Something is eating my ulva. I’m culturing the green algae, collected from seagrass beds near the lab, in 60L mesocosms provided with flow through sea water from dump buckets. To promote growth, I provided each mesocosm with Osmocote (slow release fertilizer). But, instead of improving the culture is steadily declining. Small, pin prick holes have appeared throughout the algae.

 

So, what’s happening?

Hypothesis 1: Mesograzers are to blame. After closer inspection there are very few amphipods, isopods, and other grazers in the mesocosms. I removed all large mesograzers, but the culture has not improved.

Hypothesis 2: Too much fertilizer. I’m not sure how the added N could be hurting the culture (possibly promoting microbial growth that could be degrading the ulva?), but I removed it just to check. After 5 days without fertilizer there is no marked improvement.

Hypothesis 3: Force of water from dump buckets is too stressful for the thin, sheet-like algae. I’ve turned down the water flow to the dump buckets and repositioned the cultures to receive a less direct wave “dump,” but the culture still looks poor.

Hypothesis 4: Too much sun? To address this potential problem, I’m going to put a vexar cover over each culture. This may also help dissipate the wave force from the dump buckets.

 

Which hypothesis wins? Stay tuned (or please e-mail me if you have any suggestions!).