Tide Pool Ecology
Overview
Rocky intertidal zones are among the most studied ecosystems in ecology, and for good reason. A walk from the high-tide line to the low-tide line takes you through dramatically different communities in just a few meters. Organisms sort themselves into vertical zones based on their tolerance for desiccation, heat stress, and wave exposure.
Tide pools within these zones are microcosms of marine life. A single pool might contain sea anemones, hermit crabs, snails, chitons, coralline algae, and the occasional sculpin—all packed into a space the size of a bathtub. The classic experiments by Connell, Paine, and Menge in the Pacific Northwest revealed that both physical stress and biological interactions (competition, predation) structure these communities, with their relative importance shifting across the tidal gradient.
What You'll Do
Explore a simulated rocky intertidal shoreline during low tide. Place quadrats at different tidal heights—splash zone, high intertidal, mid intertidal, and low intertidal. In each quadrat, identify and count the organisms present: barnacles, mussels, sea anemones, sea stars, various algae, snails, limpets, and crabs.
Document zonation patterns by recording which species appear at which tidal heights. Measure how community composition, species richness, and percent cover change as you move down the gradient. Consider which factors—physical (desiccation, temperature extremes) or biological (competition for space, predation by sea stars)—best explain the patterns you observe.
Learning Objectives
- Identify major rocky intertidal organisms and their characteristic zonation patterns
- Conduct quadrat-based surveys along an environmental gradient
- Distinguish between physical factors (desiccation, heat) and biological factors (competition, predation) controlling zonation
- Create species distribution maps across the intertidal gradient
Background
Joseph Connell's barnacle experiments in Scotland (published 1961) demonstrated a key principle: the upper limit of a species' distribution is often set by physical stress, while the lower limit is set by biological interactions. Chthamalus stellatus could survive in the low intertidal, but Balanus balanoides outcompeted it there. Meanwhile, Balanus couldn't tolerate the desiccation stress of the high zone.
Robert Paine's removal experiments in Washington State added another layer. When he removed the predatory sea star Pisaster ochraceus from intertidal plots, mussels (Mytilus californianus) took over and excluded other species. Paine coined the term "keystone species" to describe the outsized effect of this single predator on community diversity.
These experiments made the rocky intertidal a model system for community ecology. The zonation is visible, the organisms are accessible, and the experimental manipulations are straightforward. This simulation recreates that experience, letting you survey the gradient, observe the patterns, and work through the same logic that Connell and Paine used.