Hydrodictyon; What It Is and How to Treat It

by Deborah Lee

Hydrodictyon 100x (m)

The nets of Hydrodictyon still look like nets even if they are small, released colonies. Each cell is connected to two other cells at the ends to form a network.

100x (m) far-red fluorescence filter

Green algae have autofluorescence when excited with ultraviolet light, which is visible under the far-red filter (as well as under the red filter).

400x (m)

Under 100x and 400x magnification, the cells are longer than they are wide and have a net-like (reticulate) chloroplast right up against the cell wall (parietal).

400x (m) far-red fluorescence filter

Each cell contains a large central vacuole that aid in buoyancy. The colonies or mats in a pond can undergo sudden buoyancy changes so they may appear and disappear quickly.

This is a really pretty alga, it’s my favorite. Hydrodictyon, commonly called “water net,” is a colonial planktonic alga with large cells that are connected to form a reticulate pattern. Colonies can be very large in appearance, sometimes over 40cm wide and up to one meter in length.

hydrodictyon in water
Figure 1. This is how Hydrodictyon colonies will look in a pond when they float to the surface. It’s usually a pretty nice bright green color.
Hydrodictyon in water
Figure 2. If you put your hand in a pond with floating Hydrodictyon colonies/mats, you will often see it break apart as some of the smaller colonies separate from the larger colonies.
Figure 3. Hydrodictyon forms a small colony inside of every cell of the original colony. When the small colonies are formed, the cell they were in ruptures and the small colony is release and generally floats at the surface.
Hydrodictyon can reproduce asexually by autocolony formation in which each cell in the colony produces a new cylindrical net of small cells. It can also reproduce sexually by producing gametes that fuse to form zygotes and eventually release a colonial net. Due to the nature of how this alga reproduces, it can quickly overtake eutrophic ponds, lakes, and slowly moving streams, generally those with hard water.

Hydrodictyon can be difficult to treat. Significant improvements in treatment efficacy of have been observed by blending the biocatalyst PondZilla Pro into pesticide tank mixes ( i.e. chelated copper, flumioxazine, diquat, endothall). PondZilla Pro improves treatment response time and facilitates the breakdown of dead algal cells. In addition, it is recommended to follow applications with a nutrient removal strategy (Temperature Driven Solutions or MuckBiotics) to reduce nutrients in the sediments and water column due to Hydrodictyon often being found in eutrophic waters.

About the Author

Deborah Lee is a senior Microbiologist at Natural Lake Biosciences, with 11 years of experience in microbial communities and their relationship with nitrogen and ammonia in aquatic ecosystems. Deborah’s testing on aquatic plants and algae in the Natural Lake Biosciences lab has led to many product developments and improved formulations. Her expertise in microbiology, algae, and aquatic plants is invaluable.

Landon, Aeration expert

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