Witman, J. D., Smith, F.

Rapid community change at a tropical upwelling site in the Galapagos Marine Reserve

2003

Biodiversity and Conservation

12

1

25-45

The high biodiversity of tropical marine communities has attracted considerable interest, yet we still lack a clear understanding of the tempo of diversity change in these systems. Knowledge of the conditions associated with fast or slow community assembly in the tropics would enhance our ability to predict recovery from natural and anthropogenic disturbance and to conserve biodiversity. Here we report an unusually rapid doubling of species richness within a year in a tropical, subtidal sessile invertebrate community in a protected (non-extractive) zone of the Galapagos Marine Reserve (GMR). Diversity changes in the rock wall community were accompanied by large increases in the percent cover, density and/or biomass of sponges, barnacles, ascidians, and an ahermatypic coral, Tubastrea coccinea, over the 1-year study period (1999-2000). Barnacle (Megabalanus peninsularis) and ascidian (Didemnum cineraceum) biomasses increased by an order of magnitude from 1999 to 2000. The greater abundance of sessile invertebrate prey was accompanied by significant increases in the abundance of barnacle and Tubastrea predators (Hexaplex princeps, Asperiscala billeeana). An estimated 37% of barnacle tissue biomass production was consumed in 1 year. Temperature monitoring during the study period showed that this site is characterized by strong upwelling, where rapid, 3.0-9.0 degree C decreases in temperature occurred at harmonics of the semi-diurnal tidal periodicity during warm (January-February), but not during cool months (June-July). Short-term acoustic current meter measurements revealed strong, highly variable upwelling at the study site, with events ranging from 2-111 min in duration and maximum upwelling velocities of 32.3 cm s super(-1). These findings suggest that the turnover of diversity and biomass may be unusually rapid at tropical upwelling sites, especially where invertebrate predators are protected from harvesting. Consequently, upwelling sites may warrant special consideration in the planning of marine reserves to ensure the conservation of biodiversity.

Community composition/Species richness/Biomass/Upwelling/Marine environment/Tropical environment/Nature reserves/Coral/Marine parks

10.1023/A:1021200831770

ASFA Abstract