Invasive Species and Their Effect on Relative Abundance of Native Species in the Wild

By Brent Mello

My research is intertwined with the research of a graduate student, Eleanor DiNuzzo. Through the last two summers, she has surveyed the same three rocky intertidal sites in Massachusetts for four species: Hemigrapsus sanguineus (Asian shore crab), Carcinus maenas (green crab), Nucella lapillus (Atlantic dogwhelk), and Mytilus edulis (blue mussel). I first learned about these four intertidal species last year when I started to help with Eleanor’s intertidal surveys. I was taught how to identify the different species, as well as the sex of the crabs. 

In early April, the sites were visited for the first time for the season. We were making sure the sites were still prepped for our surveys. At each tide height, 0m, 0.5m, and 1m, we located the rocks that had been tagged with “dog tags.” If any rock had lost the tag applied from the previous years, we had to apply a new tag. Only two new tags had to be applied this year. We utilized marine epoxy that we had in the lab. I have included a picture below of me using epoxy to bond our tag to the rock. I have also included a picture of the tag bonded to the rock two months later during our June surveys.  

In my original grant proposal, I had planned for the possibility that most of the tags had fallen off over the winter. Since this was not the case, the money for the drill, masonry bits, and anchor kit was not needed. I did not want to spend the granted money on unnecessary tools. 

Our next visits to the sites were planned for May 5th-7th, but we encountered external issues that made us have to drop these survey dates from our data.  

The June surveys were a success and were conducted on June 6th-8th. During our surveys, we would get to the site about a half hour prior to the A.M. low tide. This would give us time to prep for our surveys. Once we got to the sites, we located the 0m marker as quickly as possible. In some locations, the tide could chase us out, so getting to the mark as early as possible allotted more time for our surveys. After the 0m mark was found, a 30-yard transect was set up. Five random numbers were generated per tide height between 1 and 30, which were used to place down the quadrat for surveying. I have included a picture of the 1m X 1m quadrat we used in our surveys.  

Once each quadrat was placed, surveying began. One person was set as the data recorder, while the other 2 or 3 surveyors were tasked with searching each quadrat for the four targeted species. Each quadrat followed the same procedure, which I will give step by step. Firstly, we began by moving seaweed out of the way while also searching through it for any of our species of interest. We tried to be minimally invasive and would remove seaweed as little as possible, more so trying to rearrange it. The next step was to search the rocks for and collect Nucella, Mytilus, Carcinus, and Hemigrapsus. We would collect a max of 10 mussels (Mytilus) and as many of the other species present in the quadrat. Crabs (Hemigrapsus or Carcinus) smaller than 10mm were not collected and were called out to the recorder as small, followed by species type. Once the visible species were collected without disturbance, we proceeded to turn over rocks and collect every individual we could, placing them in a bucket. After all rocks were overturned and returned to their initial locations, we began measuring the individuals collected while simultaneously sexing the crabs. Their sizes were measured using battery-powered calipers. The calipers from the previous year were not damaged by the moisture, and we were able to use them. For this reason, I did not use the original plan to buy the waterproof calipers yet. We may need to order more calipers if the current ones get damaged during our future surveys. The research will proceed through the summer with three survey days each month ending in September. After each month’s surveys, data will be transferred from the survey sheets to an Excel spreadsheet. I have included a picture of the survey sheet below from one of our June surveys. 

After the last survey in September, statistical analyses will begin. The statistical tests will be run in R, which I learned the basics of in Bio 430 last semester. I very much look forward to applying the use of R to real-life biological studies, as well as becoming more familiar with other features of the system. The goal is to use non-metric multidimensional scaling (nMDS) in R to compare community composition at different tide heights and locations. I will be using the last three years of survey data for these statistical comparisons aiming to find a significance difference in community composition to see the effects of the presence of the invasive Hemigrapsus in New England coastal rocky intertidal zones. By December, I plan on completing the statistical analyses and having a manuscript ready for submission. 

I would like to thank the OUR department for the grant approval back in January, as well as the support this provides not just for me, but for all undergraduate researchers. Since there may be unexpected expenses that arise over the summer, I would like to request an extension on the grant money. I plan to use it wisely for tools or programs that may be necessary or will benefit the research as a whole.  

Extra pictures from the surveys: 

Picture of me holding a gravid (pregnant) Carcinus maenas 

 

         Hemigrapsus and how they are measured and sexed 

 

         Nucella 

 

Every survey is accomplished with a team effort, so I have included a team picture from one of our June surveys.