Propagating Gracilaria parvispora (Hawaiian Ogo) by Division

How to propagate the red macroalga Gracilaria parvispora by fragmentation and tumbling in a refugium for nutrient export and high-value tang food.

Overview

Gracilaria parvispora, the Hawaiian ogo, is a red macroalga in the family Gracilariaceae with bushy, tubular fronds. The genus Gracilaria occurs in warm waters worldwide and seasonally in temperate seas, with a center of diversity in the Western Pacific, and cannot survive below about 10°C. Gracilaria species generate over 90% of the world's agar and are eaten across Filipino, Hawaiian, Japanese, Korean, and Sri Lankan cuisines.

In the reef hobby Gracilaria is prized because it is highly palatable to herbivorous fish — tangs in particular — and its effective nutrient uptake makes it well suited to aquarium refugiums. Aquarists like growing it precisely because fish enjoy eating it, so it doubles as a living food source and an export tool.

Propagation Method

Gracilaria is propagated by division and fragmentation of its branched fronds. Each separated piece continues growing on its own, so you simply split a healthy clump into smaller bushes. Pieces can be left to tumble freely in a refugium or loosely anchored among rock to grow out.

Step-by-Step

Pick a healthy, richly colored clump with firm, bushy red fronds.
Divide it into several smaller branched pieces by pulling or cutting apart the fronds.
Place the divisions in a lit refugium with moderate, turbulent flow.
Let pieces tumble freely so all sides receive light, or wedge loosely among rock.
As the fragments grow, periodically harvest and re-divide to expand the colony.

Conditions for Healthy Growth

Moderate lighting in a refugium drives steady growth of the red fronds.
Stable warm marine conditions; the genus cannot survive below about 10°C.
Effective access to nitrogen and phosphorus, which the alga takes up efficiently.
Turbulent, tumbling flow to keep clumps moving and evenly illuminated.
Full marine salinity consistent with its warm-water, refugium-friendly nature.

Maintenance

Harvest regularly by thinning the macroalgae; removing biomass is what actually exports absorbed nutrients from the system. Feed the fresh trimmings to tangs and other herbivores as high-value grazing food, and re-divide retained pieces to keep the refugium colony vigorous.