ROLE OF PHYSICAL REFUGIA - IMPLICATIONS FROM A MASS SPONGE DIE-OFF INA LOBSTER NURSERY IN FLORIDA

In 1991 and 1992, cyanobacterial blooms depleted sponges, the primary refuge of juvenile Caribbean spiny lobsters, in similar to 20% of the nursery in the Florida Keys, USA. Long-term data from the affected mid dle Keys were used to study the impact of sponge loss, juvenile abunda nce, recruitment and shelter use. A manipulative experiment (1991-93) involved artificial shelters on 27 similar to 0.5-h sites. Conditions on 19 sites over the affected similar to 500 km(2) area were compared before and after the blooms. The entire nursery (similar to 10,000 km( 2)) was surveyed to estimate the impact of the disturbance on total ju venile recruitment. Refuge and lobster abundances declined and the pat tern of shelter use changed on previously sponge-rich sites without al ternative shelter (solution holes, coral heads, cement blocks, etc.). Although sponge loss often locally reduced juvenile abundance, the juv enile lobster population overall declined by similar to 5%, The availa bility of alternative, previously underused shelter (solution holes, c oral heads, etc.) in the affected region, continued production in the larger unaffected nursery region, and high postlarval supply that fort uitously coincided with sponge loss all offset a stronger effect. Howe ver, postlarval supply is unlikely to remain high until the sponges re populate the middle Keys (10+ years), so a major factor ameliorating t he effect of sponge loss on lobster recruitment may disappear.