Seagrass meadows - uncovering a watery world
New Zealand’s seagrass meadows are important, but threatened, coastal habitats that we still know little about. Scientists from NIWA are undertaking a nationwide survey of these vibrant underwater meadows, to find out more about the life they support and their wider role in the marine ecosystem.
7 March 2006
Seagrass meadows occur throughout New Zealand and are an important habitat in near-shore coastal environments. They are known to play an important role as settlement and nursery sites for fish juveniles from a range of coastal species, including snapper, trevally, parore, spotties and pipefish. They also support a high density and biodiversity of invertebrate species, including prey species of fishes and birds. Sea-grasses also supply significant amounts of organic matter, through shedding roots and leaves, which may fuel other parts of the ecosystem.
The extent of seagrass meadows has been drastically reduced over the past 100 years as a consequence of human impacts on estuaries and the coast. These include increasing sedimentation, changing light regimes, eutrophication, sewage, reclamation infilling, and dredging. For instance, the once extensive beds in Whangarei Harbour (some 12-14 km2, out of a total harbour area of about 100 km2) have been completely lost, as have large beds in the Manukau, Waitemata, Tauranga, and Avon-Heathcote estuaries. Research is in progress in Whangarei Harbour to assess the potential for restoration and determine whether the environment is now capable of supporting seagrass populations.
Our ability to manage seagrass habitats is hampered by a lack of knowledge. While our understanding of seagrass dynamics and its ecological roles has greatly improved over the last decade, many large knowledge gaps remain. By surveying the plants and animals living in selected seagrass beds, and the blade height and biomass of the seagrass itself, we aim to significantly advance our understanding of these unique and important habitats.
Background information
Sub-tidal seagrass is especially important as a habitat to small fishes and invertebrates, but has been badly affected by human impacts. Only small, but valuable, remnants remain in coastal locations such as off the Cavalli Islands (Northland), Urapukapuka Island (outer Bay of Islands), and Great Mercury and Slipper Islands (Coromandel/Bay of Plenty). Areas still containing large seagrass beds tend to be located further away from high human populations and their associated impacts, and include large meadows in Parengarenga and Rangaunu harbours (Far North), Farewell Spit and Whanganui Inlet (top of the South Island), and around the estuaries of Stewart and Chatham Islands.
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