Costs and benefits of changing sampling methods in marine protected area long-term monitoring

To confirm their effectiveness, long-term monitoring of marine protected areas (MPAs) is critical. Such longitudinal sampling can, however, pose problems of methodology, particularly as the preferred tools may evolve over time... [ view full abstract ]

To confirm their effectiveness, long-term monitoring of marine protected areas (MPAs) is critical. Such longitudinal sampling can, however, pose problems of methodology, particularly as the preferred tools may evolve over time and new approaches emerge. My project evaluated how data from two methods, line intercept transect (LIT) and photoquadrat (PQ), which were used sequentially in MPA monitoring, estimated percent coral cover in a series of MPAs in the central Philippines. Ideally, of course, one survey method would be used well and consistently, but what happens when procedures are suboptimal and must be changed?

Analyzing three years of data when both LIT and PQ were applied, we found that LIT generated higher cover estimates than PQ, perhaps because of the smaller sample sizes in LIT. However, subsampling LIT data to increase sample sizes allowed comparison of estimates by these two methods. This led me to realize that PQ data detected significant cover change over three years whereas LIT data did not, probably because PQ data had larger sample sizes from wider spatial ranges (and thus more statistical power). Our study addresses realities in long-term monitoring about how to reconcile different data sets. The results also contribute to MPA development and management.