Daphnia magna
A large water flea collected from LRB Aquatics and introduced to the Freshwater Lake in April 2026 as a trophic bridge between suspended algae and the crayfish and shrimp community; the entire population was lost overnight, eliminated by oxygen depletion and 83.6°F surface heat in the low-flow system.
Daphnia magna is one of the largest Daphnia species, a millimeter-scale freshwater filter feeder collected from LRB Aquatics on April 4, 2026, and introduced to the Freshwater Lake the following day as a trophic bridge between suspended algae and larger consumers. The entire population was lost overnight: oxygen depletion from the low-flow system and surface water temperatures of 83.6°F exceeded the species' tolerances. The trial was an intentional diagnostic and its failure drove the decision to use Moina as a heat-tolerant alternative.
Daphnia magna is a freshwater cladoceran native to ponds and slow-moving lakes across Europe, North America, and much of the temperate world. Adults reach up to 5 millimeters in body length, making this one of the largest species in the genus. The transparent body reveals the beating heart, internal organs, and developing embryos to the naked eye.
D. magna feeds by drawing water through a feeding current created by the beating of its five pairs of thoracic legs. Fine setae (bristles) on these legs form a filter basket that retains suspended algae, bacteria, phytoplankton, and fine organic particles. The filtered material is compacted into a food ball and passed to the mouth. At high densities, Daphnia can dramatically clear algal blooms from the water column within days.
D. magna is a cold-water adapted species with an optimal temperature range of roughly 15 to 25°C (59 to 77°F). Activity and reproduction decrease above 25°C and the species typically cannot survive extended exposure to temperatures above 28 to 30°C (82 to 86°F). The Freshwater Lake's surface temperature of 83.6°F (28.7°C) measured on April 6, 2026 was at or above the upper survival threshold.
D. magna is sensitive to dissolved oxygen levels. In still or low-flow water, overnight respiration by the entire biological community (animals, plants, and microbes consuming oxygen) can reduce dissolved oxygen well below daytime levels. Without aeration or water movement to replenish oxygen, the steep overnight drop in a warm, low-flow system can fall below Daphnia survival thresholds by morning.
Under favorable conditions, D. magna reproduces by parthenogenesis: females produce unfertilized eggs that develop into genetically identical females, allowing rapid population growth. Under stress, sexual reproduction is triggered: males appear and fertilized resting eggs (ephippia) are produced; these are encased in a protective shell that can survive desiccation, freezing, and digestion. Ephippia can persist in sediment for years and hatch when conditions improve.
Daphnia magna is a key trophic intermediary in freshwater systems. Its large body size relative to other microcrustaceans makes it highly accessible to fish, large invertebrates, and other visual predators. In natural ponds, D. magna populations cycle dramatically with predation pressure: high fish predation suppresses Daphnia, which allows algae to bloom; low predation allows Daphnia to clear the water of algae. This is the foundation of the "clear water phase" observed in European lakes after Daphnia population explosions in spring.
In miniBIOTA's intended trophic design, Daphnia magna was selected to occupy the role of suspended-algae filter feeder and direct prey for the Slough Crayfish and ghost shrimp. Its larger body size compared to Moina and other microcrustaceans makes it a more efficient energy package for larger invertebrate consumers. The intended role was documented explicitly: a biological link between primary production from suspended single-celled algae and higher consumers such as the crayfish and shrimp community. The failure of this introduction highlighted a persistent trophic gap in the system, partially addressed by the subsequent Moina introduction and the April 5, 2026 removal of the Flagfish, which opened the lake to microcrustacean expansion by removing a major predator of the zooplankton layer.
Several hundred Daphnia magna were collected from LRB Aquatics (a filter-free natural aquarium system operated by Lucas, a fellow YouTuber) on April 4, 2026. The source was chosen because organisms from LRB Aquatics were already adapted to low-intervention, ecosystem-style conditions closely aligned with the miniBIOTA philosophy. The introduction was an intentional diagnostic trial: the temperature and oxygen concerns were known in advance, and the failure was acknowledged as an expected possible outcome. The April 8 retrospective note states: "the introduction was proceeded with as an intentional trial to test the limits of what this system could support and to expand knowledge of which species can successfully integrate."
Several hundred D. magna introduced April 5, 2026, collected from LRB Aquatics. Animals were swimming strongly at introduction. By the morning of April 6, the entire population was gone with no movement in the water column; other organisms were unaffected. Two contributing factors identified: oxygen depletion from low-flow overnight conditions and surface temperature of 83.6°F (28.7°C) exceeding the species' upper tolerance. Introduction was an intentional diagnostic trial; failure was an expected possible outcome. Pivot to Moina made on April 6, 2026 as a heat-tolerant alternative for the microcrustacean trophic layer.
Primary consumer and suspension filter feeder; grazes suspended algae and fine particles from the water column. Intended as a trophic bridge between the suspended-algae base (Single-Celled Algae) and higher consumers (Slough Crayfish ID 25, ghost shrimp). The large body size of D. magna relative to other microcrustaceans was the key design rationale: larger prey items are more efficiently captured and utilized by larger invertebrate consumers. Population did not survive to fulfill this role.
Cold-water adapted species with a narrow upper temperature tolerance. The combination of warm surface temperatures (83.6°F) and oxygen depletion from overnight community respiration in a low-flow system exceeded the species' limits. The Freshwater Lake's current thermal and flow profile is structurally unsuitable for D. magna without modifications to aeration and temperature control.
No reproduction occurred in miniBIOTA. The population was lost overnight before any clutch development could take place. Whether any ephippia were produced during the brief introduction period is unknown.
No ecological interactions were documented in miniBIOTA; the population was lost overnight before any interactions could be observed. Intended consumers were Slough Crayfish and ghost shrimp.
Follow this species across the habitats where it currently appears in the miniBIOTA biosphere.
