Advancing an Ecosystem Approach in the Gulf of Maine

Spatial Patterns of Subtidal Benthic Invertebrates and Environmental Factors in the Nearshore Gulf of Maine

Stephen S. Hale


Abstract.—Spatial patterns of subtidal benthic invertebrates and physicalchemical variables in the nearshore Gulf of Maine (Acadian biogeographic province) were studied to provide information to calibrate benthic indices of ecological condition, determine physical-chemical factors affecting species distributions, and compare recent data with historical biogeographic studies. Knowledge of the distribution of species and how they are affected by biotic, environmental, and anthropogenic factors is essential to the pursuit of ecosystem-based management. Five years (2000–2004) of data from 268 reference stations of the National Coastal Assessment were used. Multidimensional scaling done on Bray-Curtis similarity matrices of species’ relative abundance (367 species) showed faunal transitions around Cape Ann and Cape Elizabeth, with a weaker transition around Penobscot Bay. The southernmost area shared 41% of its species with the northernmost area. An ordination of environmental data (temperature, salinity, sediment percent silt-clay, depth) correlated well with the ordination of benthic relative abundance data (R = 0.75, p < 0.03). Temperature was the most important factor affecting broad species distribution patterns, followed by salinity. A multivariate regression tree first split the fauna at a temperature of 16°C. Species richness increased with increasing salinity but showed no relationship with latitude or percent silt-clay. Accuracy of benthic indices for the nearshore Gulf of Maine might be improved by taking biogeographical differences among subregions into account. These results provide a foundation for ecosystem-based management, valuation of ecosystem services, conservation, and ocean spatial planning.