Field Week Fun

I’ve just come to the end of the field week for my MRes Marine Biology course in Plymouth, and I think it’s safe to say it’ll be a contender for best week of the course!

There were three practical elements to field week – a ¬†full day and a half day on the Marine Biological Association’s research vessel, the Sepia, and a plankton ID lab using some of the samples collected on the boat.

I was in the third group, so didn’t start until Wednesday, which was my full day out on the Sepia. We met at the boat at 7.30am but were a bit delayed getting out of the harbour due to the high tide and lock times. Once we headed off, we made our way across Plymouth Sound to the Tamar Estuary, which lies between Devon and Cornwall.

We did two beam trawls (aka towing a big net), one reasonably far up the river at Kingsmill Lake and one closer to sea at West Mud.

As the Sepia crew pulled up the first beam trawl at Kingsmill Lake, they managed our expectations by telling us not to expect things like cod… before pulling a cod out of the net! This was apparently the first time they had recorded one so far up the river, which was exciting for everyone.

Pulling up the beam trawl

We had a pretty good haul, with sole, plaice, lots of crabs, dragonets, gobies, shrimp, etc., which we sorted, IDed and counted before releasing back into the sea and heading to West Mud.

Our first trawl at West Mud was less fruitful, although it did bring up one very pretty red mullet. So we tried again and hit the jackpot! We had a thornback ray, a lesser spotted catshark, an entire basket of spiny starfish, bib, velvet swimming crabs, spider crabs, and much more. My favourite critter ended up being a hermit crab who had greedily found itself both an anemone and a shell and so was sporting some very funky tentacles and pink spots.

Due to the late start and two pretty successful trawls we were running a bit behind schedule, so we put off the van Veen grab for another day and motored out beyond the Breakwater to collect some plankton samples. The crew deployed two drift nets, one with a fine mesh and one with a coarser mesh, and we were lucky enough to spot a porpoise go by the boat!

Overall an excellent day, topped off by a pint in the pub and being in bed by 8.30.

The next afternoon I had my plankton ID practical. I’m not going to pretend this excited me in quite the same way as being out on the Sepia, especially as I am truly shocking at using microscopes, but it was cool to look at the water samples we had collected, which definitely didn’t look like they had anything in them, and see a massive diversity of phytoplankton and zooplankton – diatoms, dinoflagellates, copepods, radiolarians, and various larvae. The bad weather had even apparently stirred things up enough that we had benthic (bottom dwelling) creatures that shouldn’t have been in our water column samples.

On Friday morning I had my last trip out on the Sepia. The sea was a bit rough so we tucked in behind Plymouth Breakwater to attempt an underwater camera. This was a great teaching moment for the crew regarding the limitations of these less invasive survey methods, by which I mean the visibility was far too bad to actually see much of anything. Luckily they had some footage they’d prepared earlier to show us the lovely pink sea fans around Breakwater Fort, an incredible and rare long-lived hard coral colony. I’m even more fortunate that I’ve dived the site before and seen them for myself!

They then showed us how to take some oceanographic measurements by dropping a CTD (conductivity temperature depth) sensor off the back of the boat which takes up to 16 recordings per second to build a picture of the temperature and salinity through the water column that can be uploaded in real time, or within a few minutes back on the boat. They do this for all of their surveys and can use it to identify the thermocline when taking plankton samples, allowing them to sample plankton from both water layers.

Deploying the CTD

Afterwards, we deployed the van Veen grab that we hadn’t had the chance to do on Wednesday. van Veen grabs are essentially a large set of mechanical jaws that scoop up a sample of the sediment. This mud can then be placed in a sieve and hosed through to identify some benthic critters (mostly worms). The weather was starting to close in on us, so the skipper decided to motor back to harbour, meaning we were hosing through and sorting samples while holding on to the boat with one hand and being battered by the rain and the wind! It was a pretty fun adventure and we all arrived back to port laughing.

van Veen grab

I’ve had such a good time on the Sepia this week so was very excited to hear from the vessel manager that there are opportunities to volunteer on board for their fish trawl surveys, something I’m definitely planning on over the rest of this year. Massive thanks to the crew of the Sepia for having us on board and looking after us!

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