Field Investigation of the Influence of Bulkheads on Meiofaunal Abundance in the Foreshore of an Estuarine Sand Beach
Keywords:Sediment activation, shore-parallel structures, wave action, meiofaunal habitat.
A one-day field investigation was conducted on an estuarine sand beach foreshore in Raritan Bay, New Jersey to document meiofaunal abundance at sites fronting bulkheads and at an adjacent site where no bulkhead is present. Data on waves, water temperature and salinity were gathered over a spring tidal cycle. Data on meiofauna and sediment characteristics were gathered at low water across the foreshore at three sites: Site 1 where a bulkhead intersects low on the profile; Site 2 where there is no bulkhead present; and Site 3 where a bulkhead intersects high on the profile. Mean grain size of sediments is in the range of medium to coarse sand; mean grain size is slightly finer at locations fronting the bulkhead at Sites 1 and 3 compared to a similar profile elevation at Site 2. Significant wave heights, measured on the low tide terrace, ranged from 0.08 m at high water to 0.27 m during rising tide. Peak wave periods ranged from 2.0 to 2.7 s. Greatest net change in sand surface elevation (0.07 m) and depth of sediment activation (0.23 m) over the tidal cycle occurred at the base of the bulkhead at Site 1. Data from the top core segments at Site 1 reveal lower meiofaunal density at the base of the bulkhead compared to the sampling station lower on the profile and to sampling stations at a similar profile elevation on Sites 2 and 3. One way ANOVA reveals a significant difference in alongshore meiofaunal density between the sampling station fronting the bulkhead at Site 1 and at sampling stations at a similar profile elevation at Sites 2 and 3. Increased energy at the base of the bulkhead at Site 1 resulted in the transport of meiofauna with eroded sediments. Bulkheads constructed low on the profile can have the greatest negative impact on individuals from near the base of the structure. Construction of bulkheads higher on the intertidal profile does not appear to alter the suitability of the beach matrix as habitat.