Big fish eat smaller fish, smaller fish eat zooplankton, zooplankton eat phytoplankton, and phytoplankton produce their own food. If smaller fish eat all of the zooplankton, what’s to stop the phytoplankton from multiplying out of control? If the big fish eat all of the smaller fish, will the big fish still be able to sustain their population? Whenever an organism is added to or taken away from an ecosystem, it acts like a pebble thrown into a pond. There’s the initial splash, then there are ripples that radiate outward affecting everything in their path.
In 2008, a “pebble” was thrown into Lake Minnewaska. This pebble was a type of minnow called a Golden Shiner. Exactly how the Golden Shiners entered the lake is not certain, however they are a common bait fish so it is possible that they were introduced to Lake Minnewaska by someone who was hoping to hook the catch of the day! If that was the case, the odds would have been against that fisherman. For several decades prior to the occurrence of the shiners, there were no fish reported in the lake. Lake Minnewaska has been very acidic in the past, making it an unhospitable environment for most fish to live in. Recently, the pH in the lake has begun to rise to a level closer to neutral, making the lake more inhabitable for fish.
The introduction of a predator to the food web in Lake Minnewaska caused a trophic cascade. A trophic cascade is when a top predator is added to or removed from a food chain. The effects of the addition or loss of this predator are experienced all the way down the food chain. The shiners’ predation on the zooplankton drastically decreased their population. The ripple continued spreading outward because the loss of the zooplankton meant the loss of a major plant consumer. The phytoplankton could then grow and multiply without restraint. The result was an algal bloom in 2011 that turned the lake green and decreased the visibility to less than three feet. As a result, the Minnewaska Swimming Beach was closed for a month that summer.
The algal bloom showed us that Lake Minnewaska’s ecosystem had been severely altered by the shiner introduction. Another ‘pebble’ was tossed in 2012; the “big fish on the block” made its appearance. Largemouth bass entered the lake and filled a role at the top of the food chain. Bass are avid predators, and they began preying on the shiners. Electrofishing, the use of a weak electrical current in the water to temporarily stun fish, has been used in the lake every year since the shiners appeared in order to monitor the fish populations. In 2013 there was a large population of 10,000 – 15,000 golden shiners and 700 – 800 largemouth bass in Lake Minnewaska. In 2014 no shiners were observed during electrofishing and the number of bass had increased by 60%. Did the bass population increase because they had an ample food source in the shiners? What will happen to the bass population now that they have lost this food source? We can only wait and see.
Post by Laura Davis, Park Educator, Student Conservation Association/AmeriCorps Intern, Minnewaska State Park Preserve.
Sources:
Dr. Richardson SRBP Lecture at Suny New Paltz February 2015.
“Baitfish Regulations.” General Regulations. DEC, http://www.dec.ny.gov/outdoor/31416.html. 24 June 2015.
Richardson, David C. “Why Is Minnewaska Lake Turning Green: Changes in Acidity and Fish in the Sky Lakes.” Shawangunk Watch 18 (Summer 2013): 1-3. Print.
Lauren Jorgensen, Kristen Husson, and Karen Terbush. Minnewaska State Park Preserve Lake Minnewaska Water Quality Report. Rep. Albany: NYOPRHP, 2012. Print.
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