Marine Biology最新文献

Foraging specialisations are common in animal populations, because they increase the rate at which individuals acquire food from a known and reliable source. Foraging plasticity, however, may also be important in variable or changing environments. To better understand how seabirds might respond to changing environmental conditions, we assessed how plastic the foraging behaviours of short-tailed shearwaters (Ardenna tenuirostris) were during their non-breeding season. To do this, we tracked 60 birds using global location sensing loggers (GLS) over a single year between 2012 and 2016 with the exception of 8 individuals that were tracked over 2 consecutive years. Birds predominantly foraged in either the Sea of Okhotsk/North Pacific Ocean (Western strategy) or the southeast Bering Sea/North Pacific (Eastern strategy). The eight birds tracked for 2 consecutive years all returned to the same core areas, indicating that these birds were faithful to foraging areas between years, although the time spent there varied, probably in response to local changes in food availability. Overall, 50% of the birds we tracked left their core area towards the end of the non-breeding period, moving into the Chukchi Sea, suggesting that the birds have flexible intra-seasonal foraging strategies whereby they follow prey aggregations. We hypothesise that seasonal declines in chlorophyll a concentrations in their primary core foraging areas coincide with changes in the availability of large-bodied krill, an important food source for short-tailed shearwaters. Decreasing prey abundance likely prompts the movement of birds out of their core foraging areas in search of food elsewhere. This strategy, through which individuals initially return to familiar areas but disperse if food is limited, provides a mechanism that allows the birds to respond to the effects of climate variability.

Over the last three decades, the advent and the continuous sophistication of telemetry devices have revolutionized our understanding of how pelagic sharks move and exploit their three-dimensional underwater habitat, with implications for management and conservation. In this study, conventional (4,648) and electronic (18) tags were used to assess the horizontal and vertical movements of blue sharks, Prionace glauca, and their vertical overlap with shallow and deep-set longline fishing gears in the southwestern Atlantic Ocean. Results revealed prolonged permanence in the area, large-scale displacements, including trans-equatorial, trans-Atlantic and Indian–Atlantic movements, and high daily displacement rates. Blue sharks showed an extensive use of the water column and considerable variability among and within individuals in vertical behavior, involving normal and reverse diel vertical migrations, surface-oriented behavior, extended use of mesopelagic waters, and occasional extreme dives into bathypelagic waters. Depth distribution appeared unrelated to size or sex but was influenced by the time of day and temperature, with deeper and colder temperatures consistently found during the day. The moon cycle affected the vertical distribution of some sharks but not others. Temperature-depth recorders deployed on hooks, combined with depth distribution from electronic tags, provided insightful information on the species’ vertical overlap with shallow- and deep-set longline configurations. Encounterability values were higher during nighttime and lower during daytime for both longline configurations, but were largely affected by the individuals’ vertical behavior, highlighting the importance of accounting for environmental conditions besides fishing gear configuration and métiers. This novel information on blue sharks’ movements and fishery interactions in the South Atlantic Ocean can inform future management and conservation strategies.

Pacific Sardine (Sardinops sagax) in the Northeast Pacific Ocean are aged for stock assessments assuming the formation of two otolith growth bands (one opaque and one translucent) a year, but the periodicity of band formation has not been fully validated. To validate our ageing method, we investigated the periodicity of band deposition and somatic and otolith growth rate across a range of temperatures. Live Pacific Sardine (mostly age 0) were collected, marked with oxytetracycline (OTC), and raised in captivity at different temperatures (13 °C, 15 °C, 17 °C, and 21 °C) for up to one year. There was no clear pattern between temperature and somatic growth rate. Otolith growth rate was slower for Pacific Sardine in captivity at 13 °C than at 17 °C. All individuals that were in captivity for one year (n = 21) deposited 2–3 growth bands distal to the OTC mark. Therefore, Pacific Sardine deposited bands in their otoliths at the rate expected for the formation of annuli across ecologically relevant temperatures (13–21 °C) in captivity. Vateritic otoliths were rare but did display an OTC mark at approximately the same distance from the otolith edge as the aragonitic otolith in the pair. The results of this study build upon previous validation research for Pacific Sardine and support the ageing methodology used for this species by all ageing laboratories in the US, Canada, and Mexico.

Tylorrhynchus osawai, nereidid polychaete that is considered to support estuarine biodiversity, undergoes a unique epitokous metamorphosis for reproductive swarming. The reproductive swarming of this species has been observed in Japan for more than 100 years; however, the benthic phase of this species has not been well researched. In this study, we aimed to elucidate the morphological allometry and life history, specifically the reproductive swarming, of this species. To accomplish this, surveys were conducted to collect atokes and epitokes from a tidal river in Kyushu, Japan. A total of 1670 T. osawai specimens were collected and preserved in 80% ethanol. The body widths of these specimens were measured, while several intact specimens underwent additional measurements of body length and the number of chaetigers. The morphological allometry of this species differed between atokous and epitokous forms, indicating that its heteronereis form might be suitable for migration from a tidal river to the ocean. The survey results pertaining to the benthic phase of this species indicated that its lifespan was approximately one year or longer. In addition, the settlement, growth, and maturity of this species exhibited a degree of plasticity, potentially influenced by habitat landscapes and sediment conditions. Based on the surveys conducted on reproductive swarming, climate change could have caused the peak of reproductive swarming to shift slightly later than that of several historical observations. Our findings contribute to elucidating the ecological significance of epitokous metamorphosis in nereidid polychaetes and to conserving T. osawai populations.

Niche theory predicts that similar species cannot occupy the same geographical space when resources are limited. Sympatric seabirds, such as auks, are ideal models for investigating niche differentiation because they share life history traits and form breeding colonies that rely on common prey items. Auk differentiation may be driven by variations in body mass and wing size, diving capacity, and visual acuity leading each species to forage at different distances, depths, or times of day, respectively. However, previous auk studies have produced diverse results, leaving us with an incomplete understanding of their foraging differentiation across spatial, environmental, and temporal dimensions. In 2021, we tested niche differences at the Mingan Archipelago National Park Reserve, Québec, Canada (50°11′ N, 63°13′ W) by utilizing GPS and time and depth recorders to track the positions of breeding Atlantic puffins (Fratercula arctica), razorbills (Alca torda), and common murres (Uria aalge), which were then paired with environmental data. There was high niche overlap in geographical foraging areas, with auk wing size and mass not appearing to influence their foraging distance. Instead, auk foraging was partitioned over different depths and times of day. Although razorbills and puffins generally exploited shallow foraging areas, puffin foraging activity occurred in deeper waters and at different times of day than razorbills. Murres foraged in the deepest benthic areas and were the only species to forage at night. Our study therefore suggests that auks could be facilitating their coexistence by exhibiting temporal and spatial differences in their foraging behaviours and locations.

Abstract

Marine top predators are expected to adjust their foraging behaviour at multiple time scales concomitantly with changes in forage fish availability. Rhinoceros auklets Cerorhinca monocerata rearing chicks at Teuri Island, Japan Sea, fed on anchovy Engraulis japonicus in 2012 and 2013 (anchovy regime) but switched to sand lance Ammodytes spp in 2019 and 2020 (sand lance regime). Here, we studied their at-sea behaviour using the GPS locations of 33 birds and the depth-acceleration records of 26 birds, and compared their foraging behaviour between these prey regimes. At the trip scale, auklets used offshore waters (> 50 m sea depth) and coastal waters in the anchovy regime but used mainland coastal waters (< 50 m sea depth) in the sand lance regime. In the sand lance regime, the birds also conducted more overnight 2- to 4-day trips in 2020 and spent more time flying during 1-day trips as they fed in further areas compared to the anchovy regime. At the dive scale, auklets frequently dove to both < 5 m and 20–30 m depths in the anchovy regime but mainly to < 5 m depth in the sand lance regime. Within each dive, auklets showed a greater number of fast/strong wing stroke events in the anchovy regime than in the sand lance regime. These changes in auklet behaviour reflected the different habitats, depth distribution, and swim speed of the targeted prey species. Our study shows the behavioural flexibility of a wing-propelled flying-diving seabird in response to the inter-annual shifts in the dominant forage fish community. It also indicates the ecological constraints on the mechanisms determining nest productivity in this day-foraging/night-provisioning seabird.

Abstract

Slowly sinking small particles in surface seawater are proven to be one of the major contributors to the mesopelagic carbon flux. Phytoplankton can respond rapidly to changes in the marine environment, so assessing the efficiency of their downward export can better constrain the relationship between carbon biomass and sinking fluxes. Here, we measured the sinking rates of individual phytoplankton (φ_indiv) after being subjected to Luzon cold eddy (LCE), warm eddy (WE) and spring warm pool (SWP), and explored the main influencing factors affecting cell sinking. The φ_indiv in the euphotic zone of the central South China Sea (ceSCS) was measured using the SETCOL method during the inter-monsoon period in April 2017. Diatoms (mainly rod-shaped) were sinking faster under the influence of SWP, with the highest carbon fluxes in the surface layer; WE leading to slow sinking of dinoflagellates, rapid sinking of cyanobacteria and a significant reduction in the number of phytoplankton species; diatoms sinking slowly due to the LCE. The φ_indiv of cylinder-shaped and rhombus-shaped cells in diatoms and fusiform-shaped and ellipsoid-shaped cells in dinoflagellates were significantly modulated by cell size. The setae structure of Chaetoceros can modulate the sinking behavior well in different environments. Our results indicate that in the open ocean, the shape and size of cells, the unique ecological niches of different species, and the original localization of cells are essential for the modulation of sinking.

Quantitative data on cephalopods collected in ten multidisciplinary surveys (20–2000 m) between 2004 and 2012, together with original oceanographic and satellite data, were analyzed using multivariate techniques. Statistical analyses were based on presence–absence matrices by species and hydrological variable indices. The results show that cephalopods are distributed in two main zoogeographical groups separated by latitude: “Temperate water” and “Tropical water” clusters. They extended by temperate and tropical regions, separated by a geographical boundary, Cape Blanc, particularly strong in the case of coastal species between these groups. For the total fauna, we have identified a third particular cephalopods’ cluster, the “Upwelling” cluster (22°–17°N), characterized by a higher diversity and dominance of oceanic cephalopods. This is proposed as a new zoogeographical region that would coincide with the area of greatest productivity, intensity and permanence throughout the year of the canary current upwelling, confined between the north of Cape Blanc and the south of Mauritania. The results confirm the strong relationship between the three zoogeographical regions (temperate, tropical, and upwelling) and certain water bodies that characterize the regional hydrology. This paper deepens into the zoogeography of the cephalopods from Northwest Africa (Central-Eastern Atlantic), providing a new, more detailed insight into the region and its boundaries in relation to the oceanography.

The number of individuals to be sampled is a key element in the sampling design of any study as it directly affects the estimations and inferences made. Additionally, in cases where several replicates per individual can be taken, it is important to define how the sampling effort will be distributed between the intraindividual and interindividual components (within and between individuals, respectively). Determining how samples should be distributed among these components can help optimize the available resources and reduce bias in the estimations. To study population trophic diversity, the total niche width (TNW) is usually estimated, which is an approximation of resource diversity at the population level. TNW is the sum of the resource diversity consumed at the intraindividual (replicates) and interindividual (individuals) level. In this study, the effect of prioritizing the number of individuals or the number of replicates on the accuracy and precision of TNW estimations was tested. Multiple isotopic (δ¹³C and δ¹⁵N) values per individual in populations with different degree of individual specialization were simulated. Then, isotopic data from natural populations within the same species (available published studies) were used to assess the results obtained with simulated data. It was found that TNW estimations were more accurate and precise when prioritizing the number of individuals over the replicates, along the entire individual gradient of trophic specialization. Therefore, it is advisable to prioritizing the number of individuals. This methodological contribution should be considered in future studies that use repeated measures of isotopic data to estimate TNW.

Non-indigenous species (NIS) establish and thrive on floating artificial substrata along mid-latitude shores, which might serve as propagule reservoirs and stepping stones for their dispersal. However, often, the NIS are not able to colonize the adjacent seafloor, where high predation pressure by benthic predators might inhibit them. To test this hypothesis, we quantified and compared consumption rates of standardized bait (squidpops) in four water depth zones (sea surface, sub-surface, midwaters, seafloor) in five representative regions in the Southeast Pacific, covering oceanic Rapa Nui (Easter Island; 27°S, 109°W; November 2022) as well as the Chilean continental coast (29–41°S, 71–73°W; March–June 2022). We found a strong overall effect of water zonation, with significant bait consumption being limited to the seafloor and occurring only sporadically in other depth zones. Consumption frequencies also differed between experimental regions but were not influenced by latitude or mean sea surface temperature. An analogous experiment with the NIS Ciona robusta, conducted at one sampling site, showed that the occurrence or absence of predation per site and water depth zone, but not the exact consumption rates, concurred between both bait types. Our results confirm that predation in SE Pacific temperate shallow waters mainly depends on benthic predators that cannot reach higher zones of the water column. These findings have far-reaching implications, as they indicate that predation rates in mid-latitude systems might be underestimated through commonly used water column-based experiments. For a comprehensive estimation of predation pressure in a given system, future studies should consider differences between vertical water zones.