Durvillaea antarctica Production in Relation to Nutrient Cycling at Marion Island

Summary

An account is presented of the production of Durvillaea antarctica at Marion Island, including its inter-relationships with higher trophic levels. Biomass was determined for shores with differing degrees of exposure. Data from aerial photography indicated that 48% of the coast is exposed and directly struck by swells, 33% is sheltered or parallel to swell direction, 15% is large boulder or block shore, and 2% is sandy or small-pebble beach. The total fresh mass of D. antarctica, approximately 3,300 t (ww), is situated with varying proportion along each shore type of the island. Calorific content varies with season and with plant organ. Recruitment generally takes place after August on sites having become available after autumn and winter storms. Production in a re-colonizing stand of kelp sporelings is equivalent to 172 × 10³ kJ m⁻². Low erosion rate and high mortality is a feature of the D. antarctica population. The primary contributors to mortality are grazing by intertidal herbivores and occasional, violent storms. Holdfasts are weakened by boring isopods. Affected plants are torn free and cast onto beaches during storms, where they are attacked by grazing Amphipoda in the spray zone. Beyond this zone, decomposition takes place through bacterial action.