Temperature, not salinity, drives impact of an emerging invasive species

Spatial distribution and effects of temperature rise on coastal free-living nematode community in the South Caspian Sea

In the present study, the spatial distribution of coastal free-living nematodes was first investigated at six different stations. The highest density, number of species, and Shannon diversity were recorded at Sisangan station. Subsequently, Sisangan station was chosen for studying the responses of the coastal free-living nematode community to increased surface water temperature (Field control = 20 °C, Treatment 1 = 24 °C, Treatment 2 = 27 °C, and Treatment 3 = 30 °C) experimentally over a period of 50 days. A total of thirteen species from eleven genera were identified. The genus Daptonema and the species Daptonema karabugasensis being the most dominant in all treatments. The highest total density and total Shannon index were recorded in the T3 treatment. There were no significant differences in the total number of species and the evenness index among the treatments. Changes in temperature significantly affected the community structure, primarily due to the presence or absence of specific species. SIMPER analysis showed that some species like Daptonema karabugasensis, Tripyloides marinus and Adoncholaimus araelensis were dominant within the community, although their relative abundance declined at the T2 and T3 treatments. In contrast, the relative abundance of Chromadorella parapoecilosoma and Chromadorita tenuis increased with rising temperatures in these treatments. The number of gravid females and juveniles also rose with temperature, peaking in the T3 treatment. As the temperature rose, the proportion of predators/omnivores (2B) in the community gradually increased, although the epistrate feeders (1B) remained dominant across all communities.

Monitoring of environmental DNA from nonindigenous species of algae, dinoflagellates and animals in the North East Atlantic

Monitoring the distribution of marine nonindigenous species is a challenging task. To support this monitoring, we developed and validated the specificity of 12 primer-probe assays for detection of environmental DNA (eDNA) from marine species, all nonindigenous to Europe. The species include sturgeons, a Pacific red algae, oyster thief, a freshwater hydroid from the Black Sea, Chinese mitten crab, Pacific oyster, warty comb jelly, sand gaper, round goby, pink salmon, rainbow trout and North American mud crab. We tested all assays in the laboratory, on DNA extracted from both the target and non-target species to ensure that they only amplified DNA from the intended species. Subsequently, all assays were used to analyse water samples collected at 16 different harbours across two different seasons during 2017. We also included six previously published assays targeting eDNA from goldfish, European carp, two species of dinoflagellates of the genera Karenia and Prorocentrum, two species of the heterokont flagellate genus Pseudochattonella. Conventional monitoring was carried out alongside eDNA sampling but with only one sampling event over the one year. Because eDNA was relatively fast and easy to collect compared to conventional sampling, we sampled eDNA twice during 2017, which showed seasonal changes in the distribution of nonindigenous species. Comparing eDNA levels with salinity gradients did not show any correlation. A significant correlation was observed between number of species detected with conventional monitoring methods and number of species found using eDNA at each location. This supports the use of eDNA for surveillance of the distribution of marine nonindigenous species, where the speed and relative easy sampling in the field combined with fast molecular analysis may provide advantages compared to conventional monitoring methods. Prior validation of assays increases taxonomic precision, and laboratorial setup facilitates analysis of multiple samples simultaneously. The specific eDNA assays presented here can be implemented directly in monitoring programmes across Europe and potentially worldwide to infer a more precise picture of the dynamics in the distribution of marine nonindigenous species.

Effects of shipping on non-indigenous species in the Baltic Sea

Shipping is regarded as an important vector for aquatic non-indigenous species (ANIS) worldwide. Less attention has been paid to its role in relation to environmental and economic causes of introduction and establishment, the knowledge of which is necessary to assess effects of changes in regulations on shipping. The purpose of this study was to estimate the impact of shipping on the incidence of ANIS in the Baltic Sea compared with environmental and economic factors. To this end, a production function was estimated with count data on ANIS (response variable) and shipping, environmental and economic factors as explanatory variables. Regression results from different regression models showed that shipping has a significant impact on ANIS incidence and can account for up to 38% of the number of ANIS in the sea. Predictions of the impact of measures implementing the Convention for the Control and Management of Ships' Ballast Water and Sediment indicated a reduction by 17% in the number of ANIS, which was counteracted by an expected increase in shipping traffic.

Functional responses of an invasive mud crab across a salinity gradient

Environmental gradients may alter the ecological impacts of invasive alien species. In marine systems such as the Baltic Sea, current salinity is variable and seawater freshening is projected in future, potentially facilitating novel keystone predators. Here, we examine the influence of salinity variation in the western Baltic Sea (i.e. ambient 10, then 7 and 4 ppt) on the functional response (FR) of the Harris mud crab Rhithropanopeus harrisii towards benthic macroinvertebrate prey at different densities. Rhithropanopeus harrisii displayed a Type II FR across salinities towards larval chironomids, due to a consistently high resource consumption rate at low prey densities. Feeding rates were significantly reduced at 4 ppt (mean 6 chironomid prey killed day^-1) compared to 10 ppt and 7 ppt (9 killed day^-1). Search efficiencies tended to be greatest at 10 ppt, whereas handling times were shortest - and maximum feeding rate highest - at the intermediate 7 ppt. These results suggest a slight reduction in predatory impact by R. harrisii at lower salinities. Nevertheless, across most prey densities, FRs were not significantly different, indicating sustained interaction strength across a range of salinity regimes.

The Effects of Temperature on the Development, Morphology, and Fecundity of Aenasius bambawalei (=Aenasius arizonensis)

Simple Summary

During biological invasions, insect pest outbreaks often occur because they escape the control of natural enemies from their place of origin. However, some natural enemies can migrate with pests to effectively inhibit their damage. Whether temperature changes can shorten or enhance the reproductive developmental period of accompanying natural enemies is an important determinant of whether they can effectively migrate with pests. Aenasius bambawalei is a predominant accompanying parasitoid of the important invasive pest Phenacoccus solenopsis. To understand the effect of temperature changes on the development of the reproductive systems of this parasitoid, we compared differences in its development, morphology, and fecundity under different temperatures. The results showed that high temperature could significantly shorten the pupal developmental duration, increase the length of the hind tibia, and accelerate gonad development. Our results indicated that moderately high temperature was conducive to the reproduction and development of the parasitoid and may be related to the more females offspring. This is the first report of the impact of high temperature on the pupal development, morphology, and fecundity of A. bambawalei.

Abstract

The effects of high temperature on the developmental, morphological, and fecundity characteristics of insects, including biological invaders and their accompanying natural enemies, are clear. Phenacoccus solenopsis (Homoptera: Pseudococcidae) is an aggressive invasive insect pest worldwide. Aenasius bambawalei (=Aenasius arizonensis Girault) (Hymenoptera: Encyrtidae) is a predominant accompanying parasitoid of this mealybug. Our previous studies showed that temperature change induced an increase in the female offspring ratio of A. bambawalei. However, whether this increase is the result of a shortened or enhanced development period of the reproductive systems of A. bambawalei remains unknown. Here, we compared the pupal development, hind tibia of female adults, and fecundity of A. bambawalei under different temperatures to clarify the development and morphological changes induced by high temperature and to better understand its potential as an accompanying natural enemy. Our results showed that, at a high temperature (36 °C), the pupal developmental duration of A. bambawalei was only 0.80 times that of the control, and the length of the hind tibia was 1.16 times that of the control. Moreover, high temperature accelerated the developmental rate of gonads and increased the numbers of eggs and sperm. These results indicated that experimental warming shortened the pupal developmental duration, altered the hind tibia length of female adults, and facilitated the fecundity of A. bambawalei. These findings will help to understand the adaptation mechanisms of accompanying natural enemies. Furthermore, these findings will help to make use of this behavior to effectively control invasive pests.