Tag Archives: smooth cordgrass

marsh-sunrise

Does Diversity Matter in the Salt Marsh? A Look Back

Dr. Randall Hughes has collaborated with WFSU on this blog since 2010. We have spent years visiting her research sites in Saint Joseph Bay, where Randall conducted a multi-year study on salt marsh biodiversity funded by the National Science Foundation. The study has concluded, and Randall has published several papers on her findings. Here is what she has found.

This is Saint Joe Bay week on the Ecology Blog.  Wednesday, August 20th, at 7:30 pm ET: WFSU premieres the eighth season of Dimensions, and our Saint Joseph Bay scalloping EcoAdventure. 

Dr. Randall Hughes Northeastern University
Just a bunch of grass?  Not to the larval shrimp, juvenile mullet, pinfish, fiddler crabs, mussels, periwinkle snails, and blue crabs that make use of the habitat, or the birds and sea turtles that go hunting there.

Just a bunch of grass? Not to the larval shrimp, juvenile mullet, pinfish, fiddler crabs, mussels, periwinkle snails, and blue crabs that make use of the habitat, or the birds and sea turtles that go hunting there.

As you drive along Highway 98 towards St. Joseph Bay (SJB), one of the most common views outside your window is of the salt marsh.  From the car, it looks like a beautiful but monotonous meadow of green and/or brown, depending on the season, often intersected by tidal channels. So I won’t blame you if “diversity” is not the first word that comes to your mind as you gaze out the window. But diversity is exactly what I set out to find out about when this project first started – how much diversity is there in the marshes of St. Joe Bay, and what (if any) effects does it have? And now, several years later, I finally have answers to share!

First, let’s revisit what I mean about diversity. There are 2 main types that I have focused on for my research:

Species diversity, or the number of different species in an area. If you garden, you can think of it as the number of different vegetables or flowers you plant.

Genetic diversity, or the number of different genetic individuals (or genetic variants) in an area. Using the garden example, this would be similar to the number of different tomato varieties you plant in your garden.

Randall Hughes and Ryan Coker in an FSUCML Greenhouse

Randall and technician Ryan Coker tend to plants in an FSU Coastal & Marine Lab greenhouse. Before Randall and her team could begin to test their theories about marshes and marsh grass, they needed to create controlled marsh units of a comparable size, and needed to know the genetic identity of the grass in their plots.  Randall grew this grass for two years before conducting those experiments.

Wait – why so much talk about plants? Don’t animals have diversity too? Animals do have diversity, and this diversity matters – for one, having more species of fish on a coral reef means the corals grow better. But plants are the foundation of the marsh – if you have no plants, you have no marsh. So I have focused on the species and genetic diversity of the plants and tested how it affects the number and diversity of animals that live there (which includes animals that we like to eat, such as blue crabs). The dominant marsh plant species in many areas is cordgrass (Spartina alterniflora), and we created a greenhouse full of known genetic individuals to use in many of our experiments. Here are some of the highlights of what we have learned, with a little background on each, and links to the published articles where you can learn more if you’re interested:

1. Increasing the number of plant species in the marsh, even just from one species to two, can reduce the negative effects of a hungry periwinkle snail.

Periwinkles are really common in the marsh, and when conditions line up just right (the periwinkles are hungry, the cordgrass is already stressed from something like drought) they can mow down the cordgrass. We don’t see this happen very often in SJB, and I wondered if that was because there’s another really common plant species – needlerush – that often grows with the cordgrass, that the periwinkles also seem to like, at least for climbing on to stay out of the water and away from their predators. So we did an experiment where we planted cordgrass with and without needlerush and with and without periwinkles, and we found what I had expected: having needlerush neighbors around means the periwinkles don’t mow down the cordgrass!

Randall published these findings in the Ecological Society of America Journal.

2. Contrary to conventional wisdom that a few cordgrass individuals (also known as “clones”) rule the marsh, genetic diversity can be quite high, with as many as 9 distinct individuals living together in an area the size of a hula hoop.

periwinkles on cordgrass

Smooth cordgrass (Spartina alterniflora), the foundation species of a coastal salt marsh. Before she could understand how the genetic diversity of this species affects the health of a marsh, Randall needed to know how many genetic individuals were present within the ecosystem.

Genetic diversity is really important for the ability of plants and animals to respond to stress or change, and so it’s something we often want to know, but the bummer about it is that it’s not nearly as easy to measure as species diversity. You can’t just look at two cordgrass plants and tell whether they are the same or different genotypes! I teamed up with Dr. Katie Lotterhos to use little snippets of DNA to tell us whether the cordgrass plants we collected from the marshes around SJB were all a few closely related individuals, or whether there were lots of different individuals around. It turns out that even though they all look pretty much the same, there is a lot of genetic diversity in our marshes.

Randall and Katie published these findings in the Inter-Research Science Center’s Marine Ecology Progress Series (link is a PDF).

Monoculture plot- four genetically identical cordgrass individuals.  In this specific experiment, plots are composed off one, two, or four separate individuals.  Do plots with higher diversity fare better?

A monoculture plot of four genetically identical cordgrass individuals. In this experiment, similar to the one described to the right, plots were composed of one, two, or four separate individuals. Did plots with higher diversity fare better?

3. Changing the number of cordgrass clones living together in an area the size of a hula hoop affects how well the plants grow, as well as how many animals share that space. These effects of diversity may be particularly important when plants are first colonizing an area, such as in restoration efforts.

Once we knew how many different genetic individuals shared a hula hoop-sized area in natural marshes, we did an experiment to see how changing that number affects how well the plants grow. This experiment took a long time to prep, because we first had to grow a bunch of plants in the greenhouse so that we could keep track of who was who. After that, the experiment itself was pretty simple: plant 1, 3, or 6 different clones inside a hula hoop (well, in this case it was a modified hula hoop made of less expensive irrigation tubing) at the edge of the marsh, and watch them grow over time.

Randall published these findings in the British Ecological Society’s Journal of Ecology.

4. Just like you and me, different cordgrass clones have unique characteristics – some are tall, some are short, some do well in a crowd, and some like a little breathing room. And the animals that live amongst these plants, such as mussels and fiddler crabs, can go from being friends to enemies depending on which clone they are interacting with.

Even though I said before that all cordgrass plants look similar, it just so happens that when you grow the same clones in the greenhouse for a few years, you start to see slight differences among them. And these differences that seem pretty minor to us are really important to the small animals like fiddler crabs and mussels that live on and around the plants. So, in part to test this idea that different clones have different relationships with fiddler crabs and mussels, and in part just to do an experiment with fiddler crabs because I think they are cool, we set up an experiment using different cordgrass clones growing with just fiddlers, just mussels, or both. And although typically mussels and fiddlers are both “friends” with cordgrass (in that they provide it with nutrients and oxygen in the sediment to help it grow), that is not a universal truth – some cordgrass clones did not benefit (or even were harmed) by having mussels and fiddlers around.

Randall, her graduate student Althea Moore (whose investigation of a similar relationship between mussels and another marsh plant we covered in 2013), and Randall’s oyster collaborator Mike Piehler published their findings in the journal Oikos.

It’s a little disconcerting that ~ 4 years of work can be boiled down into these 4 highlights. Of course there are loads of details I’m leaving out, as well as other ongoing projects that will tell us even more about the effects of diversity in the salt marsh. That’s how the scientific process works – you gain some answers, and those answers lead to new questions! Job security for a curious mind…

This material is based upon work supported by the National Science Foundation under Grant Number 1161194.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Keep up with the latest posts, environmental coverage from the WFSU News department and more at @wfsuIGOR.

GIC

Grasses in Classes: Kids Learn to Build a Salt Marsh

Rob Diaz de Villegas WFSU-TV

Last week, we took a good look at the coastal salt marsh- an ecosystem with a lot to offer but that is seeing die-off across the world. Around Choctawhatchee Bay, schoolchildren are doing something about this.

Two “spoonbills” fight for lima bean. Students at the Laurel Hill School did more than plant marsh cordgrass on the coast. At this station, they were given three types of tools to use as beaks: clothespins, spoons, and chopsticks. With those beaks, the “birds” had to forage for food. The exercise taught them about the adaptations that give animals different advantages. The best adapted beaks got the most food.

IGOR chip- sedimentation 150

Finding out about Grasses in Classes was one of the pleasant surprises of the year so far.  The Choctawhatchee Basin Alliance and AmeriCorps start with a similar premise to the In the Grass, On the Reef project: to foster appreciation for coastal ecosystems like oyster reefs, seagrass beds, and salt marshes.  We write and make videos for a general audience; Grasses in Classes goes into schools.  What they do goes beyond lesson plans and worksheets.  These kids grow smooth cordgrass (Spartina alterniflora), the foundation species of a coastal salt marsh, in their classrooms.  Then they go to Choctawhatchee Bay and plant it.  How awesome is that!  You can see in the video how much the cordgrass spreads out over the course of the year, a powerful visual affirmation to the Laurel Hill School students that what they’re doing is having an impact and will benefit that coastline for years to come.

A few yards from their marshes are restored oyster reefs like the ones CBA builds in the bay.  They’re frequent collaborators, the salt marsh and oyster reef.  Marshes, oyster reefs, and seagrass beds join to create an estuary of critical importance to Gulf fisheries, sheltering most seafood species fished there at some point in their life cycles. As was said in both this and the O.Y.S.T.E.R. Recycling video, marshes and oyster reefs fight erosion.  Marshes also filter stormwater runoff (check this list of everything that flows off of asphalt).  And yet, probably because no amount of horseradish makes Spartina grass palatable, marshes don’t always capture the popular imagination as oyster reefs do.  I hope we can change some of that in the coming weeks.

That’s where the CBA might have us beat.  Through their work, a generation of schoolchildren is getting that appreciation the wet and dirty way, by actively restoring that habitat where development had removed it.  And with the school year recently concluded, CBA and AmeriCorps are gearing up for next year by hiring 13 full time employees to continue to carry the program out.  Click here for more information.

Kayla Mitchell helps a Laurel Hill student plant a Spartina plant.  Spartina is the foundation species of a coastal salt marsh.

Kayla Mitchell helps a Laurel Hill student plant a Spartina plant.

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How Can We Prevent Salt Marsh Die-Off?

2 Minute Video: Do Marshes Combat Die-Off Through Biodiversity?

Data on “cold” and “warm” episodes compiled by NOAA and the National Weather Service correlate warm episodes with events Randall and David care about: the ruining of oyster reefs south of Saint Augustine by crown conchs in 2005, the Apalachicola oyster fishery crash last year, and the die-off of salt marsh habitats at the turn of the millennium.  These episodes are part of a normal climatological cycle, though recent droughts during warm years have been severe.  
Dr. Randall Hughes FSU Coastal & Marine Lab/Northeastern University

Mineral Springs Seafood's Dusty Murray empties a crab trap by a salt marsh off of Ochlockonee Bay.  Blue crabs are one of the many animals that make use of the salt marsh habitat.

Mineral Springs Seafood's Dusty Murray empties a crab trap by a salt marsh off of Ochlockonee Bay. Blue crabs are one of the many animals that make use of the salt marsh habitat.

IGOR chip- biodiversity 150We’re going to shift our attention a bit to another intriguing intertidal habitat – the salt marsh. We’ve focused a lot recently on oysters, and how David is applying what we’ve learnedfrom our oyster research the last few years to try to understand the crash of the Apalachicola oyster fishery. There is something inherently interesting and fascinating about oysters, despite the fact that they look a lot like not much more than really sharp rocks. And of course, there is urgency to understand the oyster problems in Apalachicola because of the very real and immediate human costs associated with the fishery collapse.But now, my goal is to convince you that the salt marsh is just as fascinating as oyster reefs, even if it is not a highly visible fishery in trouble. Think of me as the parent trying to get you to appreciate your broccoli, after David already gave you your chocolate cake. I’m going to get you to LIKE your broccoli.

The “broccoli” in this scenario is none other than salt marsh cordgrass, Spartina alterniflora, a familiar character on this blog. In addition to oysters, cordgrass has been the focus of most of my research in FL. Why, you may ask? Why study broccoli when you could be studying chocolate cake all the time? The parent in me is tempted to use the catch-all phrase “Because it’s good for you!” But I’ll refrain, and instead give you a few actual reasons:

1. Oyster and cordgrass really aren’t all that different.

What do oysters and cordgrass have in common? At first glance, it may not seem like much. Oysters are animals; cordgrass is a plant. Oysters are tasty (depending on your palette); cordgrass is inedible. Oysters support a community of fishermen, at least in better times; cordgrass doesn’t.

Except this last distinction, which may seem intuitive, is not actually true. Cordgrass, and salt marshes more generally, support a wide range of fishery species including blue crabs (as you can see in the video), mullet, and sea trout. Studies in Florida estimate that marshes provide up to nearly $7000 per acre for recreational fishing alone. And like oysters, salt marshes provide more benefits for us than simply what we can eat, including protection from storms, increased water quality, and erosion control.

2. Plants are cool.

I know I don’t have to convince any of you gardeners out there about the beauty of plants. Give them a little sunshine, some nutrients, and a little water, and they do their thing. And cordgrass can even manage in salt water! There’s something to be said for low maintenance study organisms.

An AmeriCorps volunteer waits for students on Choctawhatchee Bay.  They will be planting Spartina alterniflora as part of the Grasses in Classes Program.

A year ago, that full-bodied marsh in the background looked just like the rows of small cordgrass shoots leading up to it. Both were planted by Laurel Hill School students as part of the Choctawhatchee Basin Alliance's Grasses in Classes program.

Not only that, but you can plant a single cordgrass stem, leave it alone for a few months, and return to find that it has expanded to 20 stems, all from the same individual!  (Or, if you’re lucky enough to be part of Grasses in Classes, you can admire successive years of growth from single transplants.) This “clonal expansion” is impressive, and it makes answering some of the research questions that I’m interested in pretty easy to address – I can test whether some individuals are better at expanding than others, or whether they withstand stresses like grazing better, or whether having a mix of individuals is better than lots of stems of the same individual. I can ask these questions using oysters too, but it is a lot more difficult. Even we ‘eat your vegetables’ advocates like taking the easy way out sometimes.

3. Marshes are in trouble too.

Although not in the headlines of the local papers at the moment, cordgrass has experienced significant declines in the Gulf of Mexico in the past, and salt marsh loss is a historic and ongoing problem in many parts of the world. And in some cases, the same problem can contribute to the loss of marshes and oysters. For instance, drought has been linked to salt marsh die-off in the Gulf, and drought-induced stress can make the plants more sensitive to other stresses such as grazing by snails. (As we’ve discussed before, drought and increased salinities can also make oysters more sensitive to predators and disease.) Because of the many benefits that marshes provide, it is in our best interest to understand the causes of these losses and try to prevent / counteract them.

Marsh Periwinkle (Littoraria irrotata) climbing cordgrass (Spartina Alterniflora) in a St. Joe Bay salt marsh.

Marsh Periwinkle (Littoraria irrotata).

For these reasons and more, I’ve been conducting lots of experiments the past few years to (a) understand what factors increase / decrease how sensitive cordgrass is to it’s major grazer, the marsh periwinkle, and (b) figure out if having more cordgrass individuals (or “genotypes”) makes the marsh less sensitive to change. We’ll highlight these experiments in the coming weeks as part of our quest to spark your fascination with the salt marsh!

Music in the video by Cross(o)ver.  The maps used in the animation were generated by the National Drought Mitigation Center.  Special thanks to Mineral Springs Seafood for taking us along as they emptied their crab traps.

This material is based upon work supported by the National Science Foundation under Grant Number 1161194.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

A long time in the making

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150

As I mentioned in my last update, we have been working to set up a new marsh experiment in St. Joe Bay. The goal of the experiment is to see whether the genetic diversity of marsh cordgrass (Spartina alterniflora) affects how quickly or abundantly the plants grow, or influences the number of fiddler crabs, grasshoppers, snails, and other critters (like Ibis??) that call the plants home. But what is genetic diversity, exactly, and why do we think it may be important?

IMG_1812

A flock of Ibis resting among our experimental marsh plots.

Spartina is a clonal plant, which means that a single “individual” or clone made up of many stems can dominate a large area (low diversity), or there can be lots of different individuals mixed together (high diversity). In our surveys of marshes in the northern Gulf of Mexico, we find that there can be as few as 1 and as many as 10 clones in an area of marsh about the size of a hula-hoop. You may notice that our experimental plots are about that same size, though we used irrigation tubing rather than actual hula-hoops (not as fun, but more practical and less expensive!). We’re testing whether the differences in genetic diversity (1 vs. 10 clones) that we see in natural marshes has any influence on the marsh community.

A single experimental plot of Spartina that is 1m in diameter.

But why genetic diversity? We know from experiments by other researchers that Spartina clones grown individually differ in height, how many stems they have, and other characteristics. These same plant traits affect the critters that live in and among the plants – for example, periwinkle snails preferentially climb on the tallest plants. Because different animals may be looking for different plant traits, then having greater diversity (genetic and trait) may lead to a greater number of animal species that live in that patch of marsh. Or, a single clone may be the “best”, leading to higher numbers of animals in lower diversity areas.

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A view of the existing marsh behind our experiment.

As my title alludes, this experiment has taken a long time to come to fruition, in large part because it’s impossible to look at any 2 stems in a marsh and know for certain whether they’re the same individual or not. Unlike some clonal plants such as strawberries, where there are multiple berries connected by a single above-ground “runner”, Spartina has runners (aka, rhizomes) that connect stems of the same genetic individual under the ground, making it difficult to tell which stems are connected to which. We have 2 ways to get around this problem: (1) we use small snippets of DNA (analyzed in the lab) to tell clones apart, and (2) we start with single stems that we know are different clones and then grow them separately in the greenhouse until we have lots of stems of each different clone. It’s this latter part that has delayed this experiment – it has taken much tender loving care from Robyn over the last 2 years to get our Spartina clones to grow in the greenhouse to the point that we have enough of each clone (36 small flowerpots of each, to be exact) to plant in our experiment.

IMG_2394

Emily and Robyn work to remove existing rhizome material from around the plot edges.

But plant we finally did! With lots of help from members of the Hughes and Kimbro labs, we got all the sand in the experimental plots sieved (to remove any existing root material) and all the plants in the ground the Thursday and Friday before Thanksgiving.

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Team Hug-bro (Hughes and Kimbro) helping sieve sand!

 

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Meagan and Randall get the easy job - planting the plants.

Now we get to wait and see (and take data) whether Spartina genetic diversity matters for the marsh plant or animal community. There won’t be any quick answers – the experiment will run for at least 2 years – but we’ll be sure to keep you up-to-date!

Randall’s research is funded by the National Science Foundation.

Tricks or Treats? And more on the effects of predators in marshes.

Dr. David Kimbro FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150Unlike most of the experiments that I’ve conducted up to this point in my career, the oyster experiment from this past summer does not contain a lot of data that can be analyzed quickly.

For example, predator effects on the survivorship of oysters can be quickly determined by simply counting the number of living as well as dead oysters and then by analyzing how survivorship changes across our 3 experimental treatments (i.e., cages with oysters only; cages with mudcrabs and oysters; cages with predators, mudcrabs, and oysters).  But this simple type of data tells us an incomplete story, because we are also interested in whether predators affected oyster filtration behavior and whether these behavioral effects led to differences in oyster traits (e.g., muscle mass) and ultimately the oyster’s influence on sediment characteristics.  If you recall, oyster filter-feeding and waste excretion can sometimes create sediment conditions that promote the removal of excess nitrogen from the system (i.e., denitrification)

oyster_exp_3box

As we are currently learning, getting the latter type of data after the experiment involves multiple time-consuming and tedious steps such as measuring the length and weight of each oyster, shucking it, scooping out and weighing the muscle tissue, drying the muscle tissue for 48 hours, and re-weighing the muscle tissue (read more about this process here).

After repeating all of these steps for nearly 4,000 individual oysters, we can subtract the wet and dry tissue masses to assess whether oysters were generally:

(a) all shell…“Yikes! Lot’s of predators around so I’ll devote all of my energy into thickening my shell”

(b) all meat…“Smells relaxing here, so why bother thickening my shell”

(c) or a mix of the two.

For the next two months, I will resemble a kid with a full Halloween bag of candy who cannot wait to look inside his bag to see whether it’s full of tricks (nonsensical data) or some tasty treats (nice clean and interesting data patterns)!  I’ll happily share the answer with you as soon as we get all the data in order.

Because of this delay, let’s explore some new research of mine that examined how predators affect prey traits in local marshes and why it matters.

P1000167

There are two main ingredients to this story:

(a) tides (high versus low) dictate how often and how long predators like blue crabs visit marshes to feast on tasty prey.

(b) prey are not hapless victims; like you and me, they will avoid risky situations.

attach.msc1In Spartina alterniflora systems, periwinkle snails (prey) munch on dead plant material (detritus) lying on the ground or fungus growing on the Spartina leaves that hover over the ground.  Actually, according to Dr. B. Silliman at the University of Florida, these snails farm fungus by slicing open the Spartina leaves, which are then colonized by a fungal infection.  If snails fungal farm too much, then the plant will eventually become stressed and die.

So, I wondered if the fear of predators might control the intensity of this fungal farming and plant damage.

For instance, when the tide floods the marsh, snails race (pretty darn fast for a snail!) up plants to avoid the influx of hungry predators such as the blue crab.

After thinking about this image for a while, I wondered whether water full of predator cues might enhance fungal farming by causing the snail to remain away from the risky ground even during low tide.  Eventually, the snail would get hungry and need to eat, right?  Hence, my hypothesis about enhanced fungal farming due to predator cues.   I also wondered how much of this dynamic might depend on the schedule of the tide.

Before delving into how I answered these questions, you are probably wondering whether this nuance really matters in such a complicated world.  Fair enough, and so did I.

Addressing this doubt, I looked all around our coastline for any confirmatory signs and found that Spartina was less productive and had a lot more snail-farming scars along shorelines subjected to a diurnal tidal schedule (12 hours flood and 12 hours ebb each day) when compared to shorelines subjected to a mixed semidiurnal schedule (2 low tides interspersed among 2 high tides that are each 6 hours).  Even cooler, this pattern occurred despite there being equal numbers of snails and predators along both shorelines; obviously density or consumption effects are not driving this pattern.

Marsh_foodweb

Ok, with this observation, I felt more confident in carrying out a pretty crazy laboratory experiment to see if my hypothesis might provide an explanation.

attach.msc5

Enter Bobby Henderson.  This skilled wizard constructed a system that allowed me to manipulate tides within tanks and therefore mimic natural marsh systems; well, at least more so than does a system of buckets that ignore the tides.

Deck_schematic1

Within each row of tide (blue or red), I randomly assigned each tank a particular predator treatment.  These treatments allowed me to dictate not only whether predators were present but whether they could consume & frighten snails versus just frightening them:

-Spartina only

-Spartina and snails

-Spartina, snails, and crown conch (predator)

-Spartina, snails, blue crab (predator)

-Spartina, snails, crown conch and blue crab (multiple predators)

-Spartina, snails, cue of crown conch (non-lethal predator)

-Spartina, snails, cue of blue crab (non-lethal predator)

-Spartina, snails, cues of crown conch and blue crab (non-lethal multiple predators)

attach.msc6After a few weeks, I found out the following:

(1) Predators caused snails to ascend Spartina regardless of tide and predator identity.  In other words, any predator cue and tide did the job in terms of scaring the dickens out of snails.

(2) Regardless of tide, blue crabs ate a lot more snails than did the slow moving crown conch and together they ate even more.  This ain’t rocket science!

(3) In this refuge from the predators, snails in the diurnal tide wacked away at the marsh while snails in the mixed tide had no effect on the marsh.

diurnal-mixed_2box

Whoa…the tidal schedule totally dictated whether predator cues indirectly benefitted or harmed Spartina through their direct effects on snail predator-avoidance and farming behavior.  And, this matches the observations in nature… pretty cool story about how the same assemblage of predator and prey can dance to a different tune when put in a slightly different environment.  This study will soon be published in the journal Ecology.  But until its publication, you can check out a more formal summary of this study here.

If this sort of thing happens just along a relatively small portion of our coastline, I can’t wait to see what comes of our data from the oyster experiment, which was conducted over 1,000 km.

Till next time,

David

David’s research is funded by the National Science Foundation.