This Week In The Lab

Does algae and shell hash from riprap make it into neighboring sediments?

You can find subtidal riprap all over the place in urban marine ecosystems.  It’s often like a patchy network of little islands in a sea of soft sediment.  On each of the islands is vibrant hub of reef-associated species – fish, algae, invertebrates of all shapes, colors, and sizes.  Collectively, these riprap-dwelling species generate a lot of biomass, particularly in the form of algae and shell hash.  Eventually, I’ll be testing whether these materials alter the soft sediment communities nearby.  But for now, I simply want to test whether the materials produced by riprap-dwelling organisms make it into adjacent habitats.

Divers entering water to collect soft sediment

This was my reason for embarking on a series of dives recently at Alki Pipeline and Elliott Bay Marina’s breakwater.  With the invaluable help of two dive buddies, Rhoda Green and Dave Thoreson, I was able to get my hands on lots and lots of dirt!  At each site, we lay out three transects extending perpendicularly from riprap.  We collected core samples at 1m, 7m, and 15m along each transect and put them into plastic bags.  After a lot of heavy lifting, we got the samples back to the lab, where I sit now (procrastinating by writing this) with my work cut out for me.  Over the coming weeks, I’ll be sorting through the sediment, quantifying algae, shell hash, sediment grain size, and macrofauna.

I’ll keep you posted on findings as they arise. For now, it’s time for me to get busy.

 

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Photo of tentacles of giant Pacific octopus
Ecosystem Services

Octopus protection in Puget Sound

It’s official – A state commission voted yesterday to prohibit hunting of giant Pacific octopus at 7 popular dive areas around Puget Sound. This marks the end of a long process that started last Halloween, when an octopus was harvested at Cove 2, a popular site for local divers in West Seattle (see article in Seattle Times). Fishing for octopus at the site was legal at the time and the hunter had the proper permitting, but the episode troubled many in the dive community who view octopus as a charismatic species that should be conserved.  Following the controversy, the Washington Department of Fish and Wildlife assembled a panel to review the rules surrounding octopus harvest in Puget Sound.  Yesterday’s vote comes in response to the findings from that panel and from the options set forth by WDFW.

Illustration of giant Pacific octopus

Illustration by Ivan Phillipsen. Check out his drawings and blog at: http://www.wildpnw.com/

You can see the news release from WDFW on the decision here.

An overview of the rule-making process and findings of the advisory panel is provided by WDFW here.

I suspect the decision is receiving mixed responses from divers and hunters. While reporters and other community members are much better suited to follow these aspects of the story, I’d like to highlight why I think this story is so important. In my mind, this is an example of a conflict over the ecosystem services provided by urban marine resources.  In Seattle, we are lucky to have an urban marine ecosystem that is vibrant, full of life forms that come in all shapes and sizes.  As such, the system provides a variety of ecosystem services: strong recreational fisheries for crab, lingcod, shrimp, and other shellfish, extensive opportunities for SCUBA diving and encounters with octopus, six gill sharks, wolf eels, and marine mammals, transportation to and from local islands and suburbs, maritime commerce, and so on.  In an ideal world, all of these services are thriving, providing city residents with a connection to nature and an awareness of the urban marine ecosystem of which we are all a part.

As urban marine ecosystems become cleaner and healthier, conflicts over the use of the resources provided by these ecosystems will undoubtedly arise. How do we want to resolve these conflicts?  What should the objectives be?  Who should be in charge?  How can all users of urban marine ecosystems be incorporated into the process?  WDFW’s recent process to explore alternative options for octopus is one example of how such conflicts can be addressed, and it’s one of the first well publicized processes that I know of. Whether you agree with their final decision or not, I think it’s a great jumping off point for a much needed and even broader discussion: How would we, as urban communities, like to move forward with managing urban marine resources?

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Photos of benthic habitat when urchins are present versus absent
This Week In The Lab

Herding urchins

This week in the lab!.. Setting up kiddie pools on the dock at MaST aquarium.  Why you say?  I’m preparing for an experiment with urchins!

Urchins have a very patchy distribution in the Seattle area.  Using field surveys and underwater photography, I have found differences in the marine community between sites where urchins are present and absent (see image above).  Rocky sites with urchins tend to be characterized by encrusting algae, bare rock surfaces, and occasional large blades of kelp.  Rocky sites without urchins are dominated by a diverse range of red macroalgal species, which may support a different suite of mobile invertebrates.

Photos of benthic habitat when urchins are present versus absent

Sample images of the marine community at (a) a site in Elliott Bay where urchins were present and (b) an adjacent site where urchins were absent. Underwater photography allows us to collect data on the flora and fauna at different sites much more efficiently than was possible in the past. Photos are taken on SCUBA dives using a randomized survey design. Back in the lab, we test for differences in the biological community at two sites by quantifying the percent cover for each algal and invertebrate species in the frame and then using multivariate statistics.

Although I was able to detect differences in the biological community at sites with and without urchins, I don’t know whether these differences are actually caused by urchins until I test this hypothesis experimentally in the field. Starting in late August, I will transplant urchins from the kiddie pools at MaST to a site in Elliott Bay where urchins are currently absent. The urchins will be kept there for several months while I monitor the algal and invertebrate life around them and watch for changes in community structure.

Urchins are faster than you might expect and keeping track of them once you’ve transplanted them to a new site turns out to be quite challenging. In a pilot study, I was only able to find 4 out of 10 urchins after they had been transplanted to a new site. In the full experiment, it’s important that I be able to keep urchins on experimental plots. Otherwise, I won’t know whether the plots were actually subjected to urchin feeding. So, I need to develop a way to contain them within a fixed area. That’s exactly what I’ll be experimenting with in the kiddie pools at MaST.

Thanks to the facilities provided by MaST, I can develop and test alternative urchin containment techniques in a controlled setting prior to implementing them in the field. My objective is to find the least invasive urchin containment technique that meets the following criteria:
(1) Contains urchins without significantly altering the physical conditions (such as water flow) of experiment plots
(2) Does not affect urchin feeding
(3) Allows for free movement of other invertebrate species (such as chitons, snails, crabs, etc.) in and out of experimental plots

Tanks should be up by next week.  I’ll keep you posted!

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