis of two Porites sp. coral cores sampled in the southwestern Pacific at Tonga (20º16’S; 174º49’W) and Rotuma islands (12°29’S; 177°06’E). Coral skeletal materials were analyzed using an extensive multi-proxy approach to provide optimal hydroclimate and sea surface temperature reconstructions (δ18Oc and sw, Sr/Ca, Li/Mg, U/Ca, Sr-U), while complementary δ13C, B/Ca, and δ11B analysis on both cores allowed for the reconstruction of surface seawater carbonate chemistry changes and pH variability spanning the period from 1779 to 2004. Coral δ18O results from both cores suggest similar freshening and/or 0.47-0.63°C warming of the regional sea surface over the last three decades of the 20th century when converted using previously published δ18O to SST sensitivity of -0.21‰ per °C. Tonga’s Porites sp. δ11B signature indicates a long-term secular decreasing trend suggesting an increasing rate of acidification since 1779, with a pronounced depletion since the 1950s by -0.0626‰ y-1. We also observe a concurrent depletion of coral δ13C indicating the changes to the oceanic DIC reservoir (Tonga: -0.028‰; Rotuma: -0.027‰ y-1 since 1968) and the uptake of anthropogenic CO2 in the tropical Pacific lowering the 13C isotope signature, also known as the oceanic Suess effect.
A warming Gulf of Mexico – Environmental and climatic changes recorded by a Siderastrea siderea coral from the northern Cuban coast
Marie Harbott1, Henry C. Wu1, Henning Kuhnert2, Carlos Jimenez3, Patricia González-Díaz4
1) Leibniz Center for Tropical Marine Research, 2) MARUM-Faculty of Geoscience & Center for Marine Environmental Sciences, 3) The Cyprus Institute, 4) Centro de Investigaciones Marinas Universidad de La Habana
A warming Gulf of Mexico – Environmental and climatic changes recorded by a Siderastrea siderea coral from the northern Cuban coast The Gulf of Mexico is a vital region for the Atlantic Meridional Overturning Circulation (AMOC), which fuels the exchange of heat between the tropics and the polar regions. A weakening of the AMOC would have dire consequences for the planet. First observations and ocean models show that this process has already started. Very limited knowledge on the components of the AMOC, such as the Loop Current, makes it difficult to understand its dynamics as well as changes in strength since the onset of the industrial revolution. Currently, there are no publicly available, continuous in-situ measurements for the southeastern Gulf of Mexico or reconstruction attempts for this region, showing the necessity for high resolution climate achieves. A Siderastrea siderea coral core was retrieved from the northwestern Cuban coast and analyzed as a sub-seasonally resolved sea surface temperature and hydroclimate archive. The multi-proxy approach shows an increase in temperature over the 160 years since 1845 of between 3.3°C and 3.7°C. A possible stagnation of the warming trend set in after the 1980s, indicating a potential weakening of the Loop Current. The reconstruction of δ18OSW demonstrates the ability of the coral to record its dependence on sea surface salinity (SSS). Impacts in SSS such as EL Niño Events in the Pacific region can still be detected in the Gulf of Mexico as decreases in salinity in 1992. In-situ measurements and a prolonged record after 2005 remain crucial to understanding the dynamics in the LC and its influence on the AMOC.
A multi-level coral bleaching resistance and tolerance experiment
Marleen Stuhr1, Guilhem Banc-Prandi2, Julia Cerutti3, Maoz Fine3
1) Leibniz-Zentrum für Marine Tropenforschung (ZMT); 2) Interuniversity-Institute for Marine Sciences (IUI), Eilat, Israel; 3) Bar-Ilan University, Ramat Gan, Israel
The rapid rate of climate change leads to modifications of the physical and chemical conditions in marine ecosystems, of which the rise in seawater temperatures is a major threat to coral reefs, disrupting the sensitive symbiotic relationship of coral with photosynthesizing microalgae. In the near future, coral reefs will experience marine heat waves with even higher frequency and intensity, also in the northern Red Sea. Although partly reversible, coral bleaching often leads to extensive mass mortality. How strongly a reef is affected depends largely on the corals ability to withstand heat stress and their potential to recover from bleaching. Hence, these physiological responses determine the future of reefs and identification of the underlying mechanisms is therefore a key goal of reef research. Here I present initial results and future plans of an experiment with Porites sp., Stylophora pistillata and Pocillopora verrucosa conducted in the Red Sea Simulator in Eilat, Israel, that targets the involved system-wide processes, spanning molecular to organismal levels, involved in heat wave response and recovery. The study aims to determine potential markers to identify corals that exhibit high resilience potential, compares patterns of bleaching resilience across coral taxa, and links the observed physiological responses to geochemical records.
Coral settlement on and next to effective antifouling coatings
Lisa Röpke1, David Brefeld1, Ulrich Soltmann2, Carly Randall3, Andrew Negri3, Andreas Kunzmann1
1) Leibniz Centre for Tropical Marine Research; 2) Gesellschaft zur Förderung von Medizin-, Bio- und Umwelttechnologien e.V.; 3) Australian Institute of Marine Science
In response to coral losses worldwide, innovative and environmentally friendly restoration techniques are needed to reduce algae dominances in suitable reef spots. We investigated antifouling (AF) coatings for their fouling inhibition efficiency and coral settlement as an indicator for toxicity of these coatings towards coral larvae. Three self-engineered AF coatings, (CeO2 nanoparticles (NPs), antiadhesive, and encapsulated dichlorooctylisothiazolinone (DCOIT)), were applied to the surfaces of “coral plugs” in two ways: fully-coated (FC) and partially-coated (PC). Three fouling classes (CCA, soft algae, bare substrate) were monitored over a period of 37 days and analyzed automatically with the Weka plugin in ImageJ. Subsequently, Acropora tenuis larvae were tested for settlement on the previously fouled plugs. The DCOIT-coating showed the highest average fouling inhibition (most bare substrate) of 51%. The antiadhesive coating successfully inhibited 23% of the surface’s fouling. Average A. tenuis settlement on the coatings of the FC plugs did not differ from settlement on the controls. Settlement on the DCOIT and antiadhesive coated areas of the PC plugs was lower from settlement on the control and coated NP areas. Two of the three AF coatings, the encapsulated DCOIT, and antiadhesive coating, have successfully shown solid and very local antifouling efficiency. Simultaneously, coral larvae settlement on these coatings showed opposing results between the PC and FC plugs of the same coating type. In summary, none of the coatings showed efficient antifouling properties coupled with concurrent advantages in larvae settlement. However, interestingly, settlement showed a higher trend on all uncoated treatments directly next to coated areas, than on uncoated controls. Further research on the effects of these coatings is needed to enlarge the knowledge for potential applications in reef restoration.
Interesting and surprising results from Project OASIS
Human induced increases in atmospheric CO2 levels are warming the Earth’s ocean and increasing the acidity of our marine environments. This process, known as ocean acidification (OA), is caused by the absorption of atmospheric CO2 by the oceans and is threatening the ability of calcifying organisms to build their calcium carbonate skeletons. Our understanding of the changes caused by OA in the tropical oceans is severely limited due to the lack of reliable long-term seawater pH monitoring and the difficulty in reconstructing past changes in pH and ocean chemistry. Results confirming occurrence of rapid OA over the past hundred years in the South Pacific and the Caribbean Sea based on boron isotope pH reconstructions using massive corals have been shown. The recording of increasing excess atmospheric CO2 uptake by our oceans known as the Oceanic Suess Effect has also been confirmed [See Harbott et al., and Todorovic et al. talks in this Session]. However, surprising results from Project OASIS were discovered at other locations in the Pacific Ocean. One of these locations is the Central Pacific atoll of Fanning (3º53’N, 159º17’W) that did not record a long-term secular acidification trend but instead recorded a significant increase in pH since 1887 CE (p < 0.001). Depleting coral δ13C signature from this same colony indicates the uptake of CO2 as previously anticipated in contrast to the lack of OA. Another interesting result is seen from the Makassar Strait, part of the Indonesian Throughflow (ITF), which is an important ocean current that connects the Pacific and Indian Oceans. Our coral δ13C time series from this location revealed a surprising enrichment of the stable isotope signature contrary to previously published records from many tropical regions. These surprising but interesting results from this project will be presented for the first time with possible explanations explored.
Nutrients in Coastal Waters of Mombasa, Kenya: Sources, Pathways and Implications on HABs (NOMIHAB)
Nancy A. Oduor1, Nils Moosdorf1, Cosmas Nzaka Munga2
1) ZMT; 2) Technical University of Mombasa (TUM)
Although coastal ecosystems provide critical goods and services that are essential for human well-being, they are highly threatened by nutrient pollution and organic matter discharged through sewage, industrial wastewaters, and agricultural run-offs. The discharges are driven by the increasing human population and intensified coastal development. These have been suggested to cause changes in water chemistry, affecting primary production, with the resulting conditions favoring development of harmful algal blooms (HABs) species. This study conducted in Mombasa, Kenya, a coastal city surrounded by ecologically, economically, and culturally important habitats but experiencing nutrient pollution problems, aimed at examining the sources and quantifying fluxes of essential nutrients (nitrates, phosphates, and silicates) and their effects on phytoplankton community structure and occurrences of HABs. The study tests the hypothesis that ‘increasing HABs development in Mombasa is as a result of nutrient inputs from agriculture, sewage, ballast water, industrial and tourism activities resulting from increasing coastal development’. It involved the integration of published literature and in situ data collection, laboratory analysis to detect, quantify and evaluate the temporal and spatial variation of dissolved nutrients fluxes (speciation, limitation, and molar concentrations of N: P: Si), and HABs species diversity and abundance. A field survey was conducted between August and October and samples are under processing. The study is expected y to provide information that can motivate and inform policy-based mitigation actions towards water quality improvement plans to conserve valuable coastal resources, ensure the resilience of coastal systems, public health safety, secure food, and local livelihoods. Moreover, it will form part of the vital baseline information, which can be compared with other ongoing and future environmental risk assessment and pollution monitoring-related studies in the region.
Keywords: Coastal development, nutrient influxes, marine pollution, HABs, Mombasa, Kenya