UC Santa Cruz

Ocean acidification (OA) causes negative responses in numerous marine organisms including declines in calcification, growth and development. However, responses to OA vary, and organisms differ in their tolerance of OA. These variable responses make it difficult to predict how OA will shape marine communities in the future without a greater framework of what traits or mechanisms confer tolerance to OA. This Ph.D. aims to explore some of the patterns in traits associated with tolerance to OA to better predict the acclimation potential of organisms in the future.

Chapters 1 and 2 explore how an organism that currently experiences regular variation in pH responds to chronic ocean acidification by exposing Euphausia pacifica to experimental chronic acidification. E. pacifica is relatively tolerant of chronic acidification, showing no changes to survival or molting frequency, but slower growth at low pH. Slower growth was likely caused by reduced metabolism at low pH, as oxygen consumption, ingestion, and nutrient excretion rates all declined at low pH.

Chapter 3 explored the potential for OA-sensitive species to acclimate to OA over long time periods by surveying communities of calcifying algae along a pH/saturation gradient at naturally low-pH, low saturation submarine springs off the coast of Puerto Morelos, Mexico. Total percent cover, species richness and diversity of calcifying algae were all lower at low saturation levels, however tolerance of acidification varied across genera. Hydrolithon and Peyssonnelia were more tolerant of low saturation, while Neogoniolithon, Amphiroa and Lithophyllum were more sensitive. Results provide mixed support for the hypothesis that early successional species, characterized by fast growing and thin thalli, are more sensitive to OA than later successional species with thicker thalli.

While more work is needed to elucidate relationships between certain traits and OA tolerance, this work is an important step in developing and further testing hypotheses about which traits are important in determining acclimation potential to OA.