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Kelp forests are productive and biodiverse ecosystems with high ecological, cultural, and economic importance. However, the high sensitivity of kelp to water temperature means that these ecosystems are vulnerable to marine heatwaves (MHWs), especially at the equatorward edge of their range. To date, few laboratory studies have compared the effects of MHWs of different durations or intensities on kelp, and it is difficult to determine these effects from naturally occurring MHWs in the field. We exposed juvenile sporophytes of the giant kelp Macrocystis pyrifera from Wellington, Aotearoa New Zealand to simulated MHWs three or six weeks in duration, at temperatures of 18°C, 20°C, and 22°C, corresponding to 2, 4, and 6°C above local mean summer temperatures. While all MHW treatments reduced mean kelp growth rates by over 30% relative to 16°C controls, the 22°C treatments had much more severe and wide-ranging effects, including rapid blade erosion, reduced chlorophyll fluorescence, tissue bleaching, increased δ13C values, andmortality. Nonetheless, sporophytes had some ability to recover from heat stress; within the 18°C treatment, mean relative growth rates neared or exceeded those within the control treatment within three weeks after MHWs concluded. These results support the findings of previous studies which indicate that M. pyrifera sporophytes experience a key physiological tipping point around 20°C. Additionally, our findings suggest that juvenile M. pyrifera from the Wellington population could be relatively resilient toMHWs if temperatures remain at sub-lethal levels. However, if averageMHWintensities and durations continue to increase over time, survival and recruitment of juvenile kelp could be adversely affected, thus threatening the long-term persistence of giant kelp forests near the warm edge of their range in New Zealand. [ABSTRACT FROM AUTHOR]

The influence of cold seep methane on the surrounding benthos is well-documented but the fate of dissolved methane and its impact on water column biogeochemistry remains less understood. To address this, the distribution of dissolved methane was determined around three seeps on the south-east Hikurangi Margin, south-east of New Zealand, by combining data from discrete water column sampling and a towed methane sensor. Integrating this with bottom water current flow data in a dynamic Gerris model determined an annual methane flux of 3 x 105 kg at the main seep. This source was then applied in a Regional Ocean Modelling System (ROMS) simulation to visualize lateral transport of the dissolved methane plume, which dispersed over ~100 km in bottom water within 1 year. Extrapolation of this approach to four other regional seeps identified a combined plume volume of 3,500 km³ and annual methane emission of 0.4-3.2 x 106 kg CH4 y-1. This suggests a regional methane flux of 1.1-10.9 x 107 kg CH4 y-1 for the entire Hikurangi Margin, which is lower than previous hydroacoustic estimates. Carbon stable isotope values in dissolved methane indicated that lateral mixing was the primary determinant of methane in bottom water, with potential methane oxidation rates orders of magnitude lower than the dilution rate. Calculations indicate that oxidation of the annual total methane emitted from the five seeps would not significantly alter bottom water dissolved carbon dioxide, oxygen or pH; however, superimposition of methane plumes from different seeps, which was evident in the ROMS simulation, may have localized impacts. These findings highlight the value of characterizing methane release from multiple seeps within a hydrodynamic model framework to determine the biogeochemical impact, climate feedbacks and connectivity of cold seeps on continental shelf margins. [ABSTRACT FROM AUTHOR]

It is well established that non‐native fish can become invasive and outcompete and displace native fish populations. However, little research has explored the potential benefits that non‐native fish may provide to native fish populations. To address this information gap, we examined how the availability of non‐native perch (Perca fluviatilis) as prey could benefit populations of the endemic longfin eel (Anguilla dieffenbachii) and the native shortfin eel (Anguilla australis) in two neighbouring open‐water wetlands in the Rakatu‐Redcliff wetland complex in the Southland region of Aotearoa New Zealand. The Redcliff wetland fish community comprised native fish only, while the Rakatu wetland comprised native fish and non‐native perch. We compared the size, condition, population density, population size structure and diet of eels in these wetlands. While eels were not necessarily larger or better conditioned in Rakatu wetland, their population density was three times higher than the Redcliff wetland, with young‐of‐the‐year perch comprising ca. 40% of their diet. Furthermore, juvenile eel density was four times lower in Redcliff wetland, suggesting that cannibalism may occur at this site to support the existing eel population. Based on our findings, we suggest that freshwater managers consider the predator–prey dynamics of both native and non‐native fish before removing non‐native species, to avoid unintended negative consequences for native predatory fish species. [ABSTRACT FROM AUTHOR]

Diet quality is a key determinant of population dynamics. If a higher trophic level, more fish-based diet is of higher quality for marine predators, then individuals with a higher trophic level diet should have a greater body mass than those feeding at a lower trophic level. We examined this hypothesis using stable isotope analysis to infer dietary trophic level and foraging habitat over three years in eastern rockhopper penguins Eudyptes chrysocome filholi on sub-Antarctic Campbell Island, New Zealand. Rockhopper penguins are 'Vulnerable' to extinction because of widespread and dramatic population declines, perhaps related to nutritional stress caused by a climate-induced shift to a lower trophic level, lower quality diet. We related the stable nitrogen (δ[sup.15]N) and carbon (δ[sup.13]C) isotope values of blood from 70 chicks, 55 adult females, and 55 adult males to their body masses in the 2010, 2011, and 2012 breeding seasons and examined year, stage, age, and sex differences. Opposite to predictions, heavier males consumed a lower trophic level diet during incubation in 2011, and average chick mass was heavier in 2011 when chicks were fed a more zooplankton-based, pelagic/offshore diet than in 2012. Contrary to the suggested importance of a fish-based diet, our results support the alternative hypothesis that rockhopper penguin populations are likely to be most successful when abundant zooplankton prey are available. We caution that historic shifts to lower trophic level prey should not be assumed to reflect nutritional stress and a cause of population declines., Introduction Living organisms must balance their energy intake and expenditure to grow, survive, and reproduce. Diet quality describes prey characteristics in terms of their suitability as an energy source. An [...]

Using non-lethal tissue sampling for stable isotope analysis has become standard in many fields, but not for fishes, despite being desirable when species are rare or protected, when repeated sampling of individuals is required or where removal may bias other analyses. Here, we examine the utility of fish dorsal fin membrane as an alternative to muscle for analyzing δ[sup.13]C and δ[sup.15]N ratios in two reef fish species (blue cod Parapercis colias and spotty Notolabrus celidotus) that have differing feeding modes. Both species exhibited evidence of size-based feeding from fin δ[sup.15]N values, but not from muscle. Blue cod fin δ[sup.15]N increased steadily throughout the sampled size range (213-412 mm fork length), whereas spotty exhibited a distinct ontogenetic diet shift at approximately 120-140 mm fork length after which size-based feeding did not occur. Fin membrane was higher than muscle in δ[sup.13]C in both species and in δ[sup.15]N for blue cod, but fin δ[sup.15]N was lower than muscle in spotty. The δ[sup.13]C and δ[sup.15]N fin-muscle offsets were constant in spotty regardless of size, while in blue cod, δ[sup.13]C was constant with fish size, but δ[sup.15]N offsets increased with increasing fish size. Non-lethal sampling utilizing fin tissue can be employed to estimate stable isotope values of muscle in fishes, but it is necessary to assess relationships among tissues and the effects of fish size on isotope values a priori for each species studied. Our data indicated that fin membrane may be a more sensitive tissue than muscle for detecting size-based feeding in some fish species using stable isotopes. A critical literature review revealed inconsistencies in tissue types tested, little understanding of tissue-specific trophic shift or turnover rates, and pseudo-replicated analyses leading to erroneous postulating of 1:1 relationships between tissues., Introduction In recent years, understanding spatial and temporal changes in the trophic position and foraging dynamics of reef fishes has been frequently achieved by utilizing stable isotopes of nitrogen and [...]

Aims: Aerobic methane oxidation coupled to denitrification (AME‐D) is a promising process for removing nitrate from groundwater and yet its microbial mechanism and ecological implications are not fully understood. This study used RNA stable isotope probing (RNA‐SIP) and high‐throughput sequencing to identify the micro‐organisms that are actively involved in aerobic methane oxidation within a denitrifying biofilm. Methods and Results: Two RNA‐SIP experiments were conducted to investigate labelling of RNA and methane monooxygenase (pmoA) transcripts when exposed to 13C‐labelled methane over a 96‐hour time period and to determine active bacteria involved in methane oxidation in a denitrifying biofilm. A third experiment was performed to ascertain the extent of 13C labelling of RNA using isotope ratio mass spectrometry (IRMS). All experiments used biofilm from an established packed bed reactor. IRMS confirmed 13C enrichment of the RNA. The RNA‐SIP experiments confirmed selective enrichment by the shift of pmoA transcripts into heavier fractions over time. Finally, high‐throughput sequencing identified the active micro‐organisms enriched with 13C. Conclusions: Methanotrophs (Methylovulum spp. and Methylocystis spp.), methylotrophs (Methylotenera spp.) and denitrifiers (Hyphomicrobium spp.) were actively involved in AME‐D. Significance and Impact of the Study: This is the first study to use RNA‐SIP and high‐throughput sequencing to determine the bacteria active within an AME‐D community. [ABSTRACT FROM AUTHOR]

A liquid scintillation spectrometry method for the determination of 234Th in seawater with 230Th as the yield tracer has been developed and validated. 234Th is separated from the dissolved phase by an Fe[(OH).sub.3] precipitation and is then purified using ion exchange chromatography. The counting source is prepared by taking the sample to dryness in a vial, redissolving in acid, and mixing with a scintillation cocktail. The instrument employed has a relatively low background (11 cpm) and the ability to separate [Alpha] from [Beta] activity on the basis of pulse shapes. The 234Th + 234mPa counting efficiency is 50% over the counting window employed. The limit of detection, using the above parameters, a 20 L sample, and a 400 min count is found to be 0.04 dpm [L.sup.-1]. It was also demonstrated that less advanced instruments, without [Alpha]/[Beta] separation, can also be used effectively.

Ants represent a highly diverse and ecologically important group of insects found in almost all terrestrial ecosystems. A subset of ant species have been widely transported around the globe and invade many natural ecosystems, often out-competing native counterparts and causing varying impacts on recipient ecosystems. Decisions to control non-native ant populations require an understanding of their interactions and related impacts on native communities. We employed stable isotope analysis and metabarcoding techniques to identify potential dietary niche overlap and identify gut contents of 10 ant species found in natural ecosystems in Aotearoa New Zealand. Additionally, we looked at co-occurrence to identify potential competitive interactions among native and non-native ant species. Ants fed mainly across two trophic levels, with high dietary overlap. Relative to other ant species sampled, two non-native ant species, Linepithema humile and Technomyrmex jocosus , were found to feed at the lowest trophic level. The largest isotopic niche overlap was observed between the native Monomorium antarcticum and the invasive Ochetellus glaber , with analyses revealing a negative co-occurrence pattern. Sequence data of ant gut content identified 51 molecular operational taxonomic units, representing 22 orders and 34 families, and primarily consisting of arthropod DNA. Although we generally found high dietary overlap among species, negative occurrence between a dominant, non-native species and a ubiquitous native species indicates that species-specific interactions could be negatively impacting native ecosystems. Our research progresses and informs the currently limited knowledge around establishing protocols for metabarcoding to investigate ant diet and interactions between native and non-native ant species. [ABSTRACT FROM AUTHOR]

Our Gas/EA/IRMS technique might close this calibration gap, as it can be adapted to calibrate isotope ratios in non-CH 4 gases to available liquid/solid RMs. LETTER TO THE EDITOR Arobustmethodfordirectcalibrationofisotoperatiosin gasesagainstliquid/solidreferencematerials,includinga laboratorycomparisonfor 13 C-CH 4 Although stable carbon isotope ratios in atmospheric methane (CH 4) are frequently used to constrain biogeochemical processes responsible for the increase of this powerful greenhouse gas, 1-3 certified reference materials (RMs) for isotope ratios in CH 4 have been lacking for decades. Our Gas/EA/IRMS systems enable adherence to the PIT for the measurements of gaseous/liquid/solid samples, which is critical for the calibration of isotope ratios in gases against liquid/solid RMs with high accuracy. A robust method for direct calibration of isotope ratios in gases against liquid/solid reference materials, including a laboratory comparison for 13C-CH4. [Extracted from the article]

Caulerpa is a widely distributed genus of chlorophytes (green macroalgae) which are important for their dietary, social and coastal ecosystem value. Ocean acidification (OA) threatens the future of marine ecosystems, favouring macroalgal species that could benefit from increased seawater carbon dioxide (CO2) concentrations. Most macroalgae species possess CO2 concentrating mechanisms (CCMs) that allow active uptake of bicarbonate (HCO3−). Those species without CCMs are restricted to using CO2, which is currently the least abundant species of dissolved inorganic carbon (DIC) in seawater. Thus, macroalgae without CCMs are predicted to be likely benefit from OA. Caulerpa is one of the rare few genera that have species both with and without CCMs. The two most common Caulerpa species in New Zealand are C. geminata (possesses a CCM) and C. brownii (non-CCM). We investigated the responses of growth, photo-physiology and DIC utilisation of C. geminata and C. brownii to four mean seawater pH treatments (8.03, 7.93, 7.83 and 7.63) that correspond to changes in pH driven by increases in pCO2 simulating future OA. There was a tendency for the mean growth rates for C. brownii (non-CCM) to increase under lower pH, and the growth rates of C. geminata (CCM) to decline with lower pH, although this was not statistically significant. However, this is likely because variability in growth rates also increased as seawater pH declined. There were few other differences in physiology of both species with pH, although there was tendency for greater preference for CO2 over HCO3− uptake in the CCM species with declining seawater pH. This study demonstrates that DIC-use alone does not predict macroalgal responses to OA. [ABSTRACT FROM AUTHOR]