Bioturbation by stingrays at Ningaloo Reef, Western Australia

Abstract

Stingrays are an important part of the biomass of the fishes in shallow coastal ecosystems, particularly in inter-reefal areas. In these habitats, they are considered keystone species -modifying physical and biological habitats through their foraging and predation. Here, we quantify the effects of bioturbation by rays on sand flats of Ningaloo Reef lagoon in Western Australia. We measured the daily length, breadth and depth of 108 feeding pits over three 7-day periods, created by stingrays (Pastinachus atrus, Himantura spp. Taeniura lymma and Urogymnus asperrimus) in Mangrove Bay. Additionally, an area of ~1 km 2 of the lagoon at Coral Bay was mapped three times over 18 months, to record patterns of ray and pit presence. Over 21 days at Mangrove Bay, a total of 1.08 m 3 of sediment was excavated by rays, equating to a sediment wet weight of 760.8 kg, and 2.42% of the total area sampled, or 0.03% of the whole intertidal zone. We estimate that up to 42% of the soft sediments in our study area would be reworked by stingrays each year. Based on a model predicting the probability of pit presence over time, there was a 40% probability of ray pits persisting for 4 days before being filled in but only a 15% probability of a pit being present after 7 days. Changes in pit volume over time were static, providing evidence for secondary use. Our results imply that rays play an important ecological role creating sheltered habitats for other taxa in addition to the turnover of sediments.

Dietary composition and prey selectivity of juvenile porcupine raysUrogymnus asperrimus

“…The magnitude of these roles varies between species and their habitats, thus requiring a case‐by‐case approach when attempting to describe local ecosystem functioning. Although myliobatoids are often thought to mediate prey communities (Navia et al ., ; Vaudo & Heithaus, ; O'Shea, ), in tropical marine ecosystems trophic complexity is generally high and there are both strong and weak predator–prey interactions present (Connell et al ., ; O'Gorman et al ., ). The strength of an interaction is a measure of influence over one another (Tilley, ) and only if a predator displays a strong predator–prey interaction can it potentially have strong influences over its prey species.…”

“…Myliobatoids in general are believed to serve three important ecological roles: modifying the physical benthos in soft sediment habitats through bioturbation; exerting top down control over the infaunal invertebrate populations by predation; providing the link in food webs by occupying the trophic position of mesopredator (O'Shea, ). The magnitude of these roles varies between species and their habitats, thus requiring a case‐by‐case approach when attempting to describe local ecosystem functioning.…”

The impact of sediment bioturbation by secondary organisms on metal bioavailability, bioaccumulation and toxicity to target organisms in benthic bioassays: Implications for sediment quality assessment

“…Due to the expected greater dilution of contaminant fluxes in the field, the use of laboratory-based bioassays will have exaggerated the influence of bioturbation in the present study. Nevertheless, the magnitude of sedimentary disturbance which occurs in laboratory-based bioassays will generally be miniscule compared with those experienced in the natural environment, especially where larger bioturbating organisms are present (O'Shea et al, 2012).…”

“…Differences in the amount of fine particles in the three sediments contributed to these observations (Table 1), with the mean TSS concentration for the silty-S2 High bioturbation treatment (76% <63 µm particles) being more than twice those measured for the more sandy S1 and S3 sediments (both ~30% <63 µm). The changes in metal bioavailability as a consequence of the differing amounts of fine sediment re-suspension and dispersal due to bioturbation were therefore influenced by both sediment properties (abiotic processes) and organism behaviour (biotic processes) (Meysman et al, 2006;O'Shea et al, 2012). …”

Sexual Dimorphism of the Electrosensory System: A Quantitative Analysis of Nerve Axons in the Dorsal Anterior Lateral Line Nerve of the Blue-Spotted Fantail Stingray (Taeniura lymma)

“…This investigation also revealed new insights about the relative importance of electroreception during development and between sexes; also presented are detailed morphological data on the peripheral electrosensory system to allow a complete interpretation of the functional significance of ALLN axon abundance. [O'Shea et al, 2012[O'Shea et al, , 2013. A total of 14 mature specimens (8 females and 6 males) of the blue-spotted fantail ray, Taeniura lymma , were used (disc width 25-32 cm).…”