S2 Investigation of the Marine Food Chain on Gairloch’s Beaches

While the rest of the school was away, S2 had the opportunity to explore Gairloch’s beaches with Dr Close and Mr Peter Cunningham on a Thursday afternoon and Friday morning. You can see all the photos on Flickr.

We conducted a sampling survey of the sand on both beaches and are hoping to find out if there are micro-plastics in the sand.

S2 Investigation of the Marine Food Chain on Gairloch's Beaches

Thursday saw Mr Cunningham electro fishing the Achtercairn Burn with several trout and eels being caught as well as some small plaice closer to the beach.

S2 Marine Habitats & Food Chains

On Friday we investigated the Marine Food chain on Gairloch’s main beach, first by using a Plankton net to catch Phytoplankton and the Zoo plankton which eat them. We then looked for filter feeding worms which eat the plankton, by digging in the sand. Next we used two different sized, sweep nets to try to catch the fish and marine invertebrates which feed on the worms and also the plankton.
S2 Marine Habitats & Food Chains

Lastly Mr Ian McWhinney brought his fishing boat over to the beach and came ashore with a variety of the predators of the small fish we caught in the sweep nets.

S2 Marine Habitats & Food Chains

Mr Cunningham shares some of what we found:

“Here’s a list of some of the things we found:

Zooplankton . . . with the plankton net:  Included crab or lobster larvae and other stuff too small to see without microscope. I’ll be happy to bring our microscope into the school one day with samples of plankton. There was not such a lot of zooplankton off the beach; much more in some concentrated patches where currents converge further out and around towards Melvaig.

I explained how other animals including mackerel and basking sharks can often be seen in the silvery mixing lines where the zooplankton becomes concentrated. So do jellyfish and floating things like sea weed and plastic bags!

 One jellyfish (moon jellyfish ) was recovered from the beach stranded. There was a barrel jellyfish washed up last week – I didn’t see it.  The leatherback turtles eat jellyfish – particularly barrel jellyfish.

Sand animals: We found lugworms and tube worms (sand mason worms I think) and a ragworm of some sort; and at least one other kind of worm (or bit of one). You could spend a whole session looking at worms! We also found Tellin bivalves and sea potatoes (Heart urchin).

S2 Marine Habitats & Food Chains

Sweep net of lagoon. Lots of animals here

  • Fish: dozens of juvenile plaice [rather than flounder I think] ; sandeels (maybe lesser sandeel and greater sandeel); juvenile cod (this year’s fry); gurnard sp; goby sp. (sand goby i think; it is very similar to common goby – which is found more in estuaries according to the book).
  • Crustaceans: hermit crab, shore crab
  • Molluscs: sea hare (kind of sea slug).
  • Echinoderms – think someone produced a starfish and a heart urchin, though possibly not in the net?
  • Think there was also possibly one very small purple stinger jellyfish; however I didn’t hear anyone squealing about that!

S2 Marine Habitats & Food Chains

Big sweep net: Much effort for not a lot; however two rather special story things:

  • Bob-tail squid, or little cuttlefish (Sepiola atlantica). These are great little creatures – if we had had more time I would have put it in an aquarium for all to see close up.
  • Lesser weaverfish. Venomous spines! Not good to stand on one of these in bare feet. . . you’ll find lots of stories on line of surfers who have experienced the spine. Good to wear shoes if wading about in the sea!
  • The crabs were interesting here – we got masked crab and swimming crab (?Liocarcinus depurator I think. Velvet swimming crabs can be found at low tide in the kelp around the An Dun headland).

S2 Marine Habitats & Food Chains

Ian’s animals: what a fantastic selection!

These I assume all came out of creels? Great selection . . .

  • Fish: cod (one-year old I think – a size bigger than the wee ones we found in the lagoon); flatfish (possibly a dab rather than a flounder?); sea scorpion  (not sure whether long-spined or short-spined . . . both can be found in the kelp at low tide)
  • Crustaceans: Lobster; Edible (brown) crab; Shore crab (I didn’t realise there was a local fishery for these too!); Velvet crab (I think there was one – these are often the fiercest); Spider crab (sea toad); Norway lobster (langoustine or Nephrops); Long-clawed squat lobster.
  • Molluscs: Octopus.  I decided that the Octopus is at the top of the food chain for us. Or perhaps if it had been in the bucket, the crabs they would have eaten it? Food webs can get very complicated . . .”

S2 Marine Habitats & Food Chains

 This coupled with the perfect weather constituted a really memorable and fun learning experience. Thanks to Mr Cunningham and Mr McWhinney for their time, skills and knowledge.

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