Western Channel Observatory Blog

From Angus Atkinson – from email sent on 19/3/2013

What were you doing exactly 25 years ago?

Back then, L4 was just a bone in my lower back and E1 was a rock climbing grade. Some of us were probably in nappies. In March 1988 I was at BAS and the Plymouth Plankton Mafia were rivals at the time. We just laughed at their legendary tales.

Anyway, this afternoon marks 25 years of almost continuous weekly sampling of the L4 site, half way out to the Eddystone.  Over 1000 weeks of sampling is hard to imagine until you have done, like me, a mere 6 weeks of it. Blundering around in the dark on a wet winter morning…..getting out to Rame before turning back with the weather, then having to repeat this next day………. and that is just collecting the samples.

 What is the big deal about L4? Some time series are miles longer. Our E1 site further offshore has been sampled for a century, but most long programmes are neither regular nor continuous.  Some famous efforts like the CPR survey cover huge swathes of ocean, but the temporal coverage is coarse. Others seem to have it all – regular, long-term sampling of the whole planktonic food web (e.g. Helgoland), but these sites are often shallow, just outside the lab where the land has a huge influence on the sea. L4 does have it all. We are sitting on a gold mine.

 Since arriving at PML a year ago I have been a late gatecrasher to the L4 party, but we are all indebted. Let’s just pause a second and think of the multitude of people who carried L4 along through all these years.

 Angus

Over the past few months we have noticed that we have two species of Calanus in our samples from L4. While Calanus helgolandicus and Calanus finmarchicus appear very similar to each other under a microscope, with just a slightly different head-shape and differing leg structure to tell them apart, their spatial distribution and ecological niches are quite distinct. Usually we would expect to see Calanus helgolandicus, a warm water species, but lately we have also seen Calanus finmarchicus, a cold-water oceanic species. Although Calanus numbers are quite low at the moment we are finding that C. finmarchicus are making up a large proportion of adult females, reaching 75% this week. At pretty much the Southern limit of C. finmarchicus distribution here in the English Channel it will be interesting to see how long these copepods hang around, their range is thought to be shifting northwards in response to increasing temperatures. Their numbers have decreased dramatically over the last 40 years, with consequences on the recruitment of important fish species such as cod that eat these nutritious little beasts.

From Rachel Harmer …

Since autumn, numbers of most things have dropped off, except for the copepod Oncaea, where we have observed almost double usual numbers at around 3000 per m3. Looking back at last winter, I reported high numbers of Solmaris corona, a type of jellyfish, these have been completely absent this year, and Liriope, another abundant jellyfish last year has been much lower in number.

From Claire Widdicombe:

The phytoplankton community at L4 started the year as a typical winter assemblage, low in abundance with small benthic and large pelagic species most common. The spring bloom began in earnest mid-March but did not appear to wane and continued for several months. Diversity of diatoms was high and a prolific bloom of Guinardia delicatula became infected with a small heterotrophic flagellate known as Pirsonia sp. Phaeocystis was also common. A marine slick along the SW coast especially at Plymouth at the end of May caused concern in the media. I suspect this was marine detritus from the prolonged phytoplankton bloom that had been re-suspended from the sea floor??

By mid summer the phytoplankton community resembled that typically associated with the autumn with long chain-forming centric and pennate diatoms. E. hux and Karenia bloomed for a short time in July. Unlike previous years there was another significant diatom bloom in the autumn which persisted through to November. There was also a second and prolonged coccolithophore bloom in September-December.

 So all-in-all another unusual year for the phytoplankton. Linked I assumed to the wet and turbulent (windy) weather?!

Rob Thomas has sent me the following email:

In the New Year could you encourage those working on the WCO datasets to submit the files and documentation so we can process and provide DOIs as per your request? You agreed last year that all WCO DOIs would come from BODC from this year. It would be good if we could get DOIs for all the datasets this year. Would you be in favour of setting a submission target of the end of March for the scientists responsible to compile the necessary data and documentation for all data to the end of 2012?

Current BODC inventory status available from http://www.bodc.ac.uk/partners/research_centres/pml/data_inventories/.

The L4 buoy was relaunched last Monday (11 December) after a couple of months in refit.  New for this season is a real-time feed of a trial marine global and diffuse irradiance sensor from Delta-T instruments.  Data can be downloaded from the web or viewed directly from the website.

It is hoped to keep the buoy out at L4 until around March when it will be swapped out with the old E1 buoy currently on the hard stand outside the lab.

The intention is to get the E1 buoy collaboration an operational reality during the second quarter of 2013.

From Rachel Harmer:

High numbers of Doliolids have been recently observed at L4, which are common pelagic tunicates in subtropical coastal waters, and are generally rare in the western English Channel. These were abundant throughout September.  Total zooplankton numbers dropped considerably at the beginning of May almost to winter background levels, since then numbers have gone up and down until we saw a peak in total zooplankton at the end of August due to high numbers of juvenile Calanus and other smaller copepod species.

It seems that barely a day goes by this “summer” without somewhere in the UK having a “month’s rainfall in 24 hours”. Last Friday / Saturday (6/7 July) was such an event for Plymouth with around 50 mm being recorded on the roof of PML in less than 24 hours.  This has led to some very high nitrate values (2.65 at surface, and still in the detectable range at depth) and low salinities (<34 PSU recorded by the buoy).  All this makes for a very interesting situation at L4, as the spring bloom keeps hanging on in there.

Andy Perkins (Skipper of the Plymouth Quest) has observed that the water on the way out to the E1 sampling station was ‘muddy’ in colour and on the underway sampling system the Chlorophyll a levels had been off the scale (scale maximum 5 mg.m-3).  The E1 CTD profile did indeed show a chlorophyll a abundance in the top 30m of the water column.

This week’s L4 sample (10 micron vertical net haul) confirmed the spring bloom is still going strong and is dominated, almost exclusively, by the chain-forming diatom Guinardia delicatula.

Upon closer inspection many cells were infected by a parasitic nanoflagellate called Pirsonia which can also ‘attack’ other diatom species. According to the literature this little parasite might be capable of influencing the succession of phytoplankton communities. It will be interesting to see if Guinardia delicatula is still dominant at L4 next week – I suspect not!