To preserve plankton, you've got several options. Traditional chemical fixation uses formaldehyde or glutaraldehyde, while cryopreservation involves rapid freezing with liquid nitrogen. Dehydration methods like air-drying or freeze-drying can work for some species. For microscopy, you'll need to prepare slides carefully, possibly with staining. If you're focusing on genomic preservation, quick action is key—use methods like flash-freezing or chemical stabilizers. Live culture maintenance requires mimicking natural habitats. For non-invasive studies, environmental DNA sampling is an emerging technique. Each method has its pros and cons, affecting how you can analyze the samples later. Exploring these techniques further will reveal which best suits your research needs.
Traditional Chemical Fixation Methods
For decades, traditional chemical fixation has been the go-to method for preserving plankton samples. You'll find that formaldehyde and glutaraldehyde are the most commonly used fixatives in this process. To begin, you'll need to add these chemicals to your plankton sample immediately after collection to prevent degradation.
When using formaldehyde, you'll typically create a 4% solution in seawater. It's excellent for preserving overall morphology but can cause some shrinkage. Glutaraldehyde, on the other hand, is often used at a 2.5% concentration and is particularly good for maintaining cellular ultrastructure.
You'll want to be aware that these chemicals can alter the sample's appearance and biochemical composition. They're also hazardous, so you'll need to handle them with care and use proper protective equipment.
After fixation, you'll need to store your samples in airtight containers to prevent evaporation. It's important to label each sample with the date, location, and fixative used.
Cryopreservation Techniques
While traditional methods have their place, cryopreservation techniques offer a modern approach to plankton preservation. You'll find that these methods involve rapidly freezing plankton samples to extremely low temperatures, typically using liquid nitrogen. This process halts all biological activity, effectively "suspending" the organisms in time.
To cryopreserve plankton, you'll first need to prepare your samples with a cryoprotectant solution. This helps prevent the formation of ice crystals that could damage cellular structures. Common cryoprotectants include glycerol and dimethyl sulfoxide (DMSO).
Next, you'll gradually cool the samples before plunging them into liquid nitrogen at -196°C.
One advantage of cryopreservation is that it preserves the plankton's genetic material and cellular structures more accurately than chemical fixation. This makes it ideal for studies involving DNA analysis or fine structural details.
However, you should be aware that not all plankton species tolerate the process equally well. Some delicate organisms may still suffer damage during freezing or thawing.
When you're ready to analyze your samples, you'll need to follow a careful thawing protocol to minimize cellular damage. This typically involves rapid warming in a water bath followed by gradual rehydration.
Dehydration and Desiccation Approaches
Moving from the cold storage of cryopreservation, let's explore another method for preserving plankton: dehydration and desiccation. These techniques involve removing water from plankton samples to prevent cellular degradation and maintain sample integrity.
You'll find two primary approaches: air-drying and freeze-drying. Air-drying is simpler but less precise. You'll spread plankton samples thinly on clean slides or filter paper and allow them to dry naturally. This method works well for certain species but can cause cellular damage in others.
Freeze-drying, or lyophilization, offers more control. You'll first freeze the samples, then subject them to a vacuum that sublimates the ice directly to vapor. This preserves cellular structures more effectively than air-drying.
For both methods, you'll need to take into account factors like temperature, humidity, and drying time. It's essential to prevent rehydration, so you'll store dried samples in airtight containers with desiccants.
While these techniques can effectively preserve plankton morphology, they may alter certain biochemical properties. You'll need to weigh the pros and cons based on your research goals and the specific plankton species you're working with.
Microscopy Slide Preparation
Preparing plankton samples for microscopy slides is an essential step in preserving and studying these tiny organisms. You'll need to start by selecting the appropriate slide type, typically a concave or depression slide for larger plankton or a flat slide for smaller species. Clean the slide thoroughly and verify it's free from any debris.
Next, you'll want to transfer a small amount of your preserved plankton sample onto the slide using a pipette or dropper. Be careful not to overload the slide; a single drop is often sufficient. If you're using a flat slide, gently place a coverslip over the sample, taking care to avoid air bubbles.
For staining, you can use various dyes to enhance visibility. Lugol's iodine is common for phytoplankton, while methylene blue works well for zooplankton. Apply the stain before adding the coverslip.
If you're preparing permanent slides, you'll need to use a mounting medium like Canada balsam. This helps preserve the sample long-term and improves optical clarity.
Remember to label your slides with relevant information such as date, location, and species if known.
Genomic DNA Preservation
Numerous plankton preservation techniques focus on genomic DNA, an essential aspect for molecular studies and species identification. To preserve plankton DNA, you'll need to act quickly after collection to prevent degradation. One common method is flash-freezing samples in liquid nitrogen, which rapidly halts cellular processes and protects genetic material.
If you don't have access to liquid nitrogen, you can use chemical preservatives. RNAlater is a popular choice, as it stabilizes RNA and DNA. Simply add the solution to your plankton sample and store it at -20°C for long-term preservation.
Alternatively, you can use ethanol, typically at a concentration of 95%, which dehydrates cells and inhibits enzyme activity.
For field work, you might consider using FTA cards. These specialized papers contain chemicals that lyse cells and protect nucleic acids. You'll just need to apply your plankton sample to the card and let it dry. This method's particularly useful when you're dealing with limited storage space or transportation issues.
Live Culture Maintenance
While preserving plankton DNA is vital for certain studies, maintaining live cultures offers unique research opportunities. To keep plankton cultures thriving, you'll need to provide ideal conditions that mimic their natural environment.
Start by selecting an appropriate culture medium, which varies depending on the plankton species you're working with. You'll need to maintain the correct temperature, typically between 15-25°C, using temperature-controlled rooms or incubators.
Light is essential for photosynthetic plankton, so you'll want to provide a light-dark cycle that matches their natural habitat. Use fluorescent or LED lights with timers to guarantee consistency.
Don't forget about aeration and water movement; gentle bubbling or stirring can help maintain oxygen levels and prevent settling.
You'll need to monitor nutrient levels regularly and replenish them as needed. Be vigilant about contamination by using sterile techniques and equipment.
To maintain healthy populations, you should subculture your plankton regularly, typically every 1-2 weeks. Keep detailed records of your culture conditions, growth rates, and any observations to guarantee reproducibility and track the health of your cultures over time.
Environmental DNA Sampling
Sampling environmental DNA (eDNA) offers a powerful, non-invasive method for detecting plankton species in aquatic ecosystems. To collect eDNA, you'll need to filter water samples through fine-mesh filters, typically with pore sizes ranging from 0.22 to 0.45 micrometers. It's essential to use sterile equipment and wear gloves to avoid contamination.
Once you've collected your samples, you'll need to preserve them immediately. You can do this by adding a buffer solution or freezing the filters. The choice depends on your downstream analysis plans and storage capabilities. For PCR-based analyses, ethanol preservation works well, while for metagenomic sequencing, freezing at -80°C is often preferred.
When extracting DNA from your samples, you'll use specialized kits designed for environmental samples. These kits help remove inhibitors that can interfere with subsequent analyses.
After extraction, you can use various molecular techniques to identify plankton species, such as quantitative PCR or high-throughput sequencing.
Erzsebet Frey (Eli Frey) is an ecologist and online entrepreneur with a Master of Science in Ecology from the University of Belgrade. Originally from Serbia, she has lived in Sri Lanka since 2017. Eli has worked internationally in countries like Oman, Brazil, Germany, and Sri Lanka. In 2018, she expanded into SEO and blogging, completing courses from UC Davis and Edinburgh. Eli has founded multiple websites focused on biology, ecology, environmental science, sustainable and simple living, and outdoor activities. She enjoys creating nature and simple living videos on YouTube and participates in speleology, diving, and hiking.