Population-specific Survival during Exposure to Hypoxia and Heat: Global Change Increases Stress Tolerance of the Asian Green Mussel (Perna viridis)

Abstract

Global change is defined by the combination of all aspects altered by the influence of human populations. Consequences for marine ecosystems are, for example, rising sea temperatures, ocean acidification, eutrophication, pollution, habitat destruction, and non-natural range expansion. Aim of my thesis was to investigate whether human impact can lead to a population-specific change in tolerance to environmental stress of a marine invertebrate. As study organism I chose the Asian green mussel (Perna viridis) a bivalve with a wide indigenous and non-indigenous distribution range in tropical and subtropical oceans. I compared tolerance to hypoxia and heat stress between two indigenous populations from Indonesia and a non-indigenous population from Hongkong. The indigenous populations came from habitats of different anthropogenic influence. The first, Jakarta Bay, is a polluted and eutrophicated site located close to a harbour. The second indigenous population came from a pristine nutrient-poor habitat in the Sunda Strait. The non-indigenous population was sampled in a polluted harbour in Hongkong where it exists under constant anthropogenic influence. In laboratory experiments in Bogor, Indonesia, I exposed the mussels to hypoxia and heat stress for three and ten days, respectively. The same experiments were conducted by my colleague, Charles Ma, in Hongkong. As an indicator of stress tolerance, I measured mortality of the mussels every day and calculated survivorship in every replicate as the sum of daily survival. Comparing stress tolerance between populations revealed that the non-indigenous, anthropogenic-influenced population from Hongkong was more tolerant to hypoxia and heat stress than the indigenous populations from Indonesia. Within the indigenous populations, stress tolerance of the mussels that came from the polluted site was higher. However, this was only statistically significant for hypoxia stress. The experiments showed that anthropogenic influence can increase the ability of a population to survive environmental stress. This can result either from adaptation to local or dispersal-related stress or from a better physical condition in eutrophicated environments. Both mechanisms may increase the potential of non-natural range expansion, lead to a shift in the fundamental niche of a species and facilitate biological invasion