Life Underwater series: Life of the Hydra
Life of the Hydra: the ageless benthic
The hydra is a fascinating benthic macroinvertebrate that will use its stinging cells to stun, entangle, or kill its prey before consuming it. Hydras have a low tolerance for pollution and cannot be found in impaired waters. Today we will explore how hydras prey upon other organisms. Hydras are capable of both sexual and asexual reproduction. Why does the hydra select sexual reproduction over asexual reproduction or vice versa? To explore these questions, we’ll start at the very beginning-- when the hydra eggs are first laid.
Specific environmental conditions will trigger sexual reproduction in hydras that are also hermaphroditic, meaning that they have both male and female reproductive systems. Eggs formed by female hydras will be left attached to the female, exposed while the male will release his sperm into the water for fertilization to occur. Once fertilized, the eggs become hard and are released into the water where they can withstand freezing and dehydration allowing them to overwinter. When hydras select for asexual reproduction, a small hydra will grow from the side of its parents, through a process called budding. This process is essentially the production of a genetically identical clone that will grow and break free when mature.
Fertilized eggs will transform into tiny planula larvae and attach themselves to further develop into polyps or adult hydra.
Predatory hydra may feed on the following: insect larvae: small crustaceans, water fleas, seed shrimps and copepods. Being sessile, they remain stationary for long periods and they can bend their body by attaching themselves to other substrates with their tentacles, releasing them and re-attaching. When feeding, the hydras will use the stinging cells called nematocysts that surround their tentacles that form the only bodily opening around the mouth (that also acts as the anus). These stinging cells may only be used once and will be replaced in 48 hours.
Another fascinating quality of the hydra is their ability to regenerate after injuries. For example, if a hydra is cut into several pieces a new hydra will be produced from each piece.
Fun Fact: Hydras tolerate a wide range of conditions from depths up to 350 metres in a lake, or in shallow, fast-flowing streams.
Fun Fact: Hydras are found attached to almost any hard surface and you can look for them on water lily stems, dead leaves, sticks and stones.
Fun Fact: Studies have found that hydras do not age or die of old age, they do however die of injury, starvation, disease and other unsuitable conditions.
Interested in learning more about benthic macroinvertebrates and how they can be used to measure the health of rivers and streams? Be sure to follow EcoSpark’s social media to stay updated on our Changing Currents program and our other citizen science and environmental education programs.
References
Microworlds Photography. (2018). Freshwater Microscopic Creatures. Retrieved from: https://www.microworldsphotography.com/Galleries/Microscopic-Creatures/
Carina holds a Bachelor of Honors in Environmental Studies and a diploma in Ecosystem Technology, both of which developed her interest in using geographic information systems to communicate about complex issues, such as climate change. In her role as Lead Environmental Educator, Carina designs geospatial education tools for EcoSpark’s citizen science programs. When outdoors in the field, you will often find her streamside identifying aquatic critters, communicating her enthusiasm for the outdoors, and demonstrating her dedication to stewardship practices with youth and adults throughout the GTA.