Within the "marine" community there are several active research themes:
1. Marine renewable energy (wind, tide, current, etc.). The main issue is to design MRE devices that avoid or minimize negative ecological impacts; e.g. impacts on migrating birds, fish and mammals, pollutant trapping within tidal lagoon, aesthetic concerns, etc.
2. Biodegradable substitutes. There are a lot of interests in developing biodegradable plastics to replace traditional plastics, which cause a lot of problems in the marine ecosystem.
3. Biofuel and biotechnology. Algal biofuel has been studied for many years now. Algal biotechnology is also a rapidly growing field (e.g. extracting useful chemicals from algae, using algae for bioremediation, etc.)
4. Sustainable aquaculture. There is an urgent need to transform traditional aquaculture practices to be more efficient and environmentally friendly.
5. Living with climate change. The coastal zones are some of the mostly densely populated areas, and they are also under the threat of global climate change and sea level rise. Low-lying countries are actively making preparations.
There are many others, some of which are common among all disciplines, e.g. waste reduction, conservation, carbon burial technology, energy efficiency, environmental education, etc.
I'd like to highlight the last one: environmental education. There are still people who deny human-caused climate change. Scientists can be working very hard to identify the problem and find the solution, but until the society as a whole comes to its senses, our efforts may mean very little.
I think that research on sustainability is still proliferating. Perhaps you may consider this free ebook, where I reported some of my thesis's literature review.
Should we study nature/climate change or study man? Since sustainability is a human devised concept and the human being causes imbalances in nature, IMHO the future lies in the 'Human Dimension of Sustainability', not climate change. We need to know the nature of man and his addictive behavior in consuming more and more energy and resources, more than what is needed. Without addressing this issue, all other research will go down the drain. The Human being is the central issue. Nature can take care of itself, IF left alone.
Agreed that human being is the central issue, all the same, are we not looking at human society as part of nature? That nature which can wreck havoc if is indiscriminately exploited? The human dimension of the climate change also needs to be considered in this respect.
Yes, man's behavior in compulsively using more & more energy without considering which, all future research IS useless is of SUPREME importance.