DOI: 10.3391/ai.2025.21.3.203309

Authors: Lidia Garcia, Jennifer L. Ruesink, Andy Suhrbier, David Beugli, Rachel Flannery, Lindsey Parker, Emily W. Grason

Abstract: Estuaries are highly invaded ecosystems exhibiting many novel species interactions. This project addressed how predation from native and non-native crabs influences density of non-native clams along an estuarine gradient in Willapa Bay (Washington, USA). Recruitment of both Manila clams (Ruditapes philippinarum) and soft-shell clams (Mya arenaria) was greater up-estuary (south), likely from retention of locally-produced larvae. Three independent predator trapping efforts had higher catch of non-native European green crabs (Carcinus maenas) towards the ocean (north), setting up opposing predator and prey densities for exploration of top-down effects. Dungeness crabs (Metacarcinus magister) were 87% less abundant than green crabs and showed no regional difference in density in the single trapping effort where they were counted. Two field experiments investigated whether protection from nets impacted clam counts along the estuarine gradient. Excluding predators significantly increased survival of small Manila clams in both experiments, despite differences in duration, spatial scale, and whether clams were outplanted. Large Manila clams benefited only in the longer experiment. However, the protective effect of nets was unrelated to green crab catch, suggesting that the range of abundances observed in Willapa Bay during this study did not result in an additive mortality effect on clams. While abundances currently remain lower than other locations where impacts to clams have been documented, green crabs have increased rapidly in the past decade, and densities will likely continue to grow, particularly in the southern portion of the estuary. Thus, the lack of detected predation effects by green crabs in these experiments could be a transient phenomenon dwarfed by other post-recruitment losses of clams.

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DOI: 10.3391/ai.2026.21.1.180751

Authors: Marco Boschiero, Chiara Facca, Francesco Cavraro, Simone Redolfi Bristol, Anna Gavioli, Federico Riccato, Matteo Zucchetta, Piero Franzoi

Abstract: The Atlantic blue crab (Callinectes sapidus) is among the 100 worst invasive species in the Mediterranean Sea, causing significant ecological and economic impacts. The aim of this study is to investigate key aspects of the species’ biology and ecology during its demographic outbreak in a Northern Adriatic area significantly affected by the species’ invasion. Year-round sampling was carried out across a short spatial gradient encompassing lagoon, estuarine, and marine habitats. This comprehensive approach aimed to elucidate the invasive success of the blue crab. Our findings shows that the species resulted widely distributed across all habitat types, with significant differences among stations, seasons, and sexes, with females being prevalent in higher salinity marine and outer lagoon waters during spawning season. These findings, along with the spatiotemporal analyses of the condition factor and the presence in the lagoon of various cohorts of juveniles over the year, highlight the completion of the complex life cycle of the blue crab on an extremely small spatial scale. Moreover, with an average of over 2 million eggs laid per female and a prolonged spawning season, the species reveals a robust reproductive potential, likely favoured by the short distance between mating and spawning habitats. In conclusion, the results of this study underscore the critical role of the short spatial environmental mosaic in facilitating the invasive success of C. sapidus, providing relevant data for managing this unprecedented demographic explosion.

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DOI: 10.3391/ai.2025.20.2.154614

Authors: Yuriy Kvach, Halyna Gabrielczak, Anastasiia Lepekha, Mikhail O. Son, Sergii Khutornoi

Abstract: Biological invasions pose a significant threat to aquatic ecosystems, and the spread of uncontrolled non-indigenous species can have detrimental effects on biodiversity, ecosystem processes, and economic activities. The Chesapeake blue crab, Callinectes sapidus, native to the western Atlantic Ocean, is non-indigenous in the Black Sea region. This study presents novel findings on its presence and breeding in the Black Sea, particularly in North-Western part within the territorial confines of Ukraine. The study provides evidence of successful reproduction by a female blue crab with eggs in this non-native habitat, i.e. off the coast of Ukraine. Furthermore, molecular DNA barcoding analysis revealed the Ukrainian crab to be of a haplotype found in Italy and the United States, indicating potential connectivity between the Black Sea population and other established populations. Additionally, other haplotypes were detected in the Black Sea region, suggesting the possibility of multiple introductions and admixture between non-indigenous populations of different origins. The successful establishment and spread of C. sapidus in the Black Sea region may be attributed to its adaptability to a wide range of environmental conditions and the lack of natural predators or competitors in the invaded regions. This crab is commercialized in the USA, which may have implications for fisheries and aquaculture activities in Ukraine.

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DOI: 10.3391/ai.2025.20.1.151447

Authors: Catherine E. de Rivera, Amy A. Larson, Benjamin G. Rubinoff, Luna R. Soto, Seth L. Wright, Edwin D. Grosholz, Gregory M. Ruiz, Andrew L. Chang

Abstract: The nature and strength of biotic interactions change along stress gradients, but the importance of these interactions across estuarine gradients is under studied. Here, we examined how consumption varies across estuarine salinity gradients by deploying standardized baits (‘squidpops’) to measure consumption pressure along the gradients of five estuaries in Oregon, USA. The relationship between consumption and stress was nonlinear: consumption pressure peaked slightly at mid salinity and decreased at low salinity, especially as temperature increased, in the five estuaries studied. This finding does not support either of two existing models for consumption across gradients, including the Consumer Stress Model and a consumer extension of the Salinity Range Model. The pattern of consumption aligns better with the Prey Stress Model or the Invasion Stress Model, and the latter predicts that successful invasion by stress-tolerant predators extends consumption pressure further upstream along estuarine stress gradients than the Consumer Stress Model. Although these estuaries have been invaded by the crab Carcinus maenas, our catch data did not support the expected greater numbers of these invasive, stress-tolerant predators mid estuary or an expected relationship with native predators, as C. maenas was trapped in low abundance throughout each estuary. While our catch data did not directly support the Invasion Stress Model, we found that individual C. maenas ate more squid in lab experiments when at intermediate salinities than fresher salinities. Overall, our field and lab results suggest consumption peaked at mid estuary, at intermediate to high stress, in these temperate estuaries. The Invasion-Stress Model needs more testing to evaluate whether it, the Prey Stress Model, or a new model is best supported and can predict ecological impacts from changes in precipitation patterns and biological invasions, as well as other environmental stressors for estuarine food webs.

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DOI: 10.3391/ai.2023.18.3.103350

Authors: Veijo Jormalainen, Essi Kiiskinen, Veera Hauhia, Sami Merilaita

Abstract: In the Archipelago Sea as in most other parts of the Baltic Sea, the bladder wrack (Fucus vesiculosus) is a foundation species of the littoral communities of the rocky shores. It sustains a community of epiphytic algae, herbivorous crustaceans and molluscs and various fish. Recently we have noticed a steep decline in the occurrence of the herbivorous crustaceans and molluscs in many sites in the Archipelago Sea. We hypothesise that a key factor contributing to this decline is the recent introduction of the Harris mud crab (Rhithropanopeus harrisii), which was first sighted in 2009 in this region. Importantly, because there are no native crabs in the northern parts of the Baltic Sea, the mud crab is a completely novel kind of predator in the ecosystem and the herbivorous crustaceans and molluscs may be particularly susceptible to it. Here, we document a dramatic decline of the typical herbivores occurring on the bladder wrack, possibly indicating an ongoing regime shift, by comparing our recent samples from across the Archipelago Sea with data collected a decade before the sighting of the mud crab. Moreover, we demonstrate a spatio-temporal association between the decline, particularly of the key herbivore species, the isopod Idotea balthica, and the establishment of the mud crab. We also present experimental evidence for a strong predator-prey -link between the mud crab and the isopod I. balthica. Finally, we discuss the possible consequences of the community change and scrutinise alternative explanations for our observations.

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DOI: 10.3391/ai.2023.18.2.105548

Authors: Christine Ewers, Monika Normant-Saremba, Heleen Keirsebelik, Jonas Schoelynck

Abstract: The geographic expansion and abundance fluctuations of invasive species offer unprecedented insights to investigate potential mechanisms underlying the distribution-abundance relationship, one of the most universal patterns in community ecology. However, the abundance of invasive species is rarely documented in the needed detail. Data from historical records, scientific and popular literature, citizen science and expert interviews were synthesized to obtain insights into the long-term expansion and abundance cycles of the Chinese mitten crab, one of the world’s 100 worst invasive species. Thus for the first time, global long-term data on population size fluctuations have been correlated with the global spatiotemporal invasion history of a non-native species. Geographic expansions and increases in abundance co-occurred in the 1930s and again since the 1990s in agreement with the distribution-abundance relationship. Furthermore, a regional case study for the German river Elbe indicates that increases in abundance may be driven by improved riverine water quality and rising sea surface temperatures. Environmental restoration and climate change therefore benefit this invasive species, and could lead to further geographic expansion and increases in abundance.

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DOI: 10.3391/ai.2023.18.1.103301

Authors: Tuantong Jutagate, Wachira Kwangkhwang, Samnao Saowakoon

Abstract: The Australian red-claw crayfish (RCC) Cherax quadricarinatus (von Martens 1868) (Crustacea: Decapoda: Parastacidae) has been introduced and promoted for freshwater aquaculture in many countries including Thailand. This study i) evaluates the growth performance of RCC in near-natural conditions relative to captive conditions and ii) investigates how successfully RCC can compete with a trophically and functionally analogous native species. Growth of RCC was compared among two aquaculture systems (concrete tank and earthen pond) and a treatment with simulated natural conditions. After 12 months of rearing, total length and weight were greatest in the earthen pond and poorest in the near-natural treatment, with significant differences in total length between the near-natural treatment and the two culture systems. Length-weight relationships showed that the RCC had positive allometry in the culture systems but negative allometry in the near-natural treatment. Competition was evaluated by means of a biotic resistance test and an additive–substitutive experiment between RCC and the native freshwater crab Esanthelphusa dugasti (Rathbun, 1902) (Crustacea: Decapoda: Gecarcinucidae). Specific growth rates after 90 days of the experiments suggest that the crab inhibited growth of RCC. This implies that the invasion of RCC in Thai waters could be limited by competition from resident freshwater crabs.

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