OSCILLATING SALINITY SYSTEM (2011):

TWO TIERS, GRAVITY POWERED - The top tier holds a freshwater reservoir, the bottom tier holds a mixing reservoir.  Both reservoirs are  immersed in a bath of flowing seawater to ensure that all water being mixed is at the same temperature.… — TWO TIERS, GRAVITY POWERED - The top tier holds a freshwater reservoir, the bottom tier holds a mixing reservoir. Both reservoirs are immersed in a bath of flowing seawater to ensure that all water being mixed is at the same temperature.

Technology: This two-tiered tank system uses digitally controlled actuated ball valves to drain and fill tanks according to natural tidal cycle intervals. Salinity could be readily diluted and concentrated like natural signals found in tidal estuaries. Both tiers of the system are flow-through, requiring only gravity and head pressure to move water, ambient water baths for temperature control, and stand pipes to control volume. Temperature controlled seawater is precisely mixed to create custom and consistent salinity profiles associated with daily high and low tide intervals programmed in seven day increments. The system was designed such that graduate and undergraduate students were able to operate and maintain it, and has been collecting publishable data since 2011.

Science: Studying animal behavior and physiology in tidal estuaries can be difficult to recreate in lab settings. Creating estuarine conditions synchronized to local natural conditions with local seawater in a lab setting maximizes similarity to in situ environmental conditions and minimizes animal stress during acclimatization. In this particular instance, salinity and tidal regimes were manipulated to simulate and estimate the physiological stresses invasive species might experience or tolerate living at habitat extremes. They also allowed for direct comparison of physiological differences between green crab (Carcinus maenas) color morphs under identical conditions.

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A better picture of the water baths.

Moving Water

Actuated ball valves on programmable timers coordinated filling times. Gravity was all that was used to move and drain water. Standpipes determined volumes, and barbed fittings of different diameters controlled flow rates.

Freshwater Control

The freshwater reservoir was fitted with a standpipe to establish a fixed volume. A programmable timer filled the freshwater reservoir, which sat in a water bath, chilling the freshwater to that of the seawater.

Mixing Reservoir

The mixing reservoir was fitted with two valves with separate standpipes. One established a level for full salinity conditions, and the other, at a greater height increased container volume to accommodate the addition of a volume of freshwater to alter the salinity. This is where the specimens were placed during trials.

Actuated Ball Valves

Digital Timers

Located at the top right of the photo, digital timers provided open/close signals to control the ball valves.

Staying Put

False floors were used to suspend the reservoirs above all of the standpipe and the drain plumbing. To protect the plumbing and and to prevent the reservoirs from floating, ratchet straps were used to secure everything in place.