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A Survey of Oyster Research with David Kimbro at the BOP-CCERS June Fellowship Colloquium

By Heather Flanagan
July 10, 2016
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David Kimbro of Northeastern University, our guest lecturer for the June BOP-CCERS Colloquium.

At the Billion Oyster Project, we talk a lot about how oysters are a keystone species- a species that plays a unique and crucial role in an ecological community.  The originator of the term, Bob Paine, passed away last month- a remembrance of him in The Atlantic describes him as a “giant of ecology” whose pioneering coastal environment experiments beginning in the 1960s “showed that not all species are equal, and that some—like the starfish—are secret lynchpins of the natural world.”  Our scientist in residence from The Nature Conservancy, urban marine ecologist Michael McCann, described him as “the guy who convinced marine ecologists that they need to do experiments (not just make observations) out in nature, and not just the lab.”  Today, researchers in this tradition are how we know, and in some cases, can even quantify with a dollar amount, how vital oysters are to New York Harbor and the entire East Coast.  For our Billion Oyster Project Curriculum and Community Enterprise for Restoration Science (BOP-CCERS) June Fellowship Colloquium, we were extremely lucky to have one of those researchers as a guest lecturer: David Kimbro, Assistant Professor, Northeastern University Department of Marine and Environmental Sciences. 

On his website, David describes his work as studying “why coastal habitats such as salt marshes and oyster reefs thrive in certain areas, but not in others. We use broad-scale monitoring to detect patterns and then follow-up experiments to establish causal relationships. Because these habitats enhance biodiversity, support commercial fisheries, buffer coastal erosion, and improve water quality, our research is important for maintaining key ecosystem services that benefit society.”  At the Colloquium, David shared his and others’ research, walked the fellows through his experimentation process, and challenged the fellows to come up with oyster-based experiments of their own.

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David introduced the role coastal ecosystems play in humans’ lives by showing a light map of the United States to emphasize that people “hyperconcentrate around estuaries- that’s just another symbol of how people are drawn to the coastal environment.”  (According to NOAA’s estuary education page, 22 out of 32 of the world’s largest cities are located around estuaries.)  As for the oyster’s role in estuaries, “oysters are a foundation species- simply by being present and growing, they create a lot of habitat” and that “as oyster reefs go, that’s the way your ecosystem is going.”  How are those ecosystems doing worldwide?  In the “Global status of oysters” map below (based on a 2011 study), areas marked in red indicate “functionally extinct” reef conditions.  

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New York Harbor is one of those areas, but unfortunately, we’re not the only region to have caused and suffered the almost total decimation of wild oyster populations.  David introduced the work of researcher Michael Kirby, whose 2004 study “Fishing down the coast: Historical expansion and collapse of oyster fisheries along continental margins,” demonstrates a striking trend: “Fishery collapse began in the estuaries that were nearest to a developing urban center before exploitation began to spread down the coast. As each successive fishery collapsed, oysters from more distant estuaries were fished and transported to restock exploited estuaries near the original urban center.  This moving wave of exploitation traveled along each coastline until the most distant estuary had been reached and overfished.”  

On the East Coast, where European colonizers established population centers in the North beginning in the 17th century, this means that the remaining oyster reefs are located in the South.  Kirby’s graph, below, shows the correlation between reef degradation and distance from Wellfleet, Massachusetts, using ‘historical proxies” (Kirby describes these as “measurable descriptors that ‘stand in’ for desired but unobservable phenomena”- since he couldn’t go back in time and directly observe oyster reef conditions in the past, Kirby used proxies like the earliest laws regulating an oyster fishery):

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Graph from Kirby’s study via Proceedings of the National Academy of the Sciences of the United States of America.

David also displayed a map from Kirby’s study that demonstrates this phenomenon:

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After establishing the global status of oyster reefs and the timeline for their degradation, David posed a question to the group- “so what?”  Based on research he’s conducted, “oyster reefs can provide valuable ecosystem services in addition to harvestable income.”  In one experiment measuring biodiversity, when his team added oyster shells (not even live oysters!) to a salt marsh edge, a mud flat, and a salt marsh with seagrass, “they all increased in abundance compared to controls.”

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David also detailed work other researchers have undertaken to measure the impact of oysters on water quality.  Oysters eat phytoplankton, a type of plankton that gets energy from the sun through photosynthesis.  (It’s worth noting that the term “plankton” is a general one that includes an extremely diverse group of organisms that live in the water column and can’t swim against the current.  Plankton includes animals visible to the human eye like krill as well as single-celled organisms like phytoplankton.)  Like plants, phytoplankton consume carbon dioxide and produce oxygen, and they also need nutrients (in varying amounts depending on the species) like nitrate, phosphate, silicate, calcium, and iron.  

Plankton sample from the University of Oslo including phytoplankton (like diatoms and dinoflagellates) and zooplankton (consumers that do not produce their own energy like phytoplankton). http://www.mn.uio.no/ibv/livet-rundt-studiene/studentblogger/annie-s-blog/under-the-microscope.html

Plankton sample from the University of Oslo including phytoplankton (like diatoms and dinoflagellates) and zooplankton (consumers that do not produce their own energy like phytoplankton).

Single-celled plankton collected in the Atlantic Ocean, including diatoms, dinoflagellates, radiolarians and foraminiferans. Photo from “Plankton- Wonders of the Drifting World” via CBS News.

Single-celled plankton collected in the Atlantic Ocean, including diatoms, dinoflagellates, radiolarians and foraminiferans. Photo from Plankton- Wonders of the Drifting World via CBS News.

These nutrients can become too readily available, according to NOAA, “from wastewater treatment facilities, runoff from land in urban areas during rains, and from farming.”  The same chemical agricultural fertilizers that foster extra growth in plants also encourage phytoplankton and other algae.  (“Algae” is another blanket term like “plankton” that refers to a wide range of “aquatic, plant-like organisms.”  All phytoplankton are algae, but all algae are not phytoplankton.)         

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Suspended matter caused by runoff in the Chesapeake Bay before and after heavy rainfall via NOAA.

Unfortunately, this triggers a phenomenon known as “algal blooms,” which lead to “dead zones,” or the condition known as “eutrophication.”  Phytoplankton growth explodes with the influx of nutrients, but so does waste from the organisms that consume it.  And when the supply runs out, the phytoplankton die and are consumed by bacteria, who use up a tremendous amount of oxygen in the process, causing “hypoxia.”  The marine life that depends on oxygen either dies or leaves, essentially becoming “biological deserts.”  The second largest dead zone in the world is in the Gulf of Mexico:

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Photo credit: NOAA

NOAA has a great visualization of this process:

David explained how oysters can affect this phenomenon.  Besides merely filtering phytoplankton and removing it from the water column, when oysters consume algae, their waste creates conditions in the sediment that are more favorable to bacteria that can reduce the nitrates that contribute to algal blooms.  Oysters aren’t a denitrification silver bullet, but David noted that “there’s good evidence that oyster reefs can prime this pathway to help us get a handle on this eutrophication process.”  It’s even a way to put a dollar amount on the value of the ecosystem services oysters provide- he shared an analysis that found that an acre of oyster reef was estimated to yield $3,000 worth of denitrification services annually (read more about that here).

(As a part of the phytoplankton discussion, David also explained how researchers can determine how extensive oyster reefs were in a given area using sediment cores.  Diatoms, a type of phytoplankton, have cell walls made out of silica- or, as our UMCES partner Bill Dennison put it, “glass houses.”  They look like this, if you’re into the wonderfully obscure Victorian hobby of diatom arrangement:

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Phytoplankton are found throughout the water column, but in an area full of industriously filtering oysters you’ll mostly find benthic diatoms [ones that are near the bottom].  Without oysters, you’ll find more planktonic diatoms [ones floating closer to the surface].  Scientists literally count the ratio of benthic or planktonic diatom “shells” [technically called a “frustule”] in a sample to study this.)  

Oysters, in certain conditions, can also buffer coastal erosion.  David cited a 1997 study by Meyer et al that dumped oyster shells in sections of coastlines in North Carolina and followed the marsh accretion rates over time plus loss to erosion.  In some cases, these reefs did buffer erosion, but it depended on where disturbances like severe weather systems hit.  The buffering benefits of oyster reefs were thus affected by where the reef was located, and the degree to which the shoreline faced a certain direction.

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Some of the most exciting parts of David’s talk involved his work on the impacts of predation on oysters.

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Mud crabs like this one are predators of baby oysters…

A mud crab found in one of our Governors Island oyster restoration stations!

…but oyster toadfish are predators of mud crabs:

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Photo from The River Project- you can listen to their recording of an oyster toadfish here: http://www.riverprojectnyc.org/research_10bioacoustic_bio.php

The consumptive effect of the oyster toadfish eating mud crabs helps oyster survival, but there’s a non-consumptive effect as well: fear.  When a cameraman filming David’s work pointed out the distinctive sounds an oyster toadfish makes, he decided to test whether crabs responded to these “bio-acoustic cues.”  Which, of course, meant that a “crab hearing test” was in order:

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While organisms respond to a number of chemical cues in the water that can also account for prey behavior, David’s work demonstrated that crabs responded differently to predator and non-predator sounds, showing that underwater soundscapes can play a role in oyster survival.

Check out the videos below to hear the sounds different mud crab predators make:

Black Drum Fish:

Catfish:

Oyster Toadfish:

Another study looked at the impact of environmental factors.  In some cases, changes in the environment not only stress a prey species like oysters, but can also create conditions that are more favorable to predators.  In this case, clammers and oystermen had noticed that a historically rich oyster area had experienced a rapid reduction in living oyster biomass.  David and his team designed experiments out in the field, using open and closed cages in different locations along the coastline, and they also used a “historical ecology” method of surveying different stakeholders about when they believed the oysters had started to decline.  They ultimately determined that a recent lack of fresh water caused salinity to spike, which favored the reproductive success of conchs, an oyster predator.  Prior to 2005, with normal salinity patterns, conchs had existed in the system, but the oyster population had evolved to deal with that.  When things got dry, it lead to oyster deaths.

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David wrapped up his presentation with a “minds on” activity for the fellows- determining where they thought bio-abundance of oysters would peak, given a salinity map of New York Harbor (found here under “bottom salinity”).  He also asked them to come up with simple research questions and design experiments to test them.  In terms of the fellows’ work in middle school classrooms, he noted that “in order to interpret experiments, you need a canvas of observations that tell you what experiment to conduct,” and that “I think they’re [observations and experiments] are equally important.”  The teachers found this dovetailed nicely with the fact that their students love to observe organisms in their oyster restoration station and in-class tanks.

For the last part of the night, BOP Curriculum specialist Annie Lederberg posed a big question to the fellows- where would you site an oyster reef in New York Harbor?  Using a collection of maps, fellows worked on this question in groups while monitoring their thought processes and recording all the questions they developed in the process.  

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Teachers came up with questions like: 
Where were the best oyster reefs historically?
Where is the safest place, regarding predators, for an oyster reef?
Where would there be natural protection for a reef?
How would currents affect the oysters?
Does the type of shoreline matter?
Does being in a flood region affect erosion?
What’s the purpose? What’s the benefit? How to restore it?
Where are the CSO’s located?
How can we weigh the costs versus benefits of exposures to wave action?
Would the reef be endangered by shipping or industry?
How do we prioritize different categories of restorative value of the oysters?

As a follow up, Annie asked them, “What was exciting and/or scary and/or overwhelming about taking on a question with this many variables?”  Dayna Navaro of Soundview Academy commented that “once you focus on one area at a time, it allows you to zero in- it’s like dissecting a frog.”  Clarissa Lynn of Central Park II noted “I already have students who think in these huge questions- so finding ways to satisfy their curiosity in interesting ways is great.”  Annie also asked when teachers could time an activity like this, with Olivia Bello of KAPPA III suggesting teachers could do the activity at the beginning of the year and the end, to see how it shapes the questions they ask.  Dayna pointed out that it’s a great opportunity for something interdisciplinary.

The June Colloquium was an extremely rich learning opportunity for the fellows and everyone from BOP-CCERS in attendance, and it was a great way to wrap up before summer break.  A huge thanks to David Kimbro for stopping by- if you’d like to see more of his work, there are a couple of awesome YouTube videos along with articles listed on his website.  And a big thanks as well to the fellows for their commitment to restoration education this school year!

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