Assessment of benthic disturbance associated with stingray foraging for ghost shrimp by aerial survey over an intertidal sandflat

Abstract

1 2 One notable type of bioturbation in marine soft sediments involves the excavation of large pits and 3 displacement of sediment associated with predator foraging for infaunal benthos. Batoids are among 4 the most powerful excavators, yet their impact on sediment has been poorly studied. For expansive 5 temperate tidal flats, only relatively small proportions of the habitat can be sampled due to physical 6 and logistical constraints. The knowledge of the dynamics of these habitats, including the spatial and 7 temporal distribution of ray bioturbation, thus remains limited. We combined the use of aerial 8 photogrammetry and in situ benthic sampling to quantify stingray feeding pits in Tomioka Bay, 9Amakusa, Japan. Specifically, we mapped newly-formed pits over an 11-ha section of an intertidal 10 sandflat over two consecutive daytime low tides. Pit size and distribution patterns were assumed to 11 scale with fish size and reflect size-specific feeding behaviors, respectively. In situ benthic surveys 12were conducted for sandflat-surface elevation and prey density (callianassid shrimp). The volume 13 versus area relationship was established as a logistic function for pits of varying sizes by 14 photographing and refilling them with sediment. This relationship was applied to the area of every 15 pit detected by air to estimate volume, in which special attention was paid to ray ontogenetic change 16 in space utilization patterns. In total, 18103 new pits were formed per day, with a mean individual 17 area of 1060 cm 2 . The pits were divided into six groups (G1 to G6 in increasing areas), with 18 abundances of G1, G2+G3, and G4−G6 being medium, high, and low, respectively. Statistical 19 analyses using generalized linear models revealed a marked preference for the higher prey-density 20 areas in G1 and the restriction of feeding grounds of G4−G6 to the lower shore, with G2+G3 being 21 generalists for prey density and sandflat elevation. The lower degrees of overall bioturbation by G1 22 and G4−G6 were spatially structured for the eight sub-areas demarcated by prey density and sandflat 23 elevation, while G2+G3 homogenized the state over the sandflat. The newly-formed pits' sub-areal 24 2 mean numerical, excavated-areal, and displaced-sediment-volume densities per day were confined to 25 small ranges: 0.14−0.17 m −2 , 132−223 cm 2 m −2 , and 551−879 cm 3 m −2 (latter two including 119 26 shallow non-pit excavations). These bioturbation rates are positioned at relatively high levels 27 compared with those by rays from other geographic regions. The present procedure is applicable to 28 the assessment of disturbance by any surface-sediment excavators on tidal flats if their pit 29 dimensions are discernible from the air. 30 31

Parasitism in ecosystem engineer species: A key factor controlling marine ecosystem functioning

“…We also recognize that the consequences of such interspecific interactions are obviously not limited to sedimentary biogeochemical processes and certainly influence the overall functioning of coastal ecosystem through many other different pathways. For example, the reduction of mud shrimp burrowing capacities could enhance foraging rates of epibenthic predators such as demersal fish (Takeuchi & Tamaki, 2014). Therefore, aside from alteration of host engineering traits and population dynamics, bopyrid parasites would mediate a resource subsidy, which might profoundly alter (a) food web properties and energy flow and (b) population dynamics of other non-host benthic invertebrates (Sato et al, 2012).…”

Transient biogeochemistry in intertidal sediments: New insights from tidal pools in Zostera noltei meadows of Arcachon Bay (France)

“…Several studies have shown the occurrence of circular pools in intertidal flats of different coastal systems (e.g., Smith and Able, 1994;Van der Laan and Wolff, 2006;Takeuchi and Tamaki, 2014,…”

“…The intertidal flat consisted of silty loam sediment colonized by a dense meadow of the dwarf eelgrass Zostera noltei. Although their origin is still not known (i.e., hydrodynamic vs. biological structure; see discussion in Van der Laan and Wolff, 2006;Takeuchi and Tamaki, 2014), the tidal pools presented consistent features in Arcachon Bay. Aerial photos of the sampling site enabled to estimate a surface coverage of 20% for the tidal pools ( Figure 1C).…”

Reduced horseshoe crab abundance and feeding activity beneath intertidal oyster aquaculture structures in the Delaware Bay

“…The two types of feeding pits vary by size, with the average pit diameter for horseshoe crabs being 20cm, while ray feeding depressions are considerably wider (up to 1m diameter) and deeper (Orth, 1975). We used aerial imagery to assess the distribution and abundance of feeding pits in our study area (Takeuchi and Tamaki, 2014). To compare the prevalence of feeding depressions beneath aquaculture structures and adjacent open areas, we delineated all structures in GIS that did not have oyster bags on top of them at the time our aerial imagery was taken.…”