Sheppard and Ricciardi 2025

Sheppard NLM, Ricciardi A. 2025. Influence of warming on the functional responses of invasive omnivores, Procambarus crayfishes. Canadian Journal of Fisheries and Aquatic Sciences 82: 1-8. https://doi.org/10.1139/cjfas-2024-0334

Abstract

The red swamp crayfish (Procambarus clarkii) and the marbled crayfish (Procambarus virginalis) are congeneric invasive species whose potential impacts in the Great Lakes basin have generated concern. In laboratory experiments, we tested the functional responses of these omnivores to two common food resources, insect larvae (Chironomus bloodworms) and aquatic macrophytes (Eurasian milfoil Myriophyllum spicatum), to gain predictive information on their per capita effects under present (18°C) and projected future (26°C) climate scenarios for the basin. The maximum feeding rate of P. virginalis was higher at 18°C than at 26°C when presented with bloodworms but did not differ between temperatures when presented with macrophytes. By contrast, the feeding rate of P. clarkii did not change with temperature for either food resource. Due to their larger mean size, P. clarkii exhibited higher rates of resource (bloodworm and macrophyte) consumption than P. virginalis at both temperatures. These results suggest that trophic impacts of P. virginalis will dampen with increased warming, whereas P. clarkii will sustain larger impacts irrespective of temperature within the range tested.

 

Keywords: None provided.

Talking Marmorkrebs to the streets

 

 

Pleased to hear that Marmorkrebs were part of a show promoting outdoor activities,

 

Brianna Naklicki from the Ontario Federation of Anglers and Hunters was handing out information booklets to visitors passing by. She works for the organization’s invasive species awareness program.

On a table in front of her are jars containing examples of species of concern in the province, including zebra mussels and marbled crayfish.

Her job at the show was to spread awareness about invasive species around lakes and forests to all who will listen.

 

Ontario is, so far, the only place in North America where Marmorkrebs have been found in the wild, and is the largest jurisdiction to ban Marmorkrebs.

External links

Outdoor show hooks nature lovers into shopping local

Update on Marmorkrebs in Warsaw, Poland

A couple of recent news articles are reporting on the presence of Marmorkrebs in Warsaw. This location was already in my map of Marmorkrebs introductions. A bioblitz located seven individuals in Morskie Oko Park back in 2019.

Fast forward six years to 2025, and the population is estimated at 100,000 crayfish.

 

The article notes that there are removal efforts, but they can’t drain the pond, so culling them requires catching them by hand or trap. And in typical local media style, they stress the expense.

 

I do appreciate the safety warning:

 

 The expert emphasized that rakes do not attack a person if they are not provoked to do so. 

I don’t know of any crayfish that voluntarily attacks people with anything more than a pinch.

External links

Wpuścił raka do stawu w Warszawie. "Doprowadził do niepowstrzymanej ekspansji" (He released a crayfish into a pond in Warsaw. “He led to unstoppable expansion”)

 

Warszawa zmaga się z inwazją raka marmurkowego. Ekspert ostrzega (Warsaw is struggling with marbled crayfish invasion, expert warns)

 

Photo by Adrian Grycuk - Own work, CC BY-SA 3.0 pl, https://commons.wikimedia.org/w/index.php?curid=101324805

Everyday sexism

Always nice to stumble across a video mentioning marbled crayfish. I’m kind of used to them showing some other random crayfish species, but this one has a new thing that made me pause.

This video is titled, “This guy copies himself 2,000 times!”

Since marbled crayfish are all female, a better title would be, “This gal copies herself 2,000 times.”

Eiler and colleagues 2025

Eiler A, Stensrud E, Osman O. 2025. Detection of marbled crayfish Procambarus fallax. protocols.io. https://dx.doi.org/10.17504/protocols.io.q26g78199lwz/v1

 

Abstract

Taqman QPCR assay for marbled crayfish Procambarus fallax.

 

Keywords:  None provided.

 

The Crayfish Almanac

Don’t know how I missed this last year, but Michigan State University released Great Lakes Almanac to Invasive Crayfish.

It has one of the best short identification guides for Marmorkrebs I’ve seen. Click to enlarge!

Marbled crayfish (or marmokrebs) originated in the aquarium trade and are often called the self-cloning crayfish. All marbled crayfish are female and the offspring are clones. This species is of high concern because a single individual can produce an entire population in a short time.

This species has a distinct marbling pattern, but other species may look similar. Male crayfish with this pattern are not marbled crayfish.

To determine if its a female, look for a round pocket-like feature located on the underside between the last pair of walking legs. This is the sperm pouch (called an ‘annulus ventralis’) .

External links

Great Lakes Almanac to Invasive Crayfish 

Golubev and colleagues 2024b

Golubev AP, Ulashchyk EA, Bodilovskaya OA. 2024. Modeling the growth of the invasive river crayfish species Procambarus virginalis (Decapoda, Astacidea) under different temperature conditions. https://www.researchgate.net/publication/387918897_Modeling_the_growth_of_the_invasive_river_crayfish_species_Procambarus_virginalis_Decapoda_Astacidea_under_different_temperature_conditions

Abstract

In the marbled crayfish Procambarus virginalis, the dependence of the duration of inter-larval intervals on body weight and the magnitude of body weight gains for individual inter-larval intervals in the temperature ranges 15.3–17.9 °С, 7.5–18.9, 19.1–20.8, 21.0–22.8, 22.9–25.2 and 25.3–28.9 °С was determined. The growth curves of individuals in these temperature ranges and the sum of effective temperatures (Sef) of individuals during juvenile growth and breeding periods were calculated from these data. The average Sef value for the juvenile period of P. virginalis (until newborn individuals reach a body weight of 1.4 g) in the studied temperature ranges is 4316 degree·days at the biological zero temperature of 7.6 °C. For the breeding period (until reaching the body weight from 1.4 g to the limit weight of 15 g) – respectively 10630 degree·days and 3.0 °C. Based on the annual dynamics of mean monthly temperatures in six continental water bodies within the invasive range of P. virginalis (Sweden, Belarus, Germany, Slovakia, North Macedonia and Malawi), Sef values were calculated for the periods of the year during which juvenile growth and reproduction of sexually mature individuals are possible. In temperate water bodies located in Sweden, Belarus, Germany and Slovakia, Sef values during the juvenile growth period vary between 1083 and 2099 degree·days. In the more southern body of water in Northern Macedonia, this value reaches 2990 degree·days, and in the tropical African body of water in Malawi it reaches 7076 degree·days. Consequently, newborn individuals of P. virginalis, which in water bodies of the temperate zone of Europe hatch in the first half of summer, can reach sexual maturity only in the third summer of life, and in a tropical water body – already in the first summer of life. Sef values for periods of the year favorable for the growth of sexually mature individuals in the studied water bodies of Europe increase from 2031 degree·days (water body in Sweden) to 4657 degree·days (water body in Northern Macedonia). In the tropical water body of Malawi, this figure reaches 8058 degree·days, i.e. the maximum life span of P. virginalis in this water body does not exceed two years. Nevertheless, throughout the entire range, sexually mature individuals of P. virginalis are capable of producing no more than 2–5 clutches of eggs per life cycle.

Note: The ResearchGate page includes a link to the DOI 10.46646/2521-683X/2024-4-18-34. At the time of this writing in January 2025, this link is not working. I will update this entry with more information if I learn more.