Good vibrations under the Suffolk sun …

Latitude_2016_Cladophora_#1

After writing 371 blog posts, mostly about algae, you will forgive me if I tell you that the first thing I noticed about this picture was the algal flocs on the pond behind the sheep – the pink, fluorescent sheep – quietly nibbling the grass in the Suffolk countryside …   This is the Latitude Festival 2016 and I had to pass these flocs (and that flock) every time I walked from my tent to the arena or back.  By Sunday morning, the temptation to lean over the bridge and fish out a handful using a handy reed stem was too great.

Unfortunately, the specimen had to live in a small plastic bag stuffed into my shirt pocket whilst I stood around in a hot field at a music festival for several hours (Prince Charles talks to his plants; I take mine to listen to Laura Mvula and The Lumineers …).   By the time I got it under a microscope, I could confirm that the rough wiry filaments were a sparsely-branched variant of Cladophora glomerata, mixed in amongst some other algae including (probably) Spirogyra and Mougeotia but, having just written a post on how to take great pictures of algae, I do not feel that I should share these particular images with you all.

Latitude_2016_Cladophora_#2

A view of the Cladophora glomerata flocs in the lake at Henham Park, location for the Latitude Festival (left) and a close-up of a handful of Cladophora filaments (and some Lemna fronds).

The glorious weather had one unfortunate consequence for me, as my feet and legs turned red after I had sat in the morning sun for too long before applying sunscreen.   That, in turn, led me to wonder how these particular algae survive floating on the surface of a pond in the full glare of the sun all day.   I have written in the past about how some algae produce extra pigments to protect them against high light (see “An encounter with a green alga that is red” and “Fake tans in the Yorkshire Dales”); however this Cladophora was also exposed to high light but has no on-board sunscreen. What is happening?

Think of sunlight as a stream, the cell as a mill using the stream’s energy, and the waterwheel as the photosynthetic apparatus.   Too much sunlight sets the wheel spinning so fast that there is far too much energy for the mill to use.  Something has to be done with all that excess energy, otherwise the mill’s machinery will be damaged.   Cladophora, and other green algae (which are the ancestors of all land plants) have compounds called xanthophylls which act like sponges inside the cell, soaking up the excess energy and then dissipating it as heat (the process is called “quenching”).  D1, one of the proteins associated with the photosynthetic machinery, can be damaged if strong light is not sufficiently quenched but cells also have a clever mechanism whereby the psbA gene that replaces this damaged D1 is switched on by light.   This ensures a steady supply of replacement D1 to keep the photosynthetic machinery running as smoothly as possible.

The algae, in other words, can sit in the cool water of Henham Pond secure in the knowledge that evolution has provided them with the tools they need to keep their photosynthetic machinery in top-notch condition throughout a hot July weekend.  The only question left is what did they think of the music?   The algae stuffed into my shirt pocket were not amused, but that might be because that particular microenvironment is far from ideal for algal growth.  I have found one paper that subjected rose plants to different types of music.  This particular study showed Indian classical music and Vedic chanting to have positive effects on growth whilst rock music had negative effects, possibly due to its vibrations.   It is, I have to say, not the most rigorous study I have ever seen (I can’t even find an impact factor for this particular journal) but it gives food for thought.  Fortunately, the rock music used in the study (death metal) did not feature on the Latitude bill.  35,000 people would argue that this rather narrow study needs to be broadened out to encompass the huge diversity of modern music.   At Latitude, we encountered only good vibrations …

Latitude_Lumineers_Mvula

Latitude 2016.   The Lumineers (left) and Laura Mvula (right) entertaining the crowds on Sunday afternoon.

References

Chivukula, V. & Ramaswamy, S. (2014). Effects of different kinds of music on Rosa chinensis plants.  International Journal of Environmental Science and Development 5: 431-434.

Fujita, Y., Ohki, K. & Murakami, A. (2001).  Acclimation of photosynthesis light energy conversion to the light environments.   Pp. 135-171.  In: Algal Adaptation to Environmental Stresses (edited by L.C. Rai & J.P. Gaur).  Springer-Verlag, Berlin.

Häder, D.-P. (2001).  Adaptation of UV Stress in algae.  Pp. 173-202.  In: Algal Adaptation to Environmental Stresses (edited by L.C. Rai & J.P. Gaur).  Springer-Verlag, Berlin.

Vershinin, A.O. & Kamnev, A.N. (1996).  Xanthophyll cycle in marine macroalgae.  Botanica Marina 39: 421-426.

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The complex ecology of a submerged stone …

I was back at Smallhope Burn last week (see “Nitzschia and a friend…”), albeit a few kilometres further downstream from the site I discussed back in September.   Despite my visit being in mid-November, many of the stones I picked up here had tufts of young, healthy-looking Cladophora glomerata with, between them, apparently bare rock surface on which I could see the tiny, almost-black shells of Ancylidae snails.   These have rasping mouthparts and move across the stone surface grazing on the microscopic algae (probably mostly diatoms) that inhabit it.   Though the surface of the rock looked bare and felt rough to the touch, there is almost certainly a thin “sward” of diatoms and other algae here. Otherwise, the Ancylidae (the “cows” of my underwater pastures) would not be here.

Cladophora_&_Ancylidae

A boulder from Smallhope Burn covered with tufts of Cladophora glomerata interspersed with Ancylidae snails with (right) a shell of an Ancylidae snail on my fingertip.   The shell is about two millimetres across and the boulder is about 30 centimetres across.

Under the microscope,I can see several different types of diatom, though most look as if they live on or around the Cladophora rather than in the patches between the tufts.   Cocconeis pediculus and Rhoicosphenia abbreviata are both common epiphytes (see “Cladophora and friends”) whilst Diatoma vulgare and Melosira varians form chains that are loosely-attached to the substrate and, if detached, will easily become entangled within the Cladophora tufts.   The Navicula species are both motile forms that can glide in and around the filaments in search of light.   I suspect that my standard method of sampling diatoms (brushing the tops of stones vigorously with a toothbrush) is a little too coarse to get a true indication of how the diatoms differ between the bare patches and the Cladophora tufts.

Smallhope_Burn_diatoms_Nov2

Diatoms from Smallhope Burn, Low Meadows, November 2014. a. Cocconeis pediculus; b.,c. d. Rhoicosphenia abbreviata; e., f. Diatoma vulgare; g. Ulnaria ulna; h. Melosira varians; i. Navicula tripunctata; j. Navicula gregaria.   Scale bar: 10 micrometres (1/100th of a millimetre).

Our thinking on the ecology of Cladophora has changed over the past few years. If you consult literature from the 1970s, you’ll see a general agreement that Cladophora prefers waters that are rich in nutrients. This is, indeed, my own observation but, at the same time, you can find a lot of Cladophora in rivers with quite low levels of nutrients and, sometimes, no or little Cladophora in rivers that are nutrient-rich. A recent paper from Ireland helps put these observations into perspective, by demonstrating that the quantity of Cladophora is strongly influenced by the density of grazers as well as the quantity of nutrients.   My suspicion is that grazing invertebrates can keep Cladopora under control until a “tipping point” is reached when either the density of grazers drops or production of Cladophora acceleratesers to an extent that the grazers can’t keep up with the rapid growth of the alga, at which point the bed becomes smothered.   It may even be an example of the “alternative stable states” theory developed by Brian Moss and colleagues for the Norfolk Broads, though that would take some more work to confirm.

References

Moss, B. (2010). Ecology of Freshwaters. A View for the Twenty-First Century. 4th Edition. Wiley-Blackwell, Oxford.

Sturt, M.M., Jansen, M.A.K. & Harrison, S.S.C. (2011). Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river.   Freshwater Biology 56: 2580-2593.

Whitton, B.A. (1970). The biology of Cladophora in freshwaters. Water Research 4: 457-476.

 

Cladophora and friends

I was back at Stockerley Burn last week (see “A case of mistaken identity?”) and was surprised to find that the Oedogonium that was so prolific back in June has now almost completely disappeared and the stream bed is now dominated by Cladophora glomerata. How do I know?   Look at the illustration below: even with the relatively weak magnification offered by a hand lens you can see the characteristic branched structure that distinguishes it from an unbranched species such as Oegogonium.   There is almost nothing else that could be confused with Cladophora in our freshwaters, so long as you perform this simple test.

I saw Cladophora glomerata at almost all of the sites I visited during this trip, which was not a great surprise as it is a very common species in enriched lowland rivers and streams.   However, the Cladophora filaments did not have their characteristic green colour at many of these sites, mostly tending to a brownish hue due to the large numbers of diatoms which were growing on and around these filaments.

Cladophora_filaments

Left: Filaments of Cladophora glomerata on my fingertip, showing the characteristic branched structure; right: a wet mount of Cladophora photographed with a macro lens. The entire structure is about four millimetres long.

Two of these diatom-smothered filaments are illustrated below.   You can see the upright, curved cells of Rhoicosphenia abbreviata, each attached to the filament by a small mucilage pad, along with some lower-profile cells, with an oval outline. These belong to the genus Cocconeis and I think I could see at least two species (C. pediculus and C. euglypta) though it is hard to be sure when examining them in the live state.   The cells on the lower of the two images do look more like C. pediculus to me.   There are also a few cells of Fragilaria, again standing erect on the filament.

The second image shows another filament from the same location but this one is covered almost entirely with Cocconeis cells (mostly C. pediculus, I think). The lower, more streamlined, profile of these makes them more suited to situations where they are more exposed to the current.   Indeed, I suspect that there are subtle differences in the composition of this epiphyte flora throughout the tufts of filaments though it is hard to do more speculate when these differences are at a scale that is difficult to either see or handle whilst standing in a stream.

What effect do all these epiphytes have on the growing Cladophora?   The diatoms are trapping sunlight that would otherwise have been used by the Cladophora so the net effect of all of these is akin to moving a houseplant from a well-lit window ledge to a dark corner.   On the other hand, Cladophora grows very quickly so an probably stay one step ahead of the epiphytes most of the time. There is evidence that prolific epiphyte growth leads to the eventual death of some aquatic plant.   This has been suggested in the Norfolk Broads where gradual increases in nutrients favoured epiphytes which, in turn, smothered their host plants (slower growing than Cladophora), leading to the long-term deterioration of the unique habitats of the Broads.

Cladophora_epiphytes_#1

Epiphytes on a Cladophora filament from Stockerley Burn, August 2014; a. Rhoicosphenia abbreviata; b. Cocconeis sp (from above: valve view); c. Cocconeis sp (from the side: girdle view); d. Fragilaria sp. Scale bar: 10 micrometres (1/100th of a millimetre).

Cladophora_epiphytes_#2

Cocconeis cells epiphytic on a filament of Cladophora glomerata.   Scale bar: 10 micrometres (1/100th of a millimetre).

 

A case of mistaken identity?

Imagine, just for a moment, that someone makes a list of the plants growing in a river or any other aquatic habitat and includes a category called “unidentified dicotyledon”.   Most botanists would throw up their hands in horror. Yet they probably have a category on their field record sheets for “filamentous green algae” which they use on a regular basis. It takes time, after all, to take a specimen back to the laboratory to check under the microscope and, let’s face it, the identification guides that are available are not very user-friendly and are full of unfamiliar terminology.

A slight variant on this particular sin is to record all the filamentous green algae that you encounter as Cladophora glomerata.  You are on a fairly safe bet here because a) it is a very common alga; and, b) no-one is likely to check.   However, there are a few algae that can be easily mistaken for Cladophora, especially if you are not paying close attention.

Last week, I did a survey of some streams draining into the River Browney, a tributary of the River Wear in County Durham.   Most showed evidence of enrichment which was not surprising as there were small sewage works, arable cultivation and a fish farm within these catchments.   And, as a result, it was no surprise to find that Cladophora dominated the stream beds at several sites.   One site, however, had thick wefts of filaments which looked and felt like Cladophora but, when viewed under the microscope, were quite different.

StockerleyBurn_BogleHole

Stockerley Burn at Bogle Hole,   About half the river bed is covered by thick wefts of filamentous green algae up to about 30 cm in length.

I found three different species of green alga entangled in these wefts. There was some Cladophora glomerata but the most abundant of the three was a species of Oedogonium (see “The River Wear in summer”), characterised by unbranched filaments and cap cells.   66 species of Oedogonium have been recorded from Britain and Ireland but we know little of their ecology. Whilst some forms are common in lowland, nutrient rich rivers and streams such as this one, I have also found Oedogonium in remote, low-nutrient environments such as the River Ehen in Cumbria.   It pays to be careful, in other words, and to make sure that your “Cladophora” really is Cladophora. The easiest way to do this is to check for branching using a hand-lens. If you can’t see branching in the field, take a specimen back to the laboratory and check it under a microscope. Some populations of Cladophora are much more sparsely branched than others, so you may simply confirm your original suspicions. Oedogonium is, in fact, a very distant relation of Cladophora, despite their similarity when viewed with the naked eye. Mistaking Oedogonium and Cladophora is equivalent to  confusing your best friend with a sea squirt (see “Who do you think you are?”).

More about Oedogonium in the next post.

Oedogonium_StockerleyBurn

Filamentous algae in Stockerley Burn: main picture shows the wefts of (mostly) Oedogonium; inset shows cells from a single filament with the cap cells arrowed (scale bar: 10 micrometres, 1/100th of a millimetre).