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Notes: Abstract Carbon budgets were modelled for temperate anthozoan-dinoflagellate symbioses involving the sea anemones Cereus pedunculatus (Pennant), Anthopleura ballii (Cocks) and Anemonia viridis (Forskäl), and the zoanthid Isozoanthus sulcatus (Gosse). Irradiance regimes experienced at 1.5 and 9 m on sunny and cloudy days in summer were assumed. Photosynthetic capacity (P max gross) and efficiency (α) were considerably higher in I. sulcatus than in the other Anthozoa. P max gross and α also differed in A. viridis from different localities. At 1.5 m on sunny days, zooxanthellae would require 1.80 to 5.89% of the carbon fixed in photosyn-thesis for respiration and growth, and translocate the remainder (94.11 to 98.20%) to the host. Productivity would decrease with increasing depth and cloud cover, resulting in a decrease in the potential availability of carbon for translocation. At 9 m on cloudy days, 37.82 to 87.84% of the carbon fixed in photosynthesis would be required for zooxanthella respiration and growth in C. pedunculatus, Anthopleura ballii and Anemonia viridis, leaving just 12.16 to 62.18% for translocation; the translocation rate would still exceed 95% in I. sulcatus. The potential contribution of zooxanthellae to the host's daily respiratory carbon requirements (CZAR) would be 72.6 and 72.1% in Anthopleura ballii and C. pedunculatus, respectively, at 1.5 m on sunny days, and would decrease to just 2.1 and 0.7%, respectively, at 9 m on cloudy days. These Anthozoa therefore require a heterotrophic source of carbon to survive. The CZAR in Anemonia viridis from different locations would be 140.6 to 142.9% at 1.5 m on sunny days, but would be 〈100% under the other assumed irradiance regimes. The CZAR in I. sulcatus would be 181.5% at 1.5 m on sunny days, and would only be 〈100% when at 9 m on cloudy days. Under favourable conditions, A. viridis and I. sulcatus are potentially autotrophic and may have surplus carbon available (15.69 to 43.89% of the gross photosynthetic production) for tissue biosynthesis, reproduction and storage. However, when field conditions are considered on an annual basis, the general need for heterotrophically-derived carbon in temperate Anthozoa is suggested.