Abstracts session 5

Fieldwork at home? Experiments at MAREE during Corona and beyond


Abstract 109

Effect of Different Light Intensities on Antioxidant Activity, Total Phenolic Content and Chlorophyll a in Sea grapes (Caulerpa lentillifera)

Mia Pribbernow1,2, Revathi Achuthan1,2

1) ZMT, 2) Marine Botany Uni Bremen

Caulerpa lentillifera (also ‘green caviar’) are edible green algae, featuring high nutritional benefits like antioxidant activities and are popular for their caviar-like texture. The demand for sea grapes is increasing and culture mainly takes place in SE-Asian countries in shaded ponds, due to their light sensitive nature. Light can trigger antioxidants, including phenolic compounds. But excessive light can also cause relocation of chlorophyll pigments, leading to discoloration and potential negative customers’ purchasing behaviour. Therefore, this study was conducted to investigate the effect of different light intensities (0-600 µmol photons m-2 s-1) on antioxidant activity (AOA) and total phenolic content (TPC). Also, potential chloroplast movement was tracked by measuring chlorophyll concentrations of different parts of algae (stolon, frond base and tip) and quantifying algal color. Exposure of sea grapes to high irradiances (600 µmol photons m-2 s-1) led to an approximately 2-fold increase in AOA and 1.8-fold increase in TPC compared to the initial. However, while the chlorophyll a content was similar among thallus parts at 50 µmol photons m-2 s-1 , under high irradiances (400 µmol photons m-2 s-1) stolons showed higher concentrations compared to the frond, indicating a chloroplast relocation.

Abstract 110

Microsensor measurements of reactive oxygen species in Pocillopora damicornis during a standardized short-term heat stress assay

Marlen Schlotheuber

WG Reef Systems, ZMT

Human-induced climate change causes an increase in the intensity and frequency of marine heat waves, which is one of the main drivers of coral bleaching and reef degradation. The underlying mechanisms that cause the breakdown of the mutualistic symbiosis between the coral host and its photosynthetic symbiont are not completely understood. While reactive oxygen species (ROS) and oxidative stress have long been stated as major triggers of the symbiosis breakdown, previous studies demonstrate the pivotal role of more complex pathways within the coral holobiont. Therefore, it is essential to resolve the role of ROS in coral bleaching and its impact on the photosynthetic efficiency of the symbiont. Microsensor measurements offer the unique opportunity to measure ROS production at the polyp level. This study uses ROS microsensors on corals exposed to standardised short-term heat stress assays within coral bleaching automated stress systems (CBASS). Specifically, we aim to identify i) how much hydrogen peroxide is produced by the coral, ii) the impact of removing external ROS on the photosynthetic efficiency of Pocillopora damicornis and iii) the direct relationship between increasing thermal stress and hydrogen peroxide production by the photosynthetic symbiont of Pocillopora damicornis. As data collection is in progress (until March 2022), we focus on describing the rationale of the study and the assembly of instruments within an experimental set-up made possible through the synergy among the MAREE, the Max-Plank Institute of Marine Microbiology, and the University of Konstanz.

Abstract 111
A mesocosm study: Effects of increased CO2 levels and temperature on tropical seagrass and macroalgae species

Jessica Schiebe


Marine benthic macrophytes build one of the most productive and diversity-rich marine ecosystems worldwide, seagrass meadows. Especially in the tropics, benthic macrophytes provide multiple ecological functions and present the key primary producers. Seagrass meadows currently facing a “global crisis” due to local and global anthropogenic stressors, dropping at a rate of over 7% per year worldwide, with around 29% of the world’s seagrass stock already lost. Ocean warming is projected to hasten the decrease of seagrass meadows, as temperature is generally the dominant range limiting factor. On the other hand, ocean acidification and the increase in oceanic CO2 are expected to benefit most marine macrophyte species. Since research is still limited on how climate change will affect tropical seagrass meadows in the future, a multi-stressor mesocosm experiment was conducted in the Marine Experimental Ecology (MAREE) facilities at the ZMT. The aim of the experiment was to determine morphological, physiological, and biogeochemical responses of important seagrass and macroalgae species dominating seagrass communities along the coast of Zanzibar Island to a changing environment. Selected seagrass (Thalassia hemprichii, Cymodocea serrulata, Halodule uninervis) and macroalgae species (Halimeda opuntia, Chaetomorpha sp., Laurencia sp.) were exposed to increased temperature (27 and 32°C) and CO2 concentration (400 ppm, 600 ppm), individually and in combination over nine weeks. Overall, the three seagrass species exhibited a positive response to increased temperature in terms of morphology and physiology, whereas the macroalgae Laurencia sp. reported a severe reduction in the biomass. Apart from a decrease in the δ13C isotope level no substantial effect of increased CO2 levels on the morphology and physiology of the macrophyte species were found. The findings of this study indicate that seagrasses will be more resistant to ocean warming than macroalgae under a moderate CO2 increase and climate change scenarios projected for the year 2060.

Abstract 113
Prospecting and Manipulating Carotenoids in the Endosymbiotic Jellyfish Cassiopea andromeda for human nutrition

Holger Kühnhold


Marine resources provide an affluence of bioactive substances that could possibly serve as novel food additives and nutraceuticals to enhance human diet and animal feed. The endosymbiotic mangrove jellyfish Cassiopea andromeda might be an exceptionally promising species in this context. Next to fast growth rates, wide global distribution and  robustness towards environmental change, C. andromeda is a semi-sessile benthic species, which makes it very well suited for captivity culture. Moreover, through its close symbiosis with microalgae, C. andromeda  contains valuable functional pigments, such as  carotenoids with strong nutraceutical properties. In this study, we investigated the carotenoids contained in the C. andromeda holobiont and tested the potential of light (spectra and intensity) for induced manipulation of  pigment composition and concentration. Over the experimental time, growth (weight and diameter) and activity (umbrella pulsation) of the jellyfish was monitored. Moreover, the maximum quantum yield of photosystem II (photosynthetic efficiency; Fv/Fm) was determined, using a portable pulse amplitude modulation (PAM) chlorophyll fluorometer. Pigment analyses were performed using reversed-phase high-performance liquid chromatography (HPLC). Four light accessory pigments (chlorophyll c2, β-carotene, diadinoxanthin and peridinin) were found next to chlorophyll a, in C. andromeda. Peridinin was the most prevalent carotenoid, followed by diadinoxanthin and β-carotene. Light changes did not significantly affect carotenoid concentrations. However, jellyfish treated with green-red light conditions exhibited significantly lower umbrella pulsation rates. Given that the uptake of carotenoids is indispensable for animals and humans, the exploration of natural carotenoid sources is highly relevant to enhance its accessibility for human consumption and animal feed. This study provides first insights into prospecting and manipulating the C. andromeda holobiont for marine carotenoids. We propose to further investigate the nutritional value (e.g. antioxidants, fatty- and amino acids) of C. andromeda and explore its potential to counteract malnutrition, especially in countries of the global south.