Final answer:
The Portuguese establishment of trade networks had positive effects on the global economy, but resulted in significant negative impacts on African states due to the disruption of trade and the slave trading practices.
Step-by-step explanation:
The positive and negative effects of the Portuguese seizing ports around the Indian Ocean can be seen from multiple perspectives. One positive effect was the establishment of new trade networks that contributed to the global economy through the exchange of spices, textiles, gold, and ivory.
However, the negative effects included the disruption and decline of local African trade, looting and sinking of rival ships, colonization efforts that often led to conflict, and the detrimental impacts of slave trading. African states suffered under Portuguese control, particularly due to the slave trade where many coastal states essentially became conduits for captured individuals bound for European slavers.
The best matching option that describes the positive and negative effects of the Portuguese seizing ports around the Indian Ocean would be: 1) Positive effects on trade and economy, negative effects on African states due to slave trading.