Syncopation and synchrony: Phenological dynamics of Pyropia nereocystis (Bangiophyceae) in central California

Pyropia nereocystis is an annual northeastern Pacific-bladed bangialean species whose macroscopic stage epiphytized the annual canopy forming bull kelp Nereocystis luetkeana. I examined three in situ facets of these epiphyte-host dynamics in the central California region: (1) spatial and temporal variation in the presence of P. nereocystis epiphytes as a function of host density, (2) the relationship between individual host morphology and epiphytic P. nereocystis biomass, and (3) the ecophysiological growth ramifications for subtidal transplants of both life stages of P. nereocystis. Swath canopy surveys and whole host collections were conducted at five sites between November 2017 and February 2019. Additionally, transplants of P. nereocystis gametophytes and sporophytes were conducted across multiple subtidal depths. I observed temporal changes in the proportions of hosts epiphytized by P. nereocystis, with differences in seasonal persistence of P. nereocystis among sites and between years. Biomass of P. nereocystis was positively correlated with individual host stipe length, stipe surface area, and the primary principal component (PC) of stipe morphometrics denoted by principal component analysis (PCA). Gametogenesis in P. nereocystis epiphytes was spatially heterogeneous and limited for the 2018–2019 cohort due to comprehensive removal of hosts by the February 2019 sampling period. Transplants of P. nereocystis gametophytes yielded similar growth responses among depths, and sporophyte (conchocelis) transplant areal growth was positively correlated with transplant depth. These findings detail spatiotemporal complexity and multi-scale (individual, site, and whole region) phenological nuances for central Californian P. nereocystis epiphytes.