Progress Report Only
Economic and environmental sustainability of Maine working waterfronts has declined as capture fisheries that support them have consolidated or collapsed. Adoption of sustainable aquaculture has become critical to the diversification of the working waterfront in Maine. Emerging as a foundational aquaculture species in Maine are rope-grown farmed blue mussels (Mytilus Edulis). Considered among the highest quality mussels on the market they command a premium yielding market prices upwards of $8.00/lb with a seemingly insatiable market demand.
Any yet, the blue mussel in the Gulf of Maine (GoM) is struggling in the face of climate change. The GoM is rapidly warming (Pershing et al., 2015), producing physiological disruptions (Lesser, 2016) and bringing with it acidic waters, invasive predators, competitor species. The result is an alarming decline in wild intertidal populations (Sorte et al, 2016.) Furthermore, in summer 2016 an unexplained mortality event of farmed mussels led to a loss of ~$60,000 worth of mussel stock on one farm in Casco Bay, Maine.
Despite this, there has been no assessment of the condition, pathology, or parasitology of farmed blue mussels in Maine. We propose an intra-seasonal health and condition assessment through combined histopathological and biochemical analysis of pathology, reproduction and fatty acids in mussels farmed in Casco bay, Maine.
Results will inform farmers of when their crop is healthy, stressed, and nutritious, the development of best management practices to mitigate product loss, and serve as an important pathological baseline for monitoring farmed mussel populations as the GoM and climate continue to change.
Maine rope-grown farmed blue mussels (Mytilus Edulis) have garnered a reputation as some of the highest quality mussels on the market commanding a premium farm-gate value and yielding market prices upwards of $8.00/lb. The industry is currently incapable of filling market demand and is poised for sustainable expansion. However, in the face of climate change the GoM is among the most rapidly warming portions of our global oceans (Pershing et al., 2015), making farming blue mussels in the Gulf of Maine not without its challenges and risks. In fact, mussels appear to be already struggling in the GoM; a recent alarming study reported on the severe long term decline in this species within the intertidal zone along the entire 3,500 mile coast of Maine (Sorte et al., 2016) and evidence suggests severe sub-lethal impacts and metabolic depression in response to climate change stressors as the organismal level (Lesser, 2016). In fact, farmers in the mid-coast Maine region during the 2016 growing season reported spontaneous mass mortality of market size product following spawning out of synch with normal reproductive cycles. This reproduction-mortality coupled phenomenon is indicative of severe stress in sessile marine invertebrates and has been documented previously in farmed mussels (Myrand et al., 2000). Despite these alarming events, there is paucity of data pertaining to the condition, pathology and parasitology of mussels in Maine. A histopathological and biochemical baseline for the region is needed in order to effectively monitor for changes in the health of farmed mussels in Maine in the face of a changing climate and a warming GoM.
OUR GOAL IS: To assess the intra-seasonal health and condition of farmed mussels in Casco Bay, Maine to
provide valuable information to farmers on when their crop is the most healthy, stressed, and nutritious.
OUR QUESTION IS: How do fatty acids, storage tissue abundance, reproduction and pathology vary in farmed
blue mussels in Casco Bay, Maine both temporally and spatially?
OUR OBJECTIVE IS: Through a partnership with Bang’s Island Mussel Farm in Casco Bay to use a combination
of environmental monitoring, histopathology (a cost effective tool used to assess health and condition of mussels)
and fatty acid analysis (measure of energy storage vs. expenditure due to metabolic maintenance) to determine how storage tissue quantity and quality (Adipogranular and Vesicular Connective Tissues coupled with fatty acid
quantity and profile) as well as the severity and presence of pathological indicators vary seasonally across farm
sites with different environmental conditions and within the same site.
This will serve as an important pathological baseline for monitoring farmed mussel populations in the future allow
for the development of best management practices to mitigate product loss either through limited handling during
periods during stress, optimization of stocking densities, raft spacing.
Materials and methods
Our approach leverages the farmer and farm crew to collect samples and deploy environmental monitoring equipment. This allows for greater sample sizes than the research team would be able to collect alone due to logistics of working at sea and the expense of boat time. Twice monthly, beginning in February, 2017 through the end of the sampling window for the project (December 2018) our partner farmer will collect mussels from two separate farms sites, in two size classes: juvenile (shell length 30-50mm) and market size (>50mm shell length). During each collection, enough mussels are harvested from each size class to be parsed across three different laboratory assays: Histology, Fatty Acid Analysis (FAA), and Stable Isotope Analysis (SIA). This large sample set will allow for a robust comparison between each farm site, especially with regards to histological analysis.
In addition to the site level sampling conducted by the farmer, researchers travel to the farm site at Clapboard Island in order to conduct more extensive sampling. During these occasions mussels are collected in the same size classes as are collected by the farmer: juvenile and market size. For these sampling events, mussels are collected at each raft present at the farm site in order to assess raft to raft differences within a site.
Environmental Data Collection
Additionally at each farm site is deployed an array of environmental monitoring equipment & data loggers. Parameters measured include temperature, light, dissolved oxygen and salinity. In addition to these data, we will pursue datasets of opportunity available via regional weather and tide stations as well as oceanographic buoys deployed in the bay as a part of the Maine EPSCOR Sustainable Ecological Aquaculture (SEANET) project (http://maine.loboviz.com/).
Immediately after harvest, mussels are put on ice and transported to the UNE Marine Science Center where they are worked up for each analysis. For every mussel collected, basic biometric data are collected including Shell length, width, and depth, total weight, shell weight, and meat weight (wet), as well as a colorimetric estimate of gender.
Mussels destined for histology are fixed in 10% zinc buffered formalin in seawater solution for 24 hrs prior to rinsing and storage in 70% ethanol. Prior to histological processing, mussels are cut dorsoventrally in the center of the mussel, just anterior of the foot and byssal gland. Mussels are sectioned at 5um thickness at 1mm intervals, a total of 5 sections per mussel, and stained with Hematoxylin.
Mussels of each size class are chosen and cleaned of fouling organisms. The mussel is then shucked and removed from the shell. The meat is then placed in a lipid-cleaned vial -80ºC. because of the expensive nature of lipid and fatty acid elucidation, lipid samples will be archived and analyzed based upon storage tissue inferences observed via the histological analysis. Selected samples will be analyzed for fatty acid content and profile by Bigelow Laboratory for Ocean Sciences via extraction and methylation to Fatty Acid Methyl Esters (FAMEs) with internal standard (C19:0) using approach of Breuer et al. (2013) modified for fish tissue, based on Parrish et al. (2015). Quantification will be by GC/MS using Supelco 37 component FAME standard, to confirm compound identity and for individual compound calibration relative to the internal standard.
Accessory data: Stable Isotope Analysis
While not included in the initial award, our partner laboratory, the Byron Marine Ecology Lab, routinely conducts stable isotopic analysis (SIA) of marine invertebrates for assessment of trophic station and food web analysis via carbon and nitrogen. We collect mussels for SIA in the hope their analysis may shed greater light on the food and food web connections to mussel storage tissue ratios, fatty acids, and reproduction. The meat is then placed in a labeled and ashed 20mL vial and stored in a freezer. Frozen samples are freeze dried for 24 hours (more time may be necessary for larger mussels) then either placed back in the freezer or crushed using a mortar and pestle. Samples are crushed to a fine powder, returned to their respective vials and can be frozen indefinitely (OR placed in a Tupperware with desiccant). 1(microgram) of powder is weighed out and packaged in foil. Samples are then sent to an outside laboratory for analysis of carbon and nitrogen.
Histopathology has been monitored continually as samples have been processed. It is important to note this is only 50% of the way through the project and any insights at this point are preliminary. AS part of this section, included are two student reports (pdf format) completed during the past year that will be built upon and unified with environmental, lipid and isotope data as well as with samples collected in months 12-20 of this 24 month project.
Parker_Katherine_2018 (please ignore NSF language at end of report. NSF/Main EPSCoR funds were leveraged as student stipends to conduct this work)
All lipid samples are being archived in cold storage and will be analyze in bulk at the conclusion of sampling for cost savings.
At this point, the study is only 50% complete. Thus far, we have established the dominant pathological indicators and agents the present in blue mussels on our partner farm. In addition we now have a detailed window into the reproductive cycle and timing at the farm sites as well as refined methods for assessing storage tissue ratios using image analysis software. Over the course of the next year, we will continue intensively sampling, send out lipid samples for analysis sand begin to build the picture of health and reproduction in farmed blue mussels in Casco Bay, Maine.