By Nancy Steinberg
Benthic ecologist Sarah Henkel has a special place in her heart for all creatures, great and small, that live on the bottom of the ocean. Whether they burrow into the sediment, cling onto rocks, or crawl along the sea floor, she’s interested in where and how they live, and the habitats that support them. She and her colleagues and students are applying this vast knowledge of the deep to evaluate potential effects of wave energy converter installations on the marine environment.
The first step towards evaluating such effects is coming to a more complete understanding of baseline conditions at sites where wave energy devices may be tested or installed permanently. To that end, Henkel and others have been constructing one of the most complete pictures of a large swath of ocean bottom off the West Coast to see what “normal” looks like. In a study funded by the federal Bureau of Ocean Energy Management (BOEM), Henkel and OSU geologist Chris Goldfinger examined benthic habitats and communities at eight sites from Ft. Bragg, CA to Gray’s Harbor, WA. In 2010 through 2012, Goldfinger first mapped the sites using high-resolution sonar. Then Henkel used remotely-operated vehicles (ROVs; essentially remote-controlled underwater robots) to examine hard-bottom habitat and animals and took samples in soft-bottom habitat nearby to see who lives there.
“The idea was to go to these eight places and determine the relationship between the animals and their habitats. Then when a developer wants to use a new piece of the sea floor, maybe there are some basic measurements we can take to have a pretty good idea of what lives there so we can avoid expensive biological surveys by extrapolating from what we already know,” she explained.
“It’s an amazing baseline data set, but it can also be used for planning purposes,” she continued.
Henkel and her team found some interesting and somewhat unexpected results. She was not surprised to observe a clear difference in the community of organisms found in muddy vs. sandy bottoms. But it was a little more surprising to find that a very small proportion of mud mixed in with sand can make a big difference. Communities of benthic organisms in sand and in only very slightly muddy sand can be quite different. In addition, while the three-dimensional complexity of the habitat matters a lot – smooth rock and smooth rock covered with boulders or cobbles supported quite different communities – what does not seem to matter is whether smooth rock is covered with a veneer of mud.
Henkel and her colleagues have also begun to examine the potential effects of wave energy installations as well. Since June of 2010, they have been attempting to collect benthic samples every other month (easier in June, August, and October than the rest of the year!) at the North Energy Test Site offshore of Newport to determine the seasonal and interannual changes in the normal benthic communities there. For this study, they are collecting sediment samples and benthic organisms using a box core and a small trawl. They have paid particular attention to sampling before, during, and after buoy and instrument deployment, including the WET-NZ device deployment in summer 2012 and the Ocean Sentinel deployment in summer 2013 (no wave energy device was tested that summer, but the Ocean Sentinel itself bobbed in the waves for a number of weeks).
“In summer of 2012, we detected no difference in the benthos when sampling before, during, and after deployment,” Henkel says. However, she acknowledges that her sampling stations that summer needed to stay on the periphery of the site; she could not safely sample close to the device moorings or between the device being tested and the Ocean Sentinel test platform.
After the Ocean Sentinel was towed home in the fall of 2013, however, its anchors were left in the water. This gave Henkel the opportunity to get close to those moorings and examine the sediment and benthos more closely.
This time they found a small accumulation of “shell hash” (broken up bivalve shells) near the anchor moorings that had not been there before the moorings were put in place. “These were shells that came from the beach. We suspect it was material that would normally have been transported offshore but it was blocked by the anchors,” she explains. The underlying sediment hadn’t changed at all, so this was the only small difference they found.
Henkel’s benthic monitoring is only one of the ways in which potential environmental effects of wave energy development are being studies at the site. Scientists are also conducting baseline studies of sea bird and marine mammal use of the NETS site, and a team is also “listening” to the site to determine ambient noise level in the ocean there, in order to compare it to the noise generated by wave energy devices. Look for articles about these research projects in future newsletters.
As work at the South Energy Test Site – the grid-connected site where devices will eventually be tested off of Newport – proceeds, Henkel is starting to conduct similar studies there as well. One focus of that work will be looking at use of the site by Dungeness crabs. “We’ve heard from fishermen that crabs will not enter crab pots unless the pots are electrically grounded,” Henkel says (the fishermen put zinc anodes into the pots to address this issue). The implication of this observation is that the crabs are sensitive to electromagnetic fields, perhaps including those emitted by undersea electrical cables. “Because SETS will be cabled to shore, we have a special focus on crabs at the site,” Henkel explains.
So, why all these benthic studies in the first place? What effects on bottom-dwelling organisms might occur as a result of wave energy installations off our coast? For one thing, they will probably act as artificial reefs. “Wave energy devices are not unique,” Henkel says. “Any time we have put concrete and steel in the ocean, fish are attracted to it, barnacles and other organisms colonize it. That’s an effect we’re fairly certain we’ll see.” If the devices attract rockfish, for example, fishermen might be very pleased, but organisms that are typically prey for rockfish will not.
For her part, Henkel is glad for the opportunity to gather extensive baseline data before the industry gets much farther along. “The more baseline data we have, the better,” she asserts. “We didn’t have this opportunity before oil platforms and dams were built, so this opportunity for baseline studies is terrific. I think we’re being good environmental stewards.”