DOI: 10.5061/dryad.pc866t1pz
title: Heatwave induced invertebrate predation reshapes the plankton community

description: Climate change stressors including warming and heatwaves can alter
 zooplankton composition and dominance patterns in shallow lakes, which can
 disrupt ecosystem function and curtail ecosystem services. To understand
 such changes, we performed a mesocosm experiment with controls reflecting
 the present temperature conditions and a treatment reflecting a future
 climate change scenario, including heatwaves of 0-8°C. In the future
 climate scenario, the predatory invertebrate, Mesostoma exerted a strong
 top-down control particularly on Daphnia, resulting in a switch in the
 herbivore dominance to Ceriodaphnia. Cyclopoid copepods were the least
 affected taxa but showed tendencies to sustain longer into the winter at
 elevated temperatures. A complementary predation experiment revealed that
 Mesostoma feed at a higher rate on Daphnia than on Ceriodaphnia and
 cyclopoid copepods. In addition to the food-chain alterations, the algal
 biomass and cyanobacteria increased with warming which has considerable
 implications for management of shallow lakes.
description: 12 outdoor mesocosm (0.7 m diameter and 1 m height) were set up
 at Lund University in April 2020 and two treatments were applied (n = 6)
 from 14th of July to 13th July 2021. Each mesocosm contained 400 L water
 and 500g of homogenized sediments from lake Ringsjön, southern Sweden
 (55°51′43.2″N, 13°32′24″E). The controls were mirroring present
 environmental conditions (‘Present’) and the heated treatments, the future
 climate warming scenarios (‘Future’), which included heatwaves from 0°C to
 8℃ above ambient temperatures (average 4℃) (IPCC, 2013). Temperature in
 each mesocosm was recorded every 10 sec using loggers. 
 We sampled zooplankton populations every two weeks. Water was
 collected using a Plexiglas™ tube (length = 1 m, diameter = 70 mm, volume
 = 3 L) from three locations across the diameter of each mesocosm (2 closer
 to the sides and 1 in the middle). All 9 L of water were pooled, mixed in
 a bucket, and 5 L of that water was filtered using nylon mesh of 55 μm
 pore size. The organisms collected on the mesh filter were rinsed into a
 100 ml transparent bottle, preserved with Lugol's acid solution, and
 stored at 4°C for later enumeration. Copepods were identified and counted
 to order level, whereas, cladocerans and other larger invertebrates were
 identified and counted to genus level at 32× magnification using a
 stereomicroscope (Olympus SZ‐40). We also took water samples directly from
 the surface of each mesocosm and then immediately analyzed them for total
 chlorophyll a (Chl a) on a fluorometer (AlgaeLabAnalyser, bbe moldaenke,
 Schwentinental, Germany). The total concentration of major phytoplankton
 groups, namely, green algae, cyanobacteria, cryptophytes, and diatoms were
 also measured. <em>Mesostoma</em> predation
 rate on <em>Daphnia magna</em>, <em>Ceriodaphnia
 spp.</em>, and cyclopoid copepods were determine following the
 procedure suggested by Lehman and Sandgren (1985). For each prey species,
 500 ml tap water [temperature: 19 to 21°C] and 10 individuals of prey were
 placed into six glass jars. The number of <em>Mesostoma
 </em>individuals (3 to 4 mm) then added increased sequentially from
 1 to 6 in each jar. The experiment lasted either for 24 hrs. or until
 there were only 1-2 individuals of prey remaining in each jar. After that,
 Lugol's acid solution was added to each jar to stop the experiment
 and the remaining prey individuals in each jar were counted.
description: Please take a look at the "README" file before checking
 the datasets.