Genetic comparisons of temperature tolerances of a candidate sea vegetable crop, Alaria esculenta

Genetic comparisons of temperature tolerances of a candidate sea vegetable crop, Alaria esculenta

Summary

The project is well underway to develop sea vegetable aquaculture on the Maine coast in order to produce higher yields of species that are currently wild-harvested. To study direct temperature effects on growth and heat acclimation, we are examining Alaria esculenta from different areas in the Gulf of Maine to see the effects of heat acclimation. It is important to investigate these effects at both life stages, the sensitive haploid gametophyte and the heartier diploid sporophyte, as both determine the future distribution of this subarctic species in a warming ocean. At this stage of the experiments, we are focusing on the collection of representative A. esculenta strains from differing water temperature exposures within the Gulf of Maine. We are then culturing these lines at the genotype level all at the same temperature, and then will compare both growth and gene expression of the same genotype at lower (12°C) and higher temperatures (18°C+). These experiments will define temperature tolerance and reveal marker genes for additional, economical identification of temperature-tolerant strains with high growth rates.

Objectives/Performance Targets

At this stage of the project, our focus is on objectives (1) to identify temperature-tolerant (TT) seedstock strains of Alaria esculenta gametophytes for Maine sea vegetable aquaculture (SVA) and (4) to promote sea vegetable aquaculture in Maine by attending conferences and forums and working directly with harvesters.

Our first performance target (1) is being fulfilled: after some difficulty in determining proper comparative sites, we selected a southern site at Two Lights State Park in Portland, ME and a northern site at Carrying Place Cove Rd. in Lubec, ME. Our original search area was in northern Massachusetts and Schoodic, ME, but upon further temperature analysis and discussion with leading members of UMaine’s Satellite Oceanography Data Lab, we determined that both historical and recent sea surface temperatures (SSTs) at the two sites were too similar. The Gulf of Maine is one water system circulated in a general cyclonic pattern by the Gulf of Maine Coastal Current (GMCC), which splits into two principal branches along the coast, causing different parts of the coast to be exposed to different water temperatures; our two selected sites, Two Lights and Lubec, offer a great comparison of the differing SSTs caused by each branch. Four reproductively mature sporophytes were haphazardly selected from each site, mature sporophylls from each sporophyte were cleaned, treated briefly with a 0.01% betadine solution to eliminate protists and placed into circulating 12°C sterile seawater (4 umol photons m2/s, 12:12 L:D photoperiod) to obtain a dense suspension of zoospores. Zoospore release was patchy and random, but after a few water changes and constant monitoring, a healthy set of zoospores settled to form gametophytes (total of 8 individuals released zoospores, with bi-weekly sterile seawater changes and ¼ strength WES nutrient supplement). Gametophytes were allowed to grow in constant light to maintain vegetative growth. Once gametophytes reached ~5-7 cells in length, individual genotypes from each individual were plated into separate wells (bi-weekly changes continued). Once individual genotypes grew up to be macroscopic (visible to the naked eye), they were fragmented and placed into circulating 12°C sterile seawater with ¼ strength WES nutrient supplement. Within a few weeks, the amount of material necessary for temperate acclimation will be sufficient. After discussing with both a statistician and bioinformaticist, a minor change in treatments will commence. Rather than both decreasing and increasing the temperature of an aliquot of each genotype, we shall maintain an aliquot of each genotype at the control temperature of 12°C and then slowly acclimate the other aliquot to 18°C+ to ensure that the growth and gene expression differences are only due to heat acclimation potential in strains that can be applied to Maine’s aquaculture. Wet biomass will be taken both before and after heat acclimation experiment to measure the effect of temperature on relative growth rate of A. esculenta gametophytes.

The first outreach project of our fourth objective (4) is completed. We presented project objectives at Maine’s Seaweed Festival (see Impacts and Contributions/Outcomes).

Accomplishments/Milestones

Objective 1: determined SST comparative sites upon further oceanographic analysis of the Gulf of Maine; collected and cleaned sporophylls to procure zoospores; released zoospores and germinated gametophytes; successfully isolated individual genotypes from each site; vegetatively growing out genotypes for gene expression analysis.

Objective 4: participated in the Seaweed Scene at the first annual Seaweed Festival at the Southern Maine Community College Waterfront. We also attended the workshops and activities related to seaweed industries: farming, food products, beauty products, art installations, etc.

I also participated in two additional conferences to gain more skills for the gene expression analysis necessary to this project. I attended the Porphyra RCN meeting at the Schoodic Institute, Acadia National Park to participate in a QIIME workshop and an R Statistical Analysis workshop. I also attended an Applied Bioinformatics course at the Mount Desert Island Biological Laboratories: we focused on both secondary and tertiary analyses of RNA-Seq gene expression and on how to create vector figures for publication of results.

Impacts and Contributions/Outcomes

Sea vegetable aquaculture (SVA) is a unique commercial opportunity for Maine, with the potential to create businesses similar to long-existing shellfish and lobster fisheries, with minimal investment, capitalizing on pre-existing infrastructure. Our target audience includes Maine aquaculturists and displaced fishermen who are potential sea vegetable farmers, and seaweed harvesters who can expand with an alternate production method. It is important to bring together these constituencies with aquaculture and macroalgal researchers to understand the practical application of this business opportunity. We have started conversations with organizations like the Eat Local Foods Coalition of Maine and the Maine seafood network to promote sea vegetable integration into local diets. We have also already developed a network within the local school system to encourage students, as well as citizen scientists, to participate in seashore macroalgae surveys. During these projects, we will start a dialogue with participants about future climate change and what impacts that may have on Maine’s coasts.

I attended the Maine Seaweed Festival that supports Maine’s economy by introducing the public to the diverse uses and benefits of seaweeds. Part of the festival is designated to seaweed industry participants to present new innovations that will benefit seaweed production. I was invited by SeaGrant Extension Associate Sarah Redmond to explain the importance of my research and lay out my general objectives. Additional festival events included talks by Shep Erhart, CEO of Maine Coast Sea Vegetables, Ltd. who has agreed to grow out some of my Alaria esculenta strains on his farm and by Sarah Redmond who has helped by with site assessment and collections of sporophytes.

Collaborators: