LIFE HISTORY AND MULTIPLE ANTIPREDATOR DEFENSES OF AN INVERTEBRATE PELAGIC PREDATOR,BYTHOTREPHES LONGIMANUS

Abstract

Multiple antipredator defense strategies and their interactions were examined in a field study of the predatory planktonic waterflea Bythotrephes longimanus in Lake Constance, at the northern fringe of the European Alps. Because of its large body size and conspicuousness, Bythotrephes is a preferred prey of freshwater fish. We observed seasonal changes in life history and morphology and diel vertical migration, all best understood as a response to fish predation. Bythotrephes population dynamics were characterized by pronounced population growth in late spring, maximum abundances in June, and a steady decline toward the end of the season. In late spring, high population growth rates were achieved by means of large clutches, low investment in individual offspring, and small size at first reproduction. While the population was still increasing, a marked life history shift occurred. The reproductive strategy of females switched toward high per‐offspring allocation at the expense of clutch size. This change in reproductive behavior resulted in an increase in the size of neonates and was accompanied by an increase in the size at first reproduction. Such a life history shift is typically observed in the presence of gape‐limited predators, which points to the importance of juvenile fish as the principal vertebrate planktivores in Lake Constance. The length of Bythotrephes defensive spina increased throughout the season, reflecting increasing predation pressure, probably owing to seasonally increasing mouth gape size of juvenile fish. In contrast to the predictions of the predator‐avoidance theory, the migration amplitude of large and conspicuous Bythotrephes was small as compared to other zooplankton species. We argue that theory and data can be reconciled if the migration behavior of Bythotrephes is considered as a result of an interaction of predator defenses in the presence of predominantly juvenile, gape‐limited fish. As Bythotrephes achieved protection because of its life history and spina, the costs of large diel migrations may outweigh the benefits.

Dynamics of the invasive spiny water flea, Bythotrephes longimanus, in Lake Simcoe, Ontario, Canada

“…Years of high Bythotrephes abundance were predicted by low black crappie abundance, the warmest epilimnetic temperatures, and high cladoceran abundance; conversely, the lowest Bythotrephes abundance was predicted by the highest black crappie abundance, lowest epilimnetic temperatures, and, except for 2006, the lowest cladoceran abundances. Top-down control of Bythotrephes abundance by planktivorous fish has been implicated in lakes in both its native (Straile andHalbich 2000, Palmer et al 2001) and invaded (Coulas et al 1998, Pothoven and Vanderploeg 2004, Pothoven et al 2007, Young and Yan 2008, Young et al 2009) ranges. The incorporation of Bythotrephes as a main prey item into the diets of large-sized fishes in Lake Simcoe is unsurprising given that Bythotrephes is a large, conspicuous member of the plankton community, with a prominent compound eye, bright pigmentation, and large coloured brood pouch (Barnhisel andHarvey 1995, Rivier 1998).…”

“…For example, variations in its morphological features and body size may relate to defense against planktivorous fishes (Straile and Halbich 2000) or energetic tradeoffs related to balancing growth and reproduction (Enz et al 2001, Branstrator 2005. The population size of Bythotrephes may be limited by bottom-up effects such as the availability of herbivorous crustaceans (Dumitru et al 2001, Strecker andArnott 2008), particularly in the spring months , as well as top-down control by fish (Coulas et al 1998, Jarnagin et al 2004, Young and Yan 2008, Young et al 2009.…”

“…The population size of Bythotrephes may be limited by bottom-up effects such as the availability of herbivorous crustaceans (Dumitru et al 2001, Strecker andArnott 2008), particularly in the spring months , as well as top-down control by fish (Coulas et al 1998, Jarnagin et al 2004, Young and Yan 2008, Young et al 2009. Temperature influences population growth rates by affecting hatching rates (Yurista 1992, Brown andBranstrator 2011), generation time (Lehman and Branstrator 1995), mode of reproduction (Straile andHalbich 2000, Manca et al 2007), or prey consumption (Yurista et al 2010). Because Bythotrephes is a visual predator (Muirhead and Sprules 2003), light availability impacts its foraging abilities (Pangle and Peacor 2009).…”

Role of diapause in dispersal and invasion success by aquatic invertebrates

“…As most freshwater Cladocera, in native habitats Bythotrephes switches from parthenogenetic to gamogenetic reproduction at the end of a season and even then the densities of males and females with resting eggs are relatively low (Straile & Hälbich 2000). Number of resting eggs per female Bythotrephes in the eastern Gulf of Finland varies usually between 2 and 3 with the maximum of 4 (Krylov et al 2004).…”

Different effects of planktonic invertebrate predators and fish on the plankton community in experimental mesocosms

“…This concept suggests that the promotion of efficient planktonic herbivores through decreased biomass of planktivores by piscivores can reduce the biomass of phytoplankton. This general pattern can be modified by altered life histories or other interactions among particular species such as defence mechanisms in prey (Jeffries, 1988;Kolar and Wahl, 1998;Straile and Halbich, 2000). These findings are widely used during food web manipulation with the ultimate goal to improve water quality management (i.e., biomanipulation techniques) (Berg et al, 1997;Beklioglu, 1999;Ha et al, 2013).…”