Science Advisory Report 2008/059

Ecological Assessment of Irish Moss (Chondrus crispus) in Basin Head Marine Protected Area

Summary

• The form of Irish moss found in Basin Head lagoon is distinct because it does not attach to the bottom but is held by byssal threads of mussels, is found almost exclusively in the non-sexual reproductive stage and replicates by fragmentation.
• Conditions in Basin Head lagoon have produced and sustained this distinct form for decades.
• There has been a large decline in the bed area, proportion cover, density, and biomass of Irish moss in Basin Head lagoon over the period of study, 1980 to 2008.
• Estimates of biomass, which were 110 t in 1980, are at the lowest value of just over one (1) tonne in 2008.
• Possible actions to mitigate the decline of Irish moss would depend upon the factors which are most likely to contribute to the sub-optimal conditions for the Irish moss in Basin Head lagoon.
• The cumulative effects of inputs of nutrients into the basin with subsequent annual green algal blooms and poor water quality are considered to be important contributory factors to these sub-optimal conditions for Irish moss.
• The recent invasion of green crab and its intensive predation on blue mussels which anchor the moss, is considered an important stressor to the Irish moss population and the Basin Head ecosystem.

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