Fish community and food web responses to a whole-lake removal of coarse woody habitat

Humans tend to simplify the littoral zones of lakes during the development process by removing and decreasing input rates of coarse woody habitat (CWH). I conducted a whole-lake removal of CWH on Little Rock Lake, Wisconsin to simulate one effect of residential lakeshore development in order to address how CWH loss influences: (1) fish growth rates and production; (2) the intensity of fish predator-prey interactions; (3) the location and strength of fish predator-prey interactions in lakes varying in complexity of littoral structural refuges; (4) fish methyl mercury (MeHg) concentrations; and (5) largemouth bass (Micropterus salmoides) population dynamics in the absence of fishing.; Fish growth rates decrease in the absence of CWH because bass and yellow perch (Perca flavescens) tend to exhaust the most energetically favorable prey and then become less selective by consuming less favorable prey. Terrestrial subsidies become increasingly important during this process, suggesting that CWH influences lake productivity. Without a CWH refuge and fishing, bass can exert such extreme top-down predation pressures that some prey fish populations may be extirpated. High amounts of CWH concentrate predator-prey interactions on edge habitats. With low amounts of CWH, predator-prey interactions are more intense increasing the probability of species-specific extirpations. CWH retains sediments and promotes the burial of mercury. Physical removal of CWH can exacerbate and prolong the negative effects of McHg accumulation in aquatic food webs. Individual fitness measures (growth, survivorship) respond quickly to fishery closure, whereas population fitness measures (abundance, recruitment) respond over longer, generational timescales. A tradeoff exists between fishing and CWH such that coexistence of predator and prey populations occur under two scenarios: (1) fishing of top predators and little CWH; and (2) no fishing and abundant CWH. In either scenario, the strong top-down effects of predators are dampened by fishing through decreases in abundance of apex predators or by CWH through decreases in piscivore foraging success. Collectively, CWH plays a diverse and critical array of indirect and direct roles in aquatic ecosystems by increasing system productivity, promoting species diversity, allowing coexistence of predator and prey populations, and stimulating the burial of toxic heavy metals.