Published on October 28, 2025.
- New ROV Improves Aquaculture Site Visits
- Shellfish Illness Investigations
- Harmful Algal Blooms in a Changing World
- 2025 American Oyster Biotoxin Closures
New ROV Improves Aquaculture Site Visits
By Meryl Grady and Lisa White, DMR Aquaculture Division
As part of the lease application process, DMR is required to conduct a site visit for all proposed standard and experimental lease sites. DMR also has the discretion to conduct site visits for proposed standard lease expansions. The purpose of the site visit is to gather information about the proposed lease site and surrounding areas as required by law and rule. The information documented during the site visit includes, but may not be limited to, bottom composition, water depth, observed flora and fauna, relative abundance of commercial and recreational species, evidence of fishing activity, distances to shore, and navigation channels and moorings. Historically, most underwater assessments were conducted via SCUBA dive using various types of video recording equipment.
In 2023, DMR started using a remotely operated vehicle (ROV) to conduct site visits. Using the ROV nearly tripled the amount of site visits DMR was able to complete in one year, without compromising quality. The ROV requires one less person in the field and is quicker to deploy and recover when compared to diving. However, the ROV that was initially used was almost 20 years old and in need of replacement. This summer the Aquaculture Division acquired a new ROV, made possible by a grant from the Maine Aquaculture Innovation Center (MAIC).
The new ROV provides much better video resolution (4K), as well as sonar to aid in underwater navigation and assist with object identification in low visibility environments. Additionally, the new ROV has real-time location tracking meaning the position of the ROV is known at all times, both above water and underwater. This allows staff to more precisely mark the location of an object, such as eelgrass. The new ROV offers many additional features for the science team to explore, and its introduction has significantly improved data collection.
Many thanks to MAIC for their generous support and for helping to ensure that the lease application process is as efficient as possible!
Shellfish Illness Investigations
By Richard Riddell, DMR Shellfish Inspector
As Shellfish Inspectors for the Bureau of Public Health we have many responsibilities. Our main duty is implementing state and federal regulations for the wholesale and interstate commerce of shellfish, but one unique aspect of the position is investigating reported illness due to the consumption of bivalve mollusks in retail trade.
As summer approaches and the temperatures increase more people find themselves traveling and vacationing along the coast of Maine. One of the great features of coastal Maine is the fresh and abundant seafood. As people consume seafood on their travels and temperatures rise, the risk of exposure to foodborne illness increases. This can be caused by just about any food item, but we focus on illnesses caused by the consumption of bivalve mollusks i.e., clams, mussels, oysters, anything with two shells.
The Maine Center for Disease Control receives all complaints of foodborne illnesses; their epidemiologists quickly get to work interviewing and tracking down possible items that have been consumed. Any consumption of shellfish related to the illness is sent to the DMR Inspection Program for follow up to see if the illness is related to shellfish and to complete a traceback to see where the shellfish were purchased and what may have been the breakdown in handling of the shellfish that caused the illness.
The Shellfish Inspectors touch base with other agency inspectors from the Dept of Health and Humans services (DHHS) or the Dept. of Agriculture, Conservation and Forestry, depending on where the illness originated. In most cases it falls within the guidelines of DHHS as most foodborne illnesses are found at eating places such as restaurants or take-out. DHHS inspectors investigate food code related violation in the restaurant setting, while DMR inspectors investigate shellfish storage and handling and collection of tags and invoices of the shellfish in question. First a determination is made if there were signs of cross contamination or mishandling by the restaurant or take out, then the dealer tags and invoices are used to trace back the shellfish to its origins of harvest.
Once the Shellfish Inspectors have the dealer tags and invoices they can go to these dealerships and trace back every step that this product made before being shipped out. The shellfish dealerships have very strict rules set forth by the Food and Drug Administration’s National Shellfish Sanitation Program (NSSP) under the section called the Model Ordinance (MO). In the MO all shellfish handling regulations are listed and must be followed to sell shellfish through intrastate and or interstate commerce. As part of the investigation, the implicated shellfish can be found in the records of the dealership and reviewed to make sure each regulation was met prior to the shellfish being sold.
Once all the information is collected a report is written with guidance as to what may have caused the illness and to help prevent illnesses in the future. For more information reach out to your Shellfish Inspector or contact us at: DMRPublicHealthDiv@maine.gov
Harmful Algal Blooms in a Changing World
By Kevin Lachapelle, Marine Resource Specialist II
Harmful algal blooms (or HABs) are not a new phenomenon. They can occur in any large body of water, fresh or marine, and have traditionally adhered to a predictable seasonal pattern linked to warmer summer water temperatures. A HAB can refer to a number of different species of algae or phytoplankton, but the key characteristics of one are a large, sudden increase in numbers of a particular species that negatively impacts the health of other organisms in the ecosystem. This typically happens in one of two ways: unchecked growth and subsequent death and decomposition of large numbers of cells can deplete oxygen levels which starves other organisms of the oxygen they need to survive, or a species that naturally produces toxins can bloom resulting in dangerous spikes of toxin levels at the base of the marine food chain. This second type of HAB is particularly dangerous to people since the toxins can bioaccumulate, or increase in concentration the farther up the food chain you go, and people tend to be at the top of this food chain. That is why all coastal states that commercially harvest shellfish have a shellfish biotoxin monitoring program (including Maine).
HABs have been showing up in the news lately. Southern California has had particularly severe blooms of a toxin producing plankton called Pseudo-nitzschia for the past several years, with this year’s being one of the earliest and most damaging, resulting in the deaths of fish, seals, dolphins, and even whales. Southern Australia has been experiencing an unprecedented bloom of oxygen-depleting Karenia mikimotoi that has resulted in massive fish and shellfish die-offs affecting commercial fisheries and aquaculture. A quick internet search for HABs results in local news articles describing freshwater blooms throughout the U.S. affecting recreation and drinking water sources. The overall trend seems to indicate that HABs are starting earlier, showing up in new places, and potentially becoming more intense.
Why are we seeing an increase in the range and magnitude of HABs? A HAB can occur when environmental conditions allow for unchecked levels of reproduction in algae and plankton species present and the main factors that dictate reproduction for these species are typically water temperature and access to nutrients. Global water temperature trends show a generally warming aquatic environment which can encourage algal and plankton reproduction. Changes in ocean temperature can also affect ocean currents, transporting species of algae and plankton to places they previously did not have access to. Large upwelling currents can be a source of nutrients in the marine environment and are thought to be part of the cause for the California and Australian blooms, along with pollution from coastal runoff.
Here in Maine, we have luckily not experienced any major mortality events due to HABs. However, the DMR’s Biotoxin Monitoring Program has seen toxin occurring earlier in the season, and when a bloom does occur, there is little we can do to mitigate it other than close affected areas to harvesting until testing shows toxins have returned to safe levels. Many of the factors that contribute to HABs are things that are happening on regional or even global scales, mainly water temperature and currents. While there is little we can do at our scale as a small state to influence many of these factors, one thing we can influence and control is our coastal runoff. Be aware of where the wastewater from your house or camp goes. Limit the amount of fertilizer you use on your property. Pick up and properly dispose of your pet waste. By reducing our contributions to the nutrient load in coastal waters, we may be able to stave off or reduce the magnitude of future HABs in Maine waters. It may not result in news articles, but with HABs, no news is good news.
2025 American Oyster Biotoxin Closures
By Bryant Lewis, Marine Resource Scientist IV
The Gulf of Maine experiences annual summer blooms of Alexandrium, the phytoplankton responsible for paralytic shellfish poisoning (PSP), commonly called “red tide”. The Maine Department of Marine Resources (DMR) monitors these harmful algal blooms and tests shellfish tissues for the presence of toxins harmful to people who eat shellfish. Blue mussels are the primary shellfish tested because they accumulate toxin faster than other bivalve shellfish species. Toxin detection in blue mussels will trigger the collection of additional shellfish species which may lead to additional species-specific closures if toxin is detected at certain thresholds in these other species.
During a typical harmful algal bloom, toxin is first detected in mussels then followed by clam species, but not in American oysters experiencing the same bloom. Hypotheses have been suggested to explain that the lack of toxin uptake could stem from the possibility that the oysters may selectively exclude Alexandrium from their diet. Research has shown that American oysters appear to preferentially graze on certain algae (Weissberger and Glibert, 2021) and laboratory experiments have shown that diets largely composed of Alexandrium may be harmful to oysters (Lassurdie et al., 2015). These feeding habits may suggest that American oysters in Maine waters generally avoid feeding on this harmful algae.
DMR tests American oysters for toxin in hotspot areas once Alexandrium blooms occur. These locations serve as an early warning that toxin is present in oyster tissue and that further testing is necessary. Following closures, wet storage permit holders and aquaculture leaseholders with memoranda of understanding (MOU) with DMR may have their product tested to operate during a closure. However, these MOU had not been used for oyster testing since the last time toxin was found in American oysters in 2019. In late May 2025, paralytic shellfish toxins were detected in oysters in the Harpswell area resulting in local closures. The bloom continued to spread with DMR locations and MOU sites from Scarborough to West Bath testing high for shellfish tissue toxin (see Figure 1). Numerous locations from the Maine/New Hampshire border through Pemaquid tested above the closure threshold and were kept closed through July 11 2026 until the bloom and toxin scores declined. Figure 1 shows oyster tissue high scores in the greater Casco Bay area and Scarborough River (inset map). This was the first PSP American oyster closure in six years. The length and strength of this year’s Alexandrium bloom, which notably had been closing shellfish areas from Maine to Massachusetts, would have played a role in this uncommon closure and other environmental factors could have impacted the American oyster making this a particularly disruptive year for the oyster industry. Due to the continued expansion of floating aquaculture gear in high-risk areas, DMR is now examining additional options to increase its testing capacity in oysters for the future.
