Larval settlement of the green sea urchin, Stronglyocentrotus droebachiensis, in the southern Gulf of Maine

Settlement timing and differential settlement for the larval stage of the g reen sea urchin, Strongylocentrotus droebachiensis, in the southern Gulf of Maine was studied during the summer of 1996. Settlement densities on astro turf panels were highest in June and early July (13 to 37 m(-2) d(-1)), and peaked in mid-June (199 m(-2) d(-1)). Settlement was low to nonexistent fr om mid-July through August (0 to 2 m(-2) d(-1)). During the peak in settlem ent, no selection for substrate type was observed. In the remainder of the settlement period, differential settlement occurred, with a preference for substrate covered with live coralline algae. Test diameter of newly settled urchins varied among the substrates, with urchins sett:ling on live corall ine algae having the largest test diameter (0.43 +/- 0.01 mm). There were n o differences in test diameter among the different weeks in which sampling was done. Sustained onshore winds occurred only during peak settlement, sug gesting that wind drift currents may concentrate larvae and influence patte rns of larval settlement.