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MATERIALS AND METHODS

Macrophytes and invertebrates were collected from the intertidal zone at low tide on Appledore Island, Maine (42 59.29'N, 70 37.01'W) in June 1993. In March 1994, macrophytes and invertebrates were collected at Carrie Bow Cay (16 48.16'N, 88 04.94'W) from either the barrier reef (15–18 m) or turtle grass beds (< 1 m) near Carrie Bow Cay and at Cassiopea Cove, Twin Cays (1–2 m) lying approximately 2 km west of the Carrie Bow Cay barrier reef. In June and July 1994, macrophytes and corals were collected on patch reefs centered around Sliver Reef in Kaneohe Bay, Hawaii (21 29'N, 157 50'W) and corals were collected from Moku Manu (21 29'N, 157 48'W). All samples were stored at− 50 C prior to analysis for MAAs. Spectral data (3 scans, 300–700 nm at 2 nm intervals) were recorded using a LiCor LI-1800UW scanning spectroradiometer (LiCor, Lincoln, Nebraska) simultaneously with collection of samples for MAA analysis. Vertical attenuation coefficients (Kd) were calculated by linear regression of each wavelength with depth and with the integrated spectral irradiances for UV-B, UV-A and PAR. Kd values were used to calculate z (10%). Extraction and analysis of MAAs were performed according to the procedures in Dunlap and Chalker (1986) as modified by Shick et al.(1992). Algae and corals were extracted overnight in HPLC grade methanol at 4 C. MAA peaks were determined by UV absorbance at 313 and 340 nm using a Waters 440 absorbance detector and confirmed on a Waters 990 Photodiode array detector against known standards. MAA concentrations were normalized to soluble protein from an …