Big Ideas, Recent Research

CASU

Figure 1 from Loke et al. (2014) - A screenshot from CASU.

Figure 1 from Loke et al. (2014) – A screenshot from CASU.

Here’s a neat tool that could be of use to urban planners and restoration ecologists – CASU, the “Complexity for Artificial Substrates” program. CASU is open source software developed by Lynette Loke at the National University of Singapore and colleagues in Singapore, the Netherlands, Brazil, and the United Kingdom. The program allows users to design and visualize artificial substrates for urban waterfronts that are more complex than traditional, uniform surfaces we currently see on most bulkheads and seawalls. Since substrate complexity is tied to biodiversity of intertidal ecosystems, more complex substrates like those generated by CASU may serve as “ecological enhancements” for urban waterfronts.

Loke and colleagues originally developed CASU as part of a project aimed at increasing biodiversity on seawalls in Singapore using molded concrete tiles. By manipulating the topographic complexity of the tiles and deploying them in the field, they wanted to test whether more complex tile designs would increase the diversity of intertidal organisms. The problem is that you can define complexity in number of different ways. What specific aspects of habitat complexity actually affect intertidal diversity most and which are most important to include in your design?

CASU allows the user to modify 5 variables that affect complexity: (1) the number of object types, (2) relative abundance of object types, (3) density of objects, (4) variability and range in the objects’ dimensions, and (5) their spatial arrangement. In the case of their molded tiles, these 5 variables altered the arrangement and configuration of depressions in the tiles’ exposed surface (which are the “objects” that alter habitat complexity in their study).

Loke and colleagues describe CASU in further detail in a recent article in PLoS One. Indeed, after deploying their tiles in the field for 13 months, they did find that tiles with more complex surfaces supported greater diversity of intertidal organisms. Their subsequent work teasing apart which components of complexity are most influential for intertidal diversity on Singapore’s seawalls appears to be in press at the moment, so stay tuned for that. In the meantime though, you can download CASU using the links at the bottom of this page.

Figure 2 from Loke et al. (2014) - their caption reads: "3D models (AutoCAD drawings) of tiles with a single structural component (square-pits) at two levels of complexity generated via CASU. (A) ‘simple tile’ and (B) ‘complex tile’. (C) a fabricated 40×40×6 cm^3 concrete tile mounted onto a seawall (photograph taken one month after deployment)."

Figure 2 from Loke et al. (2014) – their caption reads: “3D models (AutoCAD drawings) of tiles with a single structural component (square-pits) at two levels of complexity generated via CASU. (A) ‘simple tile’ and (B) ‘complex tile’. (C) a fabricated 40×40×6 cm^3 concrete tile mounted onto a seawall (photograph taken one month after deployment).”

 

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This Week In The Lab

Urchins on hunger strike

The results are in.  After several months of tethering urchins and measuring their feeding rates, it seems that we can now conclusively say that tethered urchins go on hunger strike. Given that the whole operation was rather comical (try putting urchins on leashes, building little urchin boxing rings, and feeling normal!), I am tempted to present this conclusion jokingly and without the context you probably need to understand why it matters.  The bottom line is that I am still without a means of quantifying the effect of urchins on urban marine ecosystems in the field. So that’s unfortunate.

Tethered urchin

Tethered urchin

A huge thanks to the folks at MaST aquarium for letting me set up kiddie pools in on their dock and use their flow through seawater system. Throughout August and September, I used these tanks to test whether tethering impacted the way that urchins feed. Urchins exhibit an extremely patchy distribution in urban marine ecosystems. When they are present, the algal community appears to be considerably different, with less foliose red algae and a different suite of sessile invertebrates. My overarching question is whether urchins alter the community structure on rocky habitats when they are present in urban marine ecosystems, or whether these differences are the result of some other process. In order to do this, I ideally would conduct a transplant experiment, moving urchins to sites where they currently are absent and measuring any changes in community structure that result.  But pilot studies demonstrated that transplanted urchins are not easy to keep track of – they move away from transplant sites quickly, often disappearing into deep crevices between the rocks.  If they don’t stay on experimental plots where they’re transplanted, I can’t effectively quantify their effect.  Tethering was the last of several attempts to contain the urchins within experimental plots and would only have been effective if they continued to feed once tethered. Since they did not continue to feed, we can rule it out as an approach for measuring the impact of urchin feeding in the field.

What was striking about the results of the experiment was that the differences in feeding rates between tethered and non-tethered urchins were consistently so significant. I conducted the experiment with three different types of algae: Ulva sp. (fleshy green algae), Chondracanthus exaperatus (a red alga known as Turkish towel), and Laminaria saccharina (“sugar kelp”). Urchins that had not been tethered consistently ate 2-3 grams of algae per day, while tethered urchins ate less than a gram or nothing at all. Statistically, this led to highly significant differences in feeding rates.  Before-and-after weights of algae in stalls with tethered urchins did not, on the other hand, differ significantly from empty stalls where urchins were left out as an experimental control.

For now, I’m taking some time to regroup and reconsider how we can test the effect of urchins on algal communities. It is an issue that we’d love to understand better, particularly since urchins play such an important role in temperate marine ecosystems in less urbanized environments. The lesson of the day is that designing effective field experiments can be more challenging than one might expect. We’ll keep working at it though, and will let you know develops.

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Photo of noble sea lemon
Sites and Critters

The noble sea lemon

I took the photo above recently at Alki Pipeline, in West Seattle.  It’s a noble sea lemon, Peltodoris nobilis, and it’s larger than any other specimen I’ve ever seen, at almost 20 cm in length. According to Andy Lamb and Bernard Hanby, who wrote every Pacific Northwest Diver’s go-to companion, Marine Life of the Pacific Northwest, noble sea lemons can actually grow to be up to 25 cm long.

Photo of noble sea lemon eating a sponge

Photo by Marquis McMurray. Source: http://slugsite.us/bow/nudwk533.htm

Noble sea lemons are a type of nudibranch, or sea slug. Closely related to snails and terrestrial slugs, nudibranchs come in a striking array of beautiful and vibrant coloration patterns. Many have frilly (functional) adornments, such the darker-colored, fuzzy gill rosette you see here on the noble sea lemon’s back.  (The word nudibranch actually means “naked gills.”) In the front, it has two rhinophores to detect odors. Because nudibranchs have lost their shell, they have developed alternative methods of defense, including blending into their surroundings and harboring chemical toxins, which they may produce themselves or harvest from their prey and reuse.

Nobles sea lemons generally feed on sponges (and sometimes detritus), but individuals apparently have quite specific preferences when it comes to their favorite sponge species. This one on the right appears to have found its prey species of choice! I love this photo from Marquis McMurray – the noble sea lemon there is chowing down so intensely on a sponge that its face is almost completely is buried in it! From what we can tell, noble sea lemons gain chemical defenses (toxins) from the sponges they eat. When they’re eating sponges, they contain doridosine, a toxin that was found to be lethal when injected into shore crabs and mice.

We took the above photo at about 25 ft. While I didn’t see a lot of sponges in the vicinity, I’ll certainly be looking out for potential prey items of the noble sea lemon on future dives.

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Sites and Critters

Underwater video tour of Alki Pipeline

If you live in a coastal city, there is likely a vibrant marine ecosystem just beyond the shoreline you see downtown. We so rarely get to peer into these ecosystems and so it’s easy to forget (or not even know) that they exist. Maybe this will help with that – this is an underwater video taken by my dive buddy, Ed Gullekson.  We shot the video at a dive site in Seattle called Alki Pipeline.  The site consists of a large pipe that is covered in boulders, or “riprap”, to prevent erosion. The boulders have provided rocky habitat for a wide variety of organisms, including giant Metridium anemones, a diversity of red macroalgae species, rockfish, and much more:

Subtidal riprap habitats are the main focus of my research. Specifically, I’m interested in understanding how ecological processes on riprap work and how the organisms growing on riprap affect surrounding soft sediment environments in cities.

This video was taken while swimming along a fixed bearing over the riprap installation at Alki Pipeline.  Originally, we were planning to use it as a means for documenting fish abundance and diversity, which we may still do.  But we realized it might also just be of interest for folks who want to see what it’s like down there.

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Photos of marine life growing on seawall
Big Ideas

Living Seawalls for the Intertidal

It’s a bit old at this point, but I recently came across this article in Conservation Magazine on “How to Build a Living Seawall”.  It gives a good summary of work done by colleagues at the University of Washington and the University of Sydney on different seawall configurations that support greater intertidal biodiversity.  More updates as these findings are incorporated into the construction of a new seawall in Seattle…

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Recent Research

Could jellyfish blooms be attributed to “ocean sprawl”?

Photo of Jellyfish by Ole Kils

Image by Ole Kils

You may have heard that jellyfish are taking over the world’s oceans, proliferating at a rate that is unfounded by historical standards.  Is it possible that this has been facilitated by the urbanization of coastal ecosystems?

This is the question posed by Carlos Duarte and colleagues in a recent a paper published in Frontiers in Ecology and the Environment (link). Many jellyfish have two life stages: the pelagic, medusoid phase that probably comes to mind when you think of jellyfish, and a juvenile stage in which they are attached to the bottom as tiny polyps. Most previous studies that have tried to explain recent increases in jellyfish abundance have focused on the pelagic stage.  Tiny polyps are hard to find, and have thus not been a central focus for research.

That is until now… Duarte and colleagues searched far and wide for the tiny creatures.  Where did they eventually find them? On the underside of floating docks, buoys, riprap and other artificial structures. They suggest that the proliferation of artificial structures (which they identify as “ocean sprawl”) is precisely what has allowed jellyfish populations to explode.

Many questions remain, of course, and much more must be done to see if their theory holds water. While Duarte et al. found that jellyfish polyps of some species favor shaded habitats, has the increase in shaded habitat associated with “ocean sprawl” really been sufficient to facilitate the types of increases we’ve seen in adult jellyfish populations? Does the trend extend to species they have yet to test experimentally? And can we actually find these polyps on our local floating docks prior to jellyfish blooms? All of this remains to be seen.

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