Location: Bocas del Toro
Lecturer: Aaron O’Dea
For the final component of the trip, we’re spending 3 full days in Bocas del Toro to study marine ecology, diversity, and conservation and we will be completing our second set of group projects. This blog post is focused on Aaron O’Dea’s lecture on the past and present conditions of Caribbean coral reefs and a little bit about the geologic history of the Isthmus.
While designing their research, ecologists ask the foundational question of whether the ecosystem they want to study is pristine, or if human activity has induced changes on their species/population/environment of study. In regards to coral reefs, scientists such as Aaron have discovered a great, often devastating, impact from anthropogenic changes.
A primary concern of scientists is understanding the realm of possible consequences for ecological balance as a result of human-induced changes. One such example is the increasing atmospheric carbon dioxide linked to human fossil fuel combustion. In addition to increased water temperatures, our actions are reducing oceanic pH, forcing changes in the biogeochemical cycles, and significantly shifting the carbonate chemistry (decreasing calcification rates of organisms). Additionally, human activity is influencing carbon fixation rates, carbon storage capacity, and predation risk. Overall, these changes lead to ocean acidification, and scientists are studying the ecological limitations and the resilience of coral reefs.
A comparison study between modern and ancient reefs (dating back to the Holocene) in Almirante Bay in Bocas (O’Dea et al., 2014) has shown that there has been a drastic change in corals over time. The 12-meters thick record of uninterrupted coral growth shows no record of bleaching of great die-offs. The death assemblages (accumulation of dead corals) serve as a record of what lived there in the past and they have been compared over time (i.e., comparison of the abundances of various corals). It has been observed that the modern reefs are completely different in ecological space compared to the fossil reefs. The present-day reefs have not existed in the past and look completely different, which prompts us to ask WHY things have changed and what it means (in an ecological sense).
Case study: Strombus pugilis
Strombus pugilis is a marine organism that lives in a conch shell in sea grasses and is eaten by the Caribbean locals. In the local outcrops, S. pugilis have been found dating back 7,000 years (during the Holocene), 2,000-1,000 years, and are still found on the sea floor today. A size comparison of the Holocene and modern organisms have a large difference in shell size. The shell length at maturity has declined over time as a result of high predation from humans. The selective pressure is applied on the organisms to reproduce smaller conch shell sizes.
In addition to the Panamanian example, similar changes have been observed in S. pugilis on the south central coast of Jamaica. The adults have exhibited dwarfism in shell size. The typical specimens ranged in size from 20 to 60mm. It has been hypothesized that the warmer water temperatures resulting from anthropogenic change has forced the mollusks to mature at an earlier stage than previously before.
Based on the rapid rate of generally irreversible, lethal change that human actions have already influenced current ecological activity on a range of spatial scales, it is important to focus our future efforts on conservation and management of protecting the world around us. Organisms such as corals are very dynamic and can handle the small perturbations they’re exposed to diurnally, seasonally, and/or annually. However, human-induced stressors are increasing the spatial range, frequency, and the intensity of the perturbations and are very likely pushing these perturbations above the threshold ecological limitations that an organism can withstand.
- O’Dea et al. Proc. R. Soc. B (2014) 281:1782. doi:10.1098/rspb.2014.0159.
- Doney et al. Annu. Rev. Mar. Sci. (2016) 1:169-192. doi:10.1146/annurev.marine.010908.163834
- Madin et al. Global Change Bio. (2015) 22:1 44-60. doi:10.1111/gcb.13083
- Mora, C., Graham, N.A.J., and Nystrom, M. Coral Reefs (2016) 35:1271-1280. doi:10.1007/s00338-016-1479-z
- Spalding, M.D., and Brown, B.E. Science (2015) 350:769-771. doi:10.1126/science.aad0349