Urchin

Mālama Maunalua pilots new tool to address invasive algae

As part of Mālama Maunalua’s effort to restore Maunalua Bay’s habitat and associated fisheries, a primary goal is to reduce the critical threat of invasive alien algae (IAA) in the nearshore reef flat of the bay. For the past six years, our  volunteer effort to manually remove IAA through huki events has proven successful. The monitoring data shows regrowth of IAA is slow and less robust, although it does grow back.

In a partnership with the Hawaii state Department of Land and Natural Resources-Division of Aquatic Resources (DLNR-DAR), we will test a new approach to target IAA re-growth – seeding the native sea urchin, Tripneustes gratilla (collector urchin or hawae), at select sites in Maunalua Bay.

DLNR-DAR has been using collector urchins as a biocontrol in Kane’ohe Bay, which has yielded positive results on limiting the regrowth of Kappaphycus/Eucheuma spp. and Gracilaria salicornia. The hope is that the native urchins will forage upon the most troublesome IAA found in Maunalua Bay, Avrainvillea sp. or leather mudweed.

Why collector urchins? Key to maintaining low levels of IAA is the presence of native herbivores (e.g., urchin, parrotfish). The collector urchin, a native herbivore, is used because of its relative ease of handling and rearing in captivity.

What will we look for? The first batch of collector urchins was placed at three host sites in Maunalua Bay, selected based on areas of high mudweed cover and water depth. Information will be gathered to determine the efficacy of the collector urchin’s ability to maintain growth of IAA in Maunalua Bay. Data will be collected on change in IAA cover, urchin health, and urchin behavior; the data collection will abide by strict safety and monitoring protocols.

We hope this project proves successful in reducing the threat of IAA to our nearshore marine habitat. This may pave the way for a sustainable restoration action that can be replicated at a scale required in Maunalua Bay.

This is one of several projects to be undertaken by students in our Internship Program this summer. For more information about the Urchin Seeding Pilot Project or the Internship Program, please contact Pam at pweiant@malamamaunalua.org.