Combined effects of warming, acidification and the synthetic progestin levonorgestrel on the fitness of the marine amphipod Gammarus locusta (Crustacea)

On the facet of global warming, marine invertebrates are harshly challenged to adapt in a changing ocean. Global warming and increased atmospheric CO2 are causing the oceans to become warmer and more acidic. According to the 5 assessment report of the Intergovernmental Panel on Climate Change (IPCC), global mean sea surface temperature is expected to increase up to 4°C and ocean pH is expected to decrease by Δ 0.5 pH units until 2100. The stimulatory effect of ocean warming coupled with the sedative effect of low pH is lethal for marine invertebrates physiological processes. Moreover, adapting to these climate variables may become more difficult due to their possible interaction with contaminants, such as Endocrine Disrupting Chemicals (EDCs). To our knowledge there is almost no information in the literature regarding the impact of multiple climate drivers and EDCs on the aquatic organisms. Thus, in this study a combined effect of the near future ocean warming (+ 4°C) and acidification (Δ 0.5pH units) with the synthetic steroid, levonorgestrel was evaluated on the fitness of the marine amphipod Gammarus locusta. The experiment employed a full factorial design manipulating temperature [ambient (18oC) and warming (+ 4oC)], CO2 [normocapnia (pH 8.1) and hypercapnia (pH 7.6)] and the progestin levonorgestrel (LNG: L1 – 10 ng L and L2 – 1000 ng L ,control – no progestin and solvent control – vehicle ethanol (0.01%)). The study was divided in two phases: 1) pre-reproduction phase, which lasted for 21 days and 2) post-reproduction phase that continued for more 7 (± 2) days. The responses of G. locusta were evaluated through multiple outputs like survival, growth, consumption rate, fitness condition and reproductive traits (fecundity and embryonic development). Warming condition (22°C, pH 8.1) revealed to be the most negative scenario for the G. locusta survival (30% 50%) compared to the ambient condition (70% 90%). However, under the combined effect of warming and acidification the survival was higher (60% 80%). Additionally, elevated temperature reduced fitness condition and interacted with LNG, suppresing the consumption rate. In addition, elevated temperature seems to slightly suppress the growth rate, however, the acidification and LNG concentrations had a more negative effect on growth rate. On the other hand, the G. locusta fecundity was significantly reduced under higher temperature and a synergistic effect with higher LNG concentrations was detected. For the embryonic development time, a significant reduction was observed with the increase of temperature (4 6 days) compared to ambient temperature (6 – 12 days). On the other hand, hypercapnia under ambient temperature prolonged embryonic development. Our findings suggest that the future warming scenario may exceed G. locusta lethal thermal limit affecting all levels of physiological performance. On the other hand, acidification per se seems to have had some negative effects on metabolism and development of the organisms, however the impact was not so drastic like the warming condition alone. The interaction between LNG and warming revealed to be more relevant at the reproduction level, meaning that the higher the temperature and LNG concentration, the lower the fecundity recorded for this invertebrate species. Concluding, that the novelty of this research may have a strong impact on the management and conservation of coastal ecosystems on the facet of climate change.