Using Technology to Assess the Invasive Sea Squirt, Didemnum vexillum, Impacts on Fisheries and Ecosystems (Regional)

Primary tabs

Project Type: 
Research
Project Number: 
RR/CE-143
Inception Date: 
2010
Completion Date: 
2011

Participants:

Judith Pederson MIT Sea Grant Co-Principal Investigator
Franz Hover Massachusetts Institute of Technology Principal Investigator
Robert Whitlatch University of Connecticut - Avery Point Co-Principal Investigator
Emmanuel Boss University of Maine - School of Marine Sciences Co-Principal Investigator

Students Involved:

Thomas Leeuw University of Maine - School of Marine Sciences
Abstract: 
In response to a call for regional research by the U.S. Commission on Ocean Policy and the Pew Oceans Commission report, a Gulf of Maine (GOM) Regional Ocean Science Plan (ROSP; http://seagrant.mit.edu/rosi) was prepared in 2006 based on stakeholder concerns. In 2008, MIT Sea Grant (SG) College Program responded to this plan and funded a pilot project to address several concerns in the ROSP, namely impacts of invasive species, support for fisheries, and technology development to support research. In the Northwest Atlantic, including the Gulf of Maine, one of the most dominant and aggressive non-native species is the colonial tunicate Didemnum vexillum, found from Maine to Connecticut, including Georges Bank. This sea squirt has a major impact on a large regional area, where it affects fisheries, alters native communities and fouls aquaculture facilities. Our pilot project explored the use of an acoustic sensor on an AUV as a method for quickly identifying Didemnum on the sea floor. Unfortunately, the Sound Metrics DIDSON (Dual frequency IDentification SONar) did not achieve the resolution needed to distinguish Didemnum from the gravel bed.
 
Because of the importance of the valuable groundfish and scallop fisheries in Georges Bank and to facilitate ongoing regional research on this invasive species in the Northeast, here we propose to continue our work with sensors adapted for the MIT Sea Grant autonomous underwater vehicle (AUV) Odyssey IV, and perform ecological studies to better understand the impact of Didemnum in marine cobble/pebble habitats, hence assessing its role as an ecological engineer. This proposal is submitted as a regional research project that builds on the initial pilot project and supports other relevant regional concerns. The long term goal is to refine the conceptual model of Didemnum and explore options for its management and control in the context of ecosystem-based management.
Objectives: 
1. Prototype and test an optical sensor (e.g. a hyperspectral radiometer) for rapid spatial surveys that detect Didemnum
 
2. Adapt the sensor for use on the Odyssey IV, a hover-capable AUV
 
3. Map the spatial coverage of Didemnum using digital cameras and optical sensors
 
4. Examine benthic species diversity composition in the presence and absence of Didemnum mats, and develop a conceptual model of the role of Didemnum as an ecological engineer to identify critical areas for future research
Methodology: 
The first year, effort on the sensor and vehicle systems will include: (1) examination of spectral reflectance of Didemnum and other common bottom materials (from different regions and seasons) from the Gulf of Maine in a laboratory setting, (2) development of feature extraction and classification algorithms to distinguish Didemnum from other bottom materials, and (3) design of a field-deployable prototype system with spectroradiometer and an active light source.
 
The second year objectives include: (1) thorough testing of the prototype radiometer system and classification algorithms in different regions and seasons; and (2) adaptation of the system to AUV missions by including data logging capabilities.
 
The field studies will involve taking paired core samples (10 cm diameter) from the center of a mat and one meter from the edge, by divers following earlier protocols. Taxa will be sorted and identified to the lowest possible taxa and categorized as infauna or epifaunal organisms by trophic group. Data will be analyzed for diversity, changes in trophic structure in areas with and without high Didemnum coverage. Second, digital photos will the analyzed, using Image J software, to assess bottom substrate type, and estimate the percent of cover by the tunicate. Photographic images will be taken during all phases for verification, including from the AUV platform.
Rationale: 
In 2008, MIT Sea Grant (SG) College Program responded to the need for regional research and funded a pilot project to address concerns in the Gulf of Maine Regional Ocean Science Plan, namely impacts of invasive species, support for fisheries, and technology development to support research. This proposal is submitted as a regional research project that builds on the initial pilot project and other relevant regional research.
 
In the Northwest Atlantic, including the Gulf of Maine, one of the most dominant and aggressive non-native species is the colonial tunicate, Didemnum vexillum found from Maine to Connecticut, including Georges Bank. This proposal seeks to evaluate the ecological impacts of Didemnum in marine cobble/pebble habitats, assess its role as an ecological engineer, and support the design and testing of optical sensors that will be adapted for the MITSG autonomous underwater vehicle (AUV), Odyssey IV. The long-term goal is to refine the conceptual model of Didemnum as an ecological engineer and explore options for its management and control in the context of ecosystem-based management. This is an integrated effort that will proceed along two paths simultaneously, modifying an optical sensor for detecting Didemnum and adapting it for use on the AUV, as well as continuing to use photography and grab samples to evaluate the impact of Didemnum in hard substrate habitats and support fisheries management to ensure a sustainable fishery.
Accomplishments: 
2012

Researcher Finds High Tensile Strength of Tendrils Limits Breakage and Affects Dispersal of the Non-native Tunicate, Didemnum vexillum

For Didemnum vexillum, developing propagation models for populations is related to specific attributes of the sea squirt. The fragment tendrils of Didemnum form balls that are dispersed and can reattach, giving rise to a new colony. Understanding rates of fragmentation that lead to dispersal as well as larval release is needed. Data on the rate of fragmentation under specific current speeds will be used to assess spread and dispersion. A paper, “Material properties of Didemnum vexillum and prediction of tendril fragmentation,” has been published in Marine Biology in 2012 describing the high tensile strength of the tendrils. Didemnum vexillum tendrils have a higher tensile strength than other tunicates and are not easily broken by wave action except in extreme cases (e.g. , storms and some vessel generated waves).

Researcher Identifies Reflectance Specific to Invasive Sea Squirt
Using a radiometer attached to a hybrid autonomous underwater vehicle (AUV), reflectance specific to Didemnum was identified in 2012 and promises to efficiently identify the sea squirt in the field. The AUV was deployed in a marina in Hull, Massachusetts, that has Didemnum growing on pilings and pontoons through the late fall and early winter. For each cruise, a spectralon 99% reflectance calibration plate was used to remove the spectral characteristics of the illumination sources, water color and green plankton. The identifying features for Didemnum were a low plateau between 450 and 500 nm rising to a high plateau between 600 and 650 nm. The video from the AUV was posted on YouTube and shared (for example, see http://www.youtube.com/watch?v=EM4KG1uNMXM).

2011

 
Adaptation of Radiometer on REX II to Detect Didemnum in Coastal Ecosystems
REX II was used to image the pilings below the public pier in Hull, Mass. in November 2011. During the dive, extensive coverage of Didemnum vexillum encrusting the pilings along with other organisms were imaged with a camera and radiometer data were taken of spectra reflected by Didemnum. There was good visibility, so sharp and colorful imagery of the site was possible. The radiometer was used to sample a spectralon plate with ambient light only and with LED illumination at several standoff distances. These tests were used to calibrate the measured spectra of Didemnum by normalizing the spectrum of the illumination source. The initial findings show the spectra reflected by the Didemnum look very similar to those recorded in the laboratory setting. Additional field work will be performed to increase the baseline data set in order to identify detailed and unique features of the Didemnum spectra.

Publications

Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant

Journal Article

  • Leeuw, T., S. Newburg, E. Boss, W. Slade, M. Soroka, J. Pederson, C. Chryssostomidis and F. Hover (2013). Remote identification of the invasive tunicate "Didemnum vexillum" using reflectance spectroscopy. Applied Optics 52(8):1758-1763, March 2013.