Loberg Lake, Alaska was colonized by sea-run Gasterosteus aculeatus between 1983 and 1988, after the original stickleback population was exterminated. Annual samples from 1990 to 2001 reveal substantial evolution of lateral plate (armor) phenotypes. The 1990 sample was nearly monomorphic for the complete plate morph, which is monomorphic in local sea-run populations; the low plate morph, which is usually monomorphic in local freshwater populations, was absent. By 2001, the frequency of completes had declined to 11%, and lows had increased to 75%. The partial plate morph and two unusual intermediate plate phenotypes were generally rare, but occurrence of the intermediates was unexpected. These intermediate phenotypes rarely occur in other, presumably older, polymorphic populations. When low morphs first appeared, they averaged 6.8 plates per side, indicating that the ancestral plate number of low morphs is high, and their mean has subsequently declined. Contemporary evolution in this population indicates that threespine stickleback adapt to freshwater habitats within decades after invasion from the ocean, and thus phenotypes in most populations are adapted to current conditions.
Although nutrients and grazing both contribute to the formation of harmful algal blooms, research on these events has rarely considered both factors simultaneously. To ascertain the impact of nutrients and grazing on brown tides of Aureococcus anophagefferens, nutrient bioassays were conducted in parallel with dilution‐style microzooplankton grazing experiments during an intense bloom that occurred throughout Great South Bay (GSB), New York, in fall of 1999. During the study, Aureococcus represented between 25 and 85% of phytoplankton biomass and attained peak cell densities > 6 × 105 cells ml−1. Concentrations of dissolved organic carbon (DOC) and nitrogen (DON) in GSB were high (mean = 430 µM and 32 µM, respectively) during the bloom, while dissolved inorganic nitrogen (DIN) levels were low (mean = 2.5 µM). Although the experimental additions of nitrogen (nitrate or urea) typically enhanced the growth rates of the non‐brown tide phytoplankton community, such additions often had no impact on, or decreased, growth rates of Aureococcus relative to unamended control treatments. These observations suggest that growth of non‐brown tide phytoplankton depended on ambient N supply rates, while Aureococcus experienced nutrient replete growth. Dilution experiments indicated that microzooplankton grazing rates on A. anophagefferens were significantly lower than those on other algal populations. This reduced grazing pressure contributed toward higher net growth rates for Aureococcus relative to non‐brown tide phytoplankton. In sum, these results demonstrate that both top‐down (low grazing mortality rates) and bottom‐up (a high DOC/DON, low DIN nutrient regime) factors can contribute to the proliferation of brown tide blooms in New York waters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.