Q5.1. Recall that some species in the intertidal zone are mobile, while others are sessile (stationary), and this affects how individuals compete with each other. Which of the following compete for space on intertidal rocks?
Algae and Starfish
Mussels, Whelk, and Chiton
Algae and Barnacles
Whelk and Starfish
The Correct Answer and Explanation is:
Correct Answer: Algae and Barnacles
Explanation:
In the intertidal zone, space is a critical and limited resource, especially on rocky surfaces. This environment is dynamic, experiencing fluctuations in tides, temperature, moisture, and wave action. Organisms that inhabit this area have evolved different strategies for survival, including how they compete for space. Sessile (stationary) organisms, in particular, rely on available surfaces to attach themselves for feeding, growth, and reproduction.
Algae and barnacles are both sessile organisms that attach themselves directly to the surface of intertidal rocks. Because they are immobile, once they occupy a spot, they must compete with others for room to grow and access resources like sunlight and nutrients.
- Algae, particularly macroalgae (such as sea lettuce or rockweed), need surface area to anchor themselves and absorb sunlight for photosynthesis. If they cannot find space, their survival and reproduction are compromised.
- Barnacles, on the other hand, are crustaceans that cement themselves to hard surfaces and filter food from the water. They thrive in dense clusters, but their need for anchoring space makes them highly competitive.
These two groups compete directly: if barnacles dominate the surface, algae may not be able to establish themselves due to lack of anchoring points. Conversely, a dense cover of algae can prevent barnacle larvae from settling and attaching to the rock.
Now, consider the other choices:
- Algae and starfish: Starfish are mobile predators that feed on sessile animals like mussels and barnacles. They do not directly compete for space with algae.
- Mussels, whelk, and chiton: Whelks and chitons are mobile grazers or predators; mussels are sessile and do compete for space, but the group as a whole does not share a unified competition for space.
- Whelk and starfish: Both are mobile predators, and while they may compete for prey, they do not compete for space.
Therefore, the most appropriate pair that competes for space on intertidal rocks is algae and barnacles.