Changes in zooplankton and the phenology of the spiny water flea, Bythotrephes, following its invasion of Harp Lake, Ontario, Canada

Abstract

The crustacean zooplankton community of Harp Lake, Ontario, Canada, has changed appreciably since the invasion by the spiny water flea, Bythotrephes. Crustacean species richness has declined, large-bodied Cladocera have replaced small-bodied ones, and there has been a downward trend in the total abundance of zooplankton because copepod abundance has remained stable while Cladoceran abundance has declined. Although the zooplankton community has now been stable for 4 years (1995–1998), the biology of the invader has changed dramatically. In particular, there have been 10-fold differences in the mean annual abundance of Bythotrephes in this 5-year period and substantial changes in the timing of population maxima. We attribute these changes to two factors: (i) transition from a summer to a fall switch from parthenogenesis to gametogenesis and (ii) interannual differences in the thickness of a warm, dark stratum in the lake. We hypothesize that this stratum provides a refuge for Bythotrephes from predation by lake herring, Coregonus artedii.

Temperature, recreational fishing and diapause egg connections: dispersal of spiny water fleas (Bythotrephes longimanus)

“…In both lakes during the daytime, workers postulated that egg-carrying adult Bythotrephes sought shelter in epilimnetic strata between the bottom of the photic zone and the top of the hypolimnion. In Harp Lake, Bythotrephes caused shifts in zooplankton size and species composition, as they favored large-bodied cladocerans while reducing small cladoceran abundance and overall species richness (Yan et al 2001(Yan et al , 2002. These findings were similar to mesocosm investigations from a Swedish lake, within Bythotrephes' natural habitat (Wahlstrom and Westman 1999).…”

“…We emphasize that the interaction between fish and diapausing eggs is a potentially crucial component in geographic spread. Bythotrephes utilize at least three size-dependent protective traits (two morphological, one behavioral): (1) an extremely large and long tail spine that protects against YOY fish (Barnhisel 1991a, b;Barnhisel and Harvey 1995;Straile and Haelbich 2000), (2) an unusually large and thick-shelled diapausing egg that can pass through fish guts in viable condition (Jarnagin et al 2000(Jarnagin et al , 2004, and (3) vertical migration of embryo-carrying adults to a refuge layer down below the photic zone, but above the thermocline during the day (Yan et al 2001;Manca and DeMott 2009).…”

“…Moreover, the eggs are large, heavy, and settle rapidly (Jarnagin et al 2000(Jarnagin et al , 2004 unless consumed by fish. Both Yan et al (2001) and Jarnagin et al (2004) suggested that Bythotrephes abundance in Harp Lake, Ontario, Canada, and Lake Michigamme, Michigan, appeared associated with the thickness of a low-light, moderate temperature (12-18°C) refuge from planktivorous fish. Branstrator et al (2006) stressed that invasion success was favored by the presence of a deep-water, low-light but well-oxygenated refuge in many of the Minnesota lakes.…”

Linking mean body size of pelagic Cladocera to environmental variables in Precambrian Shield lakes: A paleolimnological approach

“…Cladocera face predation from two main sources: macroinvertebrates and planktivorous fish. Invertebrate predators are limited by gape size, and when they contribute the majority of predation pressure in a lake, it is common to observe larger cladoceran taxa (Nilssen & Sandoy 1990;Yan et al 2001). Alternatively, fish predators will actively seek out the largest individuals when visibility is not limited.…”

Role of diapause in dispersal and invasion success by aquatic invertebrates

“…In 1994 and 1995, females with resting eggs were noted from July, and by the end of August 50 to 80% of females carried resting eggs (Yan & Pawson 1998;Yan et al 1992; N.D.Yan, T.W.Pawson, personal communication). Later, in 1998, the Harp Lake population returned to a more typical parthenogenetic mode of reproduction during summer: first females with resting eggs were recorded in late August (Yan et al 2001). However, creation of a large pool of resting eggs in lake sediments during first years after invasion facilitated successful establishment of Bythotrephes population despite high fish predation (Coulas et al 1998) and resulted in remarkable changes in the structure of zooplankton community of this lake (Yan & Pawson 1997;Yan et al 2001;Yan et al 2002).…”