Oyster Density and Demographic Rates on Natural Intertidal Reefs and Hardened Shoreline Structures

Abstract

The ubiquitous loss of natural intertidal oyster reefs and associated ecosystem services has fueled restoration efforts throughout the world. Effective restoration requires an understanding of the distribution, density, and demographic rates (growth and survival) of oysters inhabiting existing natural reefs and how these may vary as a function of landscape-scale factors, such as tidal range and fetch distances. Furthermore, natural intertidal habitats are increasingly being replaced with hardened shoreline structures that may be colonized by oysters, yet little is known about habitat quality (as indexed by oyster density and demographic rates) of these hardened structures relative to natural habitats. The present study sought to compare oyster density, demographic rates, and population estimates (1) across estuarine landscape settings to inform natural intertidal oyster reef restoration (i.e., comparing natural intertidal reefs within adjacent water bodies that vary in tidal regimes and fetch distances) and (2) across natural habitats and human-made structures to assess variation in habitat quality between natural reefs and hardened shorelines. Oyster density, growth rates, and population estimates on natural intertidal reefs were greatest within the smaller, more tidally influenced Core Sound versus the larger, wind-driven Pamlico Sound, with no significant difference in survivorship identified between the two water bodies. Natural intertidal reefs and hardened shoreline structures were compared within Pamlico Sound only, with natural intertidal reefs hosting three to eight times higher oyster densities than hardened shoreline structures. When mean oyster density/m2 was multiplied by reef area to estimate population size, natural intertidal reefs within Pamlico Sound hosted considerably greater populations of oysters relative to hardened shorelines. The present study fills an existing need to understand oyster density and demographic rates on natural intertidal reefs and hardened shorelines to better inform future restoration and shoreline management scenarios.