Zooplankton communities in riverine systems are typically thought to be driven by abiotic forces. However, recent studies have shown that biological controls are capable of structuring these communities in large rivers and may become more influential as a river system becomes more lentic during low discharge. This study uses a long-term data set to examine several environmental variables as potential drivers of zooplankton community structure in a natural riverine lake. We hypothesized that water residence time would be the most important variable influencing zooplankton community structure. To test this, we used non-metric multidimensional scaling and correlation analysis to examine spatial and temporal patterns in zooplankton community structure. Analysis revealed that water residence time was the single most important environmental variable driving zooplankton abundance and community structure. The relationship between water residence time and taxa groups varied indicating that other taxa specific drivers had some influence on zooplankton community structure as well. Continued insight into the mechanisms driving zooplankton community structure will provide a basis for understanding zooplankton dynamics in large river ecosystems.

A protective limestone treatment was applied to an acid‐sensitive lake in northeastern Minnesota as part of the Acid Precipitation Mitigation Program. This 6–year study evaluated the impact of that treatment on lakes in the upper Midwest that experience episodes of acid stress but have not lost basic species integrity and community structure. Several changes in the fish community can be directly or indirectly attributed to the addition of 4.6 tonnes of calcium carbonate early in the third year of the study. An almost 30–fold increase in the population of Pimephales promelas(fathead minnow) a year after liming, based on mark‐recapture estimates from trap netting and snorkeling, was attributed to a pH increase and a three‐fold increase in the calcium concentration of the epilimnion. After the initial increase, the abundance of fathead minnows declined in subsequent years, as did the elevated pH and calcium concentrations. The Salvelimis fontinalis(brook trout) population also increased in the lake following application of limestone, but this was due in part to closing the lake to fishing. An increase in survival of stocked brook trout to age 1+ and an increase in growth of older brook trout after liming were attributed to the increased forage that the fathead minnows provided. Fathead minnows may have also reduced predation pressure on young brook trout by older brook trout. This study demonstrated that liming of a slightly acidic lake did not adversely affect the integrity of the fish community, and in fact may have increased the abundance and biomass of the forage fish community and indirectly increased the survival, abundance, and growth of brook trout.

Coral reef systems are in global decline. In Australia, much of this decline has been attributable to cyclic outbreaks (every ~17 years) of the coral-feeding crown-of-thorns seastar. While a native species, when in large enough densities the seastar acts like an invasive pest. Since 2012 the Australian government has invested significantly in a targeted control program using lethal injection. While this program is effective for individual reefs, it is not a complete strategy for the entire Great Barrier Reef (~2,500 reefs). In order to find a longer-term solution to the problem, in 2015, the lead author travelled to New Zealand, the United States, and Canada under a Churchill Fellowship to understand successful aquatic integrated pest management strategies and their potential application to the Great Barrier Reef. Meetings and workshops were convened with experts who specialise in risk assessment, categorisation, and management of aquatic invasive species. The experts comprised academics, applied scientists, policy makers, and a not for profit community based invasive species council. Bioinvasion management and prioritisation of management effort using risk-based frameworks were reviewed for application to the crown-of-thorns seastar. This viewpoint is novel in its approach of applying invasive species tools and perspectives to a non-invasive, native marine pest. Early detection and rapid response is key to preventing the transition of the seastar from natural densities to outbreak densities. However given the seastar is a native species already established, when in outbreak mode a multifaceted post-border management approach is essential. Private support funding models, that bridge conservation and tourism/philanthropy have proved successful in New Zealand to supplement government funded marine reserve management -this is an approach which should be explored by Australia to help manage the seastar. Dedicated support and commitment is needed to break the issue-attention cycle. On the Great Barrier Reef, a dedicated biosecurity approach should be used to maintain the seastar at natural densities, increase the time between outbreaks, protect coral cover and increase resilience of the system.

Species invasions are a leading threat to ecosystems globally, but our understanding of interactions among multiple invasive species and their outcomes on ecosystem properties is undeveloped despite their significance to conservation and management. Here we studied a large lake in Minnesota, USA, that experienced a simultaneous surge in invasive zebra mussel and spiny water flea populations. A long-term (2000–2018) dataset offered a rare opportunity to assess whole-ecosystem shifts following the co-invasion. Within two years, the native crustacean zooplankton community declined abruptly in density and productivity (−93% and −91%, respectively). Summer phytoplankton abundance and water clarity remained stable across the time series, an unexpected outcome given the high density of zebra mussels in the lake. Observational data and modeling indicate that removal of native herbivorous zooplankton by the predatory spiny water flea reduced zooplankton grazing pressure enough to compensate new grazing losses due to zebra mussels, resulting in a zero net effect on phytoplankton abundance and water clarity despite a wholesale shift in secondary production from the pelagic to the benthic food web. This study reveals the extent of direct and indirect effects of two aquatic invaders on food-web processes that cancel shifts in water clarity, a highly valued ecosystem service.

We examined the impact of copper on invertebrate community composition in a small stream (Pelican Brook) originating from a zebra mussel infested lake in central Minnesota. One bay of the lake was treated weekly with chelated copper during the summers of 2004 and 2005, resulting in copper levels in Pelican Brook ranging from 0.1 to 0.8 mg/L for three months each summer. Benthic macroinvertebrates were collected from two sites in Pelican Brook in spring and fall over four years (2004)(2005)(2006)(2007), including one pretreatment collection (spring 2004). Samples were also collected from two reference streams (2005)(2006)(2007). Ephemeroptera, Trichoptera, and Plecoptera comprised over half of the community in pre-treatment and reference stream samples. During treatment seasons, mayflies were eliminated and the community shifted to only a few taxa (Hydropsychidae and Chironomidae, primarily Orthocladiinae). Reference stream communities showed seasonal fluctuations but not the massive shifts in taxa abundance seen in the impacted sites. Invertebrate communities began to recover in the first year post-treatment (2006), and by fall 2007 Ephemeroptera and Trichoptera again accounted for over half of the taxa collected. Ephemeroptera, particularly Heptageniidae, appear to be good signal taxa for copper impacts.