3-13 Can Harvesting Regulations Drive Ecological Community Change?
To determine the different impacts that regulations of size versus overall catch may have on communities, we manipulated size (15mm, 45mm) and density (20/m2, 40/m2) of yellowfoot ‘opihi in a fully factorial manner using 36 field enclosures (0.25m2) located along the North Kona coastline of Hawai‘i Island. We evaluated algal community changes using monthly photo quadrats, and tracked growth (through changes in shell aperture area) and mortality rates of tagged individuals within each treatment.
Preliminary results after 2 months suggest both size and density of ‘opihi impact ephemeral algal communities. We used crustose corraline algae (CCA) percent cover as an initial proxy for algal community change. In both the 20/m2 and 40/m2 density treatments for the 45mm ‘opihi, and the 20/m2 treatment for the 15mm ‘opihi, CCA cover remained approximately the same. However, the 15mm ‘opihi at 40/m2 treatment was almost completely overgrown by ephemeral algae. These differences do not appear to be driven by biomass, as indicated by ephemeral algal growth in the 4/m2 ‘ophi at 45mm biomass control, but little to no ephemeral algal growth in the 160/m2 ‘opihi at 15mm control.
Preliminary growth rates indicate density dependent growth in both size classes. For 45mm ‘ophi, the highest mean growth rate was the 4/m2 ‘ophi density treatment (4.6mm2/day), decreasing to 2.7mm2/day in the 40/m2 treatment. For 15mm ‘opihi, the highest mean growth rate was the 40/m2 treatment (2.9mm2/day), and the lowest growth rate was the 160/m2 density treatment (0.5mm2/day). These results suggest that harvesting regulations and strategies may have differential impacts on both harvested species and the ecological communities in which they reside.