ABSTRACT Increasingly anomalous ocean conditions driven by climate change are fundamentally altering marine ecosystems, reshaping the distributions and movements of highly mobile species. Many migratory species rely on environmental and thermal cues to time their movements between foraging and breeding grounds, ensuring that migration occurs under favorable conditions essential for physiological processes, such as growth, development, and reproduction. Importantly, as ocean temperatures rise, intermittent corridors to essential habitats for foraging, reproduction, and development, known as “thermal corridors,” may lead to spatiotemporal shifts of the migratory patterns for many marine species. In this paper, we identify several examples of thermal corridors that vary across space and time. We discuss the periodicity of these thermal corridors, the physical features that define their spatial extent, and differences in species use. We synthesize existing evidence to suggest that intermittent thermal corridors may be more common than previously assumed, with serious implications on the life history traits and population dynamics of migratory species in a changing climate. Importantly, a deeper understanding of these climate‐driven shifts in migratory patterns is vital to inform conservation and management efforts in the context of rapidly‐changing ocean conditions.
Ocean acidification (OA) is expected to alter marine phytoplankton communities by modifying seawater carbonate chemistry, with important implications for marine food webs and biogeochemical cycling. In this study, we tested the hypothesis that comparable pH reductions achieved through different acidification methods generate distinct carbonate chemistry conditions and consequently different biological responses. A 5-day microcosm experiment was conducted using natural phytoplankton assemblages collected from the coastal Eastern Arabian Sea. OA was simulated by HCl addition (acid), CO2 enrichment (CO2), and acid-base manipulation. Changes in carbonate chemistry, nutrients, phytoplankton community composition, pigments, bacteria, microzooplankton, and organic carbon pools were monitored. As expected, the three manipulation methods produced significantly different carbonate chemistry conditions despite comparable pH reductions. Repeated-measures ANOVA and Tukey's post hoc analyses confirmed significant treatment effects for pH, pCO2, DIC, HCO3 -, CO3 2-, and total alkalinity. By Day 5, CO2 enrichment significantly increased total phytoplankton abundance and promoted microplankton dominance, driven by bloom-like proliferation of Thalassiosira sp., whereas picoplankton declined significantly. Conversely, pennate diatoms, cyanobacteria, dinoflagellates, and coccolithophores exhibited weak or negative responses. Concurrent changes in phosphate, nitrite, autotrophic bacteria, and microzooplankton indicated that nutrient availability, microbial recycling, and grazing interacted with carbonate chemistry to regulate phytoplankton succession. Our findings demonstrate that phytoplankton responses in the oligotrophic Eastern Arabian Sea are governed by the combined effects of carbonate chemistry, nutrient dynamics, and ecological interactions rather than pH alone.
Ringed seals (Pusa hispida) use sea ice year-round in the Arctic as a platform for giving birth, raising young and moulting. Arctic ringed seal population assessments are typically conducted by aerial surveys flown in the spring, when many seals haul out. However, many factors can influence whether a seal is hauled out on the ice and available for detection. Understanding the environmental factors that impact ringed seal haul-out behaviour will reduce bias in aerial surveys. We deployed camera traps near Ulukhaktok, Northwest Territories, Canada in mid-May 2023, 2024 and 2025 facing open water leads in the sea ice to document haul-out behaviour of ringed seals under varying weather conditions. We used generalized additive mixed models to analyse the presence/absence and number of ringed seals hauled out. We found that high temperatures (> -4.3 degrees C), low wind speeds (< 20 km/h), and high barometric pressure systems (101.4-101.8 kPa) increased the probability and number of ringed seals hauling out. We also found that haul-outs occurred at lower temperatures under conditions of low and moderate wind speeds, and that the number of seals hauled out increased at lower temperatures at low wind speeds. We identify specific 'ideal weather' parameters for aerial surveys, which will reduce availability bias when calculating density and abundance estimates.
ABSTRACT Non‐indigenous copepods are increasingly reported in the Mediterranean Sea, where anthropogenically disturbed coastal environments may facilitate their establishment and their co‐occurrence with native congeners. This study provides the first record of the non‐indigenous calanoid Acartia tonsa along the Algerian coast and examines its spatio‐temporal distribution relative to the native A. clausi . Zooplankton was sampled during four seasonal campaigns covering a complete annual cycle at four coastal stations of Bordj El Kiffan (eastern Algiers Bay, 36°45′ N, 3°22′ E), arranged along an anthropogenic pressure gradient from a brine‐discharge outlet to an offshore reference station. We hypothesised that (1) disturbed conditions generated by brine discharge and coastal enrichment favour the establishment of A. tonsa , and (2) as an early‐stage invader, A. tonsa currently co‐occurs with A. clausi with a high degree of niche overlap rather than excluding it. A. tonsa was recorded at all stations and seasons (4.80–5280 adults m −3 ), with a marked summer maximum, and consistently reached higher abundances than A. clausi (5.60–371.20 adults m −3 ). Both species peaked in summer and were positively associated with temperature, and niche‐overlap indices remained high throughout the annual cycle, indicating spatial and temporal co‐occurrence rather than exclusion. The relative abundance of the two congeners decreased from the enriched nearshore stations towards the offshore reference station, linking the dominance of A. tonsa to the local anthropogenic gradient.
Empirical studies demonstrating ecological speciation in marine invertebrates are limited. Two large abalone species-Haliotis discus discus and H. madaka-in the Japanese archipelago are considered to be involved in this process. Previous population genomic studies have indicated that hybridization between these two species continues because of incomplete reproductive isolation. However, owing to the limited number of samples in the previous study, the nature of hybridization remains unclear. In this study, we performed population genomic analyses of these two species using samples from multiple geographical regions. Analysis of 122 species-diagnostic single-nucleotide polymorphism loci revealed that observed heterozygosity was significantly higher in the H. madaka population than that in the H. discus discus population. ADMIXTURE analyses revealed biased introgression from H. discus discus into H. madaka populations, with the extent of introgression varying among regions. Most individuals with genomic introgression were classified as backcrosses, with no individuals demonstrating patterns consistent with F1 hybrids, indicating a bimodal hybrid zone. These findings suggest that selection may act against early-generation hybrids and that ecological speciation proceeds under geographically variable selective pressures in marine environments.
