Food Webs of Inland Saline Lakes

Inland saline lakes and alkali flats support surprisingly rich food webs, where most energy flows through just a few salt-tolerant species. At the base are salt-loving algae that feed dense populations of brine shrimp and brine flies, which in turn sustain migrating shorebirds. Understanding these connections helps you know where to look and what to expect when birdwatching on a prairie lake.

What Are Inland Saline Lakes and Why Do Their Food Webs Matter?

Inland saline lakes are closed-basin lakes in arid or semi-arid regions where evaporation concentrates salts, making the water several times saltier than the ocean. Salinity is often measured in parts per thousand (ppt); seawater is around 35 ppt, but these lakes can range from 3 ppt to over 300 ppt. High salinity limits which species can survive, so the food web is simple but highly productive. For birdwatchers, that means a few predictable food sources attract large numbers of shorebirds, especially during migration.

Who Are the Primary Producers in a Saline Lake?

The primary producers are mostly microscopic algae and cyanobacteria that thrive in salty water. They use sunlight to create energy through photosynthesis, forming the greenish or reddish tint often seen in the shallows. Some lakes also have benthic mats—layered communities of algae and bacteria on the mud. Without these primary producers, the lake could not support the brine shrimp, brine flies, or visiting birds.

What Algae and Microbes Should You Look For?

Look for a green, orange, or pink cast to the water, especially in warm, calm areas. Common types include Dunaliella, a single-celled green alga that turns red under high salinity, and filamentous cyanobacteria that form mats. In very salty lakes, the water may appear almost rusty. These colors signal active photosynthesis and the base of the food web.

How Do Brine Shrimp and Brine Flies Fit In?

Brine shrimp (Artemia spp.) and brine flies (family Ephydridae) are the key herbivores and detritivores. They consume algae and organic particles, converting that energy into protein-rich food for birds. Brine shrimp are tiny crustaceans, usually less than half an inch long, that swim upside down and are often visible in dense clouds. Brine flies spend their larval stage in the water and emerge as adults that swarm along the shoreline; both stages are eaten by birds.

Observing Brine Shrimp in the Field

On a calm day, scan the water surface for small, darting movements—brine shrimp often gather near the downwind shore. They are more active in warmer months. A simple hand lens or a clear jar can help you see their feathery legs, which they use for swimming and filtering algae.

Noticing Brine Flies Without Getting Overwhelmed

Brine flies can be abundant, but they do not bite. Adults cluster on wet mud, rocks, and shoreline vegetation. Watch for shorebirds running through the fly swarms with open bills—a behavior called "flycatching." The flies are a critical food source, especially the protein-rich larvae that birds probe for in the mud.

What Role Do Shorebirds Play in the Food Web?

Shorebirds are the top predators in the invertebrate part of the food web. They consume brine shrimp and brine flies, converting that energy into fat for long-distance migration. Different species have different feeding styles: phalaropes spin in circles to stir up prey, avocets sweep their upturned bills through the water, and sandpipers probe the mud. Their presence in large numbers is a sign of a healthy saline lake food web.

Seasonal Timing for Birdwatchers

Spring and fall migrations are peak times. In spring, shorebirds move north to breeding grounds; in fall, adults and juveniles head south. Many species time their stopovers to coincide with peaks in brine shrimp and brine fly abundance. Check local birding reports or eBird for recent sightings, and plan your visit for early morning or late afternoon when birds feed most actively.

How Does Salinity Shape the Food Web Structure?

Salinity acts as a filter. At low to moderate salinities, a greater variety of invertebrates may occur, but as salinity rises, only brine shrimp, brine flies, and certain algae persist. This means the food web becomes simpler but more concentrated. For birdwatchers, a lake with very high salinity may still host huge flocks if it has the right salt-tolerant species—fewer types of prey, but in enormous numbers.

Reading Salinity from Clues in the Landscape

You can estimate relative salinity by observing the lake's edges. White crusts of salt, lack of emergent vegetation, and reddish water all indicate high salinity. Lower salinity areas may have some salt-tolerant plants like saltgrass or pickleweed. These visual cues help you predict what food sources might be present.

Nutrient Cycling and the Pulse of Productivity

Nutrient cycling in saline lakes is driven by seasonal changes. In spring, runoff brings nutrients that fuel algal blooms. As algae multiply, brine shrimp and fly larvae populations boom. Birds arrive to exploit this abundance. When birds depart, their droppings and the decomposition of dead organisms return nutrients to the water, preparing the system for the next cycle. Understanding this rhythm helps you anticipate when the lake will be most active.

A Practical Guide for Your Next Outing

Here is a simple sequence for observing the food web:

1. Scan the water color for algae—green, orange, or pink tints indicate primary production.
2. Look for brine shrimp near the surface, especially in warm, shallow areas.
3. Check the shoreline for brine fly adults and larvae cases on mud or rocks.
4. Watch bird behavior—feeding flocks show where prey is concentrated.
5. Record your observations in a notebook or app, noting salinity indicators like salt crusts.

Bring binoculars, a spotting scope if you have one, sun protection, and plenty of water. Wear shoes that can handle wet, salty mud. Keep a respectful distance from feeding birds, especially during migration when they need to conserve energy.

Comparison of Key Food Web Players

Respectful Birdwatching at Saline Lakes

These lakes are fragile. Stay on established trails or hard ground to avoid trampling nests or crusts. Avoid flushing birds—if they take flight, you are too close. Use a scope for distant viewing. Carry out all trash, as plastics and other waste can harm birds and lake chemistry. Your quiet observation contributes to understanding and protecting these vital stopover sites.