An investigation into the effect of water velocity on the abundance of freshwater shrimp, (Gammarus pulex) in the “Baye de Clarens” river’s riffles.

What is the effect of water velocity upon the abundance of freshwater shrimp (Gammarus pulex) in the “Baye de Clarens” river’s riffles?

Having lived in Montreux, Switzerland my whole life, I was unaware that the Gammarus pulex species was so abundant in the “Baye de Clarens” river. I was very surprised to discover the large variety of species that were existent. The river is in the district of Riviera-Pays-d’Enhaut in the south-western part of Switzerland in the Canton of Vaud. It is approximately 8km long (“Baye de Clarens”). We had an easy access to this river since it is close to our school. This allowed us to get to the river quickly when it was convenient. We conducted a preliminary study before the investigation to get used to the river’s habits and to try out different methodologies. With modifications from the pilot study, it was then simpler to conduct the investigation. The river has many paths that have been managed by humans to allow individuals to walk around the river. These paths leading to many locations on the river allowed us to choose a site which was safe and suitable for the aim of our investigations.

I decided to investigate the effect of velocity on the abundance of G.pulex in the river’s riffles. Riffles are the shallow sections of the stream with higher currents therefore higher velocities than in pools (Water Life: Riffles and Pools). In addition, riffles increase water turbulence and dissolved oxygen concentration which is much needed by aquatic animals (Cook). Their rocky bottoms protect species from predators offering them shelter. Compared to riffles, pools are deep and have a lower velocity. Yet, if there are too many sediments in riffles, this may cover species’ eggs causing them to smother (Otieno). The river’s velocity is the speed at which the river is flowing.

Gammarus pulex are a diverse group of amphipod crustaceans (Chaumot, Arnaud, et al). Gammarus pulex are crucial in aquatic ecosystems as they play a central role in the detritus cycle and they are important keystone species (Chaumot, Arnaud, et al). In fact, they play an important role in recycling nutrients and transferring energy to higher trophic levels. They prefer to feed on leaf material as fungi is an important part of their diet (Graça). In addition, they are an important element in food webs by providing prey for secondary consumers. They’re predators are often birds and salamanders. G. pulex grow to the size of 21 mm in freshwater and are primarily found in Europe in waters with depth of 0 -10 meters (“Gammarus Pulex”). Nevertheless, they can also be found in North Africa, The Soviet Union, and a great part of Asia (Pinkster). Their body is divided into three segments, the head, the thorax, and the abdomen (Budd). They feed themselves with blood worms, algae, and dead animals. In addition, G.pulex tend to swim on their sides (“Freshwater Shrimp). Equally, Gammarus pulex are bioindicators, they assess the health of the environment (Parmar, Trishala K, et al.). When G. pulex mate, an uninfected male will cling to an ovigerous female for a period of time waiting for her eggs to be fertilized (Chaumot, Arnaud, et al). Breeding usually occurs from March to September, as the experiment was conducted in September, we were able to observe them mating (Maitland). Due to the limited research on the impact of velocity on the abundance of G. pulex, I have conducted my own research on various studies done on G.pulex.

On a study of the effect of habitat structure on habitat use by G.pulex in artificial streams, they were most abundant in river pools (Dahl). Though, this study discovered that low river discharge and the presence of sculpins caused G.pulex to increase their use of riffles (Dahl). This species is therefore able to evaluate differences in habitat quality and they can respond suitably (Dahl). G.pulex have been used as a study organism for ecotoxicology and to investigate the impact of plastic microfibers upon their aquatic environment (Yardy). The results of these studies concluded that they could detect microfibers in a certain range and are partially repelled by them (Yardy). Equally, it has been discovered that G.pulex are acquiring an increased tolerance to pesticides when there is low recolonization from non-contaminated refuge areas (Shahid). Finally, it has been found that Gammarus pulex that are larger than 6mm congregate in places where there are large amounts of autumn leaves if these are visible on the substratum surface (John).

While deciding to investigate the effect of water velocity on the abundance of G.pulex in riffles, I have created the following hypothesis -

It is expected that there is a higher abundance of G. pulex in riffles with lower velocities in the “Baye de Clarens” river.

Through my research, I discovered that G. pulex “prefer slow moving” water “where they can often be found in large numbers” (“Freshwater Shrimp”). This may be due to the reduced movement of water decreasing the amount of G. pulex being relocated to over areas of the river. In addition, the riffle’s rocky bottom creates protection and shelter for this species (Water Life: Riffles and Pools). Therefore, there should be a positive correlation between low velocity and the abundance of Gammarus pulex.

• Plastic tray to keep sample species from the stream.
• Hydro-prop impeller to measure velocity (30 cm length)
• Net to collect species (25 x 25cm)
• Pipette chopped in half and spoon
• Tape measure
• Invertebrate indication chart
• Stopwatch (± 0.01 seconds)
• 100cm ruler (± 0.5 mm)
• Pot for isolated G. pulex
• Rubber gloves to wash the rocks

Systematic sampling was used to collect data from the stream by intervals. Over a 15 meter transect across the centre of the riffle, data was collected at 15 intervals, each 1 meter apart. During the preliminary study, I figured that the centre of the river was an appropriate choice as there is no differences in light and shade therefore light intensity would not affect the results of this investigation. At each interval this was the method used -

• Prepare the apparatus at each location.
• With the help of a hydro-prop impeller, the velocity of the river is measured. Using a stopwatch, measure the time taken for the impeller to move to the end of the hydro prop rod. When data is processed, calculate the velocity using an equation.
• Measure the depth of the riffle with a 100cm ruler at each interval.
• Using the rock washing method, wash 5 rocks for 10 seconds each with rubber gloves. The contents coming from the rocks can then be collected by the net downstream catching the species at each location. Fig 5 represents this process.

• Empty the contents from the net in a plastic trey filled with water from the river.
• From the plastic tray, retrieve each G. pulex using a pipette or a spoon and transfer them to a separate pot. This will make counting the organisms easier. After each transfer, note down the number of G. pulex collected. An invertebrate indication chart can be used to identify this species.
• Return the organisms gently to the exact location where they were taken from to avoid them being relocated.
• Repeat this method at each of the 15 intervals. After each interval, measure 1 meter away from your current location with the ruler to reach the next location in the centre of the riffle.

• The rocks in the stream have moss on them making them slippery, so every individual should be cautious as they walk through the stream.
• Waterproof shoes such as wellies should be used to walk across the river to avoid harm to feet and legs.
• The G. pulex should be carefully brought back to the water after observation in each location where they were found.
• Take in consideration the species well - being.
• When washing the rocks, rubber gloves should be used to avoid harming your hands with any potential hazards in the river.
• After the investigation, all litter should be brought back with you to avoid pollution around the river.

According to the raw data collected, it can often be observed that the abundance of G. pulex is generally higher as the velocity is lower. In sites 1 and 10, there is a higher amount of Swimming Mayfly Lymph visible than G. pulex. Sites 1 and 10 have opposite velocity numbers therefore demonstrating that velocity may not have an impact on the abundance of Swimming Mayfly Lymph. At site 5, my classmate was doing her investigation with the use of a transect across the river from one bank to the other. Therefore, she had collected many species before me. As I collected G. pulex at this site, there were not many visible in the plastic tray. This can be seen by the small amount of 5 collected.

Along the riffle, there was a variety of different depths due to the rock distribution across the stream. Therefore, the measurements for depth were difficult to conduct as rocks could easily get in the way. As I was collecting the G. pulex, I noticed that many of them were mating or waiting to mate. The females “carry their eggs inside their bodies in a brood pouch” (“Freshwater Shrimp”). Equally, I observed a high abundance of Swimming Mayfly Lymph during my data collection, they’re seemed to be higher numbers of Swimming Mayfly Lymph present.

The velocity of water at each of the 15 sites.

This is the sample calculation that was used to calculate velocity -

\(V= 0.0277+\frac{3.2805}{T}\)

As this investigation is on the topic of ecology, there are a few uncertainties in the collection of data. While measuring the velocity, the time taken for the impeller to reach the end of the hydro prop was timed with a stopwatch on a phone. The stopwatch’s level of accuracy isn’t high since it only displays half of the smallest unit. Likewise, while measuring the depth of the river at various sites, the ruler does not display the smallest unit being 0.5 mm. Thus, this creates a lack of certainty as data is collected. The water movement of the river also made it difficult to note down the correct depth. The uncertainties have no impact on the data collection as there was a large amount of data collected. Equally, the unrelatedness between the quantitative variables is so significant that uncertainties would not have affected the results of this investigation.

I will be using Spearman’s rank to determine the relationship between river velocity and G. Pulex abundance since they are both continuous variables. I have collected 15 pairs of data which is a small sample, yet it allows me to analyse their correlation statistically.

There is no statistically significant correlation between velocity and the abundance of freshwater shrimp.

There is a statistically significant correlation between velocity and the abundance of freshwater shrimp.

Further calculations using values from the table -

\(1-\frac{(6\Sigma D^2)}{n^3-n}\)

\(1- \frac{(6× 714)}{15^3-15}\)

\(1 - {4284 \over 3360} = - 0.275\)   is the Spearman's rank coefficient

Calculated Rs (-0.275) is less than the critical value (0.521) for 15 pairs of data. Therefore, accept null hypothesis at 5% significance level. There is not a significant correlation at the 5% significance level.

I decided to use a scatter graph at is the best model to display the relationship between two quantitative variables. This will allow me to explore the effect of velocity upon the abundance of Gammarus Pulex in riffles. The results from the statistical test as well as the visual representation on the graph of the correlation between the velocity of water and the abundance of G. pulex indicate that the relationship between the two variables in unsignificant. The abundance of G. pulex is linear across the velocities measured. However, between the following range of velocities, 0.2 and 0.4 (ms^-1) there was a fluctuation in the data. The abundance of G. pulex was increased between this range. The large abundance of G. pulex as velocity was lower may be due to the slower water movement. Consequently, as the water current is lower, G. pulex can live in more stable conditions and under rocks. For this range of data, our hypothesis could be approved yet this is not the case for the rest of the data. In reference to site 2, the velocity was low (0.094 ms^-1) which means that the river was flowing at a slow speed. A number of 6 Gammarus pulex were counted at this site meaning that there is no relationship between a lower velocity and a higher abundance of G. pulex which disproves our hypothesis. In reference to site 6, where the highest number of G. pulex was collected, the velocity was high (0.330 ms^-1), this denies once again the correlation between low velocity and high G. pulex abundance.

In conclusion, the response to the following research question “What is the effect of velocity upon the abundance of Gammarus pulex in riffles?” is that the effect is varied. Throughout the investigation, it can be concluded that there is no correlation between water velocity and the abundance of Gammarus pulex as seen by the statistical test indicating that there is no significant correlation at the 5% significant level and by the scatter graph. Through high and low velocities, the effect varies. In areas with high velocities, the number of G. pulex was large in some cases and very low in others, this is reciprocal for areas with low velocities. Hence, the hypothesis created cannot be fully approved as it does not support the results of this investigation. It is therefore weakly supported since at some sites this hypothesis was approved such as site 15 where velocity was low and the G. pulex abundance was high. The results of this experiment are reliable, unbiased and so it is therefore replicable. As there was no previous investigation found on the same line of research, a precise comparison is impossible to make.

• The data collected is numerical and qualitative offering a broad range.
• There were enough samples to investigate a correlation between the two factors and complete a statistical analysis.
• The methodology allows this investigation to be replicated and compared.
• The investigation was carried out considering safety and ethics.

To extend the investigation of this internal assessment, it would be interesting to assess whether the results collected have trends in different rivers across Switzerland. Equally, determining whether seasons have an impact on the abundance of Gammarus pulex due to changes in temperature, daylight hours and precipitation. If we were to conduct this investigation in pools as well as riffles, we could have a broader range of data which could possibly answer our research question in further detail and a correlation could be found. In addition, many environmental factors could be examined such as water temperature, dissolved oxygen levels, and nutrient concentrations to determine whether they influence G.pulex abundance. By investigating further, broader conclusions could be made.

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