THE EFFECT OF OFF-ROAD VEHICLES ON BARRIER BEACH INVERTEBRATES AT CAPE COD AND FIRE ISLAND NATIONAL SEASHORES

Ginsberg, Howard; Kluft, Jacqueline

Abstract-The effects of off-road vehicles (ORVs) on invertebrates inhabiting macrophyte debris (wrack) and supratidal sands on energetic beaches in the northeastern United States were studied at Cape Cod (MA) and Fire Island (NY) National Seashores. Cores, wrack quadrats, and pitfall traps were used to sample four study beaches, which all had vehicle-free sections in close proximity to ORV corridors, allowing for paired traffic/no-traffic samples at these sites. A manipulative experiment was also performed by directly driving over nylon-mesh bags filled with eelgrass (Zostera marina) wrack that had been colonized by beach invertebrates, then subjected to treatments of high-, low-, and no-traffic. Pitfall trap samples set at the wrackline had consistently higher overall invertebrate abundances in vehicle-free than in high-traffic zones on all four beaches. Overall abundance of wrack was also higher on beaches free of vehicle traffic. In contrast, both wrack quadrats (with intact wrack clumps) and the cores taken directly beneath them did not show consistent differences in overall invertebrate abundances in areas open and closed to vehicles. The talitrid amphipod Talorchestia longicornis and the lycosid spider Arctosa littoralis, both of which roam the beach widely by night but burrow diurnally in supratidal bare sands as adults (rather than under wrack as the juveniles do), were always less abundant in beach sections open to vehicle traffic, regardless of the sampling method used. Other invertebrates, such as oligochaetes (family Enchytraeidae) and tethinid flies (Tethina parvula), which spend most of their lives within/beneath wrack detritus, showed either no response or a positive response to traffic disturbance. In the direct impact study the tenebrionid beetle Phaleria testacea (85% larvae) was significantly less abundant in disturbed wrack bags than in controls, while Tethina parvula (90% larvae) showed increases in disturbed wrack. Nonetheless, ORVs adversely affected beach invertebrates on the whole, in part by either killing or displacing some species, and by lowering the total amount of wrack, which lowered the overall abundance of wrack dwellers. For some interstitial detritivores the amount of vehicle disturbance on these beaches apparently facilitated mechanical breakdown of wrack and possibly sand surface moisture, increasing observed abundances. Our results suggest that on beaches with moderate levels of beach traffic (as at Cape Cod and Fire Island) alternating opening and closing of adjacent beaches to vehicle traffic can potentially allow recolonization of wrack clumps in newly-closed beaches from two sources: wrack-dwelling species from intact wrack clumps that are missed by ORVs and remain on the disturbed beach and wide-ranging species from adjacent undisturbed beaches. Research on the rapidity of recolonization from these sources is needed to demonstrate that recolonization would be successful, and to optimize scheduling of alternating beach closures for conservation of supratidal invertebrates.

THE EFFECT OF OFF-ROAD VEHICLES ON BARRIER BEACH INVERTEBRATES AT CAPE COD AND FIRE ISLAND NATIONAL SEASHORES

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