Community Structure in Time Past: Influence of Human Fishing Pressure on Algal‐Urchin Interactions

The sea urchin Diadema antillarum increases the relative size of Aristotle's lantern (length of demipyramid) when food limited. This provides a tool for investigating algal abundance and biotic interactions in the past. A field collection of D. antillarum provided a baseline relationship between demipyramid length and body size (test diameter). Experimental manipulations of food availability and population density resulted in shifts in relative demipyramid length. The baseline and experimental data provide a range of responses that was compared to museum specimens collected over the past 100 yr from 30 locations in the Caribbean. The relative demipyramid lengths from the museum specimens were also compared over time, and with human population density, human fishing pressure, and geographic region. The results indicate that relative demipyramid size is indirectly influenced by human activity and varies with geographic region. This suggests that human fishing pressure has influenced Caribbean coral reef community structure by affecting predator—herbivore relationships. However, this human impact may be small relative to naturally occurring variation in demipyramid size.