Publication Date

Spring 2014

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Michael H. Graham


Climate Change, Competition, Kelp, Life History, Marine Biology, Range Shifts

Subject Areas

Physiology; Ecology; Plant biology


Kelp populations inhabit some of the most dynamic environments on the planet and often exist close to the limits of their temperature tolerances. Temperature cues reproductive processes in many kelps and fluctuating temperatures can affect kelp recruitment and population persistence. Some kelps compete sexually through their microscopic life history stages by releasing a pheromone that triggers the premature release of spermatozoids of neighboring species, leading to recruitment failure. It is unknown, however, whether changing temperature modifies competitive hierarchies among kelp species. To address this issue, I investigated how temperature affects sexual competition between microscopic stages of three co-existing and possibly competitive kelps in central California. Laboratory studies were conducted to test the effects of temperature on germination, gametogenesis, fertilization, and recruitment. At 4°C, 8°C, and 12°C, Macrocystis pyrifera outcompeted Nereocystis luetkeana, but was outcompeted by Pterygophora californica. At 16°C, Nereocystis did not survive and Pterygophora sporophyte recruitment decreased relative to that of Macrocystis. All three of these kelps showed increased time to fertility of female gametophytes with decreasing temperatures. This demonstrated that temperature could alter the competitive hierarchies among these three species and suggests that increasing ocean temperatures due to climate change will favor Macrocystis over Nereocystis and Pterygophora, increasing Macrocystis' dominance along the central California coast.