Green hydra

Systematic position: The green hydra (Hydra viridissima) is a member of the phylum Cnidaria, class Hydrozoa, and family Hydridae. This species is unique due to its symbiotic relationship with Chlorella algae, which reside within the hydra's cells, providing it with carbohydrates produced via photosynthesis.

Impact on cultures: While not a pest for terrestrial farming, it is considered a nuisance in professional hydroponic setups and aquatic plant nurseries. When the population density is high, these polyps can compromise the vitality of small or delicate aquatic plant species by obstructing their surfaces.

Biology and life cycle: Hydra viridissima reproduces predominantly by budding under optimal conditions, allowing for rapid colonization of plant surfaces. In response to environmental stress, they can switch to sexual reproduction. They are sensitive to water quality and light intensity, which directly influence their photosynthetic symbionts.

Damage and harm: The harm is caused primarily by nematocysts (stinging cells) which can damage sensitive plant tissues at a microscopic level.

• Obstruction of leaf surfaces inhibiting photosynthesis.
• Competition for nutrients in the immediate water column.
• Physical attachment interfering with plant growth and propagation.

Protection measures: Management involves controlling nutrient levels (specifically phosphates and nitrates) to limit food availability for associated microfauna. Physical removal and the use of specific biological controls, such as certain fish species or targeted aquatic treatments, are highly effective in maintaining healthy plant collections.