Citation:

Hale, S., M. Hughes, AND H. Buffum. Historical Trends of Benthic Invertebrate Biodiversity Spanning 182 Years in a Southern New England Estuary. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 41(6):1525–1538, (2018). https://doi.org/10.1007/s12237-018-0378-7

Impact/Purpose:

Narragansett Bay has high benthic invertebrate biodiversity that supports many ecosystem functions and services important to people living on the surrounding shores. Over time, natural and human-driven forces have caused declines in biodiversity, resulting in changes to ecosystem functions and serviced. Historical studies can help understand environmental change and its drivers. However, sporadic sampling and lack of consistent methods makes it difficult to quantitatively assess changes in the benthic community over three centuries using conventional methods. Use of a statistical technique for measuring biodiversity called taxonomic distinctness (a measure of complexity of the community’s taxonomic tree), along with a measure that determines the similarity of two different communities, allowed such analyses. We found that the bay has steadily lost a significant amount of biodiversity since at least the mid-19th century. This loss of biodiversity has had serious implications for the ecosystem functions and services provided by benthic communities. Our study shows a partial recovery of biodiversity in the last two decades, which we suggest was a result of legislation such as the Clean Water Act and management actions beginning in the 1970s. Biodiversity is an important ecological indicator of what is happening in our environment and is being used by the Office of Water as a key indicator in the National Conditional Coastal Assessment. In managing a system as complex as Narragansett Bay, it is important to have an inventory of what species are present, to know how that inventory has changed over time, and to understand what factors forced those changes. This information is needed to assess the impacts of permitting proposed activities. Biodiversity is a useful measure in assessing whether particular EPA and state programs are effective in what they are trying to achieve for water quality and ecosystem health in our bays and coastal areas. Community similarity and taxonomic distinctness make it possible, for example, to compare the benthic community before and after recent improvements to sewage treatment plants at the head of the bay.

Description:

Benthic invertebrates support numerous ecosystem functions and services including shellfish production, energy flow to fishes, and biogeochemical cycles. The decline of marine biodiversity worldwide has raised concerns about effects on ecosystems. To examine biodiversity trends of Narragansett Bay over time, a list was compiled of all benthic invertebrate species collected from the bay since 1834. The list covers 104 studies spanning 182 years and currently holds 1214 unique taxa from 21 phyla, the majority of all animal phyla on Earth. A permuted estimator of number of species suggested there are about 300 more yet to be discovered. Widely varying sampling gear and sieve mesh sizes precluded the use of abundance data. Instead, multidimensional scaling and taxonomic distinctness were used with presence-absence data to examine biodiversity trends. The changes in community composition and decline of benthic biodiversity (p < 0.01) since 1855 are what would be expected of a community that gradually deteriorated in the face of increasing anthropogenic stressors. Taxonomic distinctness had negative correlations (p < 0.05) with human population in the watershed, total nitrogen inputs, and inputs of metals. This loss of benthic biodiversity has implications for ecosystem functions and services. As some of the stressors waned in the last two or three decades, following passage of environmental legislation in the 1970s, biodiversity appeared to show a partial recovery. An inventory of species, how it has changed over time, and understanding what caused those changes are important for assessing whether remediation programs are achieving improved water quality and ecosystem health.

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