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The importance of seaweed wrack as habitat and resource


Brenda KonarCollege of Fisheries and Ocean Sciences
University of Alaska Fairbanks



This study will determine 1) which organisms are impacted when wrack habitat is harvested/removed, 2) if the macroinvertebrate wrack communities change with the different stages of wrack decomposition, 3) the spatial and temporal variability in wrack biomass and composition, 4) the spatial variability and timing of when reproductive wrack is found and 5) how long wrack can stay reproductive after being deposited on beaches.


The issue

Wrack is an important subsistence and commercial resource harvested by people who use it for garden fertilizer. Wrack studies from other areas of the world have shown that there are significant ecological consequences on associated species when wrack is removed. After wrack has been deposited on beaches, it may also be re-suspended at high tides and may still contribute viable spores/gametes for reproduction and the sustainability of wild populations. In Southcentral Alaska, harvesting wrack is common but in most places, it is illegal. These restrictions are partly in place because so little is known about this resource. It is important that Department of Fish and Game managers and the public (harvesters) understand the effects of removing wrack from Alaskan beaches and if there are ideal times to harvest wrack to optimize harvest while reducing impacts on the wrack ecosystem. We have worked with Department of Fish and Game managers to develop this proposal.

Why is this an Alaska Sea Grant project?

This project primarily responds to the 2018–2021 Alaska Sea Grant Strategic Plan priorities: Healthy Coastal Ecosystems (supporting management concerns/interests) and Sustainable Fisheries (optimizing wrack as a sustainable resource).

How will researchers conduct their study?

This study will be based in Kachemak Bay, a model Alaska system where seaweed is carefully regulated by the Department of Fish and Game. To determine which animals are impacted when wrack is harvested, the composition and abundance of invertebrates and shorebirds using wrack will be quantified monthly and compared to non-wrack areas. To determine the succession in invertebrate communities as wrack ages, freshly detached seaweeds will be deposited monthly into beach plots and revisited to quantify temporal changes in the invertebrates. Spatial and temporal variability in wrack biomass and composition will be determined by monthly wrack collections and will be scaled-up using fixed-wing aerial surveys. To determine spatial variability and timing of when reproductive wrack is found, we will examine the monthly wrack collections for reproductive tissues and conduct spore/gamete release in the lab to ensure viability. To determine how long reproductive wrack can maintain its viability, we will place fresh reproductive seaweeds on a beach monthly and check the seaweeds for reproductive viability over time.