Pilot seagrass transplantation trials in Forsters Bay, Narooma, NSW
Summary: The last reported extent of seagrass coverage in the Wagonga Inlet, Narooma was given as 148 ha, although estimates of seagrass coverage vary considerably. The channel area consists of approximately 4 ha or 2.7% of this total coverage. The bare sand flats adjacent to the channel are naturally colonising at a reasonably rapid rate (c.a. 1 m y-1). That seagrasses are healthy in the inlet is illustrated by the fact that they are growing successfully underneath jetties, boardwalks and oyster leases. Additionally, in the quite turbid environment of the upper reaches of the inlet, Zostera sp. is growing well. Any factor that would increase this turbidity such as runoff from land clearing would be expected to impact upon these communities and possibly reduce their range. However sediments in the channel between Mill and Forsters Bay are more coarse and turbidity caused by dredging would be expected to be short-lived; and, if carried out at the appropriate time of year would be expected to have minimal impact upon adjacent seagrasses.
After more than a year pilot seagrass transplantation trials on the sand flats adjacent to the channel have shown 92% survival. In addition there has been natural colonisation in this area by both seedlings and seagrass fragments within and around the transplant area. Recent data on transplantation trials in another NSW estuary have also shown good survival. This indicates that the seagrasses in the Narooma Inlet may neither be under stress nor are they decreasing in area and that seagrass transplantation may be a viable method to increase meadow area.
Dredging a channel would remove approximately 2.7 % of the seagrasses in the inlet adjacent to a seagrass meadow that is naturally colonising and of a greater size. The bare sand flat area is approximately 40 ha and might be expected to support at least half of this as seagrass meadows in the future. It would be possible to augment the colonisation by further transplantation of the appropriate methodology using material which would be dredged from the channel. Therefore if a channel is dredged to attract tourist boat usage during holiday periods, its total impact upon seagrass meadows in the inlet is likely to be minimal.
|Murdoch Affiliation:||School of Engineering Science|
|Publisher:||Marine and Freshwater Laboratory, School of Environmental Science, Murdoch University|
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