Cwm Idwal: A Journey through Geological Time

Written by Daniel Rowen, William and Mary Class of 2014

Today, we head into the mountains for a look into Wales’ past. Cwm Idwal is a valley in the larger Snowdonia National Park that has given key insight into the geological history of Earth.  Cwm Idwal is somewhat of a geological celebrity; Darwin visited here twice (and was actually a geologist first), and some of the names of periods in Earth’s history were born out of the contributions to the field of geology made here in the UK.  The Cambrian Era comes from the Latin name for Wales, and the Ordovician and Silurian Periods refer to Welsh tribes.

Professor Colin Jago, of the School of Ocean Sciences at Bangor University, led us through Cwm Idwal and described the geological history of the area and its impact on the study of geology. Researchers in the 19th century were able to use the area to establish an order for the formation of different types of rocks but without modern radioisotope dating techniques they could not determine their age.

The rocks in the area are volcanic, dating back 450 million years to the Ordovician Period. Rhyolite was formed in violent eruptions at subduction zones that produced viscous lava flows and ash. The ash, ignimbrite, is composed of dense, hot lava and gas that move at high speeds. This has earned it the name nuée ardente, French for “glowing cloud.”  While the rock formations are initially laid horizontally at the surface of the Earth, they are submerged over time and bent by extreme heat and pressure.

On a global scale, landmasses that roughly correspond to North America and Europe were once separated by the Iapetus Ocean; England and Wales were on the “European” side and Scotland and Northern Ireland were on the “North American” side. The ocean finally closed about 400 million years ago.  The resulting collision of continental plates formed the mountains in present day Scandinavia, Scotland, North Wales, and Northern Ireland, as well as the Appalachian Mountains in the Eastern US.  200 million years ago, the North Atlantic started to open and Scotland and Northern Ireland stayed with the “European” side.

Our tour of Cwm Idwal ended in rain, but was enjoyable and informative nonetheless. The beautiful, picturesque landscape provided an opportunity for good photographs. Although most of us lean toward marine biology, Professor Jago’s excellent discussions left us with a healthy appreciation of geology and its importance in the grand scheme of things.

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Red Wharf Bay

Rather than trawling through the waters of Red Wharf Bay as we did yesterday aboard The Prince Madog, today we were there on the ground level hunting for fossils. The Bay lies in the center of a large transform fault (define: two land masses sliding against each other rather than apart or together), and because it was low tide we could walk along the fault. Our main destination was an outcrop of rock that dates back to the Carboniferous period (350-300 million years ago). The rocks were a bit overgrown but we bushwhacked our way through the vines and ventured to less plant-dominated areas.




During the Carboniferous, the (now) U.K. resided in tropical latitudes and was partially submerged due to global sea level rise. The oceans at this time were very diverse and contained a ton of interesting organisms; some are now extinct, but others are still around today.


The most common fossils we found were crinoids. They belong to the phylum echinodermata (the same as sea stars and urchins) and are still alive today.  Despite their sparse abundance now, crinoids were prolific during the Carboniferous.

At the apex of a long stalk, crinoids have feathery arms arranged around a central mouth. The stalks are made up of columnals, small round disks that are stacked on top of each other. We saw these disks fossilized everywhere; sometimes they were dotted here and there on the cliff face and sometimes they covered the whole rock face.  If you look closely, you can see some of the small fossils below:


We also discovered some fossilized coral heads (bonafide evidence that this place used to be underwater) and as brachiopods, which were also very common during the Carboniferous. Brachiopods have their own phylum and many are still here today.  They look similar to clams but have shell valves of different sizes and a pedicle, or short stalk, that enables them to attach to a hard surface.


The photo on the right show a cross-section of a brachiopod (using a ₤2 coin for scale). You can clearly see the difference between the two valves.

On that particular day, the rocks at Red Wharf Bay were simply part of a typical rocky coast landscape.  But take a second to think about it.  We were standing on an ancient ocean, touching things that were over 300 million years old, and catching a glimpse of the life that used to flourish there! So cool!

If geology like this is your thing, keep an eye out for a post later about our trip to the Snowdonian mountains; there are more rocks to come!

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All Hail the Prince Madog

Written by Stephanie Kane, WM class of 2012


The weather was daunting when we left in the early morning for our next excursion, particularly because we were planning on a full day research cruise aboard the the Prince Madog.


It was still drizzling and threatening more when we arrived at the dock, received our safety briefing from the captain, set up our gear, and climbed onto the top deck to get a unique view of the Menai Strait.  The ship was stacked five floors high, in addition to the engine room; standing up near the top provided some beautiful scenery.

As it turns out, the weather was beautiful by 10 o’ clock, and we were well under way in our task for the day. Most of our day we spent on the back deck and the adjacent cabin.


It went like this: on the back deck the ships crew used a trawl, a net that dragged along the bottom behind the boat, to pull up samples at different points in Red Wharf Bay.  The net pulled up quite a few flat fish, sea stars, urchins, and hermit crabs; we also saw the occasional edible crab, cat shark, octopus, and tiny cuttlefish…and about one billion brittle stars.  We sorted these into vertebrates and invertebrates, either in the cabin or on the back deck if the catch was big enough.  Jordan single-handedly identified and counted the invertebrates (but not all the brittle stars, because that would have been insane) and the rest of us alternated between two teams identifying and measuring the different fish species.

There were a few standouts: particularly large, particularly cool or particularly ugly organisms (these weren’t mutually exclusive).

There was a Jurassic-sized edible crab (we ate it).  There was also a weever fish or two, which have a neurotoxin in a spine on their dorsal fins.  We landed two octopuses, one of which also had a neurotoxin (I should mention at this point that we were wearing gloves while we were sorting these).  My personal favorites were the cuttlefish, which were not bigger than the tip of my thumb.

Of course there was tea available to us at all times (how could there not be) and we broke for a lunch from the galley, lentil soup, rolls, fries and a few other snacks here and there.  After all the trawling was done we went up in shifts to get a look at the navigations equipment in the bridge on the way back to the dock.  We left the ship slightly smelly and quite a bit nautical after spending very interesting day on the water.

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Foiled Again

If you recall some of our first posts, you may remember a few whines and complaints about 25 hour trips to Wales etc… Well, it turns out that the airports have done it again, and some of the members of our group finally made it home 3 days later.  This has put a significant damper on our blog-writing; there are a few more entries that cover the end of our second week in Wales — look for those soon.

In the meantime, mull over these graphs showing the data we collected on cockles.

Let’s take these graphs apart step by step.  First, note that the x-axis is the same for both graphs; it shows tidal elevation.  High is closest to the marsh and Low is closest to the water.


The y-axis for each of these graphs shows the scale of the response variable (what we are measuring).  The graph on the left is showing the number (#) of live cockles that were found at each site, and the graph on the right is showing the age (years) of cockles at each site.  Finally, the titles of these graphs indicate that they are showing us the mean (average) values from a data set.  The round dots indicate the mean, and the blue bars are showing 95% confidence intervals (ignore this jargon if statistics is not your gig).

Ok, so we’ve mentally labeled our graphs.  What are some broad observations?

1. The number of living cockles found was highest at the Medium site.

2. The mean age of cockles appears to increase as the tidal elevation decreases.

(Note: Here is where the confidence intervals come in.  Although the mean age at the Low site is higher than the mean age at the Medium site, notice that their confidence intervals overlap.  This indicates that these two means, statistically speaking, may not actually be different (or different enough).)

Before we move on, here are the graphs again so that you don’t have to scroll back and forth:

You are such a good sport for sticking with us so far! Here are some inferences and conclusions:

1. There is something limiting the population of cockles at High tidal elevations.  We know that cockles are filter feeders (they filter seawater for plankton).  Therefore, when the tide goes out, they can’t eat.  This could explain why the number (and age) of cockles found at the High site was low. We all need food to grow!

2. The age of cockles at the Medium and Low sites are similar, but the number of cockles found at these two sites is vastly different (Medium =102 and Low=18).  Because growth does not seem to be inhibited (ie no food limitation), perhaps we can infer that there is a waterborne predator that is munching on the population of cockles at the Low site; crabs are definitely a potential predator.

In order to draw more conclusive inferences, we would need to run some more experiments.  Have any ideas for some simple experiments or observations for next year that would help us draw more informative conclusions?  Leave us a comment!

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1126 Steps

Written by Domi Paxton, WM Class of 2013

After counting dog whelks, picking up marsh plants, and going over tidal zones, today we finally explored what I’m passionate about: Rocks! As a geology major, I was pleasantly surprised by all sorts of geologic formations as we traversed the 1126 steps of South Stack Island.  This island is located on the northwest coast of Anglesey and is known for its spectacular rocky cliffs, a prominent lighthouse, and nesting birds.

The geologic history of South Stack is quite interesting. Most of the rocks are Precambrian to Cambrian in age (around 500 million years), which is why some of the world’s oldest fossils have been found in that area. As we hiked down to the island, we saw various synclines and anticlines, and other geologic marvels as the rocks twisted and curved on the cliffside.


The lighthouse, which stands 28 meters tall, was completed in seven months.  Furthermore, at the time (1809) the only way to transport materials to the island was via basket and cable.  I don’t know about you, but seven months seems pretty darn impressive! We took a tour up to the top of the lighthouse, and the view was awesome. We even got to see some glimpses of porpoises in the water below. The lighthouse still has the original glass made to surround and reflect the light out to sea, pretty cool!








Before heading out from South Stack, we appropriately had a tea and coffee break; we then loaded up the vans to head to the coast to Rhosneigr, which sits on the Caernarfon Bay. The streets were bustling because everyone here is finally on “holiday!” 

We passed up cold-water surfing with the locals to investigate tide pools; we identified as many organisms as we could and collected diversity data from pools of different sizes.  Some students were even lucky enough to find a nudibranch!



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Tide pools and Tea

Written by Laila Rosenthal, WM Undergrad

We began our day working on identifying previously collected organisms in the lab at the School of Ocean Sciences.  Our species list is continuously growing; we have identified around 50 species, many of which are similar to those we see at home but slightly different.  For example, the dominant low marsh species at home is Spartina alterniflora, while the dominant species here is Spartina townsendii (be sure to ask Daniel Rowen and Jim Perry about the biogeography of Spartina when you get a chance).

Speaking of marshes, we also spent time today analyzing the density and percent cover data that we collected for low and high marsh sites at Newborough Warren & Ynys Llanddwyn National Nature Reserve.  The raw data that we collected allowed us to calculate a parameter called Relative Importance.  As the name implies, this assigns a value to each species based on how abundant they are and how much area they cover. The final analysis and discussion of this data will be presented by one student for their final presentation.

After lab, we all piled into the vans and headed to the tide pools at Cemlyn Bay. The drive was a bit long, but the trip was definitely worth it because these tide pools were much larger, deeper, and clearer than those at Shell Island. The weather actually cleared up for almost the entire time, so we had all had a great time climbing over the rocks that were exposed at low tide.

Cemlyn Bay is a unique habitat because it includes one rocky shore that is exposed to high energy (left) waves and one that is very protected (right).  The impact of energy on the biology of the system was very evident from the get-go.  The high energy habitat could be described as rocky and barren; we found barnacles covering many of the lower rocks and other organisms nestled in crevices.  At the protected shore, however, all rocks were densely covered in macroalgae.  We had to flip back mats of Ascophyllum and Fucus to find organisms of interest; furthermore, there was very little free space on rocks where barnacles could settle.  Once again, we collected height, width, and aperature measurements on a selection of dogwhelks from each site in order to make statistical comparisons between two separated populations.

The photos above show some of the algae species that we found in the tidepools on the exposed site.  The diversity is incredible, and we are trying to identify as much as possible.  We collected more specimens from Cemlyn Bay to bring back to the lab and keep in aquaria.

We eventually had to leave because rain was blowing in from offshore, but we were able to stop at a little tourist station for snacks. The owner was initially slightly appalled at our bedraggled appearance, but after asking that we remove our slightly soaked shoes (due to a few slips into tide pools), she served us a proper English tea, complete with scones, homemade jam, and clotted cream.

Tea Time!


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Written by Shenendoah Raycroft, WM undergrad

Our day began at the Ocean Sciences lab in Menai Bridge, identifying the organisms we found yesterday at Shell Island. The weather was typically Welsh—heavy rain—and not conducive to field work. To pass the time, we visited a Welsh history museum in the general direction of our field site.

Finding the weather much improved (vertical rain rather than horizontal), we headed out to Porth Trecastell to observe vertical zonation in a steep rocky intertidal area.

The intertidal zone consists of areas that are periodically exposed or immersed by the rising and falling of the tide. The highest points of this zone are reached only by splashes from incoming waves (appropriately named the splash zone), while the lowest points are only exposed during extra low tides (spring tides).

Vertical zonation

Zones within the intertidal zone can be delineated by both the geography and biology of the area. At this particular site, the steep vertical geology of the site created very drastic and apparent zonation. This is a stark contrast to the environment we encountered on Shell Island (recall Gar’s post titled The Tidal Zone), which demonstrated horizontal zonation across a flat, rocky expanse. Despite varying geology and geography, however, the same zones are present in both locations (and often at different sites around the world). The picture (left) shows two species of lichens that are frequently found on rocky coasts. Xanthoria is an orange lichen, and Verrucaria is a black lichen that coats the rocks (making them very slippery).

Intertidal Zonation (copyright Barbara Hamon)

Gar described the characteristics of each zone in his post yesterday, but here is a simplified image to jog your memory. The zones, from highest to lowest elevation are as follows:  splash zone (where we find Xanthoria, and also called the Supralittoral zone), Littoral fringe (between the Splash and Littoral zones, where we find Verracaria), Littoral zone (barnacle heavy), and Sublittoral zone (increased algae).

As an aside, we note that the Littoral Zone is densely covered in organisms, but few species are represented.  The Sublittoral Zone, on the other hand, supports a higher diversity of species that the Littoral Zone, but fewer individuals of each species.

We collected about 120 dog whelks (a predatory gastropod) and measured three components of their shells.  We measured shell height, shell width, and the size of the opening, or aperture. Our goal is to compare these measurements among dog whelks that live in high-energy areas and low-energy areas. We will do some data analysis in the lab and hopefully report back to you soon with some exciting results!

On the way back to Bangor we stopped in the town boasting the longest train station name in the UK (see title).  It translates to “The Church of Mary in the Hollow of the White Hazel near the Rapid Whirlpool and the Church of Tysilio by the Red Cave.” It is certainly a tourist hot-spot, but hey, we’re tourists aren’t we?

Upon returning to Bangor, we warmed up and headed out to dinner, finally indulging in a classic plate of fish and chips! Cheers!

PS — We just realized that your ability to comment has been unavailable.  We have changed that (hopefully), and would love to hear from you.  Thanks!

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The Tidal Zone

Post written by Gar Secrist

M.S. candidate; Advisors: Mark Luckenbach and Iris Anderson

The fourth day of our adventure in Wales found us on Shell Island, a popular camping destination during the United Kingdom’s summer holidays. But we weren’t coming to pitch a tent. Instead, we were there to explore the area’s rocky shorelines, in search of flora and fauna in the intertidal zone, where the ebb and flow of ocean tides create unique habitats for marine organisms. We were greeted by a downpour of rain—a fairly common occurrence in north Wales. We sought shelter at a nearby café, and enjoyed a (second) breakfast.  The weather soon cleared up, and we set out to begin our search.

The rocky intertidal shoreline at Shell Island.

As we made our way down the beach, collecting and photographing the local wildlife, it soon became clear that this one rocky shoreline actually included several distinctive habitats for coastal critters. These environments result from different levels of exposure to the ocean due to tides. The first habitat we encountered, called the supralittoral zone, includes regions of the beach that are covered by water only at extreme high tides. This zone is also called the “splash zone,” as it is exposed only to splashes from far-reaching waves and is rarely immersed in seawater. Rocks in these regions are often covered by lichens: plant-like growths that are actually a combination of algae and fungi, working together in a symbiotic relationship.

We spent most of our time in the next zone of the rocky beach: the littoral zone. This area is the part of the beach that is submerged by the sea during high tide, but is exposed to the air during low tide. Organisms in this zone must be able to adapt to both of these very different sets of conditions. The main requirement for surviving in this zone is having the ability to hang on tightly to rocks, in order to avoid being swept out into the ocean by the force of waves. In our search, we found plenty of barnacles that were able to do just that.  While they may appear similar to coral, barnacles are actually related to crabs and lobsters, but spend their adult life as immobile filter-feeders, firmly attached to rocks in intertidal areas.

But the barnacles have more to worry about than just the tide.  We also found plenty of predators on the rocks, ready to feast on the abundance of barnacles in the intertidal zone. Among these predators were snail-like dog whelks, as well as limpets, which have a single domed shell. These mollusks have a muscular foot which they use to hang on tightly to rocks and to crawl along in search of food, before prying open and eating prey like barnacles.

Captions:  A limpet clinging to a rock in the intertidal zone; A seafood feast: dog whelks (spiral shells in top middle) and a limpet (domed shell in bottom middle) feed on barnacles covering a rock in the intertidal zone; The underside of a limpet.  The large muscular foot makes up most of the central tissue.

A limpet with barnacles and algae growing on the shell.



Another neat thing we noticed was that some barnacles were actually growing on the shells of limpets, safe from being eaten even as the limpet fed on other barnacles attached to the rocks.  Even algae would take advantage of limpets as a growing spot—we found one limpet carrying a miniature garden of algae on its shell.




Limpets feeding on barnacles while other barnacles grow attached to the limpet’s shell.

Beneath the littoral zone is the sublittoral zone, which usually remains submerged. It is often dominated by larger species of algae. Although we didn’t explore this region at Shell Island today, we may get a chance to look at similar areas later in the course during a spring tide, when low and high tides are more extreme.  Stay tuned…



Throughout our visit, we collected a surprising variety of species, from barnacles, limpets, and whelks to algae, marine worms, and more. We’ll take these back to the lab for a closer look.  Tomorrow, we plan to visit a more vertical, cliff-like intertidal zone.  It will be exciting to see what differences we find in this new environment!

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Castles & Cockles

Written by Danny Kaufman

VIMS M.S. Candidate;Advisor: Marjorie A.M. Friedrichs

Welcome back to our continuing exploration of Gogledd Cymru! (North Wales)

Day three was our first morning with a “normal schedule.”  We managed an 8:30 start and made our way first to the Bangor Ocean Sciences campus to gather gear and drop off personal equipment in the lab.  There we split into small (3-4 person) research teams along with Philip Hollyman, M.Sc. of the School of Ocean Sciences, Bangor University, who also previously studied marine environments at Wachapreague, VA and VIMS.

Driving in two bulky vans, Mark and Jim transported our group to a small car park in Newborough Warren & Ynys Llanddwyn National Nature Reserve, from which we began our hike to the mudflats at Traeth Melynog.  This landscape was wide open, with bumpy, grassy knolls undulating into the distance.

We headed towards the beach of Traeth Melynog with an assortment of packs, buckets, shovels, quadrats, meter sticks, bags, and notebooks.  Along the way, Jim pointed out plants of interest, such as Ammophila arenaria, also known as European beach grass.  A little over an hour after our start, we crested the final hill and came upon our destination, a mudflat widely stretched out toward the shore before us.

Past the mudflat lay the Menai Strait, and visible on the other side was our first sight of a British castle.  After snapping a few picturesque photographs, we went down to the mud flat to study our target species, the cockle Cerastoderma educe L. Each team dug holes at various distances from the shore, sieved material from randomly placed quadrats, labeled, and stored cockle samples from the mudflat for later analysis at our lab.

After eating lunch in the grass, we proceeded to investigate the salt marsh just up-shore from the mudflat.  In each marsh zone and in one meter squares, we made coverage estimates and density counts for each plant species, and we measured elevation differences between our zonal quadrats.

We finished up the day with a hike back (including an encounter with several grazing horses) and then lab analysis of the cockle data.  Look for a future post with some of our results!  Thanks to the rain holding back once more, we had had another great day that was productive, enjoyable, and full of the wonderful Welsh landscape.  Keep it coming!


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Over the [Telford] Bridge and Through the Dunes, to Newborough Beach We Go!

Written By Nola Liu, William and Mary, Class of 2014

Despite our traveling difficulties, we were all very excited to finally arrive at Bangor University. Hours of waiting and jet-lag exhaustion behind us, today was a fresh start to our adventures in North Wales!  The group photo below is taken near the School of Ocean Sciences, which is located on the island of Anglesey in the town of Menai Bridge.  The body of water behind us is the Menai Strait (the one that has a 6 meter tidal range).  Also note that the rocks are covered in Lichen: hopefully someone will talk more about that later.

Group Photo in front of the Menai Strait


With a warm and hearty [Wales] breakfast (read: baps, beans, doorstops, and sausages) in our bellies, we were able to tour some of the labs at the School of Ocean Sciences.  We toured one lab that held class for over 90 students, which was the largest class lab I have seen yet.


Anglesey Map (requires Welsh to read)


After working out all of our travel logistics, Dr. Mark Luckenbach and Dr. Jim Perry decided to take us on a trip to Newborough Beach.  This beach is located on the island of Anglesey in the far south-western corner.



We didn’t expect the 3 hour hike (to the beach and back), but we enjoyed passing through woods, salt marshes, and dunes.  Along the way, of course, we stopped to identify various flora and fauna.

With dirt and sand in our shoes and on our pants, we hiked onwards….

…and the views were spectacular!

The beautiful scenery of Newborough gave us our first glimpse of how truly wonderful Wales is. This hike was a perfect end to our day, and we are ready for more!

Leave us a comment, and let us know what you think so far!  Questions are encouraged!

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