Beschreibung: Ovigerous females were collected by scraping from inner Kiel Fjord in July -August 2017 and kept under control constant temperature room (~20°C) until egg hatching. Newly hatched larvae were reared under different salinity treatments in order to estimate their salinity tolerance,. Experiments were conducted until larvae reached the megalopae stage (last larval stage) or died, The results of such study could give us a primary outlook on the dispersal ability of H. takanoi larvae along the Baltic Sea, and insights about the life cycle of H. takanoi specifically in the south-western Baltic.

Beschreibung: Crabs were collected from inner Kiel Fjord by scraping in November 2018, in order to study their tolerance to salinity and consequently their ability to establish a population along the Baltic Sea, in addition, their feeding rates were estimated under laboratory condition. Experiments were conducted in constant climate temperature room (~12 °C) at GEOMAR during December 2018.

Beschreibung: Salinity in Kiel Fjord was recorded on mostly-weekly cruises of the research vessel FK Polarfuchs from 2005 to 2018 using a CTD48M probe (Sea and Sun technologies, Trappenkamp, Germany) at a station in front of the GEOMAR Pier (“Wittlingskuhle”, Position: 54°19'69 N, 10°09'06 E). These measurements are important for better understanding the salinity as one of the important abiotic factor determine the reproduction, establishment and has an effect on many species in the Baltic Sea in general and the fjord specifically.

Beschreibung: In a warming ocean, temperature variability imposes intensified peak stress, but offers periods of stress release. While field observations on organismic responses to heatwaves are emerging, experimental evidence is rare and almost lacking for shorter-scale environmental variability. for two major invertebrate predators, we simulated sinusoidal temperature variability (±3 °C) around todays' warm summer temperatures and around a future warming scenario (+4 °C) over two months, based on high- resolution 15-year temperature data that allowed implementation of realistic seasonal temperature shifts peaking midpoint. Warming decreased sea stars' (Asterias rubens) energy uptake (Mytilus edulis consumption) and overall growth. Variability around the warming scenario imposed additional stress onto Asterias leading to an earlier collapse in feeding under sinusoidal fluctuations. High-peak temperatures prevented feeding, which was not compensated during phases of stress release (low-temperature peaks). In contrast, increased temperatures increased feeding on Mytilus but not growth rates of the recent invader Hemigrapsus takanoi, irrespective of the scale at which temperature variability was imposed. This study highlights species-specific impacts of warming and identifies temperature variability at the scale of days to weeks/months as important driver of thermal responses. When species' thermal limits are exceeded, temperature variability represents an additional source of stress as seen from future warming scenarios.

Beschreibung: Energy uptake of H. takanoi and A. rubens during the experimental period (72 and 64 days, respectively) measured under 4 temperature conditions: ambient ('constant'), warm ('constant'), ambient sinusoidal and warm sinusoidal. The experiments were conducted from July to September 2017 in the Kiel Indoor Benthocosms (KIBs), at GEOMAR Kiel, Germany. The energy uptake was evaluated at different scales summing the energy uptake for the particular scale of interest: (i) large-scale as the overall sum of the energy uptake, (ii) small-scale (Phase) of 8-day wavelength, for 2-day feeding periods were energy was summed at minimum (Min), maximum (Max) and mean temperatures after minimum (Descending) or maximum (Ascending) during each sinusoidal temperature cycle, and (iii) medium-scale (Period) of 16 days, where energy uptake was summed for 'Pre-heat' (July 19th to August 4th), 'Heat' (August 4th to August 20th) and 'Post-heat' (August 20th to September 5th). To estimate energy uptake, A. rubens and H. takanoi were fed M. edulis mussels every second day. Each individual of A. rubens received five mussels of 25 to 35 mm size (total length). For H. takanoi, 20 mussels of 9 to 12mm were offered. For A. rubens, the shell of every consumed mussel was measured. In the case of H. takanoi, the average size (10.5 mm) of the mussels offered was taken for further estimated on energy uptake. A predictive relationship between soft tissue dry weight of mussels (g) and mussel length (mm) was used to calculate dry mass and energy uptake according to Brey et al., as 18.85 Joules per mg dry mass of mussels.

Beschreibung: Size and weight of H. takanoi and A. rubens during the experimental period (72 and 64 days, respectively) measured under 4 temperature conditions: ambient ('constant'), warm ('constant'), ambient sinusoidal and warm sinusoidal. The experiments were conducted from July to September 2017 in the Kiel Indoor Benthocosms (KIBs), at GEOMAR Kiel, Germany. Wet and dry weight (g) were quantified at the start (July 12th) and at the end of the experiment (September 21st (day 72) for A. rubens and on September 14th (day 64) for H. takanoi). For this, individuals were weighed after gently blotting dry with a tissue. At the end of the experimental period, all individuals of both species were frozen (6 hours at -20°C), and dried (48hours, 80°C), and weighted to estimate dry weight.

Beschreibung: Larval stages of the abulacraria superphylum including echinoderms and hemichordates have highly alkaline midguts. To date the reason for the evolution of such extreme pH conditions in the gut of these organisms remains unknown. Here, we test the hypothesis that analogous to the acidic stomachs of vertebrates, these alkaline conditions may represent a first defensive barrier to protect from environmental pathogens. pH-optimum curves for five different species of marine bacteria demonstrated a rapid decrease in proliferation rates by 50-60% between pH 8.5 and 9.5. Using the marine bacterium Vibrio diazotrophicus which elicits a coordinated immune response in the sea urchin larva of Strongylocentrotus purpuratus, we studied the physiological responses of the midgut pH regulatory machinery to this pathogen. Gastroscopic microelectrode measurements demonstrate a stimulation of midgut alkalization upon infection with V. diazotrophicus accompanied by an upregulation of acid-base transporter transcripts of the midgut. Pharmacological inhibition of midgut alkalization resulted in an increased mortality rate of larvae during Vibrio infection. Reductions in seawater pH resembling ocean acidification (OA) conditions lead to moderate reductions in midgut alkalization. However, these reductions in midgut pH do not affect the immune response and resilience of sea urchin larvae to a Vibrio infection under OA conditions. Our study addressed the evolutionary benefits of the alkaline midgut of ambulacraria larval stages. The data indicate that alkaline conditions in the gut may serve as a first defensive barrier against environmental pathogens and that this mechanism can compensate for changes in seawater pH.