Seems to be Working
As described in the last post, I was interested in improving the growth of the food plants. Among the many parameters to consider (spectrum and intensity of light, water flow, nutrients), I decided to systematically increase the nutrient levels by carefully dosing Guillard’s f/2 formula. I have been very pleased to see a significant improvement in color, growth rate and branchiness of the Bryopsis.
Previously, growth was unimpressive. The plants were pale and rangy, and I was becoming concerned that they would not ever grow enough to keep the slugs fed. In the photo below, the finer, fuzzier stuff is Derbesia, and the thicker strands are barely recognizable Bryopsis, which should be bushy and feathery. If you can’t figure out what Bryopsis should look like, it may help to read to the end of the post and then scroll back up here.
Within a few days, the Bryopsis started looking better. In the photo below, an astute viewer might be able to see that the tips of the branches are beginning to become a darker green. With the added nutrients, cyanobacteria (the red film coating some of the plants) have also increased. With a little adjustment of the dosing, I hope to see less red and more green.
In just over a week, growth is robust, color is a satisfying, deep green, and additional branches are starting to appear. At this point, I also changed the flow pattern a little to increase the current passing through this patch.
As of a few days ago, the plants are nice and green, and almost feathery. In addition, there are patches of new growth forming in areas of high flow, so the alga is spreading. At this point, NO3 levels are a little over 10 ppm, and PO4 is about 0.5. Over the next few weeks, I am going to try to bring the levels down a little bit to discourage cyanobacteria.
So what have we learned? First, a more balanced approach to feeding the algae results in faster growth and better color. Without systematic removals and subsitutions of components, it’s hard to know which of the ingredients was limiting for growth (N, P, Mg, Mn, Fe…..?), but the mix has quickly done the job. Second, based on the quality of the growth in areas of high flow, Bryopsis seems to like a lot of current. At present, I do not know which species I have (I hope that will change by the end of next semester), but some are found in intertidal zones with significant surf.
With these lessons in mind, I will be converting the nursery tank into a Bryopsis cultivation tank to provide food for the hungry Elysia that will arrive in a month or so for the student research project.