Impacts of ocean acidification on multiplication and caste organisation of parasitic trematodes in their gastropod host

Ocean acidification is predicted to impact the structure and function of all marine ecosystems in this century. As focus turns towards possible impacts on interactions among marine organisms, its effects on the biology and transmission potential of marine parasites must be evaluated. In the present study, we investigate two marine trematode species (Philophthalmus sp. and Parorchis sp., both in the family Philophthalmidae) infecting two marine gastropods. These trematodes are unusual in that their asexually multiplying stages within snails display a division of labour, with two distinct castes, a large-bodied morph producing infective stages and a smaller morph playing a defensive role against other competing parasites. Using a potentiometric ocean acidification simulation system, we test the impacts of acidified seawater (7.8 and 7.6 pH) on the production of free-living infective stages (cercariae), the size and survival of encysted resting stages (metacercariae), and the within-host division of labour measured as the ratio between numbers of the two morphs. In general, low pH conditions caused an increase in cercarial production and a reduction in metacercarial survival. The ratio of the two castes within snail hosts tended to shift towards more of the smaller defensive morphs under low pH. However, the observed effects of reduced pH were species specific and not always unimodal. These results suggest that ocean acidification can affect the biology of marine parasites and may also impact transmission success and parasite abundance of some trematodes, with possible consequences for marine communities and ecosystems.

Middle Miocene to Quaternary diatoms in the Nankai Trough and Japan Trench

During Leg 87 of the Deep Sea Drilling Project, eleven holes were drilled at Sites 582 and 583 in the Nankai Trough, off Shikoku, southwestern Honshu, and three holes at Site 584 in the Japan Trench, off northeastern Honshu, Japan. In the former area, a low-latitude diatom zone called the Pseudoeunotia doliolus Zone is recognized in thick upper Quaternary sediments, which yield rare but characteristic admixtures of marine planktonic, marine tychopelagic-tobenthic, and nonmarine diatoms. In the latter area, all the sediments recovered contain abundant to common diatoms, allowing recognition of 12 continuous diatom zones from upper Quaternary through lower middle Miocene. Three hiatuses occur in this area around the Pleistocene/Pliocene boundary and in the upper and middle Miocene. In addition, 19 modified diatom zones for a lower Miocene through upper Quaternary interval are proposed. These middle-to-highlatitude zones are numerically coded (NPD1-NPD12) and represent the entire North Pacific. The establishment of these zones is based primarily on Leg 87 data and other DSDP materials and partially on several Japanese subaerial sequences. Correlation of the new zonal framework with previously established frameworks is attempted by the evaluation of operational usefulness of previously used datums. Resting spores of Chaetoceros and its related forms are recorded with specific intent for the first time, and possible ramifications of its frequency variation are presented. Nine new species are proposed: Delphineis sheshukovae Akiba n. sp., Denticulopsis praelauta Akiba and Koizumi n. sp., Kisseleviella ezoensis Akiba n. sp., Nitzschia umaoiensis Akiba n. sp., Thalassiosira jouseae Akiba n. sp., T. praenidulus Akiba n. sp., T. sancettae Akiba n. sp., T. umaoiensis Akiba n. sp., and T. urahoroensis Akiba n. sp. Transfers of systematic positions of the following four taxa are also proposed: Delphineis simonsenii (Mertz) Akiba n. comb., Ikebea tenuis (Brun) Akiba n. comb., Thalassiosira delicata (Barron) Akiba n. stat., and Thalassiothrixrobusta (Schrader) Akiba n. comb.