Publication Date

2019-05-02

Availability

Embargoed

Embargo Period

2020-05-01

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology and Ecology (Marine)

Date of Defense

2019-03-05

First Committee Member

Andrew Baker

Second Committee Member

Diego Lirman

Third Committee Member

Crawford Drury

Abstract

Parental effects on the early life history stages of corals are poorly understood, but with increasing climate disturbances on coral reefs, these effects may be important to understanding future survival trajectories of coral reefs. In 2014 and 2015, patch reefs in Kāne‘ohe Bay, Hawai‘i experienced widespread bleaching, in which many Montipora capitata colonies bleached while neighboring colonies did not. This study investigated whether a prior history of bleaching affected the larvae released from affected M. capitata colonies several years later. In July 2018, gametes were collected from Patch Reef 13 and selectively bred into three different parental history pools (both parents previously bleached, both parents previously nonbleached, and crosses from a combination of both parental histories) based on bleaching observations during the 2015 heat anomaly. Larvae were maintained at ambient (27.5°C) and elevated (30.1°C) temperatures in outdoor tanks shaded from direct sunlight. Maternal and temperature effects were quantified as changes in larval survivorship, size in mm2, juvenile recruit survivorship, symbiont community composition, and symbiont density. Results showed that symbiont densities decreased over 68 h regardless of temperature treatment or maternal phenotype, and that elevated temperature significantly increased the mortality of larvae. Prior coral bleaching resulted in significantly smaller larvae and a drastic decrease in survivorship when larvae were exposed to 30.1°C in the initial 24 h. Larvae crossed from both maternal phenotypes (bleached and nonbleached) experienced the highest survivorship under heat stress and were largest in size, but experienced decreases in the proportion of thermotolerant Durusdinium symbionts over 68 h. Together, these results suggest that symbiont population sizes may be too low in newly-released M. capitata larvae to have a strong effect on larval thermal tolerance, and that maternal effects on larval size are instead more important, with significant ramifications as sea surface temperatures continue to rise.

Keywords

Maternal effects; larvae; phenotype; Montipora capitata; Kaneohe Bay, HI; Symbiodiniaceae; coral bleaching; thermal stress

Available for download on Friday, May 01, 2020

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