Ellie R. Paine1, Matthias Schmid2, Elizabeth A. Brewer3, Guillermo Diaz-Pulido4, Philip W. Boyd1 and Catriona L. Hurd1
1 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart Tasmania 7001, Australia
2 Trinity College Dublin, University of Dublin, Dublin, Ireland
3 CSIRO Oceans and Atmosphere, Castray Esplanade, Hobart, Tasmania 7001, Australia
4 Griffith School of Environment, Coastal and Marine Research Centre, and Australian Rivers Institute – Coast and Estuaries, Nathan Campus, Griffith University, Brisbane, Queensland 4111, Australia
Fluctuations in seasonal abiotic factors such as inorganic nitrogen availability, irradiance and temperature control the growth of seaweeds on temperate reefs. In response to seasonal growth patterns, dissolved organic carbon (DOC) release by seaweeds is also thought to be driven by season. To explore this, we seasonally surveyed, and sampled, the seaweed assemblage at Coal Point on Bruny Island over a one-year period. Seaweeds from phyla Ochrophyta (Ecklonia radiata and Phyllospora comosa) and Rhodophyta (Lenormandia marginata, Plocamium cirrhosum and Hemineura frondosa), with various inorganic carbon uptake strategies, were used for laboratory incubations to determine release rates of DOC. Seasonal in situ seawater temperatures were maintained for the experimental incubation and irradiance was kept at 150 μmol photons m-2 s-1 across all seasons. Significant DOC release was observed for every species during spring and summer that were ~400% greater than those observed during autumn and winter. For each season, we calculate a net DOC flux from the reef at Coal Point which supports the microbial food web in this temperate region. The biomass of the seaweed assemblage did not change over the year suggesting fluctuations in the DOC flux of the seaweed bed were driven by seasonal changes to the seaweed physiology rather than amount of seaweed in the reef. Carbon and nitrogen percent dry tissue content and C:N ratios supported our results that seasonal seaweed physiology drove fluxes in DOC release.