Seaweed to the rescue: a green solution to nematode control!

Plant-parasitic nematodes are microscopic worms that damage roots and significantly reduce crop yields worldwide, making them a major threat to agriculture (Nicol et al., 2011). Although chemical nematicides have been used to manage these pests, many are being restricted because they can harm beneficial soil organisms and contribute to environmental pollution (Ntalli & Caboni, 2012). Growing concern over these impacts inspired my interest in exploring safer, natural alternatives for nematode control.

My project began after visiting the Dalhousie University Faculty of Agriculture and meeting Dr. Prashant at the Marine Bioproducts Research Laboratory, where I learned about parasitic nematodes and the potential of marine natural products as biocontrol agents. I discovered that seaweeds contain bioactive compounds with nematicidal properties that can affect nematode movement, feeding, reproduction, and survival (Ghareeb et al., 2019; Archana U. Singh & Prasad, 2014). Red seaweeds, in particular, are rich in compounds with promising biological activity (Carpena et al., 2023), and recent studies show that extraction methods strongly influence both yield and bioactivity (Cardoso et al., 2025; Bhatt et al., 2025).

This led me to investigate whether dulse (Palmaria palmata), a locally abundant Nova Scotian seaweed, could help control nematodes and how extraction methods affect its effectiveness. I was especially interested in whether a locally available marine resource could provide a practical, sustainable, and affordable tool for farmers. This research could support environmentally friendly pest management, reduce reliance on harmful chemicals, and contribute to long-term soil health, biodiversity conservation, and food security.

Natural and cultivated dulse (Palmaria palmata) was purchased for this study. Caenorhabditis elegans (C. elegans, N2 wild-type strain) and E. coli OP50 were obtained from the Caenorhabditis Genetics Center at the University of Minnesota and used in the experiments.

Step 1. Extraction and Concentration of Compounds from Natural and Cultured Seaweeds

Compounds were extracted from natural and cultivated dulse using microwave- and ultrasound-assisted extraction with methanol and water solvents. Dried dulse was ground into a fine powder, and equal amounts (0.5 g each) were placed into microwave tubes with 10 ml of 50% methanol. The samples were heated at 100 °C for 15 minutes.

For ultrasound extraction, 10 g of natural seaweed was blended with 100 mL of distilled water until smooth. An equal amount of methanol was added, and the mixture was transferred to a conical flask and sonicated for 2 hours. Both the samples were centrifuged at 4000 rpm for 15 minutes at 20 °C, and the supernatant was collected, freeze-dried, reconstituted in water (500 mg/mL) to obtain a stock concentration, and stored at −20 °C until further use.

Step 2: Culturing C. elegans and Treatment with Different Extracts

C. elegans were grown on NGM agar plates with E. coli OP50 at 20 °C. Worms at the L3–L4 stage were collected using 1 mL M9 buffer and washed twice to remove bacteria. Then, 10 µL of worm suspension was added to each well of a 96-well plate. Extracts were added to reach final concentrations of 1 mg/mL and 5 mg/mL, with a total volume of 50 µL per well.

Plates were incubated at 20 °C, and worm survival was assessed at 1, 3, 5, and 7 hours using an inverted microscope (100×). Data were recorded and analyzed using an ANOVA Tukey test.

The results showed that all four dulse extracts affected C. elegans more than the water control, causing higher levels of paralysis and death. This indicates that the extracts had a real biological effect on the worms. Two-way ANOVA showed that treatment had a highly significant effect on both paralysis and death (p < 0.001). Overall, both the type of extract and the concentration influenced how strongly the worms were affected.

As time increased from 1 to 7 hours, the effects became stronger. At earlier time points (1–3 hours), most worms were still alive, but many became paralyzed (Figure 1). The paralysis graph shows a steady increase across all treatments, with Natural seaweed ultrasound- assisted extraction using 50% methanol (NSME-U) and Cultivated seaweed microwave - assisted extraction using 50% methanol (CSME-M) reaching the highest paralysis percentages, especially at 5 mg/mL. By 5 and 7 hours, more worms died (Figure 2), and the mortality graph shows a gradual increase in death rates over time, with NSME-U consistently showing the highest mortality, followed by CSME-M. This pattern supports that paralysis often occurred first and was followed by death.

The juglone treatment acted as a positive control and caused almost immediate death, confirming that the experiment was working properly (Figure 3). In contrast, the dulse extracts showed a slower but increasing effect over time. At lower concentration (1 mg/mL), the graphs show smaller differences between treatments and the control, especially at early time points. However, at 5 mg/mL, the separation between treatments becomes much clearer, with higher paralysis and mortality values.

The Tukey post-hoc test (Table #1, p < 0.05) confirmed that NSME- U and CSME-M were significantly different from the control and had the strongest overall effects. Cultivated seaweed agitation - assisted extraction using water (CSWE- A) and Cultivated seaweed ultrasound - assisted extraction using 100% methanol (CSME-U) mainly caused paralysis but lower mortality, suggesting their extraction methods may have been less effective at isolating the most toxic compounds. Juglone showed significantly lower survival than all other treatments (p < 0.001), confirming its role as a strong positive control.

The FTIR results showed that both the wild and cultivated Palmaria palmata samples had very similar peaks meaning they likely contain many of the same compounds such as carbohydrates sulfated polysaccharides and some protein-related groups. There were a few small differences between the samples The wild sample had a peak at 1626 cm and a clearer peak at 977 cm which may be linked to proteins or certain sugars The cultivated sample had extra peaks at 1397 cm and 1344 cm which may be linked to cell wall sugars or other natural compounds.

Figure 4, shows images of live, paralyzed, and dead worms, further supports these results.

Overall, the results suggest that dulse extracts can affect C. elegans, and their effectiveness depends on both concentration and exposure time. Higher concentrations and longer exposure led to greater paralysis and death, showing the potential of these extracts as natural nematode control agents.

This experiment shows that how we extract compounds from dulse might be more important than the compound itself. The two-way ANOVA showed the extraction method had a big effect on paralysis and death of C. elegans. Ultrasound-assisted and microwave-assisted methanol extraction caused about 80–90% paralysis, which was higher than water extraction. This is likely because these methods extract more bioactive compounds from dulse.

This means that the same seaweed can give different results depending on two main things: the type of solvent used (like water or methanol) and how much energy is used to break open cells, such as with ultrasound or microwave-assisted methods. Even though the results for paralysis were statistically significant, the mortality rate was still less than 25%. In comparison, the positive control, juglone, caused 100% death within one hour. This suggests that the compounds from dulse can stop the worms from moving but aren’t strong enough yet to kill them.

If I continued this experiment, I would see what happens to the paralyzed worms over time. For example, I would check if they can still reproduce or lay eggs during their 2–3 week lifespan, because that could mean they still pose a risk to plants.

Another important result was that natural dulse worked better than cultivated dulse when the same method was used. This could be because wild seaweed is exposed to environmental stress, which may cause it to produce stronger defensive chemicals that are more effective at paralyzing or killing nematodes.

My future experiment is to study the long-term effects of paralysis on worm reproduction over their lifespan and its potential risk to plants. I will improve worm transfer methods to ensure synchronized populations and more consistent results. A key finding was that 80–90% of worms were paralyzed, while less than 25% died, suggesting dulse extracts affect muscle and nerve function more than mortality. Future studies could use LC-MS or GC-MS to identify the compounds more accurately. Next, I will test microencapsulation and combinations of dulse extracts with spices to examine synergistic effects and develop a more effective natural treatment.

I would like to thank Dr. Prashant More for supervising my research project and Dr. Ramin Bahmani for guiding me with statistical analysis. I also thank the Marine Bio-products Research Laboratory in the Department of Plant, Food, and Environmental Sciences at the Dalhousie University Faculty of Agriculture for funding my project and providing access to their facilities.

These are my references:

Archana U Singh, Prasad D (2014) Management of Plant-parasitic Nematodes by the Use of Botanicals. J Plant Physiol Pathol 2:1. doi:10.4172/2329-955X.1000116

Cardoso, C.; Matos, J.;Afonso, C. Extraction of Marine Bioactive Compounds from Seaweed: Coupling Environmental Concerns and High Yields. Mar. Drugs 2025, 23,

366. https://doi.org/10.3390/md23090366

Carpena, M., Garcia-Perez, P., Garcia-Oliveira, P., Chamorro, F., Otero, P., Lourenço-Lopes, C., … Prieto, M. A. (2023, December 1). Biological properties and potential of compounds extracted from red seaweeds. Phytochemistry Reviews. Springer Science and Business Media B.V. https://doi.org/10.1007/s11101-022-09826-z

Deepanshu Bhatt, Himanshu Tomar, Rajveer Singh, Shivani Chandel, Extraction of bioactive compounds from marine brown seaweed, Regional Studies in Marine Science,Volume 90,2025,104415,ISSN 2352-4855, https://doi.org/10.1016/j.rsma.2025.104415.

Ghareeb, R.Y., Adss, I.A., Bayoumi, S.R. et al. The nematicidal potentiality of some algal extracts and their role in enhancement the tomato defense genes against root knot - nematodes. Egypt J Biol Pest Control 29, 53 (2019). https://doi.org/10.1186/s41938-019-0153-5

Nicol, Julie & Turner, S. & Coyne, Danny & den Nijs, Loes & Sue, Hockland & Maafi, Z.. (2011). Current Nematode Threats to World Agriculture. 10.1007/978-94-007-0434-3_2. https://doi.org/10.1007/978-94-007-0434-3_2

Ntalli, N., & Caboni, P. (2012). Botanical nematicides: a review. Journal of agricultural and food chemistry, 60 40, 9929-40 .https://pubs.acs.org/doi/10.1021/jf303107j

Acadian Seaplants Limited. (2026). About Acadian Seaplants. https://www.acadianseaplants.com/

Avery’s Farm Market. (2026). Products and local foods. https://averys.ca/