Summary: This summer I am asking, “Do fragmented seagrass landscapes exhibit lower predation rates than continuous seagrass landscapes?” Predation rate is one way in which scientists can measure how fragmentation changes the way in which animals use their habitat. When I explain the ecological methodology for the investigation of relative predation rates, known as “tethering”, to unfamiliar scientists and non-scientist alike, they often return slightly shocked responses.
When I describe my research this summer to people, scientists and non-scientists alike, it is not unusual for them to respond, “Oh, that sounds pretty…weird…” I’m sure I could come up with several examples of “strange” methodologies in ecological studies which might baffle the unfamiliar person.
The methodology I am using to investigate the differences in relative predation rates between fragmented and continuous seagrass beds in Back Sound, NC, is referred to by ecologists as “tethering”. In order to “tether”, you use fishing-line to tie a relatively weak animal, in my case a juvenile blue crab (1-4 cm in width), to a garden stake. You then place that garden stake in a seagrass bed and return 24 hours later to find the blue crab either present or absent. If the crab is absent, we can assume he/she was eaten by a predator.
So now you may understand why people might find this methodology “weird”; but really, how different is this from fishing with live bait? Some tethering methods even do just this. Instead of simply tying the prey item to a stake, the prey is hooked, so the predator who eats the prey becomes hooked as well. This is an easy way to find out who the predators of your prey are.
The research question I am investigating this summer is, “Do fragmented seagrass landscapes exhibit lower predation rates than continuous seagrass landscapes?” Most people are more familiar with the concept of forest fragmentation in which logging, hurricanes, or other events break a large forest into smaller and smaller pieces or fragments. The concept is the same for seagrass. Just like forests, seagrass meadows are important for many species who call them home. Seagrass can be fragmented by changing water conditions, climate change, storms or boat propellers cutting through the meadows. Seagrass fragmentation changes the way in which animals use the seagrass landscape or may cause certain species to disappear from the landscape all together.
Predation rate is one way in which scientists can measure how fragmentation changes the way in which animals use their habitat. One might expect that as seagrass beds become more disconnected or fragmented, fewer predators would use the area and therefore there would be less predation. Another possibility is that as seagrass beds become more divided, fewer prey items are found within smaller patches making it less worthwhile for predators to visit those small patches. Perhaps these theories are true, or perhaps not; ecologists seem to be conflicted. The answer to this question is what I plan to investigate with tethering experiments this summer.
Ironically, the most common predator of small blue crabs is larger blue crabs. For this reason, in addition to putting out tethered juvenile crabs, we are deploying baited minnow traps and crab pots to see relatively how many adult blue crabs and other predators are using the continuous and fragmented seagrass beds.
As I write this, I realize that this project sounds rather simple; the majority of the data I am collecting are 1s and 0s, crab present and crab absent, respectively. But in reality, so much more effort goes into this field-based experimentation than meets the eye. I know my fellow scientists and graduate students understand this. Logistics, logistics, logistics! One of my favorite logistical difficulties to talk about are the claws. Yes, of course crabs pinch. And blue crabs are (and this I believe is scientific fact) the “orneriest” marine species with which you can work. Blue crabs, no matter how small, put up a fight. They absolutely become belligerent as you tie and glue them to fishing-line on garden stakes. My technicians and I have learned a lot (often the hard way) about how to best handle hordes of small, angry blue crabs. You tend to learn quickly when even small crab pinches hurt if they get you on the cuticle!