Patriot day
Friends, it is a busy summer! I'm not sure if you're having any trouble keeping track of my projects this summer (there are several), so let's review!
There are lab experiments on oyster larvae swimming behavior;
I have an experiment hanging off the dock to see how limpets affect fouling fauna; and
I'm studying how larvae disperse among shipwrecks on Stellwagen Bank in order to stop the spread of an invasive species.
It is this latter project that brings me to the blog today. This weekend, I visited my third site on Stellwagen Bank to deploy samplers, and it was a very interesting trip!
My day began at 5:45 am. Carl and I had stayed in Beverly, MA, north of Boston, in preparation for our early morning dive. We made our way to the dock by 6:30 and discovered many of our fellow divers were already there. The regulars are all pretty hardcore morning people. We loaded our gear onto the Gauntlet and were off.
As I descended through the water, I kept one eye on Carl and one hand on the thick white mooring line. The water around me was green, but not quite soup - I could still see. The deeper I went, the dimmer it became, until the wreck began to emerge out of the darkness beneath me. I added gas to my buoyancy compensator, cleared my mask, and gave Carl the OK sign. We had arrived at the wreck of the Patriot.
My very first task on the dive was to deploy larval traps and fouling panels on the seafloor. I dropped down beside the wreck and noticed the sand was covered by sand dollars, just the like at the Josephine Marie. I pulled a larval trap out of the mesh bag I was carrying and pushed it into the seafloor, then grabbed a set of fouling panels from Carl and set about hammering it in. Carl picked up what I wanted very quickly, and within a few minutes, we had secured both sets of samplers in the sand.
Next, I pulled out a series of smaller tubes, taped together in rows of 5, and a metallic scraper. It was time to sample my target species, Didemnum albidum. However, after just a few minutes swimming around the wreck, I realized there was no Didemnum to be found. It simply wasn't there. The Patriot actually had stunningly low biodiversity compared to some of the other wrecks on Stellwagen Bank, as it was dominated only by two species (an anemone and a hydroid) and had only small numbers of sponges and sea stars. I was very surprised.
The complete absence of D. albidum from the Patriot wreck may sound like a failure for my experiment, but it's actually an answer to my scientific question all by itself. I started this experiment to figure out which direction an invasive species, D. vexillum, was most likely to invade Stellwagen Bank from, using its native sister species as a model. I thought D. vexillum could come from the north (the Patriot wreck) or the south (the Josephine Marie). Well, there are no Didemnum of either species on the Patriot, but D. albidum was all over the Josephine Marie, along with several other species. That makes the answer pretty clear to me: Didemnum is more likely to come from the south.
When I talked it over with the boat captain later, she agreed with my suspicion. She also noted that wrecks on the northern end of Stellwagen Bank are exposed to sand scour, to the point that their organisms can be blasted off by winter storms. If true, this phenomenon would explain the low biodiversity and the absence of D. albidum on the Patriot - only species that can survive the high-energy environment or recolonize quickly can survive here.
I'll return to each of my sites in August and September to collect my samplers and see what has changed on the wrecks. We'll see if my suspicions hold!
There are lab experiments on oyster larvae swimming behavior;
I have an experiment hanging off the dock to see how limpets affect fouling fauna; and
I'm studying how larvae disperse among shipwrecks on Stellwagen Bank in order to stop the spread of an invasive species.
It is this latter project that brings me to the blog today. This weekend, I visited my third site on Stellwagen Bank to deploy samplers, and it was a very interesting trip!
My day began at 5:45 am. Carl and I had stayed in Beverly, MA, north of Boston, in preparation for our early morning dive. We made our way to the dock by 6:30 and discovered many of our fellow divers were already there. The regulars are all pretty hardcore morning people. We loaded our gear onto the Gauntlet and were off.
 |
| My larval traps and fouling panels adjacent to the Patriot wreck. Photo by Heather Knowles. |
My very first task on the dive was to deploy larval traps and fouling panels on the seafloor. I dropped down beside the wreck and noticed the sand was covered by sand dollars, just the like at the Josephine Marie. I pulled a larval trap out of the mesh bag I was carrying and pushed it into the seafloor, then grabbed a set of fouling panels from Carl and set about hammering it in. Carl picked up what I wanted very quickly, and within a few minutes, we had secured both sets of samplers in the sand.
Next, I pulled out a series of smaller tubes, taped together in rows of 5, and a metallic scraper. It was time to sample my target species, Didemnum albidum. However, after just a few minutes swimming around the wreck, I realized there was no Didemnum to be found. It simply wasn't there. The Patriot actually had stunningly low biodiversity compared to some of the other wrecks on Stellwagen Bank, as it was dominated only by two species (an anemone and a hydroid) and had only small numbers of sponges and sea stars. I was very surprised.
The complete absence of D. albidum from the Patriot wreck may sound like a failure for my experiment, but it's actually an answer to my scientific question all by itself. I started this experiment to figure out which direction an invasive species, D. vexillum, was most likely to invade Stellwagen Bank from, using its native sister species as a model. I thought D. vexillum could come from the north (the Patriot wreck) or the south (the Josephine Marie). Well, there are no Didemnum of either species on the Patriot, but D. albidum was all over the Josephine Marie, along with several other species. That makes the answer pretty clear to me: Didemnum is more likely to come from the south.
When I talked it over with the boat captain later, she agreed with my suspicion. She also noted that wrecks on the northern end of Stellwagen Bank are exposed to sand scour, to the point that their organisms can be blasted off by winter storms. If true, this phenomenon would explain the low biodiversity and the absence of D. albidum on the Patriot - only species that can survive the high-energy environment or recolonize quickly can survive here.
I'll return to each of my sites in August and September to collect my samplers and see what has changed on the wrecks. We'll see if my suspicions hold!
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