The immediate reason responsible for the decline of Masulipatnam was the annexation of Golconda by the Mughal Emperor Aurangzeb. This event had significant consequences for the city and led to its decline.

1. Annexation of Golconda:
- Golconda was a powerful and prosperous kingdom located in the Deccan region of India. It was known for its wealth and control over the lucrative trade routes.
- Aurangzeb, the Mughal Emperor, sought to expand his empire and exert control over the Deccan. In 1687, he successfully annexed Golconda, bringing it under Mughal rule.
- This annexation had a direct impact on Masulipatnam, which was a major port city and a crucial center of trade for Golconda. With the kingdom's annexation, the Mughals sought to centralize control over trade and assert their authority.

2. Disruption of trade:
- Masulipatnam had enjoyed a thriving trade network, serving as a vital link between Golconda and European powers such as the Dutch and the British.
- However, with the annexation of Golconda, the Mughals imposed restrictions on trade and monopolized it. This disrupted the existing trade networks and led to a decline in the city's economic prosperity.
- The Mughals prioritized their own trade interests and marginalized the role of Masulipatnam in the region's trade dynamics.

3. Loss of autonomy and decline in influence:
- Masulipatnam had enjoyed a certain degree of autonomy under Golconda's rule. However, with the annexation, the city lost its independence and became subject to Mughal control.
- The Mughals imposed their administrative and political systems, which often proved burdensome and hindered the city's growth and development.
- Additionally, the decline in trade and the loss of Golconda's influence further eroded Masulipatnam's position as a prominent trade center.

4. Shift in power dynamics:
- The annexation of Golconda by Aurangzeb marked a significant shift in the power dynamics of the Deccan region. The Mughals emerged as the dominant force, and their policies and control over trade had a direct impact on Masulipatnam's decline.
- This event also paved the way for European powers like the British and the French to gain influence in the region, further marginalizing Masulipatnam as a trade hub.

In conclusion, the annexation of Golconda by Mughal Emperor Aurangzeb was the immediate reason responsible for the decline of Masulipatnam. The disruption of trade, loss of autonomy, and shift in power dynamics all contributed to the city's decline as a major trade center.