ABSTRACT
Abstract The aboveground behavior of the snapping shrimp Alpheus macellarius, Chace, 1988, was studied in a shallow clear-water seagrass meadow off Bolinao, NW Philippines. The shrimp’s activity pattern was analyzed from short video records taken every hour on sampling visits during the dry and wet months. Alpheus macellarius actively moved sediment (frequency = 77 h-1), often surveyed its burrow opening (21 h-1), stacked up rubble (17 h-1), and occasionally harvested seagrass leaves (9 h-1) during the dry months. Time allocated for these aboveground activities was only 12% of its daily active period of 9 hours during daylight; A. macellarius was in its burrow during the remainder of daytime. During the wet months, the shrimp’s activity rates and corresponding time allocations were reduced by at least 34% that of the dry months and its within-burrow period consequently increased by 5%. Overall, sediment moving and harvesting activities of A. macellarius contributed frequent disturbance to the meadow: an individual shrimp remobilized, on average, ~300 g dry weight (DW) of sediment d-1 (range, wet to dry months = 204 to 346 g d-1), which projects to 112 kg y-1, and harvested 0.8 g DW of
leaves d-1 (range = 0.2 to 1.1 g d-1), or a total of 291.3 g y-1. The estimated sediment-reworking rate falls within a considerable range of 0.8 to 1.4 kg m-2 d-1 during the wet and dry months, for an average shrimp density of 2 m-2, and, correspondingly, the estimated leaf harvesting rate of 0.4 to 2.3 g m-2 d-1 represents moderate herbivory, equivalent to 12 to 42% of leaf production, respectively. Keywords: Alpheidae, bioturbation, burrowing, herbivory
Introduction Diverse faunal assemblages inhabit the different physical compartments of seagrass meadows for refuge and food (McRoy and Helfferich 1977, Leber 1985, Larkum et al. 1989). These assemblages account for the complex trophic hierarchy in seagrass meadows, together with large transient species like dugongs, green turtles, and waterfowl (Jacobs et al. 1981, Thayer et al. 1984, Lanyon et al. 1989, Preen 1995). Direct herbivory of seagrass leaves forms a significant pathway in this trophic hierarchy (Valentine and Heck 1999), which may have been underestimated in the past (Klumpp et al. 1989, Hemminga et al. 1991, Duarte and Cebrián 1996, Cebrián et al. 1997). The list of herbivores includes animals of broad size ranges and the smaller ones may contribute substantially to total herbivory, e.g., sea urchins Lytechinus variegatus (Lamarck) (Heck and Valentine 1995) and snapping shrimps of the genus Alpheus (Alpheidae, Caridea) (Stapel and Erftemeijer 1997).
