Monday, 23 December 2013
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.
Saturday, 14 December 2013
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.
Tuesday, 10 December 2013
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.