This week I was introduced to the area I worked in for the larger part of the summer: the mudflats. I had the pleasure of experiencing what it means to get stuck (and really, I mean in mud that I sunk past my knees in) and having to have the physical and mental strength to continue on. Although somewhat challenging, the mudflats are a great place to work and have fun in the process.The first trip to the mudflats I was introduced to the technique of measuring shell bags. A shell bag is mesh sac that has been filled with oyster shells. 25 of these bags were laid out last year across the flats in the Yaquina bay to provide hard substrate for settling crab larvae. They were placed throughout the different habitats in the mudflats, including bare mud and the different eelgrass species (Z. marina, and Z. japonica). These shell bags are used to help determine where crab larvae and juvenile crabs prefer to settle. By providing a substrate that is known to be favored by the crab larvae, their movements throughout the different habitats demonstrate their preference of living space. The method of investigation I learned to be somewhat extensive.
To sample shell bags, we first placed a crab corral around the shell bag. This is a small metal square that is softly pressed into the sediment surrounding the bag in order to prevent crabs from escaping. We then cut open the bag and emptied the contents into a box sieve (a wooden box with a screen in the bottom that allows water to wash through, but prevents the crabs from getting out). We then visually investigated each shell, looking for juvenile crabs. We also dug out all the mud within the crab corral down to approximate three centimeters, and sieved through that as well. If crabs were found, each individual had its carapace width measured and recorded. The carapace of a crab is the hard shell that covers the majority of their body.Also, sampling shell bags included a quick assessment of the areas within five meters around the bag. This meant picking a random spot, and dropping the crab corral there. We recorded the different types of vegetation cover in the corral, as well as sieving through the mud in it. Here, we were looking for young crabs that had migrated from the shell bags to the habitat of their choice. These assessments are what really help us determine where the crabs like to live. Although this entire process when repeated 25 times was really long (taking beyond five hours to complete) it’s still really fun. Getting covered by mud and playing with the baby crabs is what made it all worthwhile.