6. The Food Web of Hydrothermal Vent Ecosystems
Unlike most other ecosystems on Earth, the food web in hydrothermal vent systems is not essentially dependent on sunshine and photosynthesis. Rather, chemosynthetic bacteria that get energy from the oxidation of molecules in the vent fluid—especially hydrogen sulfide—form the foundation of the food chain. These bacteria can live in symbiotic associations with many different vent animals or as free-living microbes. Organisms include tubeworms, mussels, and clams that house symbiotic bacteria are primary consumers in this environment. Secondary consumers like gastropods, crabs, and prawns that either graze on the main consumers or on bacterial mats follow them. Predators like fish, octopuses, and even some kinds of sharks seen visiting vent sites occupy the top of the food chain. Around hydrothermal vents, the density of life can be astounding; biomass levels match those of the most successful ecosystems on Earth. Supported purely by chemical energy from the Earth’s interior, this vast food web shows the amazing adaptability of life and the several ways in which ecosystems can run. With some estimates implying that up to 50% of the energy from chemosynthesis being absorbed into animal biomass, the efficiency of energy transfer in these environments is shockingly great. This is quite different from ecosystems dependent on photosynthesis, where usually only roughly 10% of energy moves across trophic levels. Research of hydrothermal vent food webs has challenged our knowledge of what is feasible in terms of life’s adaptability and resilience by offering fresh perspectives on ecosystem dynamics and energy flow in harsh conditions.