Green investment and vertical alliances in the maritime supply chain

Under the background of the green maritime transportation, green investment and vertical alliances between port and shipping enterprises are effective ways to reduce maritime emissions. In this paper, we consider a maritime supply chain consisting of a port, a shipping company, and a forwarder. The port and shipping company determine individual green investment to reduce emission pollution. There are three vertical alliance strategies for the shipping company under green investment: no alliance, alliance with the port, and alliance with the forwarder. We obtain the optimal alliance strategy under the same green investment entity and the optimal choice for the investment entity under the same alliance strategy. In addition, we analyze the impacts of different alliance strategies and investment entities on consumer surplus and social welfare. The results show that whether the port implements the green investment or the shipping company implements green investment, when all three alliance strategies are feasible, there is always a higher green investment level, a higher demand, and a lower shipping service charge, and alliance strategies lead to greater profits for the maritime supply chain. Under the same alliance strategy, the choice of investment entity is affected by the green investment cost coefficient. If the green investment cost coefficient of the investor is too high, then the enterprise's green investment cannot improve the maritime supply chain profit. Therefore, port and shipping enterprises should reasonably set green input according to their own conditions to maximize the profit of maritime supply chain. Vertical alliances can improve environmental performance as well as increase consumer surplus and social welfare. In particular, under the shipping company green investment, alliance between the shipping company and downstream forwarder can precisely grasp the market demand and achieve the optimal social welfare.