Development and Refinement of Methods for Early Detection of European Green Crab Active
European green crabs are one of the most widespread marine invasive species on the planet. Where they are abundant, green crabs compete with other crabs and disturb sediment which can lead to loss of eelgrass and associated habitat essential for commercial, cultural, and ecologically important fish and invertebrate species. Green crab also are a major predator of clams, mussels, and oysters.
Green crab were established on the west coast of North America in the early 1990’s, and since then have found their way into the Puget Sound and greater Salish Sea and have been recently discovered in southeast Alaska. If green crab take hold throughout Puget Sound, they could significantly impact Tribal rights to aquatic resources, commercial and recreational fisheries (e.g., native rock crab and Dungeness crab, a $50M fishery), and the large shellfish culture industry. Early detection monitoring and biosurveillance for green crab may be successful if new populations can be detected early enough to enact control measures that will limit their establishment and spread, especially in areas where they are not currently abundant. At the USGS Western Fisheries Research Center (WFRC), we are conducting research that aims to bridge information gaps and develop and refine methods for improved early detection of green crab that can be applied to and increase the capacity of biosurveillance programs.
Current Projects
Evaluating the influence of tidal phase on the detection of green crab environmental DNA
Environmental DNA (eDNA) is a promising tool for broadly assessing the distribution of invasive green crab; however, before eDNA methods become part of a biosurveillance program, studies aimed at refining eDNA sampling protocols are needed to optimize green crab detections. This study (initiated in summer 2023) will identify whether detection of green crab eDNA is affected by the tide phase when water samples were collected. To accomplish this task, we collected replicate water samples for eDNA analysis at low tide, high tide, and during the flood and ebb tides across four different habitat categories consisting of tributaries (8), lagoons (4), tide channels (4), and marinas (5). The eDNA samples are currently being analyzed at WFRC. Information gained from this study will be useful for resource managers developing green crab biosurveillance strategies and will determine if eDNA monitoring programs may benefit by performing targeted sampling at certain phases in the tidal cycle that yield higher green crab detection probabilities while avoiding other tidal phases that yield poorer detections.
Assessing the efficacy of light traps for capturing larval green crab
This study aims to investigate whether the network of light traps used to monitor larval Dungeness crab in Washington state could also serve as a reservoir for monitoring dispersal of green crab larvae. Planktonic Dungeness crab larvae exhibit positive phototaxis and enter light traps, where they can be readily sampled and visually identified, providing quantifiable information for population dynamics. However, it is unknown if planktonic green crab larvae exhibit the same phototactic behavior. Unlike Dungeness crab larvae, green crab larvae are small and difficult to identify visually, and therefore, we seek to use DNA methods to detect green crab larvae in light traps. Our preliminary results from a pilot study suggest green crab larvae are detected in light traps. Large-scale testing of the efficacy of light traps will involve the deployment of light traps at several sites represented by different density categories of adult green crab (e.g., high, moderate, low, and none), with each density category being represented by several sites. If green crab larvae are routinely captured in light traps, then the Dungeness light trap network could be multipurposed for monitoring dispersal of green crab larvae and invasion fronts in addition to commercially important Dungeness crab.
European green crabs are one of the most widespread marine invasive species on the planet. Where they are abundant, green crabs compete with other crabs and disturb sediment which can lead to loss of eelgrass and associated habitat essential for commercial, cultural, and ecologically important fish and invertebrate species. Green crab also are a major predator of clams, mussels, and oysters.
Green crab were established on the west coast of North America in the early 1990’s, and since then have found their way into the Puget Sound and greater Salish Sea and have been recently discovered in southeast Alaska. If green crab take hold throughout Puget Sound, they could significantly impact Tribal rights to aquatic resources, commercial and recreational fisheries (e.g., native rock crab and Dungeness crab, a $50M fishery), and the large shellfish culture industry. Early detection monitoring and biosurveillance for green crab may be successful if new populations can be detected early enough to enact control measures that will limit their establishment and spread, especially in areas where they are not currently abundant. At the USGS Western Fisheries Research Center (WFRC), we are conducting research that aims to bridge information gaps and develop and refine methods for improved early detection of green crab that can be applied to and increase the capacity of biosurveillance programs.
Current Projects
Evaluating the influence of tidal phase on the detection of green crab environmental DNA
Environmental DNA (eDNA) is a promising tool for broadly assessing the distribution of invasive green crab; however, before eDNA methods become part of a biosurveillance program, studies aimed at refining eDNA sampling protocols are needed to optimize green crab detections. This study (initiated in summer 2023) will identify whether detection of green crab eDNA is affected by the tide phase when water samples were collected. To accomplish this task, we collected replicate water samples for eDNA analysis at low tide, high tide, and during the flood and ebb tides across four different habitat categories consisting of tributaries (8), lagoons (4), tide channels (4), and marinas (5). The eDNA samples are currently being analyzed at WFRC. Information gained from this study will be useful for resource managers developing green crab biosurveillance strategies and will determine if eDNA monitoring programs may benefit by performing targeted sampling at certain phases in the tidal cycle that yield higher green crab detection probabilities while avoiding other tidal phases that yield poorer detections.
Assessing the efficacy of light traps for capturing larval green crab
This study aims to investigate whether the network of light traps used to monitor larval Dungeness crab in Washington state could also serve as a reservoir for monitoring dispersal of green crab larvae. Planktonic Dungeness crab larvae exhibit positive phototaxis and enter light traps, where they can be readily sampled and visually identified, providing quantifiable information for population dynamics. However, it is unknown if planktonic green crab larvae exhibit the same phototactic behavior. Unlike Dungeness crab larvae, green crab larvae are small and difficult to identify visually, and therefore, we seek to use DNA methods to detect green crab larvae in light traps. Our preliminary results from a pilot study suggest green crab larvae are detected in light traps. Large-scale testing of the efficacy of light traps will involve the deployment of light traps at several sites represented by different density categories of adult green crab (e.g., high, moderate, low, and none), with each density category being represented by several sites. If green crab larvae are routinely captured in light traps, then the Dungeness light trap network could be multipurposed for monitoring dispersal of green crab larvae and invasion fronts in addition to commercially important Dungeness crab.