Soaking up the sunshine …

Hardly had my field kit dried out following my trip to west Cumbria than I was loading it back into the car for a trip to the Ribble valley.   I’m involved in a small project to develop a citizen science tool for assessing algae in rivers, along with Bill Brierley of the Freshwater Biological Association and Katrina Woodhead, a student at Lancaster University, and Leanne Trough of Ribble Rivers Trust.  We’re looking at streams with different levels of human impact, using the RiverFly method to assess invertebrates and a simplified version of RAPPER (see “The democratisation of stream ecology”) to assess river health.

One of the sites we visited was on the River Hodder, a tributary of the Ribble, which flows off the Forest of Bowland and eventually joins the Ribble just downstream from Clitheroe.   There are no major settlements on the Hodder and, as a result, it is a relatively clean river, with one of the best salmon, trout and grayling fisheries in the country.  On this particular occasion there was a lot of filamentous algae visible but, following the long period of warm weather and low flows, this was not a great surprise.   The big interest here was a few patches of freshwater sponge on submerged bedrock on the far side of the river from where we were working.  They formed distinct patches on the rock, with a green tinge (due to endosymbiotic Chlorella-like algae) and which yielded slightly when pressed with a finger.  

Sponges are very primitive organisms.  There is a well-known trope that if a sponge is passed through a sieve, the individual cells will reform into a new sponge, suggesting some basic cell-to-cell communication (see video here).   Inside the sponge there is also a “scaffold” of long, thin silica “spicules” which give the sponge some structural integrity and which are also useful for identification.   There are only about half a dozen sponges from freshwaters in the UK and Ireland (there are, by comparison, about 300 sponges in marine habitats).  Based on the spicule morphology, I think that the sponge we found was Ephydatia fluviatilis.  

Spicules of Ephydatia fluviatilis from the River Hodder at two magnifications.  Scale bars: 50 micrometres (= 1/20^th of a millimetre).   The picture at the top of the post shows the sponge growing in situ.  The picture frame is about 50 cm across.

Identification requires a microscope in order to examine the spicules.   By the time I got home, the green-tinged portions that I had scraped off the stones were beige whilst the overlying water in the vial was green with suspended algae, which suggested that the association was very loose.  There is, however, evidence that the sponges are actively switching genes on and off to encourage the algae to join them.  Maybe is more going on than, perhaps, we first assume.   Studies have shown that the algae do not meet all the energy requirements of freshwater sponges and prolific growths such as those we saw in the Hodder also depend on the sponges’ ability to filter particles from the water.   That, in turn, translates into a broader ecosystem benefit.   Removing particulate matter helps preserve the crystal-clear water that the Hodder’s fish need to thrive.    

This begs a rather obvious question: how good are sponges at cleaning rivers?   It will depend how much sponge is growing in the river and how dirty the water is, but all that filtration must have some effect?   On the other hand, whilst we know the Hodder to be a clean river, sponges are not restricted to unpolluted rivers.  A study in Ireland indicated that Ephydatia fluviatilis is as likely to be found in rivers below good ecological status as they were to be found in high or good status rivers.  Only one of the sponges included in this study (Racekiela ryderi) was largely restricted to clean waters.   It would be unwise to use sponges on their own as indicators of the quality of a river.  That is, however, a very utilitarian view.  Sponges are curious and ancient organisms which are largely overlooked by casual naturalists.  They are worth watching out for whenever you are wading in a river or at the edge of a lake.

References

Cocchiglia, L., Kelly-Quinn, M., & Lucey, J. (2013). Classification of freshwater sponge collection at EPA Kilkenny. Environmental Protection Agency, Johnstown Castle, Co. Wexford, Ireland, 31.https://www.epa.ie/publications/research/biodiversity/Classification-of-freshwater-sponges.pdf

Evans, K. L., & Montagnes, D. J. (2019). Freshwater sponge (Porifera: Spongillidae) distribution across a landscape: environmental tolerances, habitats, and morphological variation. Invertebrate Biology, 138: e12258.

Hall, C., Camilli, S., Dwaah, H., Kornegay, B., Lacy, C., Hill, M. S., & Hill, A. L. (2021). Freshwater sponge hosts and their green algae symbionts: a tractable model to understand intracellular symbiosis. PeerJ, 9: e10654.

Jensen, K. S., & Pedersen, M. F. (1994). Photosynthesis by symbiotic algae in the freshwater sponge, Spongilla lacustris. Limnology and Oceanography 39: 551-561.

Lucey, J., & Cocchiglia, L. (2014). Distribution of sponges (Porifera: Spongillidae) in southern Irish rivers and streams. In Biology and Environment: Proceedings of the Royal Irish Academy 114: 89-100). 

Some other highlights from this week: 

Wrote this whilst listening to: All of us Flames by Ezra Furman.

Currently reading: Suite Française by Irène Némirovsky.  

Cultural highlight:  Sally Potter’s 1992 film interpretation of Virginia Woolf’s Orlando.

Culinary highlight:  very good takeaway pizza from Flint Pizza in Heaton [https://www.flintpizza.co.uk], eaten al fresco in Heaton Park 

More from the splash zone …

It was unfortunate, but the long spell of hot weather came to an end the day before we were due to head out for our regular fieldwork in the Lake District.  The day started with rain which petered out by mid-morning. Clouds had started to lift by the time we reached Wastwater, although had still not cleared the peaks of Great Gable and Scafell Pike.   The scene in the photograph above may look idyllic, but the water was choppy, with white horses visible on the lake and waves adding an extra complication to my sampling efforts.  

One recurring feature of Wastwater is persistent growths of algae on the rocks in the lake littoral zone.   I’ve never quite been able to explain why this is the case.   We do see visible growths of green algae in other lakes nearby, but these are usually transitory phenomena whereas Wastwater’s margins nearly always have growths that are obvious with the naked eye.  Wastwater is probably the lake with the lowest level of human influence in the region, so the usual kneejerk association between algae and nutrients doesn’t really hold.   It is a conundrum still awaiting an explanation.  

As well as these green growths, however, there are also very dark crusts growing on larger boulders around the air-water interface.  I’ve written about these before (see “Notes from Wastwater …” and “Close to the edge in Wastwater …”) and Allan Pentecost has also made a study of them (see reference below).  Today, with the water levels going up and down as the waves came in, I held my camera underwater and managed to photograph these two communities in situ, revealing their clear zonation.   Spirogyra dominates in the fully-submerged zone whilst the cyanobacterial crusts are in the zone that is often exposed.

Algal zonation on an emergent boulder in Wastwater, August 2022.   The green algae in the lower part of the image is Spirogyra and the black patches in the upper part are cyanobacteria.  The picture frame is about a metre across.

Scraping the crusts off the rocks for later examination was not easy in the choppy conditions.   I just got enough to confirm that the predominate cyanobacterium was a Calothrix species, but not enough to photograph.   The Spirogyra was easier to collect: it was a broad filamentous form with two chloroplasts which is very common in the Lake District.  I’ve never seen it conjugating so cannot put a species name on it.  

This type of zonation is well known in marine environments, where tides exacerbate the effects.   In natural lakes, water levels do not fluctuate to the same extent so the potential for zonation is more limited.  There is some evidence of zonation in deep Alpine lakes (see “Depths of imagination …” and “Life in the deep zone …”) and these studies are useful reminders that our understanding of benthic algal zonation in freshwaters is limited by our capability (I wear chest waders when sampling, the Alpine studies used SCUBA).  The study in the Bodensee I discuss in an earlier post found this zonation most clearly expressed on submerged vertical rock faces which, to the best of our knowledge, do not exist in Wastwater.   Deepwater benthic algae will not be able to establish in depositional environments.  But, from my shore bound perspective, deepwater benthic algae are a subject on which I can speculate but not explore for myself.

Spirogyra filaments from the submerged zone of a boulder in the littoral of Wastwater, August 2022.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).

Wastwater empties into the River Irt, to which we travelled straight after our sojourn on the lake shore.  Both of these also had extensive coverage of filamentous algae.  Once again, algae are almost always visible at these sites despite a lack of obvious human drivers.   Quantities were greater today than we usually find at this time of year, most likely because of the long period of warm, dry weather, and this was the case at almost all the sites I’ve looked at recently.   Of note, however, was the absence of obvious growths of Torularia atrum, which was abundant when I visited in June (see “All change …”).   For every constant on this regular tour of Lake District habitats, there seems to be an inexplicable variable too.  The algae change and I learn.   

Reference

Pentecost, A. (2014). Distribution and ecology of cyanobacteria in the rocky littoral of an English lake district water body, Devoke Water. Life, 4: 1026-1037.

Other highlights from this week: 

Wrote this whilst listening to: Rocket, 2017 album by Americana/Indie artist Alex G.

Currently reading: The Country of Others by Leïla Slimani, about the last days of French colonialism in Morocco.

Cultural highlight:  Hit the Road, a film described as an Iranian Little Miss Sunshine.  

Culinary highlight:  Tasting menu at Peace and Loaf in Newcastle

It’s an ecosystem, stupid …

Our garden acquired a small pond earlier this year (see “The story of a pond”) and, five months on, the pond has acquired its first obvious algal growth.   Typing “algae” and “garden pond” into Google returns almost 10 million “hits”, and I’m guessing that the generally negative tone of the top hits will continue all the way down.  The Royal Horticultural Society set the tone with: “Algae can be a major problem in ponds, causing discoloured water, green scum at the pond edges, or dense mats of green growth under the surface. If conditions are favourable, algae will spread quickly and can harm aquatic life”.   Suffolk Wildlife Trust, by contrast, adopt a more balanced attitude: “Algae are important members of a healthy, well-balanced pond ecosystem, providing food for species at the lower end of the food-chain. To deal with algae effectively is not to eradicate it, but to prevent, or control, its excessive growth”.

The flocs in our pond were composed of Oedogonium, a green unbranched filamentous alga often encountered in this blog (see, for example “Under the weather”).   Both the websites I mentioned point to nutrients as a major cause of algae “problems” but the Oedogonium in our pond was covered with needle-like cells of the diatom Fragilaria gracilis, a species that favours nutrient-poor conditions.  Our garden receives no artificial fertiliser so there is little scope for enrichment. 

A more likely reason for the appearance of algal flocs is the warm sunny weather.  Although our pond is shaded, it still receives some direct sunlight, and the water temperature is now over 20^o: ideal conditions for any plant to grow.   We should not really be surprised that a fast-growing organism grows particularly fast when conditions are ideal.   I talked about this in Summertime Blues, describing the effects of the 2018 heatwave on the River Wear.   If climate predictions are correct then we will be experiencing more visible algal growths in the coming years in both ponds and rivers, regardless of how carefully we manage nutrients.   

Flocs of Oedogonium in our garden pond, August 2022.

So what should we do about it?   A garden pond differs from almost every other habitat with which I deal in that one person has complete agency to enact appropriate changes.  Common sense says that a light-touch hands-off approach should suffice, in order to let natural processes determine outcomes.   However, a garden pond is also an extraordinarily small habitat, so there is limited scope for a full range of organisms to create a balanced ecosystem.  The answer is to extend the principles that we apply to the rest of the garden to the pond itself: inspired by large-scale rewilding experiments such as Knepp we’ve adopted a light-touch approach to our lawn (see: “No mow May”).   For this to work, however, we need to acknowledge that a small garden cannot support the large herbivores that would naturally manage vegetation at places such as Knepp, and occasionally mow the grass to simulate their effects.

The same principle applies in a garden pond.   This is not large enough to support a balanced ecosystem where pike predate on smaller fish which, in turn, eat the invertebrates who graze on the algae.   So, instead, we need to act as the primary “grazer”, manually removing the filamentous algae at intervals using a cane or a rake.   They can then be tossed onto the compost heap or used directly as mulches on the flower beds.   The RHS website cautions that “this will only be a temporary solution” but then so is mowing your lawn.   That’s what happens when you create habitats but omit some key ecosystem components.   

Filaments of Oedogonium, along with epiphytic Fragilaria gracilis from our garden pond.   Scale bar: 20 micrometres (= 1/50^th of a millimetre)

The Suffolk Wildlife Trust cautions against manually removing filamentous algae growths as these can harbour larvae of great crested newts but this is more of an issue earlier in the year.   It does bring us full circle, however, reemphasising the point that algae are a natural part of the pond ecosystem.  Learn to love and appreciate them.  Better that than the appalling suggestion on the RHS website that adding dyes to the water will “prevent” algae.   It is an approach that may appeal to antediluvian horticulturists and golf-course groundsmen who still insist on “tidiness” but if you have the tiniest shred of interest in the natural world, you had better remember that algae are the engine rooms of natural aquatic ecosystems and treat them with the respect that they deserve.

P.S. I should add that “we”, when referring to gardening activities, is a euphemism for Heather.  I’m a non-executive director at best in that department. 

Some other highlights from this week:

Wrote this whilst listening to: Sweet Season by the American percussionist Glen Velez.  Also, several Richard Thompson records, following an excellent gig at Whitby Bay Playhouse.   Highlights include I Want to See the Bright Lights Tonight, from 1974, and some very old Fairport Convention songs including Who Knows Where the Time Goes?   It seemed wholly appropriate for a 73-year old to sing this wistful song until you remember that he and his Fairport compatriots wrote and sang these wise-beyond-their years lyrics when they were in their early 20s. 

Currently reading: Reluctant Saint by Donald Spotto, a biography of St Francis ahead of a trip to Asissi in September.   Just finished Delia Owen’s Where the Crawdads Sing.

Cultural highlight:  Brian and Charles: a new British comedy loosely-based on the Frankenstein story which, by coincidence, uses Who Knows Where the Time Goes over the closing credits.

Culinary highlight:  After my eulogy to Casa Mama in the previous post, I discovered St Pancras Square and Coal Drops Yard just behind King’s Cross Station.   Meals at Morty & Bob’s and BAO King’s Cross [ bracketed a meeting in London.