The pond gas detective: tupperware and hi-tech

The new field season is underway at Druridge Bay. Pete has been experimenting with measurements of carbon dioxide and methane fluxing in and out of the wetlands. This needs a delicate mix of high-tech gas analysing kit cunningly attached to an upside down plastic sandwich box wrapped round with an old bicycle tyre inner-tube as a flotation device. Here is Pete gently positioning the floating box over the grassy shallows of a pond in a grazing meadow. The red and blue tubes allow gasses to be pumped through the analyser sitting snuggly in its black case perched on a plastic box (it does not like water), which records the changing concentrations. Pete's design uses a small floating chamber so that we can position the box over the distinct plant communities such as amphibious grasses or submerged pondweed in the ponds. There is something very immediate about watching the measures tick up on the digital displays. Suddenly the invisible chemistry is brought to life, the molecules in the air made apparent, complementing the seeping cold and the calls of the last winter geese, who did not approve of all this fiddling about in their field. The technology is, as usual, temperamental and easy to de-calibrate with one push of the wrong button but also very impressive when it switches from prima donna to primary data collection. Pete's first try outs showed steady carbon dioxide release with methane too, although at much lower concentrations. As Spring builds and the plant growth surges he will be aiming to capture gas fluxes from different pond types and plant communities. Early results show some pond types pumping out carbon dioxide whilst others are much less active. As with their plant and animal communities it seems that ponds represent a fine-grained diversity of geochemical drivers. If we can combine the flux measures for different pond types with data on the organic carbon trapped in the sediments we should be able to identify the wetlands that make the most powerful carbon sinks, perhaps even the role of different plant communities in these processes. Just so long as the wrong button does not get pressed.....

The classic Christmas crisis: "i think these batteries are flat"

Science sometiems depends on the right bit of kit to measure, map or probe. Personally I'm a great fan of lo-fi and mostly use a pond net and a white plastic tray. Not much that can go wrong there, although the wind that whips across Druridge Bay can pick up a tray and hurl  it across a swamp with nonchalent ease. However detailed chemistry requires proper measures and we have just got a new probe which will allow Scott to measure the chlorophyll, oxygen and conductivity in his experimental ponds simultaneosuly and live in the field. It came in a tough, field protable case which was opened with glee to reveal the shiny, exciting bits and pieces. Even came with its own screw driver. Here are Dave and Scott having a first go at starting it up in the office. In perfect synchrony with the seasons the batteries that came with it were flat. How many Christmas Day mornings throughout the UK have been blighted by that howl of anguish? You see why I like a net and a plastic tray.... They'll get it working I'm sure.

This Druridge Bay pond blog has been going for just a bit over a year now. We are taken aback by the global coverage: Russia, Argentina, South Africa, Latvia, Canada... Even if you have stumbled across Ponds, Time and Place accidently I hope something of this magical landscape has lightened your day and the mysterious lives of the pond plants and animals have captured your imaginations. Merry Christmas to all our readers.

The ostracods eat their spinach

The three ostracods featured in the last blog are typical of their kind; widespread in small ponds and pools, especially those prone to drying, relying on tough eggs to resist drought. During the good times when ponds flood again they use asexual reproduction to churn out young through parthenogenesis, the process in which unfertilised eggs develop and mature. Despite the adults tough bivalve carapaces many predators catch these small prey. Dragonfly larvae and water boatmen have been shown to reduce populations significantly. The Ostracods respond by changing behaviour migrating to safer parts of the pond. Heterocyrpis incongruens reacts to chemical cues in the water, shifting to more open water and being less active. Moving about less is potentially tricky for male ostracods in search of a mate, although experiments to compare predation on sexual versus asexual individuals of Eucypris virens showed no marked difference in vulnerability. Male ostracods are unknown for some species, but it seems unlikely that being eaten is the cause of this absence. Asexual reproduction could have advantages faced with intense predation, because one female can potentially found a population.  Ostracods themselves seem to be rather generalist feeders but with some preferences. Eucypris virens has a liking for spinach when offered a variety of foods and also Tolypothrix tenuis a type of cyanobacterium, a combination humans are unlikely to encounter outside of an extreme sushi bar. Animal prey can be on the menu too, especially sickly or injured larger creatures, who can be overwhelmed by the sheer number of ostracods ganging up on them. ... perhaps, like Popeye,  it’s is the beneficial effects of all that spinach.

Schmit, O. et al (2012) Vulnerability of sexual and asexual Eucypris virens (Crustacea: Ostracoda) to predation: an experimental approach with dragonfly naiads. Fundamental and Applied Limnology, Vol 181, 207-214.

Schmit, O. et al (2007) Food selection in Eucypris virens (Crustacea: Ostracoda) under experimental conditions. Hydrobiologia, Vol 585, 135-140.

Pea shrimps: the charm of the Ostracoda

Amongst the scurrying, skipping and gliding specks at the bottom of a tray of pond life there are certain animals notorious for being tricky to identify and generally misunderstood. The jelly-bean like threesome above are all members of just such a group, the Ostracods, sometimes called pea shrimps. Most of what you can see are two valves, largely enclosing a scrunched up body with a handful of antennae, legs and other sticky out bits. They are little crustaceans, their jointed limbs at least giving away their kinship with more familiar water fleas and shrimps. Identification is tricky, largely needing a good view of the legs and antennae, “extremely difficult and can only be undertaken by a specialist ” as it says in Wolgang Engelhardt’s classic The Young Specialist looks at Pond-Life. Whilst ecologists may be wary of this awkward group geologists have a wealth of knowledge of their historic distributions, using fossils of the tough valves and the various shapes, spines and surface sculpture. Size, colour and shape are handy for the living adults and these three are fairly distinct: Herpetocypris reptans, Heterocypris incongruens and Eucypris virens. The “cypris” bit of the names is essentially saying “shrimp”. All three are a millimetre or two long, stuttering uncertainly across the sediment in search of food which can be any old detritus but they can gang up on enfeebled prey too. Although individually small their populations are robust, sustained through the ups and downs of drought and flood by desiccation resistant eggs, so they often appear in puddles and flashy pools. Heterocypris incongruens in particular seems to prefer these conditions and is lost from ponds as permanent, dense emergent plants such grasses and spike rush colonise. Under a microscope they are objects of great beauty, their valves sculpted or fringed with bristles and serrations. I am fond of these enigmatic beauties.

Flood, drought ... and now the plough

 The modestly named Small pond weed, Potamogeton berchtoldii, (or, less modestly, Berchtold’s pond weed, because that is what the Latin says) is nonetheless a canny plant, turning up in ponds across Druridge Bay, including unlikely sites in the middle of arable fields. The delicate, filigree strands of stems and leaves seem ideal to fragment, stick to birds and be carried between sites. This little pondweed also seems able to tough it out in exposed shallows or ponds with slightly higher salinity, which seems to come up from underground springs. Although it is a flowering plant this species relies on cloning to spread using ramets; individual plants that, together, form the whole vegetative colony. To over-winter the pondweed sets turions, essentially a bud, but a bud adapted to tough it out during the lean times, functionally akin to a seed or bulb  in other species. Just how tough this overlooked pondweed can be is under severe test in some of the subsidence ponds at Blakemoor Farm. The warm summer has seen water levels fall far enough for several subsidence ponds to be ploughed through, including the wide but shallow site featured on the blog as it began to dry out.

The cracked, dried soil from the sequence earlier in the year (2^nd September blog, compare the drying sequence in the photos above to the latest ploughed state of the pond at the top of the blog) is now tilled and turned, the pond which was once the summer hang out for avocets , teal and black headed gulls is barely detectable. Whether ramets and turions cope well with ploughing I do not know, although I suspect the plant will recolonise once the pond refills. On the 20th November the site was just the bare, ploughed ridges but by the 27^th a silver flash of water had puddle across the lowest part of the shallow basin. Potamogeton berchtoldii is not a rare plant: the map shows the national records from the NBN gateway data base since 1980. If anything it may be overlooked given the small size and identification challenges

The water beetles' sad end as a teenage heron's snack

The predatory beetles of the last two entries look spectacularly fearsome through a hand lens; pointed jaws which pierce prey and along which the digested innards of their victims are sucked out, clusters of simple eyes spots which suggest a very different perspective on their world. However if you are a 1 metre tall Grey Heron, Ardea cinerea, these beetles probably pass for a light snack. The experimental ponds at Hauxley are a frequent hang out for the young herons that have left the nest. They loiter, preen and wander round with no obvious purpose in a perfect echo of teenagers. They also throw up pellets, like the one in the photo above. Heron pellet contents vary greatly with time and place, as they seem to hone their hunting to fine grained variations in the available prey. Mammal remains such as voles and moles occur frequently, birds too, especially chicks, and the tough wing cases (elytra) of water beetles. Three large, ridged elytra, edged with a distinct yellow border are in this pellet, the remains of Great Diving beetles (Dytiscus) based on the size and colour. The victims were female beetles, the ridges a give-away of gender compared to the smooth wing cases of the males. The rarity of fish bones, even their apparent absence, from heron pellets has attracted comment in many more detailed studies. Why they should be missing is not clear, since plenty of other fish eating birds regurgitate bones and otter spraints are essentially fish bones in Earl Grey tea scented oil. The beetles’ wing cases are tough. Beetles body parts found in ancient soils and peat can be so intact that precise species identification is still possible allowing local habitat conditions to be worked out based on where the species live these days. Quite where these two female Dytiscus came from I cannot tell. Dytiscus beetles have never been found in the experimental ponds, so the herons must have travelled further afield. In true teen fashion they last leave the debris lying around when they’ve finished.

Acilius, the elegant plankton hunter

The Acilius larvae of the previous entry repay closer inspection. Two species of Lesser Diving Beetle are found in the UK, Acilius sulcatus and the scarcer Acilius canaliculatus. The “Lesser” is the curse of sharing the same ponds with Great diving Beetles, Dytiscus species, but the Acilius have their own strangeness and charm, less of the brute force of the Dytiscus larvae or clockwork toy look of adult Great Diving Beetles. Adult Acilius resemble submarine almonds in shape and size. They are apparently the fastest swimming of the diving beetles. However it is the larvae that are most startling. They are nektonic, meaning they live out in the open water column. Legs fringed richly with fine hairs make powerful paddles, but they often hang, stationary, waiting for prey to come in reach. Whilst they will take a variety of invertebrates they are particularly effective predators of water fleas, perhaps voracious enough to skew the distribution of these prey throughout a pond and also ferociously efficient hunters of mosquito larvae. Juvenile mosquitoes have to come to the surface occasional to replenish oxygen supplies, relying on a snorkel-like siphon to break though the water’s surface to the air above. Swimming to the surface, or even static but silhouetted against the light above makes them vulnerable to specialist hunters. Whilst Dytiscus larvae routinely capture large prey such as tadpoles (or each other) the Acilius’ delicate, elongated thorax and small head make for an altogether more refined but  equally deadly hunter. (Adult photo from Old Billuck and larvae from Biodiversity Heritage Library, Creative commons, Flickr).