The effects of thin mud deposits on the behaviour of a deposit-feeding tellinid bivalve: implications for ecosystem functioning

A laboratory experiment was conducted, to examine how feeding, siphon activity and movement behaviours of a tellinid bivalve, Macomona liliana (Iredale, 1915), were affected by thin surface layers of mud (1–4 mm) and the incorporation of mud into surface (0–2 cm) sediment. Time-lapse photography and porewater pressure sensors were used to characterise changes in behaviour before and after mud addition. Mud addition modified the sediment matrix which had an immediate effect on M. liliana behaviour; significantly affecting the rates of feeding and the degree of porewater pressurisation during feeding events. Surface activity indicated maintenance and clearance of established burrow structures and increased ventilation. Ultimately, subtle modifications in behaviour and sediment hydraulic conductivity may have consequences for nutrient exchange and benthic-pelagic coupling. Our results emphasise the need to consider the impacts of low level stressors when they affect the behaviour of structurally important species.     

Intraspecific variation in Triassic Ophthalmidiid Foraminifera from Timor

Four ophthalmidiid species are described as free specimens extracted from mudstones and wackestones of Triassic age: Atsabella bandeiraensis nov. gen. nov. sp., Karaburunia atsabensis nov. sp., Ophthalmidium sp. cf. O. primitivum Ho and Spirophthalmidium grunaui nov. sp. Analysis of morphological variation found in large suites of specimens suggests that, as in modern miliolids, apertural characteristics, chamber shape and adult test size are features that vary within narrow limits and may be used to define species. In genera with milioline coiling in the post-embryonic stage, chamber arrangement may be highly variable. Post-embryonic coiling in K. atsabensis varies from quinqueloculine to almost spiroloculine and encompasses morphotypes that, in thin-section studies, have been attributed to a number of other genera. In Timor Leste, A. bandeiraensis, K. atsabensis and S. grunaui have been found with conodonts indicative of the Carnian, but the full local stratigraphic range of these species is uncertain. K. atsabensis occurs at another locality with conodonts suggestive of the Middle Triassic or less likely Carnian. Ophthalmidium sp. cf. O. primitivum has been found at one locality associated with A. bandeiraensis and K. atsabensis in a stratigraphic succession that suggests a correlation to the Carnian or Norian. The ophthalmidiids are found commonly associated with organic-cemented agglutinated and hyaline foraminifera and at some localities common to abundant ostracods and mollusc debris. They were most common in organic-rich carbonate mud of shallow-marine environments.