The prevalence and production of turf-forming algae on a temperate subtidal coast

Abstract

This study shows that canopy-forming algae, composed mainly of fucoids and the kelp Ecklonia radiata (both Phaeophycea), dominated space on South Australian coasts relative to turf-forming algae. However, where canopy-forming algae are absent turf-forming algae are the primary occupiers of space (; 70%). On some reefs where canopy-forming algae are restricted in spatial extent, turfs can occupy as much as 40% of reefs. Turf-forming algae are an abundant component of algal assemblages, but relatively little is known about their contribution to the primary productivity on temperate reefs, relative to canopy-forming species. This study reveals that net productivity rates of turfs at one South Australian location were very high across depths (1.3–2.9gCm22 day21 or 23.2–88.0 mg C g ash-free dry weight21 day21), comparable to the values discovered on tropical reefs. Although turf-forming algae are much more productive than canopy-forming algae on a biomass basis, the annual net production per area is two to seven times lower for turfs than for canopy-forming algae. However, if negligible exudation rates are assumed for turfs (up to 1%), the biomass of carbon produced by turf algae represents 44– 71% of the carbon incorporated into biomass of kelps. Taken together, these results suggest that while canopy-forming algae can be correctly assumed to be the major source of total carbon produced on temperate reefs, the contribution of turfforming algae may be substantial to the biomass production and turnover on South Australian reefs.