It’s been approximately 8 weeks since seeding and the growlines and the Beach and Island sites are yielding significantly different results. The scene at the Island site is grim – little kelp but plenty of fouling – and the Beach site is doing well, with kelp blades nearly a foot long.

Island Site

Kelp growth is minimal and appears to be overtaken by other organisms/fouling/sea-slime.

• Low kelp growth. Blades ~7-10cm.
• Overtaken by fouling (other algae)
• Possibly a nutrient insufficiency: lack of nitrogen/nitrate/nitrite (more on this below)

Beach Site

Reasonable, albeit patchy, growth and much less fouling.

• Decent kelp growth. Blades ~20-30cm.
• Not much fouling.
• Patchy kelp growth:
  • Rhythmic? Possibly correlating with seedstring position?
  • Possibly related to seedstring inoculation method and low density of sporophytes?
    • Some studies have shown meiospore inoculation to produce higher seedstring coverage and higher kelp yield when compared to gametophyte inoculation; the latter being the method used for our seedspools.
    • See: Effect of seeding methods and hatchery periods on sea cultivation of Saccharina latissima (Phaeophyceae): a Norwegian case study.

Nitrogen

There is a range of factors affecting the kelp growth at each site – from currents and water conditions to the growline depth and access to nutrients. The latter is a biggie, and in this category nitrogen concentrations are key. Dissolved nitrogen is a primary ingredient in kelp’s diet and is essential for growth. It is one of the main things our water samples will be used to measure.

So is the dispiriting sludge-line at the Island site the result of a nitrogen deficiency?

Maybe so:

1. When starting this project, I was informed that other kelp projects in the surrounding waters (Buzzards Bay, Massachusetts) had less than stellar results due to suboptimal nitrogen levels. This information was offered as a warning rather than an attempt to discourage the project from happening; after all, the goal from the outset has been to learn by doing, experiment, and literally “test the waters.”
2. The Buzzards Bay Coalition’s Baywatchers Monitoring Program collected summertime water quality information at more than 150 stations around Buzzards Bay, Massachusetts from 1992 to 2018, HERE. Baywatchers document nutrient-related water quality and the effects of nitrogen pollution. Their reporting shows annual average NO3 − +NO2 − (nitrate and nitrite) concentrations that are 1 µmol L−1 or less. For optimal sugar kelp growth, we’re looking for levels around 5 µmol.