Coral planulae as dispersion vehicles: Biological properties of larvae released early and late in the season

Abstract

Over the last century, considerable research has been dedicated to investigating life history traits of coral planulae. However, despite the universality of coral propagules and their deduced ecological properties, there is no clear understanding of some basic biological issues such as ecological and evolutionary forces that determine sexual reproduction and larval behavior in hermatypic corals. To further evaluate ecological trajectories in sexual reproduction of the hermatypic coral Stylophora pistillata from Eilat, Red Sea, we collected 22 900 planulae from 313 S. pistillata colonies in situ during March to July (2004 to 2006). Variations in reproductive effort were observed between years, but during all reproductive seasons, the larvae tended to settle ex situ in aggregates of kin (61.71% to 82.4%; 2005 values). During a 6 mo survey, the spat grew at a rate of 3.4 to 5.4 polyps mo-1. Peaks of planula shedding were documented for April to June, suggesting a shift in reproductive seasonality compared to the preceding 2 to 3 decades. Ex situ settlement of collected larvae revealed, for the first time, settlement polymorphism of early versus late larvae throughout the reproductive season; the March settlement rate was the highest (43.7%) and June was the lowest (26.2%). A reverse trend was documented for settlement rates on the first post-planulation night, with only 2.2% settlement in March versus 46.2% in July. Early season larvae of S. pistillata are therefore capable of dispersing farther than late season propagules. These results are diametrically opposed to the 'desperate larva hypothesis,' revealing different ecological traits of early versus late season larvae. © Inter-Research 2007.