tide-minded guides

A resource for fisheries and aquaculture en​thusiasts

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Oyster bag critter id

An ID guide to organisms commonly found in, on, and around oyster grow bags ​and other aquaculture equipment used in the Gulf of Maine and North Atlantic.

Non-native and invasive

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white barnacle

(Balanus subalbidus)

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Wild Lobster Animal
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black scour weed

(Ahnfeltia plicata)

Black scour weed bleaches when dried and ​can live up to 10 years.

bladderwrack

(Fucus vesiculosus)

Bladderwrack is commonly used by other ​species, including other seaweeds and ​mollusks, as a cover during low tide to avoid ​drying out.

gULF of maine phytoplankton id

An ID guide to some of the most common phytoplankton species found in the Gulf ​of Maine and North Atlantic.

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Water quality

WHAT IS WATER QUALITY?

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Water quality is a measure of how suitable water is for various uses, such as drinking, ​recreation, agriculture, and supporting aquatic life. Factors that contribute to water ​quality include the presence of pollutants like heavy metals, pesticides, and bacteria, as ​well as the levels of dissolved oxygen, pH, temperature, nitrogen, and turbidity. ​Maintaining good water quality is essential for human health, ecosystem stability, and ​sustainable water resource management. Monitoring and managing water quality often ​involve regular testing, regulation, and implementation of conservation practices.





WHY IS MONITORING WATER QUALITY IMPORTANT?

Here are some of the major reasons to actively monitor water quality in the field of ​aquaculture:

  1. Health of Aquatic Organisms: Aquatic organisms are highly sensitive to changes in ​their environment. Poor water quality, such as high levels of pollutants or low oxygen ​levels, can stress organisms and even cause mortality. Maintaining good water ​quality ensures the health and well-being of the farmed species.
  2. Growth and Productivity: Optimal water quality conditions promote better growth ​rates and higher productivity in aquaculture systems. Factors like adequate oxygen ​levels, proper pH, and absence of toxins support normal physiological functions and ​growth of the cultured organisms.
  3. Disease Prevention: Poor water quality can weaken the immune systems of aquatic ​organisms, making them more susceptible to diseases and infections. Clean water ​reduces the risk of disease outbreaks, minimizing the need for antibiotics or other ​treatments.
  4. Product Quality and Safety: Water quality directly influences the quality and safety ​of the aquaculture products. High water quality standards help ensure that the fish ​or shellfish produced are safe for human consumption and meet regulatory ​requirements.
  5. Environmental Sustainability: Maintaining good water quality in aquaculture ​operations is essential for minimizing negative impacts on the surrounding ​environment. Preventing pollution, managing waste, and reducing nutrient runoff ​help preserve water ecosystems and maintain biodiversity.




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THE NITROGEN CYCLE

The nitrogen cycle is essential for maintaining the balance of nitrogen availability for ​primary producers (such as phytoplankton and seaweeds), which form the base of the ​marine food web. It also influences the overall productivity and health of marine ​ecosystems. Human activities, such as agriculture, industrial runoff, and pollution, can ​disrupt the nitrogen cycle and help increase the likelihood of harmful algal blooms. ​Understanding and managing nitrogen cycling processes are critical for the ​conservation and sustainable use of marine ecosystems. Below is a brief overview of the ​Nitrogen Cycle:

  1. Nitrogen Fixation & Ammonification: Nitrogen-based compounds from organic ​matter is converted into ammonia (NH3) or ammonium ions (NH4+) by nitrogen-​fixing bacteria during decomposition. High amounts of ammonia is toxic to most ​aquatic species, and environmental levels should remain nearly zero. High amounts ​of ammonia can be an indication of water contamination, such as from runoff after a ​rain storm.
  2. Nitrification: Ammonia is converted into nitrite (NO2-) and then into nitrate (NO3-) ​through the process of nitrification. This conversion is carried out by specialized ​bacteria known as nitrifying bacteria. Both nitrite and nitrate are harmful to aquatic ​life at high levels and impede oxygen absorption. Nitrate, the less toxic of the two, is ​the primary form of nitrogen available for use by most marine plants and algae. In a ​healthy ecosystem, levels of both should read nearly zero.
  3. Assimilation: Marine plants and algae take up nitrate from the water to build organic ​molecules like proteins, incorporating nitrogen into their tissues.





Marine Nitrogen Cycle

Image Source

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Harmful Algal Blooms (HABs) & Biotoxins

Biotoxins produced by certain species of phytoplankton can have significant impacts ​on shellfish and human health. To protect public health, regulatory agencies monitor ​shellfish harvesting areas for the presence of biotoxins. Shellfish harvesting may be ​closed temporarily in areas where biotoxin levels exceed safe limits. Monitoring ​phytoplankton can give aquaculturists and scientists hints as to when and where an ​algal bloom may occur and give them enough time to prepare for the potential impacts. ​Below is an overview of biotoxin accumulation in shellfish and its effects on health:

  1. Phytoplankton Production: Phytoplankton are microscopic algae that form the base ​of the marine food web (primary producers). Some species of phytoplankton ​produce toxins as a defense mechanism or as a by-product of their metabolic ​processes.
  2. Biotoxin Accumulation: Filter-feeding shellfish, such as mussels, clams, oysters, and ​scallops, can accumulate these biotoxins when they ingest the phytoplankton that ​produce them. Biotoxins often do not harm the shellfish, but they can become ​concentrated enough in the tissues of shellfish to cause serious illness when the ​shellfish are ingested.
  3. Paralytic Shellfish Poisoning (PSP): Caused by saxitoxins produced by dinoflagellates ​like Alexandrium spp. Symptoms can include tingling, numbness, dizziness, and ​nausea.
  4. Amnesic Shellfish Poisoning (ASP): Caused by domoic acid produced by diatoms like ​Pseudo-nitzschia spp. Symptoms can include gastrointestinal distress, seizures, and ​memory loss.
  5. Diarrhetic Shellfish Poisoning (DSP): Caused by okadaic acid and its derivatives ​produced by dinoflagellates like Dinophysis spp. Symptoms can include diarrhea, ​nausea, vomiting, abdominal pain, and chills.


Phytoplankton species that do not produce biotoxins can still produce large blooms in ​the right conditions, which can clog the gills of fish and shellfish and lead to mortality. ​When these blooms eventually die off, the bacteria that break down the algae during ​decomposition consume large quantities of dissolved oxygen in the water, which can ​also lead to high fish and shellfish mortality.









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Pseudo-nitzschia spp., a phytoplankton genus commonly attributed to shellfish harvesting closures.

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It may be helpful for aquaculturists to develop an action plan in the event of a HAB in ​their area. This plan could include a regular phytoplankton monitoring schedule, a list of ​contacts for when a bloom is detected (such as the Maine Department of Marine ​Resources or NOAA Fisheries), loss prevention measures, and a recovery plan.

It doesn't have to be expensive!

Monitoring water quality doesn't always require expensive high-tech equipment. ​Depending on your goals, having a general idea of what's going on in the water may be ​all you need, as opposed to having high-precision measurements.


For example, if you're an oyster farmer wanting to keep an eye on the pH of your area, ​you may only need a simple pH meter or color-coded test kit. While a more precise pH ​measurement collected from a research-grade sonde can be useful, knowing that your ​area has a pH of about 8 is as specific as the typical aquaculturist may need to be.


Below are some examples of cost-effective tools that you can use to track water quality ​in an accurate and reliable way without breaking the bank:


  1. Testing pH and nitrogen: A simple color-coded test kit, like the API saltwater test kit ​manufactured for saltwater aquariums, costs around $35 and is accurate enough to ​be trusted by serious aquarium hobbyists. It's readily available at most pet stores ​and measures pH, ammonia, nitrites, and nitrates. These chemical-based tests tend ​to be much more accurate than test strips and will give you a more precise reading.
  2. Testing salinity: A basic refractometer usually costs less than $20, requires no ​power to function, is super portable, and is highly accurate.
  3. Testing dissolved oxygen (DO): Unlike other water quality kits, DO meters can run a ​little more expensive. Also unlike other water quality parameters, DO needs to be ​read immediately since dissolved oxygen levels can change quickly as water ​conditions change. For example, while you can collect a water sample to test off-site ​for things like pH and salinity, DO levels can change between the time the sample ​was collected and the time it is tested. Do your research before investing in a DO ​meter and consider whether it's something you truly want to measure, and why. ​Typically, DO is not something an aquaculturist will need to worry about unless they ​are concerned about anoxia after a large algal bloom.
  4. Testing temperature: A basic thermometer of any kind can be used to monitor ​water temperature. For more detailed measurements over time, HOBO sensors are ​an inexpensive digital option. They're easy to use, they take periodic measurements ​on their own, and all data can be easily downloaded via Bluetooth onto a mobile app.
  5. Monitoring phytoplankton: Learning to collect and ID phytoplankton takes some ​practice and study and requires a microscope capable of at least 400X ​magnification. Consider using ID guides for the species in your area (like the one ​available on this website) to familiarize yourself with HAB species, and enroll in a ​local training or webinar hosted by specialists (such as one offered by NOAA). If ​you're unable to attend a training, YouTube is another great resource for learning ​how to collect samples using a plankton net. Be sure to find the right contact ​information for an appropriate agency that can verify your plankton IDs, like one at ​NOAA or your regional marine resources department, in case you notice a high level ​of HAB species.
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European green crabs

European Green Crabs (Carcinus maenas) are one of the world's ​most invasive non-native species. As their name suggests, they are ​native to European and North African marine environments and ​have been documented in the Gulf of Maine since at least the mid-​1800s. Green crabs have had a devastating effect on Maine's ​softshell clam and blue mussel populations, as well as regional ​eelgrass beds, which serve as a home for many young fish ​species.


This relatively small crab species offers a sweet, delicate flavor ​similar to the famous blue crabs found further south. They are ideal ​for deep-fried softshell crab dishes, savory soup stocks, and claw ​and leg meat. These crabs also make a nutritious addition to your ​garden compost, adding various minerals and aeration to your soil.


Pricing: Green crabs are $1.25/pound for mixed sizes and ​$2.00/pound for orders of large-crabs-only. 1 pound of mixed sizes ​is generally 6-10 crabs, and 1 pound of large crabs is generally ​about 3 crabs.

2024 Green Crab Monitoring

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Below is a collection of green crab population sampling data, starting from April 2024, for an area near Wolfe's Neck in Freeport, ​Maine. Data is updated periodically. Click the chart for full view.

resources

Explore Data

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