Effect of Fear to be Eaten by Predators on Commercially Important Shellfish Species; and Differential Stress Tolerance in Multiple Populations of Green Crabs

UMaine Alert

Posted: April 19, 2024 - 1:32 PM

At approximately 9:24 a.m. on Friday, April 19, a University of Maine graduate student was struck by a university vehicle on Long Road at the University of Maine campus in Orono. The student reports that they are at a local hospital with minor injuries.

Emergency services, including the Orono Fire Department, University Volunteer Ambulance Corps, University of Maine Police Department, Orono Police Department and Penobscot County Sheriff’s Office responded to the scene.

The university vehicle involved in the incident was a Chevrolet Express van. It was being operated by a university employee.

Counseling services and support are available for students, faculty or staff who may have been affected. The Counseling Center can be reached at 207-581-1392 and the Dean of Students Office can be reached at 207-581-1406.

The scene has been cleared and Long Road is now accessible. An investigation is being conducted by the University of Maine Police Department with assistance from the Penobscot County Sheriff’s Office Crash Reconstruction Unit. Any witnesses to the incident are encouraged to contact Lt. Noel Santiago at noel.santiago@maine.edu.

June 28, 2018

Project Description

The objective of this project is to characterize population-specific stress tolerance and destructiveness of green crabs from four genetically different populations, and to quantify and identify cellular mechanism of altered energy use in clams when exposed to a predator.

The green crab, Carcinus maenas, is a globally invasive species native to Europe. It was introduced to the Eastern US in the early 1800’s and then to Nova Scotia and Prince Edward Island in the 1980’s. This led to genetically different populations of green crabs on the east coast of North America. The green crab has detrimental effects on soft shell clam (Mya arenaria) populations and clam fisheries have collapsed due to green crab invasions. Growing evidence supports the idea that trophic interactions between predator and prey have the ability to alter morphological and physiological traits of the prey species. These shifts in prey species have the potential to alter future predator/prey interactions.

The current project investigates population specific differences in stress physiology, behavior, and habitat destruction. Crabs were collected in Maine (ME), Nova Scotia (NS), Newfoundland (NF) and Iceland, and incubated at 3, 8, and 16°C, and at varying salinity rates of 12, 34, and 40 parts per thousand for 48 hours. Gene and protein expression of HSP70, AMPK, and Na⁺-K⁺-2Cl^–-cotransporter was measured in heart, chelae, gill, and hepatopancreas tissue. Aggression, righting response, and treadmill running endurance were also measured. To assess damage to seagrass habitat from the animals, crabs were placed in a 5 m diameter mesocosm that contained 3 different densities of Zostera marina. Location of the crabs within the tank was quantified over 3 days by daily observations, and Z. marina damage was evaluated via frayed blades and uprooted plants.

Results and Accomplishments

Morphological and physiological changes are being investigated in both juvenile and young adult soft shell clam populations when subjected to varying densities of green crab presence. Juvenile and young adult clams were exposed to green crab chemical cues in three different densities: control (no crabs), low predation (3 crabs), and high predation (7 crabs). Juvenile clams were exposed to the crabs for six months, and the young adult clams for 72 hours. Juvenile clams were measured for shell length, siphon length, AMPK activity, HSP70, and RNA:DNA ratio, while young adults were tested for AMPK, RNA:DNA ratio, HSP70, shell opening, heart rate, and oxygen consumption (last three adult parameters tested with varying levels of both predator and conspecific chemical cues). Initial results for juveniles exhibit increased siphon length and reduced siphon thickness, as well as reduced shell length in the low predation density. Exposing adult clams to predatory chemical cues leads to reduced frequency of shell opening. These results indicate that the presence of predators affects growth rates and/or energy utilization in clams, with subsequent effects on the shellfish industry.

Results have shown that crabs from NF spent more time above the sediment than those from ME, which can lead to more seagrass disruption. Above the sediment, the crabs from ME were more destructive to Z. marina. Crabs from NS were more aggressive than ME and NF populations at all temperatures. At 3°C NS crabs were the least active on the treadmill. The NF crabs were consistently more active on the treadmill at 3°C. Ongoing analyses of the tissue samples will show whether the observed behavioral differences are mirrored in cellular and molecular stress parameters. A mechanistic understanding of the population-specific tolerance and behavior is crucial for predicting potential future invasions of this species.

Summary of Data Being Collected

Data	Type	Quantity	Location
Tissue samples of clams exposed to varying predator densities in the field and lab	Gene expression	400	Biddeford Pool
Aggression score of crabs	Aggression score of crabs	40	Biddeford Pool
Eelgrass destruction by green crabs	Observations in mesocosm	40	Marine Science Center