Manatees are large, gentle marine mammals often called “sea cows.” While they spend their lives in various aquatic environments, from coastal oceans to freshwater rivers, a common question arises regarding how they stay hydrated. It might seem counterintuitive for an animal living in water to need to drink, but manatees have adapted remarkable strategies to meet their water requirements despite their diverse habitats.
Manatees and Saltwater
Manatees inhabit both marine and freshwater environments, but they do not primarily drink saltwater for hydration. Their bodies are not well-suited to process the high salt content found in the ocean. Although they may incidentally ingest some saltwater while feeding on marine vegetation, their kidneys have limitations when it comes to efficiently excreting large quantities of excess salt.
Studies on captive manatees have shown that those kept in saltwater without access to fresh water and fed a diet of seagrass, which is high in salt, exhibited significant increases in plasma osmolality and concentrations of sodium and chloride within nine days. These changes indicate that prolonged reliance on saltwater without freshwater can lead to dehydration and physiological stress, as their kidneys have limits in filtering excess salt.
The Crucial Role of Fresh Water
Fresh water is crucial for manatees to maintain proper bodily functions. Like most mammals, manatees rely on a stable internal balance of water and salts, a process known as osmoregulation. This involves regulating the concentration of solutes in their body fluids to prevent cells from shrinking or swelling. Fresh water supports cellular function and organ health.
When manatees are in freshwater environments, they consume substantial amounts of water. In contrast, saltwater poses a constant osmotic challenge, as the external environment is saltier than their internal fluids. While manatee kidneys possess some ability to concentrate urine and excrete salt, this is not sufficient for long-term hydration from saltwater alone. Regular access to fresh water is therefore essential for their survival.
How Manatees Find Fresh Water
Manatees use various natural sources to obtain the fresh water they need. They frequent rivers, springs, estuaries, and canals, moving freely between fresh, brackish, and saline waters. Natural freshwater springs are particularly important, serving as reliable hydration points.
Manatees can also detect salinity changes, which guides them to areas where fresh water mixes with saltwater, such as river mouths and estuaries. During rainy seasons, they may even drink rainwater that collects on the surface of the ocean or from runoff. Their movement patterns are often driven by the search for these vital hydration points, including traveling upriver to find pure freshwater sources. In some instances, when natural sources are scarce, manatees have been observed seeking unusual freshwater sources, such as drainage from ice houses.