Do small overwater structures impact marine habitats and biota?

Abstract

Small overwater structures (SOWS) such as residential docks are common along marine shorelines. Large overwater structures like ferry terminals and commercial piers cast shadows that impair submerged aquatic vegetation and habitat, and alter salmon behaviour and migration. Because of large overwater structure impacts, it is possible that SOWS may also impact marine habitats and organisms. Here, we review the evidence for marine SOWS impacts, finding that relatively little research has been dedicated to the topic. Outside of reducing light and causing well-documented impacts on seagrasses in multiple parts of the world, there is inconsistent or inconclusive evidence for impacts on macroalgae or fish. There is insufficient research on SOWS to draw robust conclusions about these structures’ overall impacts on nearshore environments or how to mediate any possible impacts. Unfortunately, freshwater SOWS or large marine structures are imperfect analogues for inferring marine SOWS impacts. However, we emphasise that an absence of evidence is not evidence for an absence of impacts by SOWS. We outline critical research questions and the relevant study approaches that would address data gaps surrounding SOWS impacts and management.

A Cross-Decadal Change in the Fish and Crustacean Community of Lower Yaquina Bay, Oregon, USA

“…This highlights a tremendous decline in estuarine species abundance and richness in the section of Yaquina Bay that has been most altered by development in the last four decades (Figure 2). Similar declines in abundance have been observed following waterfront development in the southeast United States, where demersal fish and epibenthic crustaceans were less abundant in stretches of shoreline altered by rubble or bulkheads [38], while a broader synthesis aimed at evaluating the ecological impacts of overwater structures (OWSs) in the U.S. Pacific Northwest [3] found that OWSs reduce natural habitat (seagrassess) and prey (abundance and diversity of invertebrate species), and affect the movement, migration, and feeding behaviors of salmonids. Changes to Yaquina Bay have also affected community composition, as most measures of biodiversity declined between surveys.…”

“…Physical development, including shoreline armoring and construction of hardened structures, disrupts benthic communities, thereby reducing prey resources for nearshore fish and wildlife [1] and habitat available for epibenthic crustaceans [2]. It is possible that even small, human-built structures influence habitat structure, fish distribution, migration, feeding behavior, and availability of prey resources [3]. Chemical alterations, in the form of nutrient and pollutant inputs, have effects ranging from altering primary productivity and microbial community composition to changing community structure [4][5][6][7].…”