Abstract
Marine renewable energy (MRE) is under development in many parts of the world. Although the MRE industry is advancing, several challenges have slowed its growth such as uncertainties associated with environmental effects [1]. So far, studies examining the environmental effects of MRE have primarily focused on deployments in temperate regions and countries in the Northern Hemisphere. As MRE development expands into tropical and subtropical countries (between 35oN and 35oS), there is a need to examine the potential environmental effects specific to these regions and their unique habitats and species.
As of 2023, substantially fewer MRE deployments have occurred in tropical and subtropical regions than in temperate areas. However, over the last several decades, various MRE device prototypes have been tested and full scale projects planned or deployed (Fig. 1). Because many tropical and subtropical marine animals and habitats are already experiencing the disproportionate impacts of climate change, MRE development may present additional risks that could contribute to reduced biodiversity and ecosystem resilience [2]. Tropical and subtropical ecosystems host a diverse range of sensitive benthic and pelagic habitats such as coral reefs, mangroves, and seagrass beds that provide feeding, breeding, spawning, and nursing grounds for a wide variety of marine animals, including commercially important, endangered, and keystone species. To adapt MRE device deployments and develop appropriate monitoring methods and mitigation measures, the MRE community needs to better understand how potential environmental effects may differ between tropical/subtropical and temperate ecosystems.
Tropical and subtropical regions have access to all types of MRE resources: wave energy, tidal energy, and ocean current energy, as well as thermal and salinity gradients. While wave energy resources are much lower around the equator than in temperate regions, resources are typically high in subtropical regions [3] and energy from waves could be captured in places like western Australia, South Africa, off the central coast of Chile, and around islands in the north and south Pacific Ocean and in the south Indian Ocean (e.g., Mauritius). Several tropical and subtropical areas also have significant tidal resources, like Indonesia, the northern coast of Brazil, the western coast of Central America (especially near Panama and Colombia), the northwest coast of Australia, and the Mozambique canal [4]. Harvestable ocean currents, generated further offshore than tidal streams, are generally located in tropical and subtropical areas, such as off the coast of Florida and in Asia from Japan to the Philippines [5]. Temperature gradients that have sufficient thermal power capacity to generate power are non-existent in temperate regions but abound in tropical and subtropical regions [6], [7]. Ocean thermal energy conversion (OTEC) is especially regarded as a preferred source of renewable energy by tropical island nations with access to cold deep water close to shore. Finally, areas with the greatest potential extractable salinity gradient energy resources are located at river mouths along warmer coastlines, especially islands in the Caribbean, along the Gulf of Guinea coast, and in the southeast Mediterranean Sea [8].
To better understand the environmental effects of MRE in tropical and subtropical ecosystems and aid in developing MRE projects in a responsible manner, the international initiative Ocean Energy Systems (OES)- Environmental has begun to compile scientific information. So far, OES-Environmental has conducted a literature review, distributed a public survey, engaged with local experts, and conducted workshops to collect existing information, identify knowledge gaps, and determine future research needs.