Environment
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Bioindication Testing of Stream Environment Suitability for Young Freshwater Pearl Mussels Using In Situ Exposure Methods
Chapters
Summary September 5th, 2018
In situ bioindications enable determination of the suitability of an environment for endangered mussel species. We describe two methods based on the juvenile exposure of freshwater pearl mussels in cages to oligotrophic river habitats. Both methods are implemented in variants for open water and hyporheic water environments.
Transcript
This method can help answer key questions in the river ecosystem preservation field such as indications of stages favorable for young mussels that augment as well, as prediction of this which I propagate. The main advantage of this technique is that we can test juvenile growth and survival in hyporheic conditions which represent the natural juvenile environment. Demonstrating the procedures will be my colleagues Simona Nemcikova, Jan Svanyga, and Vojtech Barak.
When assembling the cages, always insert one plastic cover first, then one sheet of the plastic sieve and finally the main body on top. Put the cage into the plastic dish containing river water at the FWPM storage temperature. Ensure that the chambers are half full.
Next, load the FWPMs into a petri dish. Using a squirt bottle and strainer, sift through the juveniles to clear the detritus. Then, pipet one individual from the dish and transfer it to a dish under the microscope to check it's fitness.
Select only FWPM of good fitness. Take two photographs of each laid length wise at about 80 times magnification with the goal of measuring maximum shell length. Proceed to load all the appropriate chambers of the cage with the selected and documented FWPM.
Then, put the plastic sieve on the cage followed by the plastic cover and secure all the parts with the nuts. To set up a mesh cage for a hyporheic zone installation, pass one of the hose ends through one of the chambers and fix it in this position. Then, take the anti-clogging mesh and bind it on the bottom end of the hose.
Temporarily store the loaded cages in river water in the thermal box. For a sandy cage preparation, collect river sand and sift it through a two millimeter sieve. Then sift it through a one millimeter sieve and keep the particles between one and two millimeters.
Place an empty cage in the plastic box and then load the bottom third of the cage with sand. Next, add river water until the water is 10 millimeters above the sand level. Load the sandy cage into a 25 liter water tank and let it equilibrate to the water temperature for 12 hours before loading them with FWPM.
Transport the FWPM juveniles to the site in a field thermal box. At the field site, first immerse the thermal box in the river and remove the cage from the field thermal box. Now, start planning the cage positions.
Choose conditions typical for FWPMs such as at the edge of the main water flow. Do not place the cage in direct water flow, nor in standing water. To install mesh cages in open water use a pair of the steel spikes.
Fix the cage to the river bottom on it's side and level with the river bottom. Angle 45 degrees to the river flow downstream facing the center of the river. The lower horizontal edge should be 10 to 15 centimeters above the river bottom.
To install a sandy cage in open water fasten it to a flat stone using a net and place the cage on the river bottom. Angle the larger end against the flow at a 45 degree angle. To install either cage type in the hyporheic zone dig them into the river bottom perpendicularly to the flow of water so that the upper horizontal edge of the cage is parallel to the river bottom surface and the chambers the testing depth in the river bottom.
For mesh cages in the hyporheic zone pull out the rubber hose from under the bottom surface for water sampling during the experiment. After the planned exposure period, pull the cages out of the water and clear them of fine sediment, as well as of drifted material. Then, load them into a field thermal box filled with river water.
Once back at the lab, evaluate the FWPM by photo documenting them as before. The described methods were used to investigate the environmental suitability of FWPMs in the upper Vltava River Basin in the Czech Republic from 2014-2015. A longitudinal river profile was represented by mainstream localities at sites A through E.Tributaries of different pollution stages were tested at sites R and V.These localities were tested using sandy cages and mesh cages in free flowing water.
In addition, a gravel hyporheic zone was tested by within bed sandy cages in localities B, C, and D.The localities could be clearly distinguished based on the growth rate in the open water mesh cages despite the high within cage variability even in different growth favorable periods. In the more growth favorable exposure in 2015, the growth rate increased downstream using the mesh cages. Importantly, the survival rate was equivalently high in both seasons.
By contrast, the growth rate of open water sandy cages in 2014 varied by location. The location with the greatest growth, C, was also the location of greatest growth in 2015. While growth overall was about the same in both years, mortality was higher in 2014.
The within bed mesh cages showed a significant effect of the substrate composition on mortality. Oxygen saturated stony bottoms had a survival rate close to 100%and poorly oxygenated sand had high mortality. After watching this video, you should have a good understanding of how to install experimental mussel juveniles in the riverside to test local conditions for day
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