Development of protocols to assess the relative habitat values of urban shorelines in the New York–New Jersey Harbor Estuary

Abstract

Habitat complexity is reduced when natural estuarine shorelines are replaced with concrete seawalls in highly urbanized regions. There is growing interest and investment in rehabilitating urbanized shorelines by adding physical habitat complexity to encourage establishment of diverse and resilient ecological communities. This is challenging, as multiple factors in addition to habitat availability operate across large scales to constrain ecosystem rehabilitation in urban estuaries. Design and management of shorelines to enhance their habitat and other ecological values should be based on using scientifically rigorous information to facilitate effective and efficient use of limited resources. This study was the initial step in the development of a protocol to provide a standardized and ecologically meaningful assessment of the relative habitat values of urban shorelines varying in physical habitat complexity across New York-New Jersey Harbor. We developed a novel device with multiple colonization surfaces of standard dimensions, and a preliminary protocol manual to guide personnel in the construction and use of the device. In the subtidal zone of hard shorelines in the Harbor, mobile and sessile communities colonized mesh netting and hard settlement plates, respectively. Across all shorelines, mobile amphipods and encrusting algae were common, whilst isopods, shrimps, crabs and ascidians were common in some locations. Subtidal communities differed more between locations than between shorelines, varying in physical complexity, within locations. Increased habitat complexity did not consistently favor any particular taxonomic group across shorelines, but there were notable differences in community structure between concrete seawall and riprap revetment shorelines in some locations. However, some components of the original colonization devices were not durable enough and loss of replicate samples prevented meaningful comparisons across all shoreline types. Colonization devices were redesigned with stronger outer caging made from vinyl-coated steel, more secure settlement plate attachment and greater weight for anchorage to hard shorelines. Redesigned devices were successfully deployed on a hard shoreline subject to high water movement. Intertidal surveys using quadrats, subtidal photoquadrat surveys, bivalve surveys using scouring pads and fish surveys using minnow traps were trialed, but did not provide additional useful information for comparing the relative habitat values of hard shorelines in New York-New Jersey Harbor. The colonization device and associated measurements of abiotic variables should be refined, and they show promise for facilitating standardized assessments that could inform the future design and management of hard estuarine shorelines in the Harbor.