Carbonate removal using acids is a common practice in ecological studies. The effects, however, of acid pre-treatment on the elemental and isotopic composition of marine invertebrates as well as how these effects vary according to species’ carbonate content is little known. We examined the effects of acid pre-treatment on the elemental (%C, %N, C:N ratio (%C:%N)) and isotopic composition (δ13C, δ15N) of 28 lightly- and heavily-calcified species from Cnidaria, Mollusca, Arthropoda, Bryozoa, Echinodermata and Chordata. The present study showed that acid pre-treatment modified the elemental and isotopic composition of lightly- and heavily-calcified marine invertebrates. The shifts were clearly seen as a decrease in the %C and δ13C of heavily-calcified species while we did not detect a clear pattern for %N and δ15N (in both lightly- and heavily calcified species). Apart from carbonates, acid pre-treatment caused also the loss of organic compounds, thus confounding the interpretation of carbonate proxy (CP) -a widely used proxy for carbonate content. We recommend the use of CP solely with heavily-calcified species. For the first time it was shown that the use of δ15N values from acidified samples can introduce substantial bias in our perception about the number of trophic levels, the distribution of species and distribution of biomass across the trophic levels in a community. We have uncovered and elucidated previously unknown aspects and highlighted the challenge posed when predicting shifts in elemental and isotopic composition of species following acid pre-treatment. The present findings should be considered in future studies using acid pre-treatment as they can contribute to the optimum use of samples while avoiding bias in the interpretation of findings.

Assessing coral reef resilience is an increasingly important component of coral reef management. Existing coral reef resilience assessments are not practical, especially for developing countries. South-east Asian countries have been using line-intercept-transect (LIT) in coral reef monitoring for a long time. The present study proposes an index for assessing coral reef resilience based on data collected from the LIT method. The resilience index formula was modified from an existing resilience index for soil communities developed by Orwin and Wardle. We used an ideal resilient coral reef community as a reference point for the index. The ideal coral reef was defined from data collected from 1992 to 2009. Six variables were statistically selected for the resilience indicators: coral functional group (CFG), coral habitat quality (CHQ), sand-silt cover (SSC), coral cover (COC), coral small-size number (CSN), and algae-other-fauna (AOF) cover. Maximum values of five variables were determined as the best state, while the maximum value of CSN was determined from 1240 data-sets of Indonesian reefs. The resilience index performed well in relation to changes in COC, AOF, and SSC variables. Managers can use this tool to compare coral reef resilience levels among locations and times. This index would be applicable for global coral reef resilience assessment.

Diel and gastrointestinal changes in relation to the feeding intensity and prey composition of Apogon lineatus were investigated through the analysis of the diet contents of 174 fishes collected from the southeastern coast of Korea. Fish samples were collected at both day and night times during winter using a small bottom trawl. Stomach fullness, stomach contents index (SCI) and intestine contents index (ICI) of A. lineatus varied with day-night changes. Multivariate analyses revealed that dietary contents differed significantly between the stomach and intestine, but were similar between day and night in both stomachs and intestines. In the stomachs, prey items mostly consisted of caridean shrimps and euphausiids, while the relative contributions of amphipods and unidentifiable items tended to be high in the intestine contents, indicating that the intestines mainly contained content made up of nearly digested and/or hard shell items.

Microplastics provide an important medium for hydrophobic organic chemicals (HOCs), and the desorption of HOCs from microplastics is an important process for the dynamics of HOCs associated with microplastics. Although desorption kinetics has been studied for microplastics with ideal geometries, most of the microplastics isolated from the environment are irregular fragment-type microplastics. This study investigated the desorption of six model HOCs from polyethylene (PE) and polypropylene (PP) fragments to artificial seawater and compared the results with those predicted assuming ideal geometries (e.g., sphere and infinitely flat sheet) of microplastics. The experimental desorption was explained well by the model predictions with the characteristic radius for a sphere and the thickness for a plate estimated from visual imaging. The mass fraction remaining at the later stage of desorption was higher than the model simulation assuming a single characteristic length, likely due to the heterogeneity of the particle size distribution. Although there are inevitable uncertainties, it would be useful to assign a single length dimension in desorption modeling for even fragment-type microplastics, especially for the estimation of desorption half-life.

Ecosystem-based management is one of the most important approaches that may lead to reducing the impacts of fishing on ecosystems. In this context, we have assessed the impact of Iranian coastal fishing (using landing data of 49 exploited species) on the ecosystem of the North Sea of Oman (Sistan and Baluchestan Province), during the last decade (2002–2011), with emphasis on testing the occurrence of the “fishing downˮ phenomenon. The Mean Trophic Level (MTL) and Fishing-in-Balance (FiB) index are two indicators that we used for analysis. The data indicated that the increased total landings in this region might be related to the exploitation of marine fishery resources especially with regard to large pelagic fish. Over the past decade, moderate decreasing trends in MTL and an increasing trend in the FiB-index were observed. In this regard, an upward trend in the spatial expansion factor and also a downward trend in the piscivory index and in Primary Production Required (PPR) in the time period could all indicate a spatial expansion toward deep waters, the catching of the large pelagic piscivorous species, such as tuna, and a sign of fishing pressures on the ecosystem. The results suggest a range of fishery exploitation patterns throughout the food web but it seems that these patterns are not a consequence of ʻfishing downʼ. We suggest that the monitoring research be continued in this region and these indicators should be used to make fisheries management decisions and to prevent the continuance of this trend in future.

Rock magnetic properties of unconsolidated sediments from the Korea Deep Ocean Study area of the northeastern equatorial Pacific were analyzed to trace the time-dependent variations of sedimentary environments. For upper Pleistocene sediments, light-brown sediments predominate, whereas the lower sediments deposited in the late Pliocene are dark brown. Rock magnetic properties also clearly differ among the two distinct color environments. Values of anhysteretic remanent magnetization and low-field magnetic susceptibility are highly responsive to changes in the color of the sediment. For example, comparatively low values denote a dominance of coarse-grained magnetic minerals as observed in the lower dark-brown layers. With respect to the content of magnetic minerals, coarse magnetic grains are highly concentrated in the darker-colored sediment layers. However, both the magnetic mineral dependent parameter (S ratio) and results of the scanning electron microscope observation indicate that magnetic mineral changes did not occur along the core depth, which means that there was no apparent source change. Without distinctive source changes, the variations in the rock magnetic properties likely reflect a process by which the magnetic grains were primarily transported by enhanced wind and bottom currents and affected by diagenetic dissolution as a function of both the time from burial and the extremely low sedimentation rates after deposition.

Despite its potential significance for industrial utilization, any activities associated with the mining of manganese (Mn) nodules might have substantial impacts on benthic ecosystems. Because microorganisms respond quickly to changing environmental conditions, a study of microbial communities provides a relevant proxy to assess possible changes in benthic ecosystems associated with mining activities. We investigated fine-scale microbial community composition and diversity inside and on the surface of Mn nodules and in nearby deep-sea sediments in the Korea Deep Ocean Study (KODOS) area located in the Clarion-Clipperton Fracture Zone (CCFZ) of the northeast equatorial Pacific. Although microbial cell density was lower within nodules (3.21 × 106 cells g-1) than in sediment (2.14 × 108 cells g-1), nodules provided a unique habitat for microorganisms. Manganese-oxidizing bacteria including Hyphomicrobium and Aurantimonas in Alphaproteobacteria and Marinobacter in Gammaproteobacteria were abundant in nodules, which implied that these bacteria play a significant role in nodule formation. In contrast, Idiomarina in Gammaproteobacteria and Erythrobacter and Sulfitobacter in Alphaproteobacteria were abundant in sediments. Meanwhile, Thaumarchaeota, a phylum that consists of ammonia-oxidizing chemolithoautotrophs, were the predominant archaeal group both in nodules and sediment. Overall, microbial communities in Mn nodules were unique compared to those observed in sediments. Furthermore, the phylogenetic composition of microorganisms in the KODOS area was distinguishable from that in the nodule provinces claimed by China and Germany in the CCFZ and nodule fields in the central South Pacific Gyre, respectively.

Increasing concentrations of atmospheric carbon dioxide are causing oceanic pH to decline worldwide, a phenomenon termed ocean acidification. Mounting experimental evidence indicates that near-future levels of CO2 will affect calcareous invertebrates such as corals, molluscs and gastropods, by reducing their scope for calcification. Despite extensive research into ocean acidification in recent years, the effects on non-calcifying anthozoans, such as sea anemones, remain little explored. In Western Europe, intertidal anemones such as Actinia equina are abundant, lower trophic-level organisms that function as important ecosystem engineers. Changes to behaviours of these simple predators could have implications for intertidal assemblages. This investigation identified the effects of reduced seawater pH on feeding and contest behaviour by A. equina. Video footage was recorded for A. equina feeding at current-day seawater (pH 8.1), and the least (pH 7.9) and most (pH 7.6) severe end-of-century predictions. Footage was also taken of contests over ownership of space between anemones exposed to reduced pH and those that were not. No statistically significant differences were identified in feeding duration or various aspects of contest behaviour including initiating, winning, inflating acrorhagi, inflicting acrorhagial peels and contest duration. Multivariate analyses showed no effect of pH on a combination of these variables. This provides contrast with other studies where anemones with symbiotic algae thrive in areas of natural increased acidity. Thus, novel experiments using intraspecific contests and resource-holding potential may prove an effective approach to understand sub-lethal consequences of ocean acidification for A. equina, other sea anemones and more broadly for marine ecosystems.

Environmental challenges such as ocean acidification and eutrophication influence the physiology of kelp species. We investigated their interactive effects on Saccharina japonica (Laminariales, Phaeophyta) under two pH conditions [Low, 7.50; High (control), 8.10] and three NH 4 + concentrations (Low, 4; Medium, 60; High, 120 μM). The degree of variation of pH values in the culture medium and inhibition rate of photosynthetic oxygen evolution by acetazolamide were affected by pH treatments. Relative growth rates, carbon, nitrogen, and the C:N ratio in tissue samples were influenced by higher concentrations of NH 4 + . Rates of photosynthetic oxygen evolution were enhanced under elevated CO2 or NH 4 + conditions, independently, but these two factors did not show an interactive effect. However, rates of NH 4 + uptake were influenced by the interactive effect of increased CO2 under elevated NH 4 + treatment. Although ocean acidification and eutrophication states had an impact on physiological performance, chlorophyll fluorescence was not affected by those conditions. Our results indicated that the physiological reactions by this alga were influenced to some extent by a rise in the levels of CO2 and NH 4 + . Therefore, we expect that the biomass accumulation of S. japonica may well increase under future scenarios of ocean acidification and eutrophication.