Effects of small-sized crucian carp (Carassius carassius) on the growth of submerged macrophytes: Implications for shallow lake restoration

Abstract

Reestablishment of submerged macrophytes is considered important when restoring shallow eutrophic lakes. To improve water clarity and consequently the growth conditions of macrophytes, removal of plankti-benthivorous fish has been used. In subtropical shallow lakes, however, rapid recruitment of small fish, especially benthivores during restoration, may hamper early reestablishment of submerged macrophytes. Crucian carp (Carassius carassius) and Vallisneria natans are common species dominated in subtropical shallow lakes. To investigate the effect of small benthivorous fish on the growth of Vallisneria natans, a 28-day outdoor controlled experiment was undertaken in 12 mesocosms with three densities of Carassius carassius-low (10 g m-2), high (40 g m-2) and no fish (all in four replicates). The results showed that the fish significantly increased chlorophyll-a concentrations and periphyton biomass in both fish treatments, most significantly at high density for Chl a. This concurs with an increase in nutrient concentrations, likely mediated by fish sediment disturbance and excretion, and a reduction of zooplankton biomass (less algal grazing). Increased concentrations of inorganic suspended solids with increasing fish density further enhanced turbidity, causing shading of the macrophytes. Accordingly, the relative growth rate, ramet number and root/leaf ratio of V. natans decreased significantly at low and high fish density compared with the controls, but the effects did not depend on fish density. However, mean leaf length rose with increasing fish density, likely to allow the plants to obtain more light. Overall, our results show that not only large-bodied carp, as demonstrated frequently, but also small-sized crucian carp posed a constraint on submerged macrophyte reestablishment, and we conclude that crucian carp may hamper restoration efforts in subtropical shallow lakes. Restoration by biomanipulation should therefore target also small-sized crucian carp.

Crucian Carp (Carassius carassius) Strongly Affect C/N/P Stoichiometry of Suspended Particulate Matter in Shallow Warm Water Eutrophic Lakes

“…The major decrease in zooplankton biomass indicates that besides predating on benthic organisms ( Figure 5), crucian carp could also reduce zooplankton, potentially affecting their control of pelagic phytoplankton. Crucian carp is an omnivore, and previous gut content analyses have revealed that it may prey directly upon zooplankton, creating a community shift in dominance from large-sized cladocerans and copepods to small-sized rotifers [12]. This was exactly the pattern observed in our study (Figure 4).…”

“…Despite the reduced top-down control of phytoplankton, water Chl-a concentrations did not increase correspondingly (Figure 3a) in these eutrophic mesocosms, in contrast to the results in similar mesocosm studies in which a clear increase in phytoplankton growth was found after introduction of crucian carp [12,15,22]. We attributed this discrepancy to the different trophic states of these mesocosm experiments.…”

“…We attributed this discrepancy to the different trophic states of these mesocosm experiments. The Chl-a concentrations of Gu et al (2016) and He et al (2017) were consistently <25 µg L −1 in the mesocosms without fish [12,15], which is much lower than the level of our mesocosms (around 100 µg L −1 in the fish-absent mesocosms). Thus, the high standing biomass of phytoplankton, and increased levels of inorganic particles in our mesocosms with fish (Figure 6b), may collectively have reduced light penetration sufficiently to maintain Chl-a concentrations in the crucian carp-holding mesocosms at the same level as in those without fish.…”

“…The process often causes resuspension of sediments, resulting in an increase in turbidity, nutrient concentrations and algal biomass in the water column [8][9][10]. Furthermore, benthivorous fish also reduce zooplankton via direct grazing and/or indirect effects on suspended solids [11,12]. Therefore, benthivores have more complex influence on water physicochemical and biotic conditions than planktivorous fish [13,14].…”

The host mussel Sinanodonta woodiana alleviates negative effects of a small omnivorous fish (Acheilognathus macropterus) on water quality: A mesocosm experiment

“…Because they feed on at least 2 trophic levels, omnivorous fishes may affect lake ecosystems through various pathways. The presence of omnivorous fishes can increase nutrient concentrations, turbidity (total suspended solids [TSS], especially inorganic suspended solids [ISS]), and the biomass of both phytoplankton (Drenner et al 1998, Gu et al 2016, Zhang et al 2017, He et al 2019 and periphyton (Gu et al 2016), thereby suppressing the growth of submerged macrophytes (Miller andCrowl 2006, Qiu et al 2019). In a study including both the omnibenthivorous Common Carp (Cyprinus carpio Linnaeus, 1758) and the omni-planktivorous filter-feeding Silver Carp (Hypophthalmichthys molitrix Valenciennes, 1844), Zhang et al (2016) found that Common Carp substantially increased the biomass of pelagic algae but decreased the biomass of benthic algae (periphyton), whereas Silver Carp did not influence the pelagic or benthic algal biomass.…”