Explanation:

- Let’s break it down:

- Lipids are fats and oils found in algae, but they aren’t known for holding water—think energy storage, not water retention.

- Carbohydrates in algae mostly serve as energy reserves, like laminarin and floridean starch. Again, not really about holding onto water.

- Hydrocolloids are the big players here. These are long-chain molecules—like alginate from brown algae and agar or carrageenan from red algae—that soak up water and form gels or thick solutions. That's why they’re famous for holding water in both the ocean and your pudding or toothpaste.

- Gelatin is from animal collagen, not algae. It does hold water, but it's not plant-based and not produced by algae.