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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Background

Do algal subsidies from riprap alter soft sediment community structure?

In my last post, I provided some background information about spatial subsidies and how I think they may be playing a role in urban marine ecosystems. Specifically, I considered whether the red algae that grows on riprap may have an effect when it gets incorporated into adjacent soft sediments.

To test this, I set up a field experiment at the beginning of the summer.

Photo of enrichment plot

Enrichment plot treated with shredded read algae

The experiment consisted of a series of half-meter, circular plots, each marked at the center with a construction flag. The plots were set up in a large square grid.  In the days leading up to the experiment, I collected large amounts of shell hash and red algae from nearby dive sites.  All of the shell hash was sieved through a 0.5mm sieve. The algae were all ground up using a cheese grater so that they resembled the tiny pieces of red algae that I often find in sediment samples. Each plot then received one of the following treatments: 100mL of algae, 100mL of shell hash, 100mL of algae and 100mL of shell hash combined, 500mL of algae, 500mL of shell hash, or no treatment (as a control).  There are obviously many specific details to this that I’m leaving out, but please don’t hesitate to contact me if you have questions.

Photo of enrichment plot

Enrichment plot treated with shell hash

I’ll be collecting core samples from the plots at 8 weeks and at 16 weeks. Each sample will then be sorted and all macrofauna (worms, clams, snails, etc) will be removed.  By comparing the inhabitants of each sample, I should be able to detect whether the community of species that lives in soft sediment is affected by the introduction of shell hash and red algae, which appear to originate from riprap.

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Background

Spatial subsidies from riprap… say what?

As promised, I wanted to provide some background information about spatial subsidies and explain one way in which I think they may occur in urban marine ecosystems…

Since the late 1990s, there has been growing recognition among ecologists that the structure of ecological communities may be heavily influenced by the movement of resources from neighboring habitats. This movement of nutrients or energy has been identified by the term spatial subsidies, and has been the subject of considerable discussion in recent ecological literature. Spatial subsidies have been shown to alter the abundance of recipient species in a variety of different ecosystems.  The effects of subsidies appear to be particularly apparent among consumers of lower trophic levels (things that eat plants, for instance).  They may also impact other trophic levels, either directly or through indirect interactions.

photograph of red macroalgae on riprap

A photoquadrat of red macroalgae growing on riprap.

The introduction of artificial rocky material, such as riprap, to urban marine environments may alter neighboring soft sediment communities by providing them with new spatial subsidies.  Riprap is most commonly introduced to soft sediment environments that are not already protected by naturally occurring rocky material.  The biological community on riprap is substantially different from that in neighboring soft sediments, and has the potential to introduce a considerable amount of biomass into adjacent habitats in the form of detritus or debris.

My initial findings suggest that several species of red macroalgae may provide a flux of detrital material into soft sediment habitats. In addition, the sediment close to riprap installations is coarser than that farther away and contains shell hash from barnacles and jingle shells, which are found in high density on riprap.

Several studies have considered how soft sediment communities are altered by the presence and proximity of rocky structures, but with mixed results (see Davis et al. 1982, Ambrose and Anderson 1990, Posey and Ambrose Jr. 1994, Barros et al. 2001, Fabi et al. 2002, Jaramillo et al. 2002, Martin et al. 2005, Bertasi et al. 2007).  While some studies have found differences in the soft sediment community at varying distances from rocky substrates, the mechanism proposed to explain these differences has primarily been physical in nature. Martin et al. (2005) and Bertasi et al. (2007) attributed differences in soft sediment species richness and composition near rocky material to hydrodynamic patterns that trap coarser materials that are transported there by waves.  Fabi et al (2002) considered both physical factors and increased predation as potential reasons for differences in infaunal community structure adjacent to artificial reefs. Barros et al. (2001) provided one of the only suggestions that addition of reef-originating material into soft sediments nearby could be altering infaunal assemblages.

In my next post, I’ll tell you more about the experiments I’ve set up to test whether soft sediment communities are impacted by spatial subsidies from riprap. Thanks for reading and please don’t hesitate to contact me if you have any questions!

 

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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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This Week In The Lab

Urchin corrals

I have installed the first of what will likely be several different contraptions to contain urchins. It’s an urchin corral! You can see it here in the kiddie pool tanks at MaST aquarium:

Photograph of urchin corral out of the waterClose up of urchin corral

It’s kind of like a little urchin boxing ring!

If you’re wondering why on Earth I’m doing this, you might check out this previous post.  These urchins will eventually be used in a field experiment to test how their feeding affects the subtidal communities on artificial rocky substrates.  In order for the field experiment to work, I need to be able to keep the urchins from wondering off experimental plots.Photo of urchin pressing against edge of corral

Enter little urchin boxing rings… this is likely the first of several iterations of the urchin corral/boxing ring idea.  Over the next week I’ll be trying to figure out whether urchins are escaping and how exactly their doing it.  If I can develop a design that contains urchins effectively, the next Photo of urchin corral in kiddie poolstep will be to put something like this into the field and evaluate whether it seriously alters flow, traps algae, excludes other important critters, or changes some other aspect of the physical environment on seawalls.

In its current form, the boxing ring/urchin corral is constructed from bolts protected by pieces of artificial sponge (thanks to Rus Higley at MaST aquarium for this fantastic idea) and monofilament line (this idea compliments of my advisor, Ken Sebens). I’ll let you know what happens!

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Photograph of algae presses
Sites and Critters

Red macroalgae artwork… and some science

Algae presses are a cool and creative way to document macroalgal specimens you encounter in the field (and they make great gifts too!). These specimens came from a dive site near Centennial Park in Elliott Bay, Seattle. They represent some of the more common and dominant species I see growing on riprap. I made the presses by placing them on thick paper between two pieces of plywood held together by bolts that I then tightened as the algae dried.

These are presses of red algae species I commonly find on riprap in Seattle.  Tiny pieces of these algae are mixed into adjacent sediments.

These are presses of red algae species I commonly find on riprap in Seattle. Tiny pieces of these algae are mixed into adjacent sediments.

Riprap, the rocky material that makes up jetties, breakwaters, and seawalls, supports an abundance and wide diversity of red macroalgae.  One of the questions I’ve been most interested in testing is whether the red macroalgae growing on riprap get incorporated into neighboring soft sediments.  I recently collected sediment samples along transects extending perpendicularly from riprap installations (see earlier post), and I’m happy to say that I have a finding to report!  After weeks of sorting through the sediment samples, I have found that the amount of red macroalgae that is mixed into soft sediment decreases as you move away from riprap.

The next step is to identify whether these differences in algal content might influence the community of organisms that live in soft sediment.  In ecology, food webs that are altered by the influx of resources from adjacent habitats are said to be “subsidized” or influenced by “spatial subsidies.”  (I’ll write a post soon to give more background on the spatial subsidies literature.)

To test for spatial subsidies, I’ll be conducting field experiments in which I enrich soft sediment plots with fixed volumes of shredded red macroalgae. At the end of 8 and 16 weeks, I’ll be collecting core samples from these enrichment plots and testing for differences in community structure. More to come on that.  In the meantime, I’m excited to say riprap-originating algae do in fact make it to neighboring soft sediments… what is their affect there?  The answer to that is coming soon!

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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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This Week In The Lab

Building a macrofauna library

Vials of representative specimens for my macrofauna library

Beginning of our macrofauna library

Just back from a whirlwind trip to Friday Harbor Labs.  There, with the help of an expert, I was able to begin building my library of the species that live in subtidal soft sediments in the Seattle area. As I drove from Anacortes to Seattle, my vials of macrofauna in ethanol rode along in the passenger’s seat.  Together, we boarded a ferry for San Juan Island, where we spent the next few days looking deep into eachothers’ eyes under the romantic lighting of a dissection scope.

Vial containing Spiochaetopterus worms

Vial of Spiochaetopterus worms!

Thanks so much to Megan Dethier for all her help as I dive into the world of infauna.  You wouldn’t believe how many families of polychaetes there are, or how complicated a dichotomous key for snails can be!  We’ve made good headway though, and I’ve already accumulated a large number of tiny vials containing representative specimens (see photo).

In addition, I’m compiling a written key for lab techs that hopefully will require less time than the all knowing and ever complex invertebrate bible, Kozloff’s “Marine Invertebrates of the Pacific Northwest.”

More soon on my favorite specimens and strangest finds!

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This Week In The Lab

Soft sediments – they’re alive!!!

On Aug 3, I told you about the dives we’d done to collect soft sediments.  Tube of macrofauna in ethanolSince then I’ve spent many an hour in the lab processing the samples we collected.  Processing involves (1) quantifying the volume of riprap-originating algal material in each sample, (2) quantifying sediment grain size, (3) identifying each type of shell hash, and (4) identifying and counting all macrofauna.

Macrofauna are organisms that live in soft sediment.  Until just a few years ago, I had no idea how many critters actually live embedded in sand and mud. From above, the soft sediment landscape appears barren, almost devoid of life.  But it’s actually alive in a way I never imagined – at a tiny scale.  After many hours of picking through sand and mud in my sediment cores, I am again amazed at the density and diversity of macrofaunal life forms.  They come in all shapes and sizes, colors and textures, life histories and strategies.  Worms, clams, snails, amphipods, ostracods, sea cucumbers, and more!  It’s overwhelming.

For now, I’m simply pulling specimens out of sediment samples and storing them in ethanol (as in the photo), but I’ll be identifying them over the coming months and look forward to sharing.  Their stories are bazaar, amazing, surreal – from vicious hunters with exploding mouth parts to little arthropods that spend their entire lives moving about the seafloor in the organic equivalent of a hamster ball. I’ll highlight my favorites as they arise.  Stay tuned!

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This Week In The Lab

Urchins tanks are ready

Last week, I told you about experiments I would be starting at MaST aquarium in Des Moines, WA.  I’m happy to report that the urchin tanks (aka kiddie pools) are up and running! Urchins in kiddie pool A small number of specimens have been moved into the tanks.  I’ll let them acclimate for a week or so to ensure that everything is functioning properly.  Then, it will be time for experiments.

I’ll be trying a variety of different approaches – urchin corrals, sponge barriers, and tethering.  The objective is to find a way to contain urchins without significantly altering physical conditions (such as water flow).  With each method, and particularly with tethering, I’ll be testing whether the technique alters how urchins feed.  This is important because the urchins themselves will later be the experimental treatment in the field when I test whether urchin feeding alters the biological community on subtidal riprap.

Urchins in kiddie pools at MaST aquariumIf you have ideas about how you would contain urchins in a fixed area, I’d love to hear about it!  Submit an idea or drawing on the Contact Me page.  Or, send me your idea at:

Eliza Heery
University of Washington, Department of Biology
Box 351800
Seattle, WA 98195-1800

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