Ecophysiology and Taxonomy of Saccharina latissima forma angustissima (Laminariales, Phaeophyceae) From the Gulf of Maine, USA

The overarching theme of this doctoral dissertation was to resolve the taxonomic status of an endemic narrow-bladed kelp, Saccharina latissima forma angustissima (Laminariales, Phaeophyceae), which has a very restricted distribution of 8 nautical miles in the Gulf of Maine, USA. Since the kelp only grows on ledges and islands exposed to high ocean swells, it was unknown if phenotypic plasticity alone was driving its morphology or if the kelp was a distinct genotype (a population with heritable traits). I incorporated lab and fieldwork to discriminate genetic divergence of this kelp, investigated temperature and light requirements of the gametophytic and juvenile sporophytic stages, and its potential use for sustainable aquaculture. The final objective was to tease apart existing relationships of parapatric speciation, where gene flow is limited by the extreme habitat.

In Chapter 1, I used a multi-locus genetic approach to answer questions about the phylogenetic placement of S. latissima f angustissima. The results revealed the need for a new combination and status elevation to Saccharina angustissima comb. nov. & stat. nov. (Collins) Augyte, Yarish & Neefus. In Chapter 2, I examined the ecophysiological temperature and light tolerance of its early developmental stages, specifically looking at the response of gametophytes and juvenile sporophytes. For Chapter 3, I worked with two aquaculture companies in the Gulf of Maine to domesticate and commercially cultivate S. angustissima at two farm sites and provide data on morphometric traits, biomass yields, blade tissue analysis and ecosystem services. In the last Chapter 4, using microsatellite data, I investigated the population genetic structure of S. latissima and S. angustissima in across four sites in the Northwest Atlantic and found some genetic differentiation between the two species as well as between other S. latissima populations in Long Island Sound and the Gulf of Maine.

In conclusion, directional selection has propelled this unique kelp to persist and colonize an extreme ecological niche and speciate. This reproductive isolation has led to incipient speciation of a Saccharina sp. in the Northwest Atlantic. Finally, as a result of my efforts there has been the domestication of a new kelp crop in New England.