Exploring functional interfaces: extreme biogenic fluctuations may amplify or buffer environmental stress on organisms associated with marine macrophytes
Final Report Abstract
The aim of this project was to elucidate organisms’ ability to cope with largely overlooked – but omnipresent – strong environmental fluctuations, and to understand the interaction between the multiple global change pressures and environmental variability. Within this project, we characterized naturally occurring environmental fluctuations from small- to large scale. We clearly depict the transiently extreme conditions organisms need to cope with in interfacial habitats and showed that these fluctuations can provide alternating beneficial and stressful conditions for organisms. Overall, our data adds to a growing body of literature by (i) providing essential data on the range of microenvironmental conditions established on macroalgal blades in interaction with their epibionts and (ii) examining the neglected role of epibiont activity, their needs and feedbacks within the DBL, the BBL as well as under global change. We observed neutral (BBL for bryozoa and barnacles), beneficial (BBL for the blue mussel) as well as negative (DBL for bryozoan and barnacles) effects from fluctuations, forming a baseline to further characterize and understand physiological interactions at functional interfaces. Yet, we clearly emphasize that the DBL of macroalgae do not necessarily provide refugia at the microscale. This project highlights that biologically active surfaces further add complexity to pH fluctuations within the DBL that were herein not beneficial for calcifiers, in terms of growth. We highlight the need to consider the possibility that chemical defences might overwrite the mitigation potential offered by macrophytes. It is imperative that studies explore the concept of refugia and how this concept is defined, but also characterise their biological benefits and drawbacks. The emphasis that macrophytes will be the saving grace against acidification needs to be addressed with caution in particular for epibionts living at the macrophyteseawater interface. Though, Kapsenberg & Cyronak (9) excluded microrefugia from their definition of refugia in variable environments, yet these may represent an important training ground for species to cope with future changes. As an important substrate for many organisms, as well as their different life-history stages, they potentially play a crucial role in rendering organisms less susceptible to future changes. In the Baltic Sea, it was shown that environmental history already renders calcifiers more robust to changes in pH, yet a similar effect may derive through fluctuations and conditions within the DBL. Thus, epibiotic organism can cope with strong environmental fluctuations and even though these conditions reduced growth rates they may select for higher phenotypic plasticity and increase the adaptive capacity. Yet that warrants further investigation. Within this project, we also focused on the role of extreme events in re-structuring ecosystems. The growing frequency of extremes such as marine heat waves increased the urgency to understand what measures allow organisms to persist through such events and whether specific conditions may provide temporal refugia. The aim was to understand whether upwelling events can provide protection from severe heating similar as during coral bleaching events in the tropics. However, upwelling not only brings temperature relief, but also exposes organisms to other rather stressful conditions such as exposure to hypoxic and low-pH seawater. While adult individuals benefited from upwelling during thermal stress, their recruits exacerbated their tolerance limits during the succession of these events (thermal stress and upwelling). Thus, upwelling events following heat waves serve as a mixed blessing for Fucus spp. meadows but may help in ecosystem persistence.
Publications
- The effect of elevated and fluctuating pCO2 concentrations on the growth of calcifying marine epibionts. YOUMARES, Kiel, Germany, 2017
Johnson M, Hennigs L, Pansch C, Wall M
- (2018) Macroalgae may mitigate ocean acidification effects on mussel calcification by increasing pH and its fluctuations. Limnology and Oceanography: 63, 3-21
Wahl M, Schneider Covacha S, Saderne V, Hiebenthal C, Müller JD, Pansch C, Sawall Y
(See online at https://doi.org/10.1002/lno.10608) - Macrophytes may mitigate ocean acidification effects on associated calcifiers by increasing pH and its fluctuations – from boundary layers to canopy effects. Ocean Global Change Biology – Gordon Research Seminar, Waterville Valley, NH, US, July 14-15 2018
Pansch C, et al.
- (2019) A new mesocosm system to study the effects of environmental variability on marine species and communities. Limnology and Oceanography: Methods 17 (2), 145-162
Pansch C & Hiebenthal C
(See online at https://doi.org/10.1002/lom3.10306) - (2019) Experimental assessments on the impacts of extreme events on benthic marine predators. 12th International Temperate Reefs Symposium, Hong-Kong, China, January 6th-11th, 2019
Pansch C, et al.
- Benthic pelagic coupling and its role in modulating ecosystem response to global change. GEOMAR internal RD2/RD3 workshop, Kiel, October 28th, 2019
Wall M, et al.
