Carbonate Sediment Produced by Rock-Boring Urchin, Echinometra lucunter, and Infauna, Black Rock, Little Bahama Bank: ABSTRACT

Abstract

Bioerosion studies on Black Rock Island, Little Bahama Bank, were conducted during 4 cruises in 1982-83 on the 405-m (1,300-ft) long island of carbonate eolianite. The urchin population (mean 37 adults m-2, 92 × 103 total) bores in a 6-m (20-ft) wide zone at depths of 0.5-3 m (2-10 ft). Scuba divers using rock chisels collected rocks, some with urchins in their boreholes and similar size rocks without urchins. The samples were placed separately in 20L, 62.5 µm screen-walled buckets for 2 days (18 useable measurements). Urchins produced spherical to elliptical pellets 1-2 mm in diameter. Disaggregated pellets contained no particles greater than 1.00 mm, 46% unimodal sand (mode = 177 µm), and 54% mud. Urchins produced a mean of 242 ± 146 mg sediment urchin-1 day-1 (dry weight), equivalent to a mean of 8.9 g m-2 day-1 or 9 tons year-1 for the entire population. Urchin boreholes were 17-126 cm3 (mean = 72 cm3). Calculating from boring-rate measurements, the boreholes were excavated in 0.7-10.3 years (mean = 2.9 years). Rocks without urchins (controls) produced a mean of 0.50 ± 0.07 mg organic-free sediment cm-2 day-1 (dry weight). These particles were produced by bioerosion of an infauna (4.5-13.8 g dry weight) of eunicid and sipunculid worms, sponges, Lithotrya barnacles, pelecypods, and microborers. Inorganic sediment weight was correlated (r = 0.97) with surface area of the control rocks. Controls produced 5.0 g m-2 day-1 (36% of total), equivalent to 6.5 tons year-1. End_of_Article - Last_Page 487------------