Evaluating Biological Change in New Zealand Marine Reserves

Abstract

This study illustrates the importance of baseline surveys, why they are necessary and how best to conduct them. A proposed marine reserve site (the south coast of Wellington) was monitored for three years to establish a comprehensive baseline study. The results were used to recommend appropriate methodology for sampling in this area and also to establish which species are the best to use as indicator species to detect any possible change occurring in this area due to future reservation status. The 11 km stretch of coast surveyed, which included future reserve and control sites, was tested for heterogeneity, to prevent any future differences in sites being attributed to reservation status as opposed to natural variation. It was determined that an environmental gradient exists along the south coast, from east to west, most likely due to increasing wave exposure and increasingly strong tides and currents towards the west. An established marine reserve (Kapiti Marine Reserve) was also monitored over the same period of time to establish what differences existed in size and abundance of key species between reserve and control sites. The data collected in this investigation were also compared to data collected immediately prior to reserve establishment to determine what changes had occurred over time. Results showed that sites inside the marine reserve supported a greater species abundance, and in some cases, larger size classes. There was some evidence for a general shift in the community structure particularly in algal plants. However, these results may have been confounded by the effect of one site that appeared to have a very high natural species diversity and abundance (even before reservation status). It was concluded that the one-off survey conducted before establishment of this reserve was inadequate to use as a baseline against which to detect changes. No changes were found between the present study and the preliminary survey, although specific data analysis indicated a reserve effect. Continued sampling methodology for Kapiti Marine Reserve area was suggested. Raw data, on two key species (blue cod and rock lobster) from six marine reserves in New Zealand were investigated in an attempt to perform a statistical "meta-analysis" of the effects of marine reserves in New Zealand. A meta-analysis is different from a narrative review as it uses statistical methods to compare results across studies. This methodology has not been applied to studies of marine reserves before. The meta analysis conducted in the present investigation showed that generally marine reserves in New Zealand are having a positive effect, in terms of increasing size and abundance of individual species, as compared to control areas. There is some evidence for a latitudinal trend influencing the "effect size" (a statistical term indicating the magnitude of the treatment tested - in this case, reservation) of the reserves.