Pacific-wide contrast highlights resistance of reef calcifiers to ocean acidification

Ocean acidification (OA) and its associated decline in calcium carbonate saturation states is one of the major threats that tropical coral reefs face this century. Previous studies of the effect of OA on coral reef calcifiers have described a wide variety of outcomes for studies using comparable partial pressure of CO₂ (pCO₂) ranges, suggesting that key questions remain unresolved. One unresolved hypothesis posits that heterogeneity in the response of reef calcifiers to high pCO₂ is a result of regional-scale variation in the responses to OA. To test this hypothesis, we incubated two coral taxa (Pocillopora damicornis and massive Porites) and two calcified algae (Porolithon onkodes and Halimeda macroloba) under 400, 700 and 1000 μatm pCO₂ levels in experiments in Moorea (French Polynesia), Hawaii (USA) and Okinawa (Japan), where environmental conditions differ. Both corals and H. macroloba were insensitive to OA at all three locations, while the effects of OA on P. onkodes were location-specific. In Moorea and Hawaii, calcification of P. onkodes was depressed by high pCO₂, but for specimens in Okinawa, there was no effect of OA. Using a study of large geographical scale, we show that resistance to OA of some reef species is a constitutive character expressed across the Pacific.     

Use of hen lysozyme for protection against bacterial contamination ofin vitro embryo cultures

Summary Curative treatments with antibiotics and hen egg white lysozyme (HEWL) were used to salvage embryo cultures contaminated withBaccillus subtilis. The use of HEWL gave good control ofBaccillus subtilis, but no control ofErwinia. HEWL was better than antibiotics, being much less phytotoxic. The antibiotics piperacillin, ampicillin and imipenem were also found to be ineffective againstErwinia. HEWL, at a final concentration of 1 mg per mL, was used as a preventive and curative agent for routine use in embryo culture ofTriticum aestivum and other Triticeae, as it cured from 30% to 50% of bacterial contamination problems over a one year period. Standardin vitro culture precautions remained essential, as certain bacteria were not controlled by HEWL.     

Seasonal changes of thyroid hormones in field-collected Atlantic cod in relation to condition indices, water temperature and photoperiod

Serum T₄ and T₃ in wild Atlantic cod Gadus morhua ranged from 1 to 12 ng ml⁻¹ and from 2 to 27 ng ml⁻¹ respectively over a 3-year period. In general, the concentrations increased from summer (T₃) or early autumn (T₄) to maxima in mid-winter and declined abruptly during spring. The T₄/T₃ monthly means were lowest in summer and highest in winter. The seasonal patterns of thyroid hormones were weakly correlated with changes in water temperature. However, both T₄ and T₃ co-varied simultaneously with photoperiod. In addition, T₃ was correlated with the hepatosomatic index and condition factor during summer and autumn. It is suggested that the seasonal changes in the release of T₄ from the thyroid were photoperioddriven, and that the course of T3 was regulated by the metabolic state of the fish during the somatic growth period.     

Production and cytogenetics of hybrids of Triticum aestivum x Leymus innovatus

Summary Hybrid plants were obtained between Triticum aestivum (2n=6x=42, AABBDD) and Leymus innovatus (2n=4x=28, JJNN) at a frequency varying from 0.4% to 1.2% of the pollinated florets. Improvement of the embryo culture medium resulted in a higher frequency of embryo rescue. Eight of ten hybrids had the expected chromosome number of 35 (ABDJN). Meiotic analysis indicated that there was no homology between the genomes of the two species. Two hybrids had only 28 chromosomes. Comparison of chromosome pairing between the two types of hybrids suggested that Leymus innovatus carries genes that affect chromosome pairing and behavior. The relatively high occurrence of spontaneous doubling in the meiocytes of these hybrids may indicate that backcrossing of the hybrids to wheat should be possible, although frequent chromosome irregularities observed in the meiocytes of the hybrids may decrease the probability of success of this step, which is essential to the process of gene transfer from L. innovatus to wheat.Contrib. no. 366     

Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change

Projecting the effects of climate change on net reef calcium carbonate production is critical to understanding the future impacts on ecosystem function, but prior estimates have not included corals' natural adaptive capacity to such change. Here we estimate how the ability of symbionts to evolve tolerance to heat stress, or for coral hosts to shuffle to favourable symbionts, and their combination, may influence responses to the combined impacts of ocean warming and acidification under three representative concentration pathway (RCP) emissions scenarios (RCP2.6, RCP4.5 and RCP8.5). We show that symbiont evolution and shuffling, both individually and when combined, favours persistent positive net reef calcium carbonate production. However, our projections of future net calcium carbonate production (NCCP) under climate change vary both spatially and by RCP. For example, 19%–35% of modelled coral reefs are still projected to have net positive NCCP by 2050 if symbionts can evolve increased thermal tolerance, depending on the RCP. Without symbiont adaptive capacity, the number of coral reefs with positive NCCP drops to 9%–13% by 2050. Accounting for both symbiont evolution and shuffling, we project median positive NCPP of coral reefs will still occur under low greenhouse emissions (RCP2.6) in the Indian Ocean, and even under moderate emissions (RCP4.5) in the Pacific Ocean. However, adaptive capacity will be insufficient to halt the transition of coral reefs globally into erosion by 2050 under severe emissions scenarios (RCP8.5).     

Larval release in a sub-euphotic zone invertebrate triggered by sinking phytoplankton particles

This paper reports field results showing that the larval releaseof the snow crab, Chionoecetes opilio, in a subarctic fjordis phased with the sedimentation peak of phytoplankton particlesoriginating from the surface spring bloom, but with a lag of2–3 weeks. Further laboratory experiments with egg-bearingfemales showed a significant induction of larval release whenthey were exposed to senescent cultures of different phytoplanktonspecies, as opposed to controls and females exposed to freshcultures. These results are interpreted and discussed in thecontext of possible strategies evolved by the snow crab to enhanceits reproductive success. The field and laboratory evidencepresented here represents the first instance indicating thatphyto-detritus can act as a chemical cue for initiating andsynchronizing reproductive activities in sub-euphotic invertebrates.Selection for control of larval release by downward flux ofalgal particles may be especially important for invertebratepopulations in high-latitude areas, where the development ofplankton communities shows a high level of seasonality.     

Pseudomembranous colitis: isolation of two species of cytotoxic clostridia and successful treatment with vancomycin.

Lincomycin-resistant Clostridium sporogenes obtained from the stools of a patient with lincomycin-associated pseudomembranous colitis produced a heat-stable cytotoxin in low titre when grown in chopped meat medium. Vancomycin eradicated this strain and all other clostridia, and controlled the symptoms. When diarrhea recurred 7 days after treatment with vancomycin was stopped, clostridia including C. sporogenes and C. difficile were again isolated. The C. difficile produced a heat-labile cytotoxin in high titre that was unaffected by growth in various media and induced colitis in hamsters. Treatment with vancomycin, to which all the clostridia were sensitive, eradicated both toxic species and controlled the diarrhea. Antibiotic-induced pseudomembranous colitis may be associated with more than one species of toxin-producing clostridia. Vancomycin therapy should be continued for 10 days or more in patients with severe disease to eradicate the responsible organism.