The possibility of predator avoidance by Lake Michigan zooplankton

Abstract

Low densities of Diaptomus ashlandi, Diacyclops thomasi, and Daphnia galeata mendotae were measured at depths where Mysis relicta formed nighttime aggregations . Calculations suggest that mysid predation can not account for the rarity of prey animals at these depths, which further suggests that the prey avoided the mysids . Unlike D. galeata mendotae, Daphnia pulicaria was common in mysid aggregations . The somewhat larger size of D. pulicaria may reduce its vulnerability to mysid predation, and consequently may explain the vertical distribution differences between the two congeners . Vertical distributions of Limnocalanus macrurus and copepod nauplii showed no obvious relationships to the mysid distributions . These were the only two taxa with distributions that were correlated with chlorophyll a concentrations . All crustacean taxa were rare in the epilimnion at night when sonar recorded a dense fish school .

Recent increases in the large glacial-relict calanoid Limnocalanus macrurus in Lake Michigan

“…Spatial overlap of L. macrurus with the DCL has been seen in Lake Michigan, where midnight population maxima of L. macrurus corresponded closely with a marked DCL in August 1999, although the majority of individuals were well below the DCL at other times of day (Barbiero et al, 2005). Schulze and Brooks (1987) also found positive correlations between L. macrurus and deep chlorophyll concentrations in Lake Michigan during July, though apparently not in August. Interestingly, the only other crustaceans to show a positive correlation with deep chlorophyll in that study were copepod nauplii, which suggests the potential continued importance of carnivory throughout the stratified period.…”

Temperature gradients, not food resource gradients, affect growth rate of migrating Daphnia mendotae in Lake Michigan

“…Although we focused our study on a single zooplankton species, migration has been observed for Lake Michigan populations of Daphnia pulicaria, Daphnia retrocurva, Bosmina longirostris, Diacyclops thomasi, and Leptodiaptomus spp. (Wells, 1960;Dorazio et al, 1987;Schulze and Brooks, 1987;Barbiero et al, 2000). Our results and similar migration-related temperature effects on the growth of cyclopoid copepods (Makino et al, 2003) and calanoid copepods (Williamson et al, 1996) found in other oligotrophic lakes suggest that vertical migration may be generally important to the growth of migratory zooplankton in Lake Michigan.…”

“…Doing this may require depth-stratified sampling of zooplankton, as described in a previous study (Kuns and Sprules, 2000), that is carried out several times over 24-hour periods. Further, variable environmental factors such as predator densities can affect the magnitude of vertical migration in the Great Lakes (Schulze and Brooks, 1987;Pangle and Peacor, 2006;Pangle et al, 2007); thus, sampling at different times of year may be necessary to account for this variation. While such a sampling approach is more laborious than those often used for zooplankton, the potentially-large improvements to the accuracy of zooplankton production estimates are likely worthwhile, particularly given the importance of zooplankton to the Great Lakes ecosystem (Scavia et al, 1986;Miller et al, 1990;Makarewicz et al, 1998).…”

“…Many species of zooplankton in the Laurentian Great Lakes, including cladocerans, calanoid copepods and cyclopoid copepods (Wells, 1960;McNaught and Hasler, 1966;Carter, 1969;Dorazio et al, 1987;Schulze and Brooks, 1987;Barbiero et al, 2000;Pangle et al, 2007), undergo diel vertical migration, a behavior that is general to zooplankton in freshwater and marine systems (DeMeester et al, 1998). Although the ultimate causes of migration by zooplankton may vary among lakes (Leech et al, 2005), migration may occur in the Great Lakes as means for zooplankton to avoid predation risk (Schulze and Brooks, 1987;Pangle et al, 2007). A consequence of migration is that the environment zooplankton experience can greatly change over the course of a day which can in turn affect zooplankton production.…”

Spatial overlap of a predatory copepod, Acanthocyclops robustus, and its prey in a shallow eutrophic lake

“…) . Similarly, Melville & Maly (1981) found that vulnerable prey tended to show a lower degree of overlap in vertical distribution than less vulnerable prey with the predator Chaoborus americanus, as did Schulze & Brooks (1987) with the predator Mysis relicta . In addition, the latter authors concluded that the low degree of overlap between vulnerable prey and the predator was not directly due to cropping effects by the latter .…”