A new catalogue of toroidal-mode overtone splitting function measurements

Spectra of whole Earth oscillations or normal modes provide important constraints on Earth’s large scale structure. The most convenient way to include normal mode constraints in global tomographic models is by using splitting functions or structure coefficients, which describe how the frequency of a specific mode varies regionally. Splitting functions constrain 3D variations in velocity, density structure and boundary topography. They may also constrain anisotropy, especially when combining information from spheroidal modes, which are mainly sensitive to P-SV structure, with toroidal modes, mainly sensitive to SH structure. Spheroidal modes have been measured extensively, but toroidal modes have proven to be much more difficult and as a result only a limited number of toroidal modes have been measured so far. Here we expand the splitting function studies by Resovsky and Ritzwoller (1998) and Deuss et al. (2013), by focusing specifically on toroidal mode overtone observations. We present splitting function measurements for 19 self-coupled toroidal modes of which 13 modes have not been measured before. They are derived from radial and transverse horizontal component normal mode spectra up to 5 mHz for 91 events with MW ≥ 7.4 from the years 1983-2018. Our data include the Tohoku event of 2011 (9.1MW), the Okhotsk event of 2013 (8.3MW) and the Fiji Island event from 2018 (8.2MW). Our measurements provide new constraints on upper and lower mantle shear wave velocity structure and in combination with existing spheroidal mode measurements can be used in future inversions for anisotropic mantle structure. Our new splitting function coefficient data set will be available online.

Preliminary re-survey of the land snail fauna of Rotuma: conservation and biosecurity implications.

In May 2012 Rotuma Island, the main island of the remote Rotuma Group (Fiji), was surveyed to document the composition of the non-native land snail fauna and to investigate if populations of previously recorded native land snail species persist. From sampling at nine locations, twenty-one land snail species from eleven gastropod families were found. Of these, eight species are non-native and two of these Parmarion martensi Simroth, 1893 and Quantula striata (Gray, 1834) (Ariophantidae) are new records for the Rotuma Group. Ten of the 13 species of native land snails found — including the endemic partulid Partula leefi E. A. Smith, 1897 and the rhytidid Delos gardineri (E. A. Smith, 1897) — were detected only as empty shells. The native Ouagapia perryi (E. A. Smith, 1897) and the endemic Succinea rotumana E. A. Smith, 1897 and Sinployea rotumana (E. A. Smith, 1897) remain undetected on Rotuma Island since their first collection in 1897. The non-native, invasive predatory flatworm, Platydemus manokwari, was also found and represents a major threat to the island’s land snail fauna. This non-native species appears to be absent in many other parts of the Fiji Island archipelago and thus a re-evaluation of existing quarantine measures is required to address its potential spread to non-invaded areas. Comparisons with earlier surveys indicate a shift in the structure of the Rotuman land snail fauna over a 115-year period, with declining native components and increasing prevalence of non-native species. Further sampling, focusing on residual native habitat in less accessible areas such as coastal cliffs and offshore islets, is urgently needed to establish the conservation status of Rotuman native land snails and determine the threat posed by both, non-native snails and P. manokwari.

Aggressive Waves in the Lemon-Clawed Fiddler Crab (Uca perplexa): A Regional “Dialect” in Fiji

A population of the lemon-clawed fiddler crab (U. perplexa) in Fiji (island of Vanua Levu) was studied for types of communication (i.e., signaling via waving the male’s larger claw). Two types of signals were observed. In addition to the expected territorial display of a large and complex vertical wave that conveys its message over a typical distance of 10–40 cm (with large males signaling to other large males over the greatest distance), a short, rapid, and horizontal wave was typically directed over a much shorter distance, rarely exceeding 10 cm. This latter wave type, seemingly of an aggressive nature, differs from the vertically directed aggressive signal observed in an Australian population of this species and thus appears to be a regional “dialect” for this mode of communication.

Urinary corticosterone responses and haematological stress indicators in the endangered Fijian ground frog (Platymantis vitiana) during transportation and captivity

Physiological stress assessment is important for in-situ conservation and captive management of threatened wildlife. Leukocyte (white blood cell) evaluation, especially the neutrophil : lymphocyte (N : L) ratio, provides a logical representation of experimentally elevated corticosterone (stress hormone) in amphibians. Urinary corticosterone enzyme-immunoassay (EIA) is a rapid non-invasive tool for assessing stress responses in amphibians. To our knowledge, no one has explored the relationship between N : L ratio and urinary corticosterone in wild amphibians in a non-experimental way. This study provides a comparative assessment of relative leukocyte numbers, N : L ratios and urinary corticosterone responses of the endangered Fijian ground frog (Platymantis vitiana) during transportation and captivity. Adult frogs (n = 40) were collected from Viwa, Fiji Island for captive breeding. Frogs showed significant changes in leukocyte proportions during transportation and captivity. N : L ratios were higher 6 h after transportation and over 5 and 15 days in captivity. Urinary corticosterone responses of the frogs were also higher 6 h after transportation and after 5 and 15 days in captivity. All leukocyte proportions, N : L ratios and urinary corticosterone concentrations of the frogs returned near baseline levels after the frogs were kept in an environmentally enriched outdoor enclosure for over 25 days. These results highlight the value of leukocyte evaluation and urinary corticosterone EIAs as physiological tools for evaluating stress in amphibians.