The section Bentho-Pelagic Processes implements research projects in polar and temperate latitudes. Projects are linked to PhD or Post-doctoral research proposals and realised by AWI together with its collaborating research institutions and universities.
Projects in the Antarctic
Bentho-pelagic carbon flux on the Antarctic continental shelf
This project aims to understand the interaction between sea ice cover, export of particulate organic carbon and its mineralization at the seafloor, and how benthopelagic fluxes of oxygen, carbon, and inorganic nutrients on the Antarctic shelf are influenced by climate change.
The Antarctic continental shelf represents roughly 11% of the world’s continental-shelf area and is considered the most productive part of the Antarctic. On the shelf, primary production strongly varies depending on light conditions, sea ice cover, mixing depth and nutrient availability. In regions impacted by global warming, such as the Antarctic Peninsula, these conditions are changing, leading to the retreat of sea ice and ice shelves and to the exposure of previously covered areas to marine primary production, with important repercussions on nutrient and carbon fluxes. Further, increased calving of icebergs and increased iceberg scours are expected to affect carbon turnover near the seabed.
Distribution and ecology of hexactinellid sponges in the southeastern Weddell Sea
The aim of the PhD project is to advance our understanding of the distribution and ecological role of glass sponges (Porifera, Hexactinellida) in the shelf areas of the southeastern Weddell Sea.
Sponges are important components of the seafloor communities in many regions of the Antarctic shelf. They often dominate the benthic biomass and can form extensive sponge grounds in some areas. The most conspicuous species belong to the class Hexactinellida, or glass sponges, which form skeletal needles of silicon dioxide and can grow up to 2 m in height. They are of ecological importance, because the sponge grounds provide a complex, three-dimensional habitat for a variety of other animals and may play a significant role in the cycling of silicon and carbon. However, many questions about their ecology and mode of life remain unresolved. The objectives of my PhD project are
- to determine biomass ratios and size-biomass relationships for different glass sponge morphotypes, which can then be used to calculate glass sponge biomass from images,
- to estimate glass sponge metabolism and their impact on carbon cycling from measured pump rates and respiration, and
- to identify parameters governing their distribution, biodiversity, abundance and biomass on the southeastern Weddell Sea shelf.
This knowledge will help us to assess how these important ecosystem engineers will be affected by environmental changes.
Benthic communities of the Weddell Sea: Past, Present and Future
To describe the present situation of the benthic fauna in the Weddell Sea by using new and old samples, describe community changes form past descriptions and asses how will benthic communities be affected by the ongoing climate change.
This project uses quantitative data of multi-box corer stations and seabed images taken during several cruises with RV Polarstern. As a first step the data will be used to fill gaps in current knowledge of benthic communities to the compare the "present" state with its "past" description. Additionally, environmental data (e.g. hydrography, sediment chemistry) is included in the analysis to asses which environmental factors regulate benthic distribution. The analysis of the past and present of benthic fauna and how the environment regulates benthos will be incorporated in a model to evaluate the effect of climate change over benthic faunal communities.
Projects in Patagonia
Calcification in cold-water corals and their use as environmental archive
The aim of this PhD project is to reconstruct seawater pH and temperature by measuring the boron isotopic and elemental composition of cold-water coral (CWC) skeletons .
Organisms with a calcium carbonate skeleton can be an important climate archive as geochemical signals within their skeletons enable the reconstruction of environmental conditions. This project aims to reconstruct seawater pH and temperature at seasonal resolution using skeletons of the cold-water coral (CWC) Desmophyllum dianthus. For this purpose, field experiments are conducted in Comau Fjord (Chile), with the corals exposed to natural fluctuations in pH and temperature and combined with lab experiments at AWI treating the corals with constant pH and temperature. CWC skeletons from both approaches are then analysed for their structure (Raman spectroscopy, electron microscopy) and their elemental and boron isotopic composition (microprobe, LA-MC-ICP-MS). This combination of both field and lab experiments and the complementary application of these high-resolution analytical methods may help to better understand the process and functioning of calcification and the incorporation of different element compositions in CWC. The long-term goal is to apply these findings to the reconstruction of climate relevant parameters such as temperature and pH especially in the Southern Ocean.
Trophic ecology of the cold water coral Desmophyllum dianthus
This project aims to study the feeding patterns of the CWC in Chilean Patagonia and how they interact with their zooplankton prey.
An extraordinary community of cold water corals is present in on the steep walls of Comau Fjord in Patagonian Chile, dominated by Desmophyllum dianthus. This pseudocolonial scleractinian coral occurs in high densities over the entire marine depth range down to 400 m – in spite of low concentrations of dissolved aragonite. So far, it is not clear how the corals manage to thrive in these naturally acidified waters. Here, we suggest that a rich supply of zooplankton provides the necessary nutritional energy to allow the corals to grow even in aragonite undersaturated waters. Our study aims to explore the temporal and spatial distribution of the zooplankton, and its role in the diet and metabolism of D. dianthus. We hypothesize that zooplankton undertake extensive vertical migrations, and it is conceivable that diel and/or seasonal migrations contribute to the food supply of corals in deeper waters. Zooplankton feeding may be of particular importance to understand how corals are able to cope with ocean acidification and temperature rise in response to global CO2 emissions.
Possible trophic link between filter-feeders and the coral Desmophyllum dianthus
Understanding the trophic interactions of ecosystem engineering cold-water corals through the current era of environmental degradation and climate change, is among the most pressing challenges that biologist face.
Cold-water corals play an important role as ecosystem engineers by providing the three-dimensional structural basis and habitat for a rich associated fauna. Despite its importance, these species are among the most threatened by climate change through ocean acidification. In southern Chile, the cold-water scleractinian Desmophyllum dianthus populates the steep walls of Comau Fjord. Here its principal energy source, zooplankton, is less abundant in winter. This coral species is often associated with filter-feeders, but the nature and possible trophic significance of this relationship remains enigmatic. Dense belts of the mussel Aulacomya atra and the brachiopod Magellania venosa thrive in the productive waters above and between D. dianthus, and both, visual observation and diver-operated push net samples revealed a rain of biodeposits from these filter-feeders to the corals. This study aims to determine if microscopic plankton, which is inaccessible to corals may be accessible to the corals’ tentacles through the conversion by filter-feeders to macroscopic strings of faeces and pseudofaeces. If so, this may represent a new and so far overlooked trophic link channeling surface production to the corals.
Coral ciliary flows and boundary layer dynamics
Investigate the role of ciliary flows on the physiology, nutrition and stress resistance of corals.
Most sessile organisms have to overcome a physical barrier called "boundary layer" which limits the mass exchange between tissue and environment. Corals are no exception: as animals lacking respiratory organs, they rely on a flow of oxygen commensurate with their respiratory demands. Although it has long been known that the tissue of corals is covered with cilia, the importance of ciliary currents in the mass balance of oxygen has been highlighted only recently in stagnant water. We hypothesize that ciliary flows may play a wider role, affecting also coral feeding and stress response. We test these hypotheses using state-of-the-art microsensor and video techniques on tropical and cold-water corals.
Plankton- And cold-water COral ecology in Comau fjord (PACOC)
PACOC investigates the growth of cold-water corals (CWC) in a naturally acidified Patagonian fjord and the role of zooplankton in sustaining their nutritional supply.
Calcification and growth of CWC depends on seawater chemistry, particularly the saturation state of aragonite, the mineral composing the skeleton. The rising CO2 levels in the atmosphere are predicted to change seawater chemistry and lower the aragonite saturation state, with negative consequences particularly for the deep biota. Because many CWC live at or near aragonite saturation, already slight changes in saturation state may have dire consequences for the calcification and survival of these corals. Comau Fjord (Chile) offers a unique window into the future, where the stratified fjord allows to time-travel from aragonite-supersaturated waters near the surface to undersaturated waters at depth. Recent research has shown that the CWC Desmophyllum dianthus abounds below the aragonite saturation horizon, suggesting adaptation to ocean acidification. Because coral calcification is energetically costly, we postulate that a high supply of zooplankton food provides the metabolic energy for the coral to maintain calcification in acidified waters. The project involves observational and experimental studies on the ecology of the corals and their regulation of internal pH, their ability to cope with global CO2 and temperature rise, and the ecology of the plankton, its distribution in space and time, vertical migrations and seasonality.
Projects in the Arctic
Arctic fish under ocean acidification and warming conditions
The Arctic is expected to experience the most rapid temperature and acidification increase, causing latitudinal distribution ranges of ectotherm species to decrease and a species-specific northward shift in distribution areas, concomitant with an invasion of boreal species into the Arctic.
Boreal species such as Atlantic cod (Gadus morhua) are entering the Arctic in response to rising water temperatures, likely increasing predation pressure on the endemic key species Polar cod (Boreogadus saida). We investigated the whole-animal performance of both fish species under future ocean acidification and warming conditions in order to estimate the species’ future competitive strength. More precisely, we focused on aerobic performance such as baseline and maximum metabolism, as well as energetic investments into growth and swimming as indicators for fitness capacity under future ocean conditions. While Atlantic cod was thriving under ocean conditions projected for the year 2100, the competitive strength of Polar cod likely decreases. For instance, the growth performance of Polar cod decreased at temperatures above 6°C and the swimming performance was reduced under ocean acidification scenarios, potentially resulting in a higher vulnerability to predation and reduced success during foraging.