Sea stars are a keystone species in the rocky intertidal ecosystem. Which of the following would occur if the sea stars were removed from the ecosystem? Select two that apply.

A. The number of total species (species richness) will decrease.

B. The number of total species (species richness) will increase.

C. The mussels will overpopulate the rocks.

D. The mussels will make room for other species that want to live on the rock.

Removing sea stars from the rocky intertidal ecosystem would lead to an overpopulation of mussels and a decrease in overall species richness. Sea stars serve as a critical predator, maintaining biodiversity by controlling mussel populations. Their absence disrupts the ecological balance and reduces species diversity.

Explanation:

Impact of Removing Sea Stars from Ecosystems

Sea stars, particularly the species Pisaster ochraceus, are considered a keystone species in rocky intertidal ecosystems. Their presence plays a crucial role in maintaining the diversity of species within that environment. When sea stars are removed, significant changes occur in the ecosystem dynamics.

Effects of Sea Star Removal

The mussels will overpopulate the rocks: Sea stars prey on mussels, preventing their populations from overwhelming the rocky intertidal zone. Without this predation, mussel numbers can skyrocket, leading to overcrowding.
The number of total species (species richness) will decrease: With an overpopulation of mussels, they can outcompete other species for resources, effectively driving down biodiversity and reducing the number of species that can coexist in that habitat.

Thus, removing sea stars leads to an increase in mussel populations and a decrease in overall species richness, highlighting their essential role in the ecosystem's balance.

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