Spatial and temporal variability in juvenile coral densities, survivorship and recruitment in La Parguera, southwestern Puerto Rico

Abstract

Juvenile coral survivorship (the proportion of juvenile colonies surviving from t1 to t2) was assessed by counting, photographing and mapping all juveniles found in 2003 within random permanent 0.25m2 quadrats at four depth intervals at each of four inshore and mid-shelf reefs and at deeper habitats (>18m) in two shelf-edge reefs (N=96/reef) in La Parguera, southwest coast of Puerto Rico. Quadrats were resurveyed and photographed in 2005 to evaluate surviving juveniles, mortality and new recruits. Total number of juveniles dropped from 718 in 31 scleractinian species in 2003 to 396 in 28 species in 2005, an average juvenile survivorship of 54.8%. Mean juvenile density decreased from 1.2 (± 0.06) colonies/0.25 m2 in 2003 to 0.7 (± 0.05) colonies/0.25 m2 in 2005. Juvenile coral composition, relative abundances, survivorship and recruitment varied significantly across depth intervals within reefs and among reefs. Some species with high relative abundances in 2003 showed high survivorship in 2005 [Siderastrea siderea (28.3% and 65% respectively), Porites astreoides (15.1% and 55.6%), and Diploria strigosa (7.5% and 45.2%)]. Other taxa had relative low abundances but high survivorship [Montastraea cavernosa (4.6% and 66.7%) and Stephanocoenia intersepta (4.6% and 48.3%)]. Survivorship was significantly higher in deeper habitats at three of the four fringing reefs. Furthermore, the semi-exposed inshore, highly sedimented reefs, showed higher juvenile survivorship than the mid-shelf and shelf-edge reefs. There was no clear relationship between survivorship and reproductive mode (brooding vs. broadcast spawning) of sexual reproduction. Overall, only 78 new recruits were found in 2005.