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!

About David Malmquist

David Malmquist is the Director of Communications at the Virginia Institute of Marine Science, College of William and Mary.
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