After two full days cutting up rather smelly molluscs in the lab with first year students, Friday’s field trip with the second years to the beach at Souter, north of Sunderland, was very welcome. The aim was for the students to gain some appreciation of the diversity of the inter-tidal zone and to attempt to work out some of the evolutionary relationships between the species they found. It was a pleasure to be out in the sunshine and a rare luxury to have the opportunity just to mooch for a couple of hours, looking rather more closely than usual at the fauna on the foreshore. At low tide, all kinds of interesting organisms which dwell in the kelp ‘forest’ come to light.
Some of these are large and fairly obvious – shore and velvet crabs, rocklings, sand eels and blennys and, of course, starfish. The finding of these produces whoops of excitement from the students.
Top row: Velvet crab, Portunus puber, Blood star, Henricia sanguinolenta, Grey topshell (Gibbula cineraria) and Keeled tubeworm (Pomatoceros triqueter) remains.
Bottom: Blenny, Lipophrys pholis
However, for the observer with time, much wider diversity soon becomes apparent. It doesn’t take long to realise that there is more than one type of limpet present on the shore but the tiny blue-rayed limpets (Patina pellucida) take some finding. No bigger than my little finger nail, they have an effect disproportionate to their size on the kelp on which they graze.
Kelp fronds are translucent where the blue-rayed limpets have grazed on them
It’s not just the tiny limpets that are new to me – equally tiny molluscs with iridescent blue bands nestle under the kelp, along with a veritable ecosystem of sponges and bryozoans.
Breadcrumb sponge (Halichondria panicea), sea mat (bryozoan) and barnacles amongst Laminaria holdfasts
One thing which intrigued the students was the number of holes in the soft limestone rocks on the foreshore. I knew these were made by rock-boring bivalves known as Piddocks, but have never seen one in action before.
Common piddock, Pholas dactylus
The final delight of the day was seeing real live bryozoans encrusting the stalks of some of the upper shore seaweeds.
I know very little about these organisms, save that we found fossil ones in Guryul ravine in Kashmir (see Back to Guryul) so that’s a blog for another day!