Impacts of ocean acidification and other (global change) stressors on marine invertebrates

Resumen

The hypervariable nearshore marine ecosystem is home to intrinsic stressors for marine organisms. Global climate change and human activity are already affecting this aquatic environment and are expected to intensify over the next decades. These diverse changes include a rise in global temperature and a decrease in ocean pH. More carbon dioxide dissolves in the sea, lowers the pH, and makes the ocean more acidic. Now the main scientific challenge is to understand and predict the response of marine life to the predicted environmental change in the ecosystem. These challenges include a better understanding of the marine life’s response to changes in distribution and tribute to evolutionary changes or extinction. Species can respond to global change in a variety of ways. They can move from the environment of tolerance zone to newly available zones, can extend tolerance by summarizing and/or modifying their physiology or behaviour, and can demonstrate that the range shrinks when the environment of certain variable environmental factors is exceeded. Most marine species can respond to transformations, including behavioural or generational genetic selections that can improve perception, individual morphology, physiology, and/or performance in changing environmental conditions when undergoing periodic and rapid changes in the environment. Familiarity and adaptability to a changing environment is a type of environmental reaction due to the plasticity of an organism. In this doctoral dissertation, studies have been carried out to understand the potential physiological or biochemical effects of some global change stressors on five important marine and estuarine invertebrates: the anthuroid isopod Cyathura carinata (Krøyer, 1847), the benthic ragworm Hediste diversicolor (O.F. Müller, 1776), the sea snail Tritia neritea (Linnaeus, 1758), the most versatile amphipod Ampelisca brevicornis (Costa, 1853), and the pseudodiaptomid copepod Calanipeda aquaedulcis (Kritschagin, 1873) from the Iberian Peninsula (SW of Spain), because all of these invertebrates have been abundantly occupying and performing dynamic roles in the estuarine food chain for a long time, they have served as a viable food source for avifauna and ichthyofauna in those areas. In Chapter 3 we investigated the physiological or biochemical plasticity of OA in isopod C. carinata, and in Chapter 4 we describe how OA and ocean warming can alter the physiological and biological changes in a ragworm H. diversicolor. The effects of temperature rises and contamination of emerging pollutants such as lithium on the sea snail are discussed in Chapter 5. To determine whether OA includes propagating effects in the ecotoxicological study, the amphipod A. brevicornis is described in Chapter, 6 and finally, whether intragenerational plasticity can offset the negative effects that OA had on the life cycle of the copepod C. aquaedulcis is described in Chapter 7. To determine the tolerance and pH threshold that C. carinata could tolerate in future acidification scenarios, estuarine isopod was exposed to four pH treatments (control: 7.9; 7.5, 7.0, 6.5). Seawater acidification had a significant impact on the longevity of C. carinata, where the population density decreased significantly when treated at the lowest pH. The longevity, survival, and swimming activity of these isopods decreased with decreasing pH. Also, the swimming activity, Na+/K+-ATPase activity, and the RNA:DNA ratio of two populations of C. carinata, one in a stable environment (pH 7.5-8.0) and the other in a variable pCO2 regime (pH 3.3-8.5), were measured to assess the probable metabolic adaptability of this species. Populations in environments with a high pCO2 regime not only showed tolerance to pH 6.5 but had higher life spans and metabolic plasticity compared to habitat populations with little pCO2 conditions. These results indicate that C. carinata populations in stable environments may be susceptible to ocean acidification and can have a detrimental effect on survival and growth. Nevertheless, ocean acidification has limited effects on the energy budget and survival of C. carinata populations in highly variable habitats, indicating that they can cope with the elevated energy demand. Differences between the indicated populations probably indicate genetic differences in resistance to ocean acidification, possibly related to local adaptation, which may provide the raw materials needed to adapt to future conditions. In addition, our results indicate that population changes and metabolic responses should be considered when evaluating the response of marine crustaceans to changes in the global environment. Ragworm H. diversicolor was exposed in the laboratory to multi-stressors effects of elevated temperature and carbon dioxide levels mimicking the future OA and GC and we assess the physiological, behavioral, and biochemical changes in this species. The temperature rise exacerbated the negative effects of OA on the survival of the ragworm, delayed the excavation, and amplified the negative effects of lowering the pH on the feeding behavior of this polychaete. This is the first time this species has been shown to reduce its feeding capacity through the acidification of seawater. Wound healing and blastemal formation were slowed by these two climatic factors, which interfere with the regeneration process of the ragworm. Current results also show that even if polychaetes' metabolic capacity increases under stress conditions, organisms can still increase or maintain their energy reserves. Our results are of great importance for the environment, given that predictive conditions for climate change will affect the life, ecological and physiological capabilities of the species. This can lead to a decrease not only at the individual and population level but also at the diversity of microbes and endofauna, waste disposal in the estuary, and biochemical cycles at the ecosystem level. Therefore, the conservation of the H. diversicolor population is very important for the normal functioning of the estuary ecosystem. Sea snail Tritia neritea was exposed to lithium (Li, 0.08 mM) contamination and the rising seawater temperature (21 °C). We investigated the survival and trophic interactions (foraging behavior, success, search time, carrion preference, feeding time, and tissue consumption) of this intertidal scavenger. Trophic interactions were assessed using a Ymaze design using the same amount of two carrion species (Solen marginatus and Mytilus galloprovincialis) given simultaneously to all snails. Lithium pollution and synergistic warming reduce the survival rate of T. neritea, triggering a scenario for potential global change. Lithium contamination changes foraging behavior and increases the time it takes for snails to reach their carrion. Although T. neritea did not show a preference for the proposed carrion species in the control group, it shifted its foraging behavior to a more energetic carrion when contaminated with Li, which may represent a strategy that compensates for the high energy use required for survival. Results showing changes in the foraging activity of coastal mollusks in a global change scenario indicate potential changes in complex nutritional interactions between marine food pathways. Estuarine amphipod A. brevicornis was examined to study the physiological behavior and biochemical effects of the amphipod under OA. Wild harvested ovigerous females were reared in the laboratory and we started the experiment with 7 days old juveniles in a simulated OA scenario with four different levels of pH for a life cycle. Amphipods were incubated for up to 22 weeks to go through F1 production, successful reproduction, and hatching, and the length of F1 progeny compared to F0. The data obtained show that as the pH value of seawater decreases, mortality increases. The fertility rate reduced to 66.1% at pH 7.5 compared to the control group. The survival rate was higher in F1 juveniles than in F0 juveniles, but growth showed the opposite tendency to F1. These physiological parameters may be related to oxidative stress caused by climate-changing conditions as free radical generation interferes with cellular function, affecting the biochemical and physiological properties of the species, including burrowing, locomotory and ventilatory behaviours. This study is critical to assessing the impact of OA and providing baseline data that can be used as a guide for developing long-term strategies for delivering manageable and sustainable solutions. Copepods are an integral part of the marine food network due to their high biomass production and nutrient turnover compared to other zooplanktons in the marine ecosystem. Despite its enormous ecological role in the oceans, little is known about the effects of OA from increasing planetary carbon dioxide emissions in the future. Little information is available on the impact of OA on European copepod C. aquaedulcis. The purpose of this study was to investigate the impact of OA across multiple generations (F1 and F2) on survival, maturity, and fertility (hatching success, nauplii formation, and total adult population). C. aquaedulcis were exposed to three different pH gradients to simulate future seawater acidification scenarios. The survival rate of the copepod from nauplius to adult was significantly reduced in pH reduction and across generations. Results have also shown to have a marked effect on fertility, represented by a much smaller number of eggs per female in each generation. Similarly, hatching success showed a downward trend towards lower pH, and F1 females had significantly lower hatching success rates than F0 females. The results presented here appear to be ecologically important as the decline in the fertility of these animals can negatively affect marine feeding pathways. This is because the nutrition and growth of ichthyofauna are highly dependent on this component in the food web.