Red tides' are produced by massive blooms of:

Options

A. diatoms
B. dinoflagellates
C. red algae
D. brown algae

Explanation

**Step-by-Step Solution:**

1. **Understanding Red Tides**: Red tides refer to a phenomenon where the water appears red due to the high concentration of certain microorganisms. This is often associated with harmful algal blooms.

2. **Identifying the Cause**: The massive blooms that cause red tides are primarily due to a specific group of microorganisms known as dinoflagellates. These organisms can reproduce rapidly under favorable conditions, leading to a significant increase in their population.

3. **Characteristics of Dinoflagellates**: Dinoflagellates are unicellular, motile organisms classified within the protists. They are known for their ability to cause harmful algal blooms (HABs), which can have detrimental effects on marine life and human health.

4. **Differentiating from Other Options**:
- **Diatoms**: These are also unicellular algae but are different from dinoflagellates. They have a silica cell wall and do not typically cause red tides.
- **Red Algae**: Known as Rhodophyta, they contain pigments like phycoerythrin but are not responsible for red tides.
- **Brown Algae**: These are multicellular and contain pigments like fucoxanthin, but again, they do not cause red tides.

5. **Conclusion**: The correct answer to the question is that red tides are produced by massive blooms of **dinoflagellates**.

---