Publication Date

Summer 2021

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Michael H. Graham


central california, conchocelis, epiphyte, nereocystis, population dynamics, pyropia

Subject Areas

Plant sciences; Ecology; Botany


Macroalgal epiphytism is widespread, but many unique epiphyte-host interactions remain poorly understood. Pyropia nereocystis is an annual northeastern Pacific species that has evolved to primarily epiphytize the annual kelp Nereocystis luetkeana. I examined three aspects of Pyropia-Nereocystis epiphyte-host dynamics in the southern extent of the host’s range: (1) temporal variation in epiphtyte presence; (2) growth of gametophyte and sporophyte (conchocelis) stages using transplantation experiments; and (3) effects of epiphyte depth and host characteristics on the recruitment and biomass of the epiphyte. Pyropia exhibited a shift in presence on Nereocystis that differed interannually as a function of Nereocystis density and Nereocystis persistence. Greater clumping of unepiphytized Nereocystis and greater regularity of epiphytized Nereocystis were observed for multiple cohorts. Pyropia gametophytes grew similarly across transplanted depths, but Pyropia conchocelis exhibited greater growth with increased depth. Longer host apophyses were correlated with a deeper Pyropia recruitment and Pyropia biomass was positively correlated and thresholded by host characteristics. These results suggest regularity in epiphytism among Nereocystis populations in the central California region and spore limitation or host inhibition of Pyropia epiphytism at greater depths, despite a likely conchocelis presence at greater depths. Additionally, Pyropia may be regulated by variation in Nereocystis stipe characteristics relating to host apophyses, stipe surface area, and/or ecological effects experienced by individual Nereocystis.