In my last blog post, I introduced you to the excitement Newport offers outside of Hatfield Marine Science Center, but left you hanging on how the mesocosm project turned out.
We planned on running experiments three days in a row, leaving the mesocosms out in the field for the entire duration. We needed to collect over 360 juvenile Dungeness crab and over 18 Pacific staghorn sculpin, which proved harder than we expected. We quickly saw that we would need to adjust our study due to the natural progression of second instars growing into fourth or fifth instar crabs. The crabs were too large for the Pacific staghorn sculpins to eat, making it difficult to run a predation experiment. However, we realized that the large crab size could be a benefit as it would allow us to study the crabs’ behavior without any predation while also reducing a factor of loss when retrieving the crabs. This increase in crab carapace allowed us to reduce the number of crabs needed to 10 per mesocosm instead of 20, another benefit. We spent three days beach seining at low tide and setting minnow traps overnight to collect the necessary number of organisms.
Brett Dumbauld of USDA-ARS beach seining for juvenile Dungeness crab and Pacific staghorn sculpin in Yaquina Bay, OR.
With all of the pieces together, we were able to move forward and set-up the mesocosms in the field to begin running experiments. The mesocosms were set the same as they had been during the first trial, each containing different combinations of two habitat types (on-bottom oyster aquaculture, eelgrass, open mud) in three controls and duplicated in three treatments.
We then prepared the Pacific staghorn sculpins by starving them for 24 hours before they were put in the field. We had previously decided that we would experiment with different lengths of time that the crabs were exposed to the sculpin to see if it had any effect on their behavior. We decided to begin one trial when the water was low enough that it wouldn’t be spilling over the top of the mesocosms (about 2.5′). This trial was run for 2 hours, wherein predators were left in the mesocosms. We then reset the trial by removing and counting predators and prey before adding more organisms for a 24-hour trial which we would come back to the next morning. As we approached the mesocosms that morning with the water just around the tops, we noticed them rocking back and forth.
NOOOO! How were we going to run our 24-hour experiment without the crabs and sculpins escaping? We ran back to Hatfield during our 2-hour wait period and brought back a drill and rebar to reinforce the mesocosms, hoping it would do. Since we already had the organisms prepared, it was best to run the 24-hour experiment and just see what would happen.
We had some pretty interesting results. In the 2-hour experiment, we retrieved 95% of the crabs while in the 24-hour experiment we retrieved 106% of the crabs. This was the opposite of what we expected since the mesocosms had been rocking, but apparently some other crabs had run in rather than escape. Given that we only ran two trials, we can’t conclude any real results, but did see some patterns. Crabs preferred oyster shell over both eelgrass and open mud, whether or not there was a predator. The sculpins’ presence didn’t seem to have much impact on crab habitat selection, possibly because they had outgrown the sculpins’ ability to prey. All in all, the mesocosms were a success and Brett plans on using them again next summer, earlier in the crab season to test the second instars.
Last Friday, I presented my work and then participated in a poster session, a really rewarding experience. It felt good to share what I had been working on and I appreciated the exercise of thinking about how to communicate the project to others. It was also informative to see what the other Sea Grant scholars had been working on as well as converse with scientists about our work.
It’s been a really incredible summer living and working at Hatfield Marine Science Center. I am very grateful to have been given this opportunity and feel lucky to have had such wonderful mentors to work with. To celebrate the end of the summer and completing the final presentation and poster session, my husband guided me out on my first sea kayaking trip, exploring the sea caves beneath Cascade Head. Rising and falling with the swell is an incredible feeling, the water looking like hills around you. We watched a whale play about 100 meters away before heading into a cave. I have to say, it was pretty scary and amazing at the same time. Paddling into darkness with waves booming around you would spook anyone, right? It was cool seeing all of the birds nesting along the rock cliffs, Pacific sea nettles swimming around, and sea stars and anemone exposed at low tide. We also spotted some floating tubes which turned out to be squid eggs. All in all, the perfect end to a perfect summer and a reminder of how much we love the area. We’re hoping to move to Newport so I can continue volunteering and learning at Hatfield while looking for work.