Variation in planning-unit size and patterns of fish diversity implications for design of marine protected areas
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Variation in planning-unit size and patterns of fish diversity implications for design of marine protected areas
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    "Marine protected areas (MPAs) have commonly been used to conserve or protect communities and habitats sensitive to disturbance, provide refuge for juveniles and spawning adults of exploited species, and serve as a hedge against management miscalculations or abnormal conditions. Species-richness hotspots are often used as an important focus for identifying conservation targets. We investigated how variation in planning-unit size (i.e. 10x10 km, 20x20 km, 40x40 km, and 80x80 km) affected spatial patterns of fish species richness and identification of diversity hotspots in the Gulf of Maine - Georges Bank region of the northwest Atlantic. Data from region-wide seasonal bottom trawl surveys from 1975-2004 were used to calculate total and mean richness estimates at each spatial scale. We found that planning-unit size and spatial variation in sampling effort had a profound influence on emergent spatial patterns of diversity. Spatial patterns of sample effort were uneven and contributed to variation in patterns based on total richness, especially at the smallest planning-unit size. A bootstrap approach was subsequently used to standardize effort and to estimate mean richness in each grid cell. Hotspots, defined as those planning units representing the top 10% of species richness, shifted from coastal areas to offshore sites with steep topography near Georges Bank at coarser planning-unit sizes, for both total richness and standardized effort approaches. Hotspots with similar species composition, based on cluster analysis, had discontinuous distributions at 10-km and 20-km scales. Regressions of analysis of similarity (ANOSIM) R values versus distance between hotspot pairs, at each planning-unit size, did not indicate any strong linear relationships. Furthermore, ANOSIM procedures at each planning-unit size showed that the 10-km scale had the highest species dissimilarity (based on Global R values) among individual hotspots. These results may be attributed to the patchy distribution of multiple species based on variation in habitat affinities and fewer habitat types occurring in small planning-units. It is difficult to conclude that a large MPA is better than several small MPAs; however, we suggest that increasing planning-unit size can reduce the effect of sample size on the selection of hotspots, increase confidence in the results of such analyses, and increase probability of encompassing representative species at regional scales"--Abstract.
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