Trichodesmium's strategies to alleviate phosphorus limitation in the future acidified oceans

Global warming may exacerbate inorganic nutrient limitation, including phosphorus (P), in the surface-waters of tropical oceans that are home to extensive blooms of the marine diazotrophic cyanobacterium, Trichodesmium. We examined the combined effects of P limitation and pCO2, forecast under ocean acidification scenarios, on Trichodesmium erythraeum IMS101 cultures. We measured nitrogen acquisition, glutamine synthetase activity, C uptake rates, intracellular Adenosine Triphosphate (ATP) concentration and the pool sizes of related key proteins. Here, we present data supporting the idea that cellular energy re-allocation enables the higher growth and N2 fixation rates detected in Trichodesmium cultured under high pCO2. This is reflected in altered protein abundance and metabolic pools. Also modified are particulate organic carbon and nitrogen production rates, enzymatic activities, and cellular ATP concentrations. We suggest that adjusting these cellular pathways to changing environmental conditions enables Trichodesmium to compensate for low P availability and to thrive in acidified oceans. Moreover, elevated pCO2 could provide Trichodesmium with a competitive dominance that would extend its niche, particularly in P-limited regions of the tropical and subtropical oceans.

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.