Effect of water quality and season on the population dynamics of Cabomba caroliniana in subtropical Queensland, Australia

Cabomba caroliniana is a submersed aquatic macrophyte that originates from the Americas and is currently invading temperate, subtropical, and tropical freshwater habitats around the world. Despite being a nuisance in many countries, little is known about its ecology. We monitored C. caroliniana populations in three reservoirs in subtropical Queensland, Australia, over 5.5 years. Although biomass, stem length, and plant density of the C. caroliniana stands fluctuated over time, they did not exhibit clear seasonal patterns. Water depth was the most important environmental factor explaining C. caroliniana abundance. Plant biomass was greatest at depths from 2–4 m and rooted plants were not found beyond 5 m. Plant density was greatest in shallow water and decreased with depth, most likely as a function of decreasing light and increasing physical stress. We tested the effect of a range of water physico-chemical parameters. The concentration of phosphorus in the water column was the variable that explained most of the variation in C. caroliniana population parameters. We found that in subtropical Australia, C. caroliniana abundance does not appear to be affected by seasonal conditions but is influenced by other environmental variables such as water depth and nutrient loading. Therefore, further spread will more likely be governed by local habitat rather than climatic conditions

Effect of water quality and season on the population dynamics of Cabomba caroliniana in subtropical Queensland, Australia

Cabomba caroliniana is a submersed aquatic macrophyte that originates from the Americas and is currently invading temperate, subtropical, and tropical freshwater habitats around the world. Despite being a nuisance in many countries, little is known about its ecology. We monitored C. caroliniana populations in three reservoirs in subtropical Queensland, Australia, over 5.5 years. Although biomass, stem length, and plant density of the C. caroliniana stands fluctuated over time, they did not exhibit clear seasonal patterns. Water depth was the most important environmental factor explaining C. caroliniana abundance. Plant biomass was greatest at depths from 2–4 m and rooted plants were not found beyond 5 m. Plant density was greatest in shallow water and decreased with depth, most likely as a function of decreasing light and increasing physical stress. We tested the effect of a range of water physico-chemical parameters. The concentration of phosphorus in the water column was the variable that explained most of the variation in C. caroliniana population parameters. We found that in subtropical Australia, C. caroliniana abundance does not appear to be affected by seasonal conditions but is influenced by other environmental variables such as water depth and nutrient loading. Therefore, further spread will more likely be governed by local habitat rather than climatic conditions

Negative effect of purple loosestrife and reed canary grass on the diversity of wetland plant and moth communities

Invasive plants have the potential to reduce the diversity of species in plant and animal communities. I examined the negative effect of two invasive wetland plants, purple loosestrife and reed canary grass, on the species richness and diversity of plant and moth communities within 24 wetland study sites in the Pacific Northwest. I hypothesized that as the cover of the invasive species increased, the diversity of the local plant and moth community would decrease. Increasing cover of purple loosestrife and reed canary grass was associated with reduction in the diversity of wetland plant communities irrespective of the diversity measure examined. Moth species richness was positively correlated with plant species richness, but I found no detectable direct negative association between loosestrife and canary grass cover and moth community diversity. Wetland hydrology, soil characteristics, and topography were measured to control for potentially covarying and confounding influences on plant diversity. Temperature, ambient light, and surrounding land-use were measured to control for potentially covarying and confounding influences on moth sampling and diversity. None of these variables was significantly associated with invasive species abundance. This strengthens the conclusion that the invasive species are the cause of the decline in biotic diversity. Understanding the mechanisms that influence plant invasions will lead to more effective management strategies. I examined the role of soil nutrients in the invasive potential of purple loosestrife. I hypothesized that nitrogen was the primary nutrient limiting plant growth and that higher soil nitrogen concentrations would increase the growth of purple loosestrife within 13 wetland sites in the Willamette Valley, Oregon. Using greenhouse experiments and field studies I found that nitrogen was the primary resource limiting both plant community biomass and purple loosestrife growth. Purple loosestrife grew well in soils taken from nine wetlands currently not colonized by loosestrife. Given their similar hydroperiods, this suggests that these wetlands will be susceptible to invasion should loosestrife colonize. Plant species richness was negatively associated with soil nitrate and ammonium concentrations, This trend included invaded and non-invaded sites. Therefore, to prevent repeated invasions, management strategies should consider methods for reducing soil nutrient concentrations, particularly nitrogen

Status of the European Green Crab, Carcinus maenas, in Oregon and Washington coastal Estuaries in 2018

The European green crab (Carcinus maenas) has persisted in Oregon and Washington coastal estuaries since the late 1990s. After the arrival of a strong year class in 1998, significant recruitment to the populations occurred only in 2003, 2005, 2006, 2010, 2015, 2016, 2017 and 2018. Warm winter water temperatures, high Pacific Decadal Oscillation (PDO) and Multivariate ENSO (El Niño Southern Oscillation) Indices, and a high abundance of southern copepods are all correlated with strong year classes and vice versa (Behrens Yamada Peterson and Kosro 2015). Prior to 2015, green crabs were too rare to exert measurable effects on the native benthic community and on shellfish culture in Oregon and Washington. Following the recent strong El Niño, however, we documented the arrival of four strong year classes in 2015, 2016, 2017 and 2018. Average catch rates over the last four years steadily increased from 0.5 to 0.8 to 2.2 and to 3.2 crabs per trap. The catches in the last 2 years are much higher than in any of the previous years, including 1998. Since green crabs live for 6 years, these four consecutive year classes will produce larvae until 2024. A switch to cooler ocean conditions in the coming years will result in poor recruitment, but a return to high PDO and strong El Niño patterns would signal good recruitment and higher green crab densities. For example, green crabs were first documented in New England in 1817, but it took warm ocean conditions during the 1950’s for their numbers to build to a level at which they decimated the soft-shelled clam industry in Maine. With the recent warm trend on the East Coast, green crabs are again abundant. Not only are they preying on shellfish, they are also damaging valuable eelgrass habitat by ripping up the plants in search of food (Neckles 2015). Even though green crab abundance in Oregon and Washington is still low when compared to Europe, eastern North America, Tasmania, California and the west coast of Vancouver Island, it is imperative to continue monitoring efforts for two reasons:1) to elucidate the process of range expansion and population persistence of this model non-indigenous marine species with planktonic larvae, and 2) to predict the arrival of strong year classes from ocean conditions and alert managers and shellfish growers of possible increases in predation pressure from this invader

Status of the European Green Crab, Carcinus maenas, (aka 5-spine crab) in Oregon Estuaries. Report for 2022

The European green crab (Carcinus maenas) has persisted in Oregon and Washington coastal estuaries since the late 1990s. A strong year class arrived during the 1998 El Niño, but numbers decreased and remained below 1 per trap per day until the arrival of the 2015-2016 El Niño. Since then, numbers have increased to an average of around 4-6 crabs per trap per day for intertidal sites and ~ 9 per trap per day in the shallow subtidal. Measurable ecological impact is predicted to occur at around 10-20 per trap per day (Grosholz et al. 2011). Between the two major El Niños, recruitment of young green crabs has been sporadic, with many years of recruitment failures. But after the 2015-2016 El Niño recruitment has been good every year. The Davidson Current transporting larvae from California during the winter no longer appears to be the only source of larvae for our coastal estuaries (Behrens Yamada, Fisher and Kosro 2021). Now that the populations in Oregon, Washington and British Columbia have built up, we have evidence for local larval production and seeding from a genetically distinct population on Vancouver Island (Alan Shanks and Carolyn Tepolt, pers. com.). This report is a compilation of trapping data for Carcinus maenas from various sources and estuaries. These include the following: 1) Catches of adult crabs in Yaquina Bay using Fukui traps set in the intertidal and in the shallow subtidal. The latter were set at 22 sites along a salinity gradient from South Beach Marina to the Port of Toledo by Mitch Vance of Oregon Department of Fish and Wildlife. 2) Catches of adult crabs at 3 sites in the Salmon estuary using Fukui traps set in intertidal areas by volunteers and by Rebecca Flitcroft from the United Stated Department of Agriculture. 3) Summary of catches of crabs trapped in Coos Bay by Shon Schooler, interns and technicians of South Slough National Estuarine Research Reserve. For detailed data on various sites in Coos Bay see Schooler et al. (2022). 4) Catches of adult crabs in Siuslaw and Umpqua estuaries by Shon Schooler and interns. 5) Average catches of Young-Of-The-Year (YOTY, or Age-0) crabs at the end of their first growing season, from 4 Oregon estuaries and Willapa Bay, Washington. This 25-year data set allows us to compare catches of YOTY crabs between years and between estuaries (Figure 3)

Status of the European Green Crab, Carcinus maenas, in Oregon and Washington coastal Estuaries. Report for 2020 and 2021

The European green crab (Carcinus maenas) has persisted in Oregon and Washington coastal estuaries since the late 1990s. A strong year class arrived in the Davidson Current during the 1998 El Niño, but numbers decreased and remained below 1 per trap per day until the arrival of the 2015-2016 El Niño. Ocean indices indicate that California was the predominate source of larvae prior to the 2015-2016 El Niño (Behrens Yamada & Kosro, Behrens Yamada, Peterson & Kosro, 2015). Since then, numbers have increased steadily to an average of around 6 crabs per trap per day for Yaquina and Coos estuaries, with maximums of up to 25- 28 per trap. Measurable ecological impact is predicted to occur around 10 per trap (Grosholz et al. 2011). Between the two El Niños recruitment of young green crabs to these estuaries was sporadic with many years of recruitment failure. But since 2015 recruitment has been good every year. Since green crabs live for 6 years, these recent strong year classes can produce larvae until 2027. Evidence suggests that the Davidson Current transporting larvae from California during the winter is no longer the only source of larvae for our coastal estuaries (Behrens Yamada, Fisher and Kosro 2021). Now that populations in Oregon, Washington and British Columbia have built up, we have evidence for local production and for larvae sources from a genetically distinct population on Vancouver Island (Alan Shanks and Carolyn Tepolt, personal communication). The current cooler ocean conditions could hold recruitment in check, but a return to high PDO and strong El Niño patterns would signal good recruitment and higher green crab densities. Even though green crab abundance in Oregon and Washington is still low when compared to Europe, eastern North America, Tasmania, California and the west coast of Vancouver Island, it is imperative to continue monitoring efforts for two reasons: 1) To elucidate the process of range expansion and population persistence of European green crabs. It could serve as a model for the spread of other non-indigenous species with planktonic larvae. 2) To predict the arrival of strong year classes from ocean conditions and to alert managers and shellfish growers of possible increases in predation pressure from this invader

Status of the European Green Crab, Carcinus maenas, in Oregon and Washington coastal estuaries in 2019

The European green crab (Carcinus maenas) has persisted in Oregon and Washington coastal estuaries since the late 1990s. After the arrival of a strong year class in 1998, significant recruitment to the populations occurred only in 2003, 2005, 2006, 2010, 2015, 2016, 2017, 2018 and 2019. Warm winter water temperatures, high Pacific Decadal Oscillation (PDO) and Multivariate ENSO (El Niño Southern Oscillation) Indices, and a high abundance of southern copepods are all correlated with strong year classes and vice versa (Behrens Yamada, Peterson and Kosro 2015; Behrens Yamada, Fisher and Kosro 2020 in review). Prior to 2015, green crabs were too rare (<0.2 per trap) to exert measurable effects on the native benthic community and on shellfish culture in Oregon and Washington. But after the 2015-2016 El Niño, we document the arrival of five strong year classes. Average catches steadily increased from 0.5 crabs per trap, in 2015 to around 3 crabs per trap in 2017 to 2019. The catches in the last 3 years are much higher than in any of the previous years, including 1998. Catches in some hot spots exceed 10 crabs per trap, a level at which measurable ecological impact can be expected (Grosholz et al. 2011). Since green crabs live for 6 years, these five consecutive year classes can produce larvae until 2025. A switch to cooler ocean conditions in the coming years will result in poor recruitment, but a return to high PDO and strong El Niño patterns would signal good recruitment and higher green crab densities. For example, green crabs were first documented in New England in 1817, but it took warm ocean conditions during the 1950s for their numbers to build to a level at which they decimated the soft-shelled clam industry in Maine (Welch 1968). With the recent warm trend on the East Coast, green crabs are again abundant. Not only are they preying on shellfish, they are also damaging valuable eelgrass habitat by ripping up the plants in their search for food (Neckles 2015). Even though green crab abundance in Oregon and Washington is still low when compared to Europe, eastern North America, Tasmania, California and the west coast of Vancouver Island, it is imperative to continue monitoring efforts for two reasons: 1) to elucidate the process of range expansion and population persistence of this model non-indigenous marine species with planktonic larvae, and 2) to predict the arrival of strong year classes from ocean conditions and alert managers and shellfish growers of possible increases in predation pressure from this invader

Differential Influence of Clonal Integration on Morphological and Growth Responses to Light in Two Invasive Herbs

Background and aims: In contrast to seeds, high sensitivity of vegetative fragments to unfavourable environments may limit the expansion of clonal invasive plants. However, clonal integration promotes the establishment of propagules in less suitable habitats and may facilitate the expansion of clonal invaders into intact native communities. Here, we examine the influence of clonal integration on the morphology and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under varying light conditions. Methods: In a greenhouse experiment, branches, connected ramets and severed ramets of the same mother plant were exposed under full sun and 85 % shade and their morphological and growth responses were assessed. Key results: The influence of clonal integration on the light reaction norm (connection6light interaction) of daughter ramets was species-specific. For A. philoxeroides, clonal integration evened out the light response (total biomass, leaf mass per area, and stem number, diameter and length) displayed in severed ramets, but these connection6light interactions were largely absent for P. canescens. Nevertheless, for both species, clonal integration overwhelmed light effect in promoting the growth of juvenile ramets during early development. Also, vertical growth, as an apparent shade acclimation response, was more prevalent in severed ramets than in connected ramets. Finally, unrooted branches displayed smaller organ size and slower growth than connected ramets, but the pattern of light reaction was similar, suggesting mothe