Seagrass habitats have been the focus of much attention in recent years with increasing recognition of the important role they play in sediment stabilisation, nutrient cycling, and as nursery and feeding grounds for fisheries species and megafauna such as dugong and turtle. With globally developing carbon markets, the role that seagrasses play in sequestering carbon is also becoming more widely recognised. But while shallow water seagrasses have been heavily researched, there are vast areas of seagrass habitat in deeper water which we know very little about. Within the Great Barrier Reef World Heritage Area alone, deepwater (>10m) seagrasses occupy more than 35,000 km2 of the reef lagoon. Predominantly comprised of smaller species, these communities are capable of rapidly turning over their biomass in a matter of days. Given the vast area of these meadows, the potential rate of carbon assimilation is significant. We present preliminary findings from the first two years of an ongoing research program investigating the major drivers of seasonal recruitment and senescence in tropical deepwater seagrass meadows. The program is providing information on seagrass abundance, seed bank status, productivity, benthic irradiance, temperature and spectral quality of light across three geographically distinct locations. Results will inform the development of local management strategies for mitigating impacts from coastal developments where dredging and associated plumes and ship movements threaten the long term survival of deepwater seagrasses.

Ecologically and economically important marine habitats often occur in sheltered coastal sites associated with port and harbour development. Many of Queensland's tropical ports contain important fisheries habitats such as seagrass meadows and mangroves which provide breeding and nursery habitat for commercial prawns, fish and other biota and feeding grounds for dugong and turtle. Information on these habitats is usually required as part of the approvals process for port maintenance and development programs such as dredging or new facility development. Fisheries habitat mapping and monitoring programs have been established in several tropical ports to facilitate effective planning for port development and maintenance operations that will have minimal impacts on sensitive fisheries habitats. Habitat monitoring programs have been established in the ports of Karumba, Weipa, Cairns, Mourilyan and Mackay. The diverse physical nature and often-remote location of tropical ports required the development of some unique and varied sampling approaches. Sampling methods included a modified visual estimation of abundance technique using real time underwater video equipment and the design of specialised sampling equipment. Fisheries habitat distribution and abundance information collected was compiled into a Geographic Information System (GIS) for each port. From initial surveys long term fisheries habitat monitoring strategies for the ports were developed. Results of the monitoring programs have increased our knowledge on estuarine ecology and seagrass biology. By providing information on how these systems vary naturally we can better assess impacts from port activity. Seagrass meadows were found to be a good indicator of environmental stress and monitoring programs have enabled an assessment of the 'environmental health' of ports. The GIS of fisheries habitats has provided port managers with environmental data in a readily accessible format that assists in the design of development and maintenance programs which minimise risks to the environment. Monitoring programs have also been used to address public and stakeholder concerns and provide statutory information needed for approval of port development and maintenance programs.

Extensive areas of deepwater (>10m) seagrass meadows are known to occur in many tropical regions. More than 31,000 km2 are found in the Great Barrier Reef Region of Queensland alone and one of the world's largest continuous seagrass meadows has been mapped recently in deeper waters of the Torres Strait. Despite their extensive distribution, little is known about the ecological roles, tolerances and dynamics of these deepwater communities compared with the much more commonly studied shallow seagrass meadows from the same region. Existing information suggests deepwater meadows may be highly productive but also highly dynamic between and within years. Increasingly these meadows are coming under threat from anthropogenic disturbances and it is critical to develop our understanding of the drivers of change and tolerances of these meadows to effectively manage them. We present initial findings from a major research program to establish a better understanding of the drivers of seasonal and interannual dynamics in these seagrass communities, the role of seed banks and seagrass recruitment, and the environmental cues that drive the seasonal patterns of decline and recovery. The research program includes a detailed study of the light requirements of these deepwater species as well as developing a range of tools for monitoring and managing anthropogenic impacts such as dredging.

While research has focused on shallow water coastal seagrasses over the last 20 years, little is known of the ecological role, tolerances and drivers of their deepwater (>10) counterparts. Within the Great Barrier Reef World Heritage Area, deepwater seagrasses are estimated to occupy more than 35,000 km2 of the reef lagoon. These deepwater meadows are often within the footprint of port and shipping activity where dredging, associated plumes and ship movements are major threats to their long term survival. We present initial findings from an ongoing research program to determine the drivers of seasonal and inter-annual change in deepwater tropical seagrasses. Seagrass abundance, seed bank status and recruitment, productivity, irradiance and temperature along with detailed spectral profiles have been measured in three geographically distinct deepwater seagrass meadows since early 2012. Manipulative lab experiments were initiated in mid-2013 to assess the adaptive photophysiological characteristics of the plants. This research will identify key environmental cues which will be used in developing local management strategies for mitigating coastal developmental impacts along the Great Barrier Reef.