Connectivity of massive Porites in the Phoenix Islands Protected Area (PIPA)
Hanny Rivera, Biology Department
Advisor: Don Anderson, Biology
Global climate models predict that the central equatorial Pacific Ocean will see the largest and fastest increase sea surface temperature (Clement et al 2010). This region is also impacted by El Niño Southern Oscillation events, which can raise temperatures quickly and dramatically, over a matter of months, to levels predicted for end-of-century. ENSO events may cause even higher spikes, as they become superimposed on an increasing baseline over the course of this century. Corals are highly susceptible to increases in sea temperature and can die after a number of weeks of elevated temperatures through a process called coral bleaching (Carpenter et al 2008, Glynn 1993).
The Phoenix Island Protected Area (PIPA) is one of the largest marine reserves in the world and contains pristine coral reefs that lie far from the human impact and coastal development that can be detrimental to reefs. Geographically, however, the PIPA lies squarely in the El Niño Southern Oscillation (ENSO) impact zone and is often affected by temperature spikes and sees high inter-annual variability in temperature and other environmental conditions due to its location.
ENSO caused mass bleaching in PIPA in 2002 with over 60% coral mortality in some areas (Obura et al. 2011). Mortality rates varied vastly among islands and habitat, however, spanning a range of 12-100% mortality, suggesting certain island and/or habitat types may be more resistant to thermal stress than others (Obura et al. 2011). While the PIPA, has suffered declines in coral cover due to ENSO events in the past, long-term exposure to a highly variable climate patterns, may serve to select for corals that can tolerate high temperature stress, and have better chances against future sea temperature increases.
The protected status and geographic importance of PIPA merits intense study and a thorough investigation of the mechanisms through which reefs there may be able to survive through future changes. If PIPA reefs can serve as breeding grounds for temperature tolerant corals, it is crucial to understand where these resistant corals dispersed to in the past and may disperse to in the future, especially. Alternatively, if the PIPA reefs are not resistant, dispersal into the PIPA from less impacted islands will be fundamental to maintain the coral populations within PIPA from disappearing.
Corals from the genus Porites are some of the dominant reef members in the Pacific reefscape (Colin 2009; Glynn and Ault 2000; Potts et al. 1985). Their response to climate change stressors will be a large determinant of reef fate in many areas due to their large contribution to coral cover as well as intermediate level of temperature stress tolerance. Initial analysis of Porites colonies from the PIPA has suggested that PIPA corals are well connected with other central Pacific islands such as Jarvis. This connectivity could prove vital for the future of central Pacific reefs.
As of this writing, Kanton, the northernmost of the Kiribati Phoenix Islands, is in coral bleaching alert level 2, the highest possible. I am currently en route to the PIPA for a month-long field expedition to all the islands in the PIPA. The timing of this expedition is ideal to study the responses of corals in the PIPA to a high temperature stress event in-situ. During the expedition, I plan to collect tissue samples from Porites lobata colonies in each island site and across various reef habitats. The islands in the PIPA are currently spanning a gradient in temperature stress, which makes this natural temperature stress experiment even more informative. I will use molecular tools, such as microsatellite markers and possibly short nucleotide polymorphism (SNP) analysis, to quantify connectivity. I would furthermore like to investigate any differential gene expression between bleached and un-bleached colonies we might find in the field, though funds for gene expression analyses will not be included here. Investigating the genetic basis for resistance and resilience in the PIPA will not only add to understanding of a unique ecosystem and to the genomic knowledge of corals population, but it will also provide critical information for the future management and protection of coral reef ecosystems.
Need for funding
I am requesting funds for these molecular analyses, as my advisor, Dr. Anne Cohen, does not any a specifically designated grant for this purpose, nor a molecular lab. I obtained partial funding for molecular analysis of other tissue samples held by our lab through an Ocean Ventures Fund application last fall. However, as we will be collecting an additional 300 or so samples during this expedition, I will need to purchase additional materials, DNA extraction kits, sequencing costs, etc. in order to process the new PIPA samples. Furthermore, as I will be using another WHOI lab (I have coordinated with Dr. Ann Tarant for this), I will need to purchase my own PCR kits. These items are detailed in the attached budget.
Importance for thesis research
The central questions of my Ph.D. thesis are: a) Which reefs can we expect to best survive future climate conditions? B) By what mechanisms will they survive? and c) How will these surviving reefs later replenish and seed other more decimated areas? The connectivity analyses described here, form a central part of answering my third thesis question. Understanding this connectivity will be essential for future management of reefs and creating a map of future reef survivors.
Carpenter, K. E. et al. One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science 321, 560–3 (2008).
Clement, A.C. et al. Climate change: Patterns of tropical warming. Nat. Geosci. 3, 8–9 (2010).
Colin, P. L. Marine Environments of Palau. (Indo-Pacific Press, 2009).
Glynn, P. W. Coral reef bleaching: ecological perspectives. Coral Reefs. 12, 1–17 (1993).
Glynn, P. W. & Ault, J. S. A biogeographic analysis and review of the far eastern Pacific coral reef region. Coral Reefs 19, 1–23 (2000).
Obura, D. & Mangubhai, S. Coral mortality associated with thermal fluctuations in the Phoenix Islands, 2002–2005. Coral Reefs 30, 607–619 (2011).
Potts, D. C., Done, T. J., Isdale, P. J. & Fisk, D. A. Dominance of a coral community by the genus Porites (Scleractinia). Mar. Ecol. Prog. Ser. 23, 79–84 (1985).