Introduction From at least the 16 th century people involved in resource management were aware of and increasingly concerned at the impact of human activities on what we now call sustainability, conservation and cultural amenity of terrestrial environments. Grove (1995) provides a discussion of the origins of environmentalism from 1600 – 1860, covering concepts of conservation, preservation and protected areas developed through the work of landowners and managers. By the second half of the 19 th century these were reflected in the concepts of National Parks and the beginnings of scientific approaches to sustainability of agriculture and forestry. An appreciation that marine environments could also be vulnerable to human impacts came much later. T. H. Huxley headed a Royal Commission into the collapse of the British North Sea Herring fishery in the late 1890s. In his report he denounced as absurd the suggestion that humans were able to have significant widespread impacts upon marine environments (Cushing 1988). Since the 1960s, new technologies have removed many of the dangers and most requirements for skill in finding marine resources. The nature and volume of wastes, by products and incidental runoff from human terrestrial activity were such that PCBs are found in the body fats of animals and plants in the remotest oceans. Kurlansky (1999) made it chillingly clear that by the close of the 20 th century humans had and were determinedly applying the capacity to have significant impacts on marine environments. Despite the accumulating history of impacts, the cargo cult concept of the seas as the last frontier on the planet, unexplored, under-exploited and a source of salvation in the face of depleted or overburdened terrestrial systems, is still widely held. For countries such as Australia that have claimed large Exclusive Economic Zones the issue of identifying, managing and maximising the benefits of those zones has national significance. A series of reports and inquiries such as McKinnon et al. (1989) and the Resource Assessment Commission (1993) have underpinned progress from cargo cult to national policy (Commonwealth of Australia1998). Despite this progress, Australia’s Oceans Policy is not widely known and many of the concepts are not intuitively obvious for people with little or no experience of the dynamics of marine environments. The purpose of this paper is to introduce and discuss a number of the key concepts as well as the issues of scale and process that arise when seeking a sustainable balance in the management of marine environments. In many cases the references are to textbooks that contain more detailed coverage of the issues. The nature of marine environments The supporting and linking medium of marine environments is seawater. It is 80 times as dense as air, enabling it to support and carry large amounts of biomass with little energy expenditure. The water column alone is a comprehensive environment or habitat providing Managing marine environments: an introduction to issues of sustainability, conservation, planning and implementation R. A. Kenchington Centre for Maritime Policy, University of Wollongong, NSW 2522 email: richard.kenchington@netspeed.com.au ABSTRACT The capacity of human activities to have significant impact on marine environments was not regarded as a serious issue until the middle of the 20th century. It is now regarded as a matter of increasing urgency but the evolution of appropriate management measures presents several challenges. This paper discusses the nature and scale of marine ecosystems, their linkage through the water column and how these raise management requirements that are not easily addressed through terrestrial concepts of jurisdictional boundaries and individual rights of access or ownership. It concludes by presenting the case for a marine implementation of multiple use management characterised by a core component of highly protected reference or sanctuary sites within a larger ecosystem-scale area managed for verifiably sustainable use and providing effective buffering for highly protected coresites. Key words: Marine ecosystem, marine biodiversity, marine environment management, scale and linkage, conservation, sustainable use,Marine Protected Area Pp 41 - 48 in Conserving marine environments. Out of sight out of mind, edited by Pat Hutchings and Daniel Lunney 2003. Royal Zoological Society of New South Wales, Mosman, NSW.