Monday, 30 March 2015

The Marine Biology of Rocky Shores

So after two busy weeks of tutoring at the Millport Marine Station, I've made it back to Glasgow where there's a decently-working internet connection and I can finally share some of the photos from the trip!

The coast at Farland Point. This is a classic example of an exposed rocky shore and is frequently surveyed by visiting student groups! Click for a larger version.
Over the past week, I've been helping a couple of groups of MSc students do some short fieldwork projects to get them used to the trials and tribulations of trying to do good scientific research in real, coastal ecosystems (which very rarely behave the way you think they will!). Because their work involved gathering lots of samples from the local rocky shore at Farland Point (just a convenient 5 minute walk from the Marine Station), it gave me some time to collect some nice photographs of the marine life while the students were working. The plan I have is to eventually collate these images into short photographic identification guides or posters for different plant and animal groups (which will be freely available online), but that will probably require a bit of work to sort out! In the meantime, keep an eye on the Marine Identification galleries for updates, and enjoy this very brief guide to a typical Scottish rocky shore!

The Subtidal Zone

Extremely low tides expose the kelp beds in the Subtidal Zone, which are usually covered by the sea. Click for a larger version.

With each equinox come big tides, and this week we got some great low tides and access to the subtidal zone (the part of the beach that is normally completely covered by water), which is great for exploring. This part of the beach is home to large, brown (and edible!) kelp species, which in turn are home to some surprisingly beautiful animals like the blue-rayed limpet which lives on the underside of the fronds. If you're lucky, you might also find some fully marine organisms down here that have been temporarily exposed by the tides.

Blue-rayed limpets are often found attached to the underside of kelp fronds in the subtidal zone and are incredibly pretty. It is believed that the blue colours are used to mimic (toxic) sea slugs which keep potential predators away. Click for a larger version.

Urchins, starfish and other fully marine organisms can sometimes be found during extreme low tides. Click for a larger version.

The Eulittoral Zone

Juvenile mussels may be common on the lower shore.  Click for a larger version.

Moving further up the shore into the "eulittoral" or mid-shore, we start to find more of the familiar rocky-shore species. Everything that lives here will spend some part of each day exposed to the air between tides, so everything has to be able to cope with increasingly long periods of dessication, temperature fluctuations and fresh water until the tide comes back in. As a result, shelled animals like winkles, limpets, dogwhelks and sometimes topshells are particularly common, since they can use the shells to seal themselves away when conditions get tough. The most common species here tend to be the wracks (brown algae), barnacles or mussels, all of which compete with each other for the limited amount of space available. Whichever ones are found in the greatest numbers on your particular shore will depend largely on the local environmental characteristics.

Dogwhelks are common on rocky shores and lay eggs shaped a bit like milk bottles (or popcorn kernels) in cracks in the rocks.  Click for a larger version.

Topshells are characteristically striped (but may occur in all kinds of colours) and are some of the prettiest snails you'll find on the beach. Click for a larger version.

The Upper Shore

Common lichens of the supra-littoral (splash zone). I believe these are: (a) Tephromela atra, (b) Caloplaca marina, (c) Verrucaria maura, (d) Ramalina siliquosa (sea ivory). Click for a larger version.

At the top of the shore, we find some of the toughest conditions for marine organisms to try and inhabit, and tend to only find quite specialised plants and animals like channel wrack for example. Above that, we then reach the characteristic bands of white, yellow and black lichens that mark the edge of every rocky shore in the world! This is where the marine and terrestrial environments meet.

The isopod Ligia oceanica is the UK's largest and can reach up to about 5 cm length. It is a common inhabitant of the splash zone. It's quite cute really! Click for a larger version.
Rockpools

Rockpools look like underwater gardens along the shore, but provide refugia for a large number of species when the tides go out. Click for a larger version.

Throughout the shore, rockpools can provide refuges from the worst of these conditions and are great places to carefully watch for crabs, small fish, squat lobsters, prawns, urchins, beadlet anemones and all kinds of stranded marine creatures. You're more likely to find more of these animals lower on the shore where conditions closer to the sea aren't quite so stressful for them, but you never know what you might find. I've found that dropping a few flakes of tuna into a pool works really well to tempt out any particularly hungry and hidden scavengers. Just make sure you use tuna in brine, not oil or else you'll make the pool all oily and won't be able to see anything. Also, since lots of tuna are having a hard time of things at the moment, please try and only use fish that has been sustainably sourced!

Beadlet anemones are very easily found in rockpools, but will retract their tentacles pretty quickly when they get disturbed and can take a while to emerge again. Click for a larger version.

Shore Birds

A rock pipit relaxing and preening on the shore. Click for a larger version.

Most of the shore birds you'll find on rocky shores will be largely similar to those found in other coastal habitats. Waders typically feed on sandy or muddy shores, but often come to rocky areas to rest or preen. One little bird that I've seen a lot of around Cumbrae's rocky shores though is the Rock Pipit. This is a cute little brown bird that is resident all around the coasts of the UK and pretty much only lives on or around rocky shores. Luckily for me, one of them was feeling particularly photogenic last week, letting me get some really nice shots of it singing and preening while I was only 2-3 m away!

How I took the photographs
All the above-water photographs of the marine life in this blog post were taken with my trusty Canon 7D and the Canon 60 mm macro lens, which I haven't written a review of yet but is pretty great. The bird photos were taken with my tried and tested Canon 300 mm lens with 1.4x converter which have yet to let me down.

My Go-Pro in a Sub-Zero Housing. The flat port corrects for the distortion that the early-version housings caused when used underwater, but it does create a dark circle around the images. Whether or not you like this effect is up to you. 

The underwater photos from the rockpools were taken using a Go Pro in a Sub-Zero housing with tinted, flat viewport. This particular housing doesn't distort the image you get when using the original fisheye housings and allows the camera to focus properly underwater. I made a simple stand for mine last week by gluing and cable-tying one of the mounts onto a 2 kg diving weight and set it onto the 5-second timelapse mode which worked pretty well, except for the lack of animals in my selected pool! Still, the photographs turned out quite nice regardless, and I'll be taking this setup out again to try in some beaches that are a little less disturbed than Farland Point!