Physiological responses and scope for growth upon medium-term exposure to the combined effects of ocean acidification and temperature in a subtidal scavenger Nassarius conoidalis

Physiological responses (ingestion rate, absorption rate and efficiency, respiration, rate, excretion rate) and scope for growth of a subtidal scavenging gastropod Nassarius conoidalis under the combined effects of ocean acidification (pCO2 levels: 380, 950, 1250 µatm) and temperature (15, 30 °C) were investigated for 31 days. There was a significant reduction in all the physiological rates and scope for growth following short-term exposure (1-3 days) to elevated pCO2 except absorption efficiency at 15 °C and 30 °C, and respiration rate and excretion rate at 15 °C. The percentage change in the physiological rates ranged from 0% to 90% at 15 °C and from 0% to 73% at 30 °C when pCO2 was increased from 380 µatm to 1250 µatm. The effect of pCO2 on the physiological rates was enhanced at high temperature for ingestion, absorption, respiration and excretion. When the exposure period was extended to 31 days, the effect of pCO2 was significant on the ingestion rate only. All the physiological rates remained unchanged when temperature increased from 24 °C to 30 °C but the rates at 15 °C were significantly lower, irrespective of the duration of exposure. Our data suggested that a medium-term exposure to ocean acidification has no effect on the energetics of N. conoidalis. Nevertheless, the situation may be complicated by a longer term of exposure and/or a reduction in salinity in a warming world.

Impact of medium-term exposure to elevated pCO2 levels on the physiological energetics of the mussel Mytilus chilensis

This study evaluated the impact of medium-term exposure to elevated pCO2 levels (750-1200 ppm) on the physiological processes of juvenile Mytilus chilensis mussels over a period of 70 d in a mesocosm system. Three equilibration tanks filled with filtered seawater were adjusted to three pCO2 levels: 380 (control), 750 and 1200 ppm by bubbling air or an air-CO2 mixture through the water. For the control, atmospheric air (with aprox. 380 ppm CO2) was bubbled into the tank; for the 750 and 1200 ppm treatments, dry air and pure CO2 were blended to each target concentration using mass flow controllers for air and CO2. No impact on feeding activity was observed at the beginning of the experiment, but a significant reduction in clearance rate was observed after 35 d of exposure to highly acidified seawater. Absorption rate and absorption efficiency were reduced at high pCO2 levels. In addition, oxygen uptake fell significantly under these conditions, indicating a metabolic depression. These physiological responses of the mussels resulted in a significant reduction of energy available for growth (scope for growth) with important consequences for the aquaculture of this species during medium-term exposure to acid conditions. The results of this study clearly indicate that high pCO2 levels in the seawater have a negative effect on the health of M. chilensis. Therefore, the predicted acidification of seawater associated with global climate change could be harmful to this ecologically and commercially important mussel.

(Table 1) Ion concentrations in the haemolymph of Apherusa glacialis after incubation at different medium salinities

Amphipods living at the underside of Arctic sea ice are exposed to varying salinities due to freezing and melting, and have to cope with the resulting osmotic stress. Extracellular osmotic and ionic regulation at different salinities, thermal hysteresis, and supercooling points (SCPs) were studied in the under-ice amphipod Apherusa glacialis. The species is euryhaline, capable to regulate hyperosmotically at salinities S(R) < 30 g/kg, and osmoconforms at salinities S(R) >= 30 g/kg. Hyperosmotic regulation is an adaptation to thrive in low-salinity meltwater below the ice. Conforming to the ambient salinity during freezing reduces the risk of internal ice formation. Thermal hysteresis was not observed in the haemolymph of A. glacialis. The SCP of the species was -7.8 ± 1.9°C. Several ions were specifically downregulated ([Mg2+], [SO4]2-), or upregulated ([K+], [Ca2+]) in comparison to the medium. Strong downregulation of [Mg2+], is probably necessary to avoid an anaesthetic effect at low temperatures.

The effect of a reduction of nitrogen and phosphorus to eutrophic and mesotrophic conditions towards silver nanoparticle (AgNP) on freshwater green algae species

We investigated the sensitivity of algae towards silver nanoparticles with OECD test medium and lower nutrient concentrations under standard test conditions to improve comparability and to exclude any other confounding factor aside nutrient levels. Two unicellular freshwater microalgae Desmodesmus subspicatus and Raphidocelis subcapitata were chosen due to their status as standard test organisms for the algae growth inhibition test and the response to changes in nutrient supply was compared. The original medium was used as the reference (standard). For the other four media, the amount of either nitrogen or phosphorus in the medium was lowered from half (50%) to one-fourth (25 %) of that of the OECD guideline, resulting in the following media: 50% N, 25% N, 50% P and 25% P medium. As test substance, the OECD reference material NM-300K was used. For this reason, the characterization of AgNP was done using DLS and Absorption spectra (UV/vis). Actual silver concentrations and ionic silver concentrations were measured at the highest test concentration used (100 µg Ag L-1) in R. subcapitata treatments only to reduce the number of samples. All tests were run according to the OECD guideline 201 with sterilized 50 mL cell culture flask. Each medium was tested using the test conditions for culturing with 3 replicates. Test concentrations for both algae species were 0, 25, 50 and 100 µg Ag L-1 for OECD, 50% P and 25% P while for both N reductions, the silver concentrations were 0, 10, 25 and 100 µg Ag L-1. Samples for determining the algal density were taken at every 24 h.