The effect of the velocity of a stream on the abundance of Flattened Mayfly Nymphs (Ephemoptera Heptageniidae)Name:Abdel DarwishLocation: Court Field, Nettlecombe Courte, The Leonard Wills Field Centre, Willition, Taunton, Somerset TA4 4HTAbstract Freshwater ecosystems can be easily and unknowingly polluted by the surroundings, this can cause detrimental damage to the ecosystem. Mayflies are a biological indicator and are an effective yet simple way of measuring an ecosystems health. I collected data on the distribution of Flattened Mayfly Nymphs in order to further inform other related ecological studies. I used a kick sampling method at multiple areas to collect 15 samples and measuring the flow velocity using an impellor and hydro prop at every site. My final results showed a positive correlation of abundance to flow velocity of (dA/dV = 15.62) and using a spearmans rank test found there is a 99.5% chance my data has true correlation.Research and RationaleThe mayfly belong the one of the oldest order of insects, the Ephemoptera with an evolutionary history dating back to up to 300 million years. There are up to 50 species of Ephemoptera in the UK, I will be focusing on the genus Ecdyonurus however I am unsure of the species as it is difficult to identify the four main UK species of Ecdyonurus nymphs. The Flattened mayfly nymph does not tolerate polluted water so its presence indicates a relatively pristine habitat, making them a good biological indicator for mesotrophic conditions (3). They are considered an ecological keystone species linking detrital energy resources directly to higher trophic levels containing many species of fish which feed on the nymphs(4). Meaning the expiration in an area of Mayflies could lead to ecological collapse(4). Mayflies are useful indicators as they are relatively easy to sample, highly visible and provide evidence of effective water quality control. I will be basing my study on them as the implications of monitoring their distribution and abundance allows the ability to further inform studies regarding Flattened Mayfly Nymphs and pollution.

May Fly Life Cycle (3)The life of a mayfly begins once it's hatched from it's egg, spending up to 2 years in this Nymph form at the river bed feeding on algae and detritus, they have a very hydrodynamic form and relatively large tarsal claws, the combination of the two makes them better adapted to fast flowing currents and are found clinging to rocks or algae(1).After their nymph stage is finished, at about June or October time they rise to the surface and break through the surface tension. Once there, they shed their nymphal skin becoming an emerger until their wings dry and they take flight, they are then considered a dun as they are not able to reproduce. The dun will then undergo its second metamorphosis becoming a spinner where its only purpose it to mate. The females then dip in and out of the water dropping its eggs off, these are named Ovipositing spinners(2).The name of the order Ephemoptera is derived from "ephemeros" meaning literally "lasting a day", this is because their adult stage lasts only a day. From their first metamorphosis they lose their digestive tracts and are replaced with their sex organs and they have no functioning mouth parts. Their entire adult stage is limited by their energy reserves created as a nymph hence their short adult life span(1). Flattened mayfly nymphs prefer stony substrata such as riffles; this is because of the faster flowing current and larger stony substrata where they are better adapted to, allowing them to cling onto rocks also hiding themselves from predators. A study published in the Canadian Journal of Zoology in 1997 explored the effect of flow velocity and light on mayfly nymphs, the result showed a preference to faster flowing darker waters(5). They have obvious adaptations allowing them to inhabit faster flowing water unlike other organisms in a similar habitat which dwell in slower currents.

Tarsal Claw of Heptageniidae(1)The adaptations which lead them to preferring riffles include their tarsal claws which are very pronounced allowing them to cling on to stones and their flat hydrodynamic form reducing the resistance from the current, both of which stop them being swept downstream(1). They have a very dark/transparent camouflage reducing the chance of preditation especially when they are relatively idle when clinging. All of these adaptations expand their niche to faster shallower areas such as riffles. This presents the advantages of a reduction in competition for nutrition and space. Another study conducted in Oregon published 1984 explored the effect of substrate type on distribution of deferent species of Mayfly(6). The samples present data from large stony substrata to small sediment (