Natural Intertidal Oyster Reef Growth Across Two Landscape Settings and Tidal Ranges

Abstract

Intertidal oyster reefs are typically restored to offset the loss of reef-associated ecosystem services (e.g., improved water quality, shoreline stabilization, and fish habitat), but the scale of enhanced services is predicated on the health and growth of the restored reef. Previous work on young (<15 years) restored reefs showed the highest growth rates along the sides of reefs where they are aerially exposed 20–40% of the time, but much is still unknown about how those positions in the tidal frame change with landscape setting, tidal range, and reef maturity. This study compared the area of maximum growth among 12 natural intertidal reefs in coastal North Carolina that range between 1395 and 62 years old. The reefs include fringing and patch landscape settings in each of two estuaries with tidal ranges of 0.94 m and 1.51 m. Peak growth rates were similar among landscape and tidal settings and were faster than the rate of sea-level rise (SLR) indicating intertidal reef resilience to accelerating SLR. Flow baffling associated with fringing reefs and higher summer air temperatures in the southern estuary likely contributed to a lower position of the optimal growth zone, where growth rates are highest, in the tidal frame. Intertidal reef growth manifests differently across the range of aerial exposures at varying stages of maturity. Once reefs reached ~50 years old, the elevation of the reef crests equilibrated to ~60–70% aerial exposure and peak growth rates stabilized between 2 and 4 cm year−1 at ~50% aerial exposure. These results are a useful guide for identifying areas and cultch configurations that optimize reef growth rates, enhancing the probability for self-sustaining restored reefs.