Response to Ugarte et al.: Ascophyllum (Phaeophyceae) annually contributes over 100% of its vegetative biomass to detritus

Abstract:

Halat et al. (2015. Phycologia 54: 599–608) concluded that the commercial harvest of Ascophyllum nodosum in Nova Scotia resulted in a detrital deficit amounting to over 100% of the harvest biomass. Here we respond to Ugarte et al. (2017. Phycologia 57: 114–115) that our estimate was exaggerated. We reaffirm our conclusions that: (1) epidermal shedding results in at least a 10% annual deficit, (2) there is a reduction in storm toss as a result of the commercial harvest on the order of 10% of the commercial harvest, and (3) the detrital deficit from annual reproductive effort by Ascophyllum can be on the order of 100% of the summer/fall biomass when most harvesting occurs. Given that the impact of all of these factors will propagate into all the years between the harvest year and the year when the cut fronds regenerate to their original size, we maintain that the 100% loss that we originally proposed is a conservative underestimate of the overall impact of harvesting on the production of detritus.

Key Words::

• Ascophyllum
• Detritus
• Intertidal ecology
• Nova Scotia
• Reproductive effort
• Seaweed harvesting

ACKNOWLEDGEMENTS

We thank Katelyn MacNeil for technical assistance and funding from the Natural Sciences and Engineering Research Council of Canada to DG.