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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Big Ideas, Ecosystem Services, Recent Research

Engineering for the greater ecological good

Photo of eagle statue at Redondo Beach, WA

Invertebrate-encrusted eagle statue with a Metridium anemone growing on its wing

As coastal cities become increasingly urbanized, the surrounding waters are littered with a plethora of artificial structures. An “artificial structure” can be anything from seawalls and breakwaters to an abandoned garden statue, like this eagle (right) in South Seattle, which ended it’s long terrestrial journey at the bottom of the ocean. Though colonized by a colorful variety of organisms, artificial structures are rarely added to underwater landscapes with clear, coordinated, and ecologically-oriented goals in mind. The undersides of coastal cities can therefore become ecosystems of happenstance, a chaotic patchwork of opportunistic marine species that may or may not promote the conservation agenda of urban residents or the ecosystems services upon which urban residents rely.

But does it have to be this way? This was the question posed by Dr. Katherine Dafforn and colleagues in a recent publication in Frontiers in Ecology and the Environment (link). Using a series of case studies, they explore how artificial structures might instead be designed, or engineered, to meet specific ecological goals. For instance, to combat pollution, artificial structures could be “seeded” with seaweeds that absorb contaminants, and bivalves that filter organic pollutants. If we want to promote local biota, we could design artificial structures to mimic natural conditions, and restore natural coastal barriers, like wetlands and other shoreline features. (Here’s one such example documented by other UW biologists at the Olympic Sculpture Park in downtown Seattle. The video below shows the kelp forest ecosystem that formed at the site after old artificial structures were rebuilt with more natural materials.)

Though ecological engineering is not a new idea, Dafforn et al. are among the first to emphasize how the approach could help us realize the “multifunctional potential” of artificial structures in urban marine environments. Indeed, anyone who spends time observing marine life in cities is aware of the diversity of life these structures support and the benefits they could offer, both ecologically, and for people, if developed intentionally and with clear objectives in mind. As Dafforn and colleagues explain, these objectives do not need to be singular, as a multifaceted coastal management plan that incorporates a variety of ecological engineering projects and techniques could provide many benefits simultaneously. Perhaps it’s not too grandiose to conjecture that forward-thinking design initiatives could even realign the trajectories of humans and marine ecosystems in coastal cities so that they converge onto a single, more sustainable path forward.

 

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Panorama of Weser estuary
Recent Research

Riprap community structure in Germany

So many of the world’s coastal cities are located at the mouths of rivers. These estuarine habitats were once vast, shallow landscapes of soft sediment, but they have become speckled with hard artificial structures over the course of urbanization. Do these artificial structures provide opportunities for a new suite of species to establish and thrive? How does these species compare to those that live in the natural soft sediment habitats that remain?

These were the questions posed by Markus Wetzel and colleagues in a recent paper in the journal Marine Environmental Research. The team collected samples from riprap and soft sediment habitats at seven different sites in the Weser estuary in northern Germany. All of this work was conducted in the subtidal (below the lowest low tide), at 2-3m depth.

Nymphon sp. (a sea spider, or pycnogonid). (c) Steve Trewhella

Nymphon sp. (a sea spider, or pycnogonid). (c) Steve Trewhella

Subtidal riprap in the Weser estuary supported a diverse community of organisms, including mussels, barnacles, polychaete worms, crabs, sea stars, urchins, and even sea spiders (see photo). Riprap was also inhabited by large populations of the invasive barnacle, Amphibalanus improvisus, as well as well as invasive crabs, clams, and polychaete worms. While several endangered or threatened species were also found on riprap, the abundance of these species was not significantly different between riprap and soft sediment habitats. Overall, they found riprap communities to be more diverse than soft sediments, with 35 species found in hard substrate samples and only 12 species in sediment samples.

Wetzel and colleagues raise an interesting question in their discussion: “Do we elevate the ecological value of estuaries by adding artificial structures?” These structures do appear to increase diversity and increase opportunities for species that rely on hard substrates to establish and survive. Many of the species that live on artificial structures are suspension feeders (filter feeding from the water column), which, Wetzel et al. point out, are known to recycle nutrients and play an important ecological role. Algae that grows on artificial structures could also be subsidizing surrounding soft sediment communities (though this remains untested) and shell material from from these structures could be changing the physical characteristics of soft sediment environments in their vicinity.

The question is certainly an interesting one, but the jury is still out. To find an answer, not only is much more data needed, but we’ll also need to clarify how we want to quantify “ecological value”. Like all things, adding artificial structures to estuaries has its trade offs. It seems we would be wise to understand the full extent and character of these trade offs , as well as our criteria and objectives for evaluating them, before adding more hard substrate to our coastlines.

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Photo of Giant Pacific Octopus
Happenings, Recent Research

New discoveries about giant Pacific octopus

Last week, I posted about the 2nd Biennial giant Pacific octopus symposium that was to be held at the Seattle Aquarium. The meeting went off without a hitch. It was the first meeting I have attended in which talks from scientists were so seamlessly weaved together with talks from conservationists and educators.

Giant Pacific octopus are part of a class of mollusks called cephalopods, and possess some extraordinary characteristics. They are highly intelligent and dexterous, and are able to open jars, mimic other octopus, and get through mazes in lab tests with ease. (Here is a great article in Slate Magazine about octopus smarts.) They also have tiny structures in the cells just below their skin that allow them to rapidly change color. When watching an octopus in the wild, you’ll also see them change the texture of their skin to look impressively similar to surrounding kelps and algae. Giant Pacific octopus are the largest known octopus species, growing up to 30 feet from tip to tip. They live for 3 to 4 years and mate only once near the end of their life.

The symposium at the Seattle Aquarium last weekend presented on several aspects of giant Pacific octopus biology and ecology. Shawn Larson, curator of conservation research at the Seattle Aquarium, presented her genetic findings from specimens in Puget Sound, the outer coast, and other locations regionally. Her work suggests that there is some degree of mixing between geographically separated individuals and that there is little evidence of a genetic bottleneck, or reduction in genetic diversity, which we would expect to see if the population size had declined rapidly in association with human activities. David Scheel, from Alaska Pacific University, also gave a a fascinating talk about his work over several decades. He presented compelling evidence that giant Pacific octopus are actually comprised of two (or more) separate species, which can be distinguished both genetically and by morphological differences. In addition, he explored some interest ecological relationships between octopus in Alaska and their prey, suggesting that the adornments on some crab species, which were traditionally thought to be adaptations that make them less visible to predators, may also be texturally cryptic, meaning their texture allows them to blend in with their surroundings when octopus are groping around under the bottom sides of rocks. We also heard from Jennifer Mather, who is developing an ethogram for giant Pacific octopus, Reid Brewer, who has done extensive research on giant Pacific octopus population density in the Aleutian Islands, and many others.

Finally, the meeting honored an important figure in octopus science and conservation, who recently passed away. Roland Anderson was a biologist at the Seattle Aquarium for many years and was the reason the Aquarium began hosting this meeting two years ago. In his memory, the symposium will hopefully continue for many years to come, highlighting further discoveries about giant Pacific octopus and connecting biologists, ecologists, conservationists, and educators from all around the Pacific Rim.

 

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Photo of hydroids
Recent Research

Hydroid assemblages in Spain’s harbors versus natural rocky habitats

Here’s a cool recent paper from Cesar Megina and colleagues: Harbours as marine habitats: hydroid assemblages on sea-walls compared with natural habitats. Megina et al. compared communities of hydroids in harbors and natural rocky habitats along the southern coast of Spain.

Photo of hydroids

Photo by Peter Southwood

Quick interlude – if you’re wondering what hydroids are, here’s a good overview.  They’re essentially colonies that grow in a vast variety of shapes, sizes and structures. The colonies are comprised of lots of little polyps, but often have a medusoid phase as well, like a jellyfish.

OK, back to the story… Cesar Megina and colleagues from Spain and Italy sampled hydroids at multiple harbors and natural rocky sites on the Iberian Peninsula. They found that hydroid assemblages in harbors tended to be comprised of species that formed small colonies and put a higher proportion of their energetic effort towards reproduction. Conversely, the hydroid species growing in natural rocky habitats away from cities tended to be those that form large colonies, put proportionally less effort into their reproductive stage, and have a greater capacity for competition with other benthic organisms for space.

Harbors also tended to support a higher proportion of non-indigenous hydroid species.  This is a finding that has been extended across multiple taxa and in several other parts of the world (I’ll post soon about a recent paper on this subject from the Pacific Northwest).

Megina et al. note that they were surprised to find high species richness of sessile hydroids in harbors in southern Spain.  As the field of urban marine ecology expands, it would be interesting to see whether this is a finding that carries over to other parts of the world.

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Recent Research

Urchins and crabs vying for dominance

I’ve been thinking a lot recently about this article from Bob Steneck and colleagues: Ecosystem Flips, Locks, and Feedbacks: the Lasting Effects of Fisheries on Maine’s Kelp Forest Ecosystem. In it, they describe two distinct states of shallow subtidal ecosystems on the east coast of the US: a macroalgae dominated system in which urchins are absent and an urchin dominated state where macroalgae is absent and the rocks are covered in crustose coralline algae. This idea isn’t necessarily a new one – Steneck and others have been documenting shifts between these two states for several years.  The general perception is that urchin harvesting reduced urchin abundance in many locations, which allowed fleshy macroalgae to take over. What is new in this recent paper by Steneck et al. is that switching a macroalgal system back to an urchin-dominated form is extremely difficult, and they attribute this to one culprit in particular – crabs.  In relocating thousands of urchins to macroalgal dominated habitats, they found that large predatory crabs reeked havoc on their study subjects, brutally inflicting 100% mortality on recent transplants. Steneck et al. suggest that the crabs are present in such abundance because macroalgae helps them settle as juveniles and survive to adulthood.  In other words, when urchins eat up all the macroalgae, they are reducing habitat for baby crabs, but once the urchins are gone, baby crabs have more macroalgae than they could ever dream of and they go wild, preventing urchins from reestablishing.

I have a number of questions about this paper and I’m not sure all the pieces are there yet to make their case.  But it is an interesting idea, particularly when I think about the patchy distribution of urchins in the Seattle area.  As might be expected, I too see differences in the benthic community in places where urchins are present versus absent (see previous post), with red macroalgae dominating at sites without urchins. So where exactly are the urchins and why are they there?

Here’s a paper from Daniel Cheney and colleagues from the early 1990s: Creation of rocky intertidal and shallow subtidal habitats to mitigate for construction of a large marina in Puget Sound, Washington.  They were writing about the construction of Elliott Bay Marina in Seattle.  Although there is no explicit mention of urchins in their paper, Elliott Bay Marina is one of the only breakwaters in the area where green urchins appear to be present.  All of the urchins I’ve seen there are large adults and the benthic community includes kelps, crustose coralline algae, and fewer red macroalgal species than one finds in similar habitats nearby.  Elliott Bay Marina breakwater may be one of the most recently constructed breakwaters in the area – is it possible urchins were able to settle there before the establishment of large crabs and that the same individuals have persisted all this time?  That might mean that the system is destined to become dominated by red macroalgae when the urchins finally die off from old age…  Hmmmm…

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Photograph of ocean and riprap at dusk
Big Ideas, Ecosystem Services, Recent Research

Climate change and the proliferation of shoreline armoring

Louise Firth and colleagues recently published this article in Environmental Science Processes & Impacts: Climate change and adaptational impacts in coastal systems: the case of sea defences. It provides a brief exploration of shoreline armoring in the face of climate change. The general idea is this: as sea levels rise, coastal cities and developments are requiring increases in coastal defense structures (breakwaters, riprap, etc). These structures carry negative and potentially positive impacts for marine ecosystems. Why not construct them with these impacts in mind?

Photo of coastline with riprap and seawall

(c) Nigel Chadwick

“There is no doubt,” Firth and colleagues state in their paper, “that [armoring structures] modify the natural environment and can have deleterious impacts…” They cite research that has demonstrated how armoring structures act as stepping stones for species undergoing range expansions and how they have facilitated biological invasions. However, they may have potentially beneficial impacts as well, by supporting species of conservation importance and increasing habitat heterogeneity, as Firth et al. (2013) note.

So what does this mean for the construction of coastal defense structures? If the objective is to enhance intertidal biodiversity, Firth et al. (2013) provide these guidelines:

  • ”Build structure lower in the intertidal zone.”  Areas that are submerged for longer tend to support a greater number of species. Would this alter habitat that would otherwise be unaltered? That’s a discussion for another day I suppose.
  • Avoid smooth rocky material“, as these types of surfaces tend to be to be colonized by fewer species.  Specifically, they suggest a mixture of hard and soft rock to create greater surface roughness.
  • Create rock pools,” which should provide refuges for some species at low tide and support greater diversity.
  • Create pits” and crevices.  These provide hiding places and habitat heterogeneity.
  • Deploy precast habitat enhancement units.” Firth et al. (2013) note that a variety of such units are currently being tested around the world at the moment.  More on this soon in future posts!

 

 

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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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