Publication Date

Summer 2026

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Moss Landing Marine Laboratories

Advisor

Thomas Connolly; Maxime Grand; Mike Wood

Abstract

The 2015/16 El Niño event is one of the strongest El Niño Southern Oscillation (ENSO) events on record. Coral reefs in the Phoenix Islands Protected Area (PIPA) were exposed to the effects of the 2015/16 El Niño event and experienced moderate to severe coral bleaching and mortality. This study examines the variability in three key oceanographic variables before, during, and after the 2015/16 El Niño event within PIPA: sea surface temperature (SST), sea surface salinity (SSS), and estimated chlorophyll-a (chl-a) as a proxy for regional productivity. I used remote sensing data for SST, SSS, and estimated chl-a coupled with in-situ data obtained via conductivity, temperature, and depth (CTD) casts from Sea Education Association (SEA) PIPA research cruises during the summer months from 2015-2019. Within PIPA, I chose six reef sites to assess: Carondelet Reef, Winslow Reef, Kanton Island, Nikumaroro Island, Orona Island, and Enderbury Island. I found that SST increased, SSS decreased, and estimated chl-a decreased during the 2015/16 El Niño event compared to La Niña and Neutral years. Peaks in positive (anomalously high) SSTs were lower in PIPA compared to the Niño-3.4 Region, which is commonly used as a metric for classifying the strength of El Niños. The depth structure of temperature and salinity was altered in PIPA during the 2015/16 El Niño event. This study highlights the potential of compounding thermal stress with additional stressors on coral reefs. Further study is needed to confirm compounding stress and the long-term impacts of repeat climate events on isolated coral reefs like the ones in PIPA.

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