Foundation species create structure in a community, and understanding their evolutionary response to climate change is of utmost importance. Macrocystis pyrifera, giant kelp, is an ecologically and economically significant foundation species along the west coast of North America, supporting a diverse ecosystem that contributes to recreational fisheries, tourism, and industry. Previous surveys of M. pyrifera during years of increased water temperature have shown decreased abundance and recruitment (Grove, 2002), but no study has examined the effect of genetic variation in the response of M. pyrifera to warming. This project aimed to determine if distinct individuals of M. pyrifera exhibit similar zoospore settlement rates in warming conditions. I predicted that all individuals would have decreased settlement as the temperature increased, but that there would be variation between individuals. To address this question, I collected fertile sporophyll blades from three distinct M. pyrifera individuals at Cabrillo Beach, Palos Verdes, California, and induced zoospore release in the lab. I allowed the zoospores to settle on microscope slides at 14 ºC, 16 ºC, and 18 ºC for 24 hours before counting the settled spores/mm2. 14 ºC was the ambient temperature at collection, and I used 18 ºC as my high point as the oceans are expected to warm by 4 ºC within the century (IPCC, 2013). A two-way mixed model ANOVA was used to analyze these results, with genotype as the fixed factor.
There was no statistical difference in settlement within an individual at the three treatments. However, successful settlement did vary by individual. At 18 ºC, the highest settlement was 475 ± 51 spores/mm2, while the lowest was 105 ± 3 spores/mm2. One individual displayed higher settlement at all temperatures. Most interestingly, the two-way mixed model ANOVA results indicated a significant interaction of individual*temperature (p = 0.009). This interaction indicates that the settlement was driven more by individual than by temperature.
These results suggest that this could hold true at the genotypic level, which would be useful in kelp forest restoration projects and aquaculture. It is more efficient to focus on breeding and outplanting the more resistant genotypes, than continuing to plant those that may not succeed in the future. This study will allow for better predictions of the community structure of future California kelp forests, and therefore will lead to more efficient financial and ecological projections. Fields such as policy, fisheries management, and industry will benefit from this increased understanding.