Limnology and Oceanography: Methods最新文献

Otoliths, the functional earstones of teleost fishes, record growth in the form of microscopic increments, making them key archives of individual life histories. While increment analysis is commonly applied to modern otoliths, studies of fossil (Holocene) otoliths remain limited. Traditional methods such as light microscopy (LM) and secondary electron (SE) imaging often fail to resolve microincrements, leading to underestimation and inconsistent findings. We used backscattered electron (BSE) imaging to examine modern and radiocarbon-dated Holocene otoliths of the black goby (Gobius niger Linnaeus, 1758) from the northern Adriatic Sea. Our aim was to assess whether BSE imaging improves microincrement visibility. Standard BSE imaging outperformed LM, detecting 22.6% more increments than in thin-sectioned and 55.7% more increments than in surface-polished Holocene otoliths. High-resolution BSE imaging with extended scan times and optimized settings revealed over 250% more increments than a standard BSE workflow. These results show that imaging quality and scan strategy significantly influence microincrement detection, and that optimized BSE workflows greatly improve the resolution of growth records. Notably, microincrement visibility in the Holocene otoliths was unaffected by post-mortem alteration or radiocarbon age, indicating robust internal preservation. In contrast, LM imaging of thin-sectioned modern otoliths yielded higher increment counts than the BSE method due to their natural translucency and intact internal structures, confirming that traditional methods are effective for recent material. Our study demonstrates that an optimized BSE workflow improves the analysis of fossil otoliths and enables more complete reconstructions of fish growth over long timescales.

To calculate ecosystem metabolism, with the aim of conserving a riverine environment, gross primary production (GPP) of the riverbed and ecosystem respiration (ER) of the aquatic community need to be accurately quantified. The prevalent open-channel metabolism method requires the estimation of the oxygen transfer rate between the atmosphere and river water, which presents a multitude of challenges. Overcoming these challenges requires the creation of a water mass in the river that is isolated from the atmosphere. Therefore, by constructing an underwater tunnel using transparent sheets, we developed a method for GPP and ER measurement that requires no oxygen transfer rate. Gross primary production obtained in the midstream river using the transparent tunnel method averaged 6.59 and 4.65 g C m⁻² d⁻¹ in summer and winter, respectively, whereas ER averaged 3.46 and 2.77 g C m⁻² d⁻¹ in summer and winter, respectively. Moreover, these measurements were six to several dozen times higher than those quantified using traditional methods relying on experimentation, such as the light–dark bottle and bag method, which were closer to previous values quantified using the open-channel metabolism method. The transparent tunnel method reflected the respiration rates of the benthic community across the entire riverbed, requires no oxygen transfer rate, and can estimate ecosystem metabolism with one fewer term.

Robust and efficient monitoring of radiocesium in the marine environment has become increasingly important, especially following the Fukushima Daiichi Nuclear Power Plant accident. A liquid scintillation counter (LSC) has been used for ¹³⁷Cs analysis—which was identified as one of the hazardous radionuclides; however, a major limitation of this approach is that the target radionuclide must be purified from the sample. Therefore, we present a novel application of LSC coupled with ammonium molybdophosphate (AMP)–Poly Acry Nitrile (PAN) resin for ¹³⁷Cs determination in seawater. The method involves preconcentration and purification of ¹³⁷Cs from large seawater volumes (40 L) using a Cs-specific ion exchanger, followed by selective removal of interfering potassium (K) and rubidium (Rb) ions through optimized rinsing procedures. Potassium and Rb have radioisotopes, ⁴⁰K and ⁸⁷Rb, respectively, which are the main interferences for quantifying ¹³⁷Cs by LSC. Critical mass thresholds of K (< 0.01 mg) and Rb (< 0.001 mg) were established to avoid spectral overlap in LSC. Compared with the high-purity germanium (HPGe) detector, the LSC method yielded ~ 20-fold higher counting efficiency and enabled quantification of ¹³⁷Cs with a markedly shorter measurement time. The minimum detectable activity was 0.22 mBq L⁻¹, which is comparable to that of the HPGe method (0.2–0.6 mBq L⁻¹) at the same counting time of 80,000 s. For the same seawater samples, this method showed consistent results with the typical HPGe technique. These findings suggest that LSC combined with AMP–PAN resin is a robust and high-throughput alternative for monitoring of ¹³⁷Cs in seawater.

Intertidal zones are characterized by complex and dynamic thermal mosaics, where organisms experience extreme temperature variations influenced by microclimatic factors. However, accurately monitoring rocky shore temperatures over the long term remains challenging due to the limitations of conventional temperature loggers. Surface-deployed loggers are often prone to loss and measurement inaccuracies caused by external influences such as solar radiation and wind. Here, we evaluated rock-embedded T7.3 EnvLoggers as an alternative for monitoring intertidal substrate temperatures. We compared their performance to traditional surface-deployed loggers in terms of accuracy, long-term loss rates, and the impact of sampling frequency on detecting temperature extremes. Our results indicate that rock-embedded T7.3 EnvLoggers offer superior accuracy, with a mean bias of approximately 0.01°C, and significantly lower loss rates (~ 0.1% per year) compared to surface loggers, which exhibit loss rates ranging from 7.6% to 36.8% per year. Additionally, we found that a sampling interval of 1 h effectively captures daily thermal extremes with minimal error (< 1°C), striking a balance between accuracy and feasibility for long-term deployments. Embedding loggers within rocky substrates presents a durable and cost-effective solution for large-scale, long-term temperature monitoring, standardizes thermal assessments, is scalable, and can be easily adapted for use in other habitats.

Curcumin, a natural plant product derived from Curcuma longa, was assessed as a mitigation technique against the toxic bloom-forming dinoflagellate Karenia brevis in two mesocosm experiments taking place in 2022 and 2024. In these experiments, curcumin was applied at a dosage of 5 mg L⁻¹ to K. brevis concentrations of ~ 1.0 × 10⁶ cells L⁻¹ in 1400 L mesocosm tanks, and changes in cell concentrations, brevetoxins, and water chemistry parameters were examined over time. The 2024 experiment expanded on the 2022 experiment by examining nutrient dynamics and water clarity and explored the potential effects of curcumin on mortality rates, behavioral responses, and toxin content of hard clams (Mercenaria spp.), sea urchins (Lytechinus variegatus), and blue crabs (Callinectes sapidus). In both experiments, curcumin treatment significantly reduced algal cells and total toxins within 24 h. In the 2024 experiment, curcumin caused a significant increase in turbidity above background levels but had no significant impact on total dissolved nitrogen or total dissolved phosphorus. Additionally, curcumin appeared to have no significant effect on animal mortality or behavior after 72 h of exposure. Here we present the results of these pilot studies with curcumin and share the challenges we experienced working with mesocosms for harmful algal bloom mitigation research.

An open question in marine carbon chemistry is if organic alkalinity (or some other unidentified species) is present in non-negligible quantities in the open ocean. If organic alkalinity is indeed present, different methods for total alkalinity (TA) analysis with different titration endpoints could titrate different amounts depending on the dissociation constants (pK_a) of the acids present, resulting in meaningful differences or offsets between methods. Two commonly used methods, open-cell titration with non-linear least squares fitting and single-step titration with spectrophotometric endpoint detection, might titrate different amounts of organic alkalinity, if present, depending on their pK_a. We test this hypothesis using paired samples collected on two cruises, one in the northwest Pacific and one in the western Arctic, and analyze the TA using both methods. We found the differences to be statistically indistinguishable (∆TA_{[Open-Cell−Single-Step]} = 0.5 ± 3.9 μmol kg⁻¹_sw mean and standard deviation N = 206). Adjustment of the single-step TA to certified reference material could be obscuring a difference in the methods. The good agreement between methods indicated that the analytical method is not the cause of offsets in Pacific TA identified by the Global Ocean Data Analysis Project version 2. From these results, the presence of organic alkalinity in open ocean waters remains inconclusive but suggests that if present, the concentration is either very low or both methods titrate similar amounts.

Census-based carbonate budget assessments synthesize metrics on biologically derived carbonate production and erosion rates to generate estimates of net carbonate production (NCP). ReefBudget is a widely used in-water carbonate budget approach, but this methodology can be field-intensive and logistically challenging, limiting spatial data coverage. Large-area imagery (LAI) is increasingly used to evaluate benthic communities and offers applications to leverage existing monitoring programs for use in carbonate budget assessments. Here, we introduce a Photogrammetry-Based Carbonate Budget (PBCB) tool that uses site-level LAI datasets to expand the spatial coverage of data obtainable for carbonate budget assessments. To validate the PBCB approach, long-term monitoring data from Cheeca Rocks (Florida, USA) were used to compare PBCB carbonate budgets to in-water ReefBudget surveys and a transect-based LAI technique (six 100 m² plots sampled in 2018, 2019, and 2022). The PBCB method provided estimates of NCP similar to those of prior methodologies, enabling a means to expand transect-based approaches to larger three-dimensional datasets. While methodological variations were observed for the PBCB approach, such as lower estimates of CCA carbonate production and higher microbioerosion, these did not meaningfully impact NCP due to their relatively low contributions to reef budgets at the site. Coral species richness was > 2× higher using the PBCB method, suggesting that this site-level technique better captures the heterogeneous nature of coral reefs. This new tool represents an advancement to carbonate budget assessments by enabling larger spatial estimates of benthic carbonate production/erosion from LAI, thereby providing a more comprehensive and scalable evaluation of reef growth and persistence.

Microseira wollei is a benthic cyanobacterium that can cause harmful algal blooms (HABs) and often requires management. However, a pervasive challenge for M. wollei management is characterizing the spatial and temporal extent of an impacted area, which can be time and resource intensive. Therefore, the aim of this study was to evaluate environmental DNA (eDNA) as a method for detecting benthic M. wollei using surficial water samples. To meet this objective, this study analyzed water samples collected from areas around Lake St. Clair, Michigan, USA, including regions impacted by M. wollei and secondary rivers (e.g., Clinton River) where no apparent M. wollei biomass was present. Split water samples were analyzed for the presence of M. wollei using traditional light microscopy and compared to eDNA methods using metabarcoding with a universal polymerase chain reaction (PCR) primer. With metabarcoding, we detected Microseira genetic material from the visible onshore biomass up to 93 m into Lake St. Clair and approximately 1–2 m from lakebed biomass. Notably, M. wollei was not discerned using light microscopy of any water samples concurrently collected with eDNA, suggesting greater detection power using the eDNA tool. Our combined datasets provide evidence of the benefits of the eDNA tool in characterizing the spatial extent of M. wollei within large, shallow, HAB-impacted waterbodies and their connected waterways.