ALBERT

Description: Global change is affecting marine ecosystems through a combination of different stressors such as warming, ocean acidification and oxygen depletion. Very little is known about the interactions among these factors, especially with respect to gelatinous zooplankton. Therefore, in this study we investigated the direct effects of pH, temperature and oxygen availability on the moon jellyfish Aurelia aurita, concentrating on the ephyral life stage. Starved one-day-old ephyrae were exposed to a range of pCO2 (400-4000 ppm) and three different dissolved oxygen levels (from saturated to hypoxic conditions), in two different temperatures (5 and 15 °C) for 7 days. Carbon content and swimming activity were analysed at the end of the incubation period, and mortality noted. General linearized models were fitted through the data, with the best fitting models including two- and three-way interactions between pCO2, temperature and oxygen concentration. The combined effect of the stressors was small but significant, with the clearest negative effect on growth caused by the combination of all three stressors present (high temperature, high CO2, low oxygen). We conclude that A. aurita ephyrae are robust and that they are not likely to suffer from these environmental stressors in a near future.

Description: The ongoing acidification process of the oceans is likely to have consequences for many marine biota. Although evolutionary responses are expected during persisting environmental change, little is known about the adaptability of copepods. Therefore, we set up a 3 ½ years long selection experiment, culturing Acartia tonsa populations in water treated with 200 and 800 µatm pCO2, feeding them with algae grown in f/2 medium under 200 µatm pCO2 and in f/2 N P medium under 800 µatm pCO2. After three reciprocal transplant experiments we measured copepods' developmental rates, carbon to nutrient ratios, egg production and hatching rates. Under high CO2 conditions, stoichiometric discrepancies between the requirements of A. tonsa and its food resulted in a significantly decreased developmental rate independent from the selective history. After one year, these discrepancies appeared alleviated by an optimised homeostasis regulation of the copepods, indicating a high body stoichiometry regulation plasticity. Egg production and hatching success were unaffected by the experimental conditions, however, results indicated a premature hatching of eggs from females with a high CO2 selective history. Over the experimental period we did not detect any beneficial adaptations of the copepods cultured under high CO2 conditions of elevated seawater pCO2 and associated food quality reduction. Towards the end of the experiment, copepods cultured under elevated pCO2 and fed with high CO2 algae, showed an increased body mass and decreased prosome length. Such physiological changes could have profound long term consequences for marine copepods, food web interactions, and ultimately ecosystem structures and functions.

Description: The copepod Temora longicornis depends on constant prey availability. Given that climate change may induce food regime shifts, our research goal was to understand copepod energy allocation in relation to diet quality. The working hypothesis was that Temora performs better on the diet whose elemental ratio is closest to its own. Diatoms (Diat) and dinoflagellates (Dino) cultured in nutrient-replete (+) and nitrogen-depleted (-) conditions were fed to the copepods. Ingestion, respiration, excretion, and egg and faecal pellet production rates were measured. Carbon (C) and nitrogen (N) budgets were built to investigate differences in dietary C and N partitioning. Copepods fed with nitrogen-depleted diatoms (Diat-), which had the most different C:N ratio to that of T. longicornis, had high metabolic losses and low growth. In contrast, copepods fed with nitrogen-rich dinoflagellates (Dino+) of closer C:N ratio had high metabolic losses, but the highest investment into somatic and reproductive tissue. The results indicate that, under the current climate scenario and nutrient-replete conditions, dinoflagellates are a better food source for T. longicornis. Furthermore, ingestion, respiration, and faecal pellet integrity are adversely affected by low quality food; and egestion is a main pathway in copepods for eliminating excess carbon.