Temperature Tolerance in Alaria

Project Description

Sea surface warming is a key consideration when selecting candidate sea vegetable crop species in Maine. Researchers are investigating the temperature tolerance of edible kelp along the Maine shore to determine the effects of thermal acclimation on seedstock and crop yield.

Project personnel collected zoospores and grew up individual genotypes of eight males and females (gametophytes) of Alaria from Lubec and Two Lights in 2015 and 2016. Originally, these gametophytes were planned for study in the project’s thermal tolerance experiments, and are being held for possible trait crosses and/or cryopreservation instead. Personnel decided to use gametophytes generated from many zoospores/parent in the thermal tolerance tests completed in December 2016 to ensure there would be many genotypes to screen in these experiments.

Replicated bulk cultures were made from zoospores obtained from four parent Alaria from Two Lights State Park and four parent Alaria from Lubec, ME sporophytes; these regions represent the southern and Downeast bioregions of Maine. Aliquots of gametophytes from the heat shock experiment were collected for transcriptomic analyses, and RNA extractions were completed in Spring 2017. During Summer 2017, RNA-seq was used for deep sequencing of the experiment’s transcriptomes. Personnel are analyzing gene expression differences between controls and experimental replicates.

Results and Accomplishments

Some expected expression patterns were detected (e.g., over-expression on heat shock genes in the experimental heat treatments), but a number of other genes require analysis of metabolic pathways to understand. Researchers were concerned that the transcripts were not assembling at higher levels against the Ectocarpus and Saccharina genomes. Consequently, the transcripts are being reassembled with different parameters in Spring 2018, and analysis will continue. Selective RT-qPCR will be used to confirm RNA-Seq results (Summer 2018).

Surviving gametophytes from the heat stress experiments were transferred to kuralon spools and cultured and crossed at the Center for Cooperative Aquaculture Research (CCAR) in late Spring 2017. Photoperiod and temperature were adjusted to induce gametogenesis and fertilization followed. In late June, juvenile blades began to appear. Quigley and Aydlett sampled all controls and treatments in order to determine whether biomass/growth were similar between the controls and heat-treatments. Surface areas were higher for blades produced from the heat-treated gametophytes than from controls maintained during the experiment at 12°C.

Spools were transported to an aquaculture farm (Springtide LLC) in Frenchman’s Bay for grow-out in late September 2017. Quigley visited the farm to sample blades from controls and heat treatments in early February 2018, and Aydlett finished the analysis of surface areas. The results are the same, with heat-treatments approaching 1 m long with high surface areas; in contrast, control surface areas are statistically different and lower.

Quigley’s selection procedure to achieve heat tolerant gametophytes was tested, and both heat tolerance and high growth were present in sporophytes produced from both Lubec and Two Lights’ heat-treated gametophytes. This result has held through two measurement periods. Quigley will take a final sample in April 2018 and Aydlett will measure the outcomes.

Quigley conducted a second heat-shock experiment to establish the lethal limit for the gametophytes from Two Lights and Lubec (Summer-Fall 2017). This set of experiments exhibited some Alaria can survive far more than the predicted level of warming for the Gulf of Maine over the foreseeable future from models. It is unknown whether that degree of tolerance will be observed in blades (the commercial stage).

Samples of Alaria from wild populations versus ones grown in eutrophic sites (e.g., Saco) were sampled in 2017 and are stored in the -80°C freezer in the Brawley Lab. The results presented above have taken more analysis and field time than originally envisioned, but project personnel hope to characterize the Alaria samples’ microbiomes to observe differences. This will be an initial attempt at addressing the consumer question of food safety.

Summary of Data Being Collected

Data	Type	Quantity	Location
Growth Rate	Gametophytes	16 single genotypes	UMaine
Growth Rate	Gametophytes	Thousands of control/heat stressed	UMaine
Transcriptomic research	Sequences	10^6 or more	UMaine, Texas Tech Sequencing Laboratory or equivalent
Marker genes	Short (15-200 bp) tags	Unknown at present	UMaine
Grow-out of crosses	Sporophytes	Unknown at present	Center for Cooperative Aquaculture Research (CCAR) and Sorrento Farm
Microbiome diversity	16S rDNA sequences, V6 region	Unknown at present	UMaine and Marine Biological Laboratory (Woods Hole)