Friday, 21 February 2020

Magnitude 1.4 Earthquake beneath Doncaster, South Yorkshire.

The British Geological Survey recorded a Magnitude 1.4 Earthquake at a depth of 6 km beneath the town of Doncaster in South Yorkshire, England slightly after slightly after 3.25 am GMT on Thursday 20 February 2020. There are no reports of any injuries associated with this event, though it may have been felt locally.
The approximate location of the 20 February 2020 Doncaster Earthquake.Google Maps.
Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England. However, while quakes in southern England are less frequent, they are often larger than events in the north, as tectonic presures tend to build up for longer periods of time between events, so that when they occur more pressure is released.
The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.
Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process.
(Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.
Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here. 
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Thursday, 20 February 2020

Asteroid 2020 DU passes the Earth.

Asteroid 2020 DU passed by the Earth at a distance of about 324 900 km (0.85 times the average  distance between the Earth and the Moon, or 0.22% of the distance between the Earth and the Sun), slightly before 1.20 pm GMT on Thursday 13 February 2020. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2020 DU has an estimated equivalent diameter of 3-11 m (i.e. it is estimated that a spherical object with the same volume would be 3-11 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere more than 30 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2020 DU. JPL Small Body Database.

2020 DU was discovered on 16 February 2020 (the day before its closest encounter with the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2020 DU implies that the asteroid was the twentieth object (asteroid A - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc, which means that U = 20) discovered in the second half of February 2020 (period 2020 D).

2020 DU has a 901 day (2.47 year) orbital period, with an elliptical orbit tilted at an angle of 1.57° to the plain of the Solar System which takes in to 0.90 AU from the Sun (90% of the distance at which the Earth orbits the Sun) and out to 2.75 AU (275% of the distance at which the Earth orbits the sun and almost twice as far from the Sun as the planet Mars). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer).

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Sepiella japonica: Paternity testing reveals polyandry in the Japanese Spineless Cuttlefish.

The Japanese Spineless Cuttlefish, Sepiella japonica, is a commercially important marine species in China. Production from wild stocks reached 60 000 tons in Zhejiang Province and accounted for more than 9.3% of provincial fishing catches in 1957. The wild population of Sepiella japonica has declined since the 1980s due to over-fishing and pollution. To enhance production, artificial breeding methods are being developed in China and successful aquaculture techniques have been established in recent years. However, studies have revealed that the populations and individual genetic diversity in this species has declined under artificial conditions.An important factor that affects the genetic diversity of a population is the effective population size which in turn is greatly influenced by the mating system of a species. The mating system influences effective population size through changing the number of individuals contributing to subsequent generations. In a polyandrous mating system, females mate with several males within a single reproductive cycle in which the clustered offspring are descended from multiple males. In such a mating system, effective population size increases, and, as a result, maximizes the genetic diversity of the offspring within a single reproductive season. Some studies have confirmed that a polyandrous mating system is frequent in marine Cephalopods including the  Common Octopus, Octopus vulgaris, Deep-sea Octopus, Graneledone boreopacifica, the Southern Reef Squid, Sepioteuthis australis, the Giant Cuttlefish, Sepia apama, the Longfin Inshore Squid, Loligo pealeii, and the Spear Sqiuid, Loligo bleekeri. The female of all these species carries stored sperm from more than one male, and the effective population size is therefore significantly higher. Previous studies have shown that female Sepiella japonica store sperm in the seminal receptacle found in the buccal membrane. All else being equal, long-term sperm storage enhances the opportunity for multiple matings of this species. Moreover, multiple matings of female Sepiella japonica has actually been observed. Polyandry, coupled with sperm storage, is therefore potentially an important reproductive strategy for maximizing the genetic diversity of offspring in Sepiella japonica.

In a paper published in the journal ZooKeys on 14 October 2019, Liqin Liu of the National Engineering Laboratory of Marine Germplasm Resources Exploration and Utilization and the National Engineering Research Center for Facilitated Marine Aquaculture at Zhejiang Ocean University, Yao Zhang and Xiaoyu Hu, also of the National Engineering Laboratory of Marine Germplasm Resources Exploration and Utilization, Zhenming Lü, also of the National Engineering Laboratory of Marine Germplasm Resources Exploration and Utilization and the National Engineering Research Center for Facilitated Marine Aquaculture, Bingjian Liu, again of the National Engineering Laboratory of Marine Germplasm Resources Exploration and Utilization, Li Hua Jiang, again of the National Engineering Research Center for Facilitated Marine Aquaculture, and Li Gong, once again of the National Engineering Laboratory of Marine Germplasm Resources Exploration and Utilization, examine the mating system of Sepiella japonica experimentally, in order to understand the role of polyandry in maintaining effective population size.

In recent years, multiple paternity in several marine species has been documented using different genetic markers including allozymes, DNA fingerprinting, Random Amplification of Polymorphic DNA, and microsatellites. Microsatellites are the preferred marker because they are widely distributed in the genomes of most organisms and are highly polymorphic. Paternity studies based on microsatellites have become increasingly common, and the number of studies using microsatellites has increased. Several microsatellite markers have been isolated and characterized for Sepiella japonica and used to evaluate the genetic structure of its populations. Liu et al. used the previously described microsatellite markers to investigate whether multiple paternity occurs in Sepiella japonica.

Sexually mature adult Sepiella japonica were obtained from the Fujian Shacheng Harbor Cultivation Base in Fujian Province, China. A sample of 200 wild adults was captured using traps and kept mixed into a cage (9 m3). Seawater parameters were continuously maintained at 25–27 °C and 23‰ salinity. From this sample, seven mating pairs were randomly chosen as breeders to produce the next generation. All behavioral interactions were recorded using closed-circuit television with infrared to observe individual animals. Each mating pair was gently captured and placed in a spawning tank until oviposition. Egg strings derived from each clutch were transferred to a hatchery tank. After hatching, 280 offspring were randomly collected for population genotyping, maintained in a tank until they reached a pre-determined age.

Total genomic DNA was isolated from each offspring and from the muscular tissue of the respective parents. Three microsatellite loci, chosen from four loci (CL168, CL327, CL3354, CL904) developed specifically for Sepiella japonica were used to study genotypes for parents and their offspring.

Parents and their offspring were genotyped by determining alleles at three of the four microsatellite loci. Liu et al. considered evidence from at least two loci to be necessary for estimation of multiple paternity, because evidence from one locus may have been caused by mutations or genotyping error. They determined paternal alleles through subtracting the maternal alleles from offspring in a brood. The minimum number of sires for a clutch was assigned by counting the number of paternal alleles at each locus. Any instance of more than two possible paternal alleles at any loci indicated multiple paternity in a clutch.

Mating behavior in Sepiella japonica involves courtship of a female by a male, and females may copulate with multiple males. Mating pairs mated in the head-to-head position during which males transfer spermatophores to the buccal membrane of the females or to an internal seminal receptacle. The spermatophores that are deposited around the buccal area extrude the sperm mass to form spermatangium. Then the spermatangia attach to the buccal membrane where slowly released sperm are used for fertilization. Liu et al. found that the male flushed water strongly when he was close to the female buccal area prior to mating with the female. This behavior is thought to dislodge sperm from previous males. They also found obvious courtship rituals and agonistic behaviors after sexual maturity. Males are generally capable of mating early in life (3–6 months maturity) and will continue to mate until senescence. However, the females do not generally lay eggs after copulating until fully mature. The duration of spawning in Sepiella japonica varied from 21 to 30 days. Females lay multiple eggs (from tens to hundreds of thousands) by extruding them from the ovary and then they die shortly after spawning.

Sepiella japonica mating in the head-to-head position. Liu et al. (2019).

Three of the four microsatellite markers were chosen to test paternity in seven offspring clutches. These loci exhibited three or more alleles and were polymorphic in each individual. Lui et al. chose the locus which followed Mendelian inheritance to analyze paternity. Two hundred and eighty-seven individuals were genotyped at three loci, seven adult females and 280 offspring. The analysis was highly reproducible. Lui et al. analyzed paternity including sampled males and non-sampled males that had copulated with females prior to capture.

Almost all females were heterozygous at these loci (CL168, CL327, CL3354, CL904), except for CL327 in the clutch B female. For clutches A and E, three different alleles which the father contributed were observed at the three chosen loci, suggesting that these two clutches had been sired by at least two males. The offspring of four females (B, C, D, and F) had three or four paternal alleles in each locus, and three paternal genotypes were observed in all loci. The number of paternal genotypes at these three loci indicated that females B, C, D, and F had mated with three different males. Within clutch G, five different alleles were detected at loci CL168 and CL3354, two of which were from maternal alleles. Clutch G showed four alleles for the locus CL904 in addition to the two alleles detected in the female. Four different paternal genotypes were estimated in clutch G, suggesting the female G was fertilized by at least four different males.

Lui et al. observed female Sepiella japonica mating with different males during the reproductive period, a behavior also recorded in other species of Cephalopods. The benefits of multiple mating not only may raise the potential for genetic diversity but also increases the possibility of offspring survival. It has previously been shown that female Southern Dumpling Squid, Euprymna tasmanica, that mated with different males had larger eggs than those that mated with one male, indicating that females may obtain nourishment from the seminal fluid of several males. Male Cephalopods exhibit 'flushing behavior' in which they remove fresh spermatangia from previous males. In the Golden Cuttlefish, Sepia esculenta, the males remove sperm by using the hectocotylus (a modified arm used by some male Cephalopods to transfer sperm to the female) instead of flushing water. The males in Lui et al.'s study also exhibited such behavior, flushing the buccal area of the female with water, when mating with a previously mated female.

Microsatellite markers are particularly useful in paternity studies because of their polymorphism, codominance, and repeatability. Cephalopod biologists have determined multiple paternity in many species, including Squid and the Deep-sea Octopus, Graneledone boreopacifica. In this study, at least three paternal allele genotypes were found in all seven clutches indicating that at least two males were responsible for each brood. This result was in accordance with previous studies where multiple paternity was also found in the Giant Cuttlefish, Sepia apama. Multiple paternity in Sepiella japonica offspring indicates that sperm from different males must be mixed within the female’s reproductive tract. These sperm deposited around the buccal mass were used differentially to fertilize eggs, after a process of sperm competition or mediation by female choice.

Despite the prevalence of multiple paternity in cephalopod species, these studies show widely differing incidences of multiple paternity. In Lui et al.'s study, multiple paternity was demonstrated in all sampled clutches (100%). In the Giant Cuttlefish, Sepia apama, one-third of the females mated with multiple males and 67% of females’ eggs had multiple sires. Several factors have been confirmed to be related to the variance in incidence of multiple paternity observed in cephalopod species, e.g., sperm allocation, mating systems, sperm competition, and female choice. Moreover, as suggested for the Spear Squid, Loligo bleekeri, males who were the last to mate fertilized 85–100% eggs in four broods tested. However, in the multiple paternity study of the Longfin Inshore Squid Loligo pealeii, the mate order is not the most important factor in determining paternity; however, no clear hypothesis has yet emerged to explain which factor is essential in the multiple paternity of Sepiella japonica. Further work should be carried out to understand paternity patterns and to investigate different factors affecting multiple paternity in this species.

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Wednesday, 19 February 2020

Crocodylus siamensis: Siamese Crocodiles hatch eggs in the wild in Cambodia, for the second time in a decade.

The conservation organisation Fauna & Flora International has reported a clutch of Siamese Crocodile, Crocodylus siamensis, hatchlings being observed in the Veal Veng Crocodile Sanctuary on the Stung Knong River in Pursat Province, Cambodia, only the second time the species has been seen breeding in the wild in Cambodia in a decade. Ten hatchlings have been observed at the site, a large clutch for the species, which is classed as Critically Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species.

 A hatchling Siamese Crocodiles, Crocodylus siamensis, in the Veal Veng Crocodile Sanctuary in Cambodia this year. Southeast Asia Globe.

Once found across Southeast Asia, Borneo, Java and Sumatra, the species is now thought to be extinct in Malaysia, Singapore, and Brunei, with about 250 adult Crocodiles in the wild in Cambodia, about 100 in Vietnam, and an unknown number in Laos. There are also small surviving populations in East Kalimantan (Indonesian Borneo), and possibly Thailand and Java. There are also successful captive-breeding programs in several places, which gives some hope for the survival of the species, though as the greatest threat to the wild populations is considered to be habitat loss, it is unclear if it will ever be possible to release captive-bred Siamese Crocodiles into the wild.

A captive-bred Siamese Crocodile at the Phnom Tamao Wildlife Rescue Centre in Cambodia. Southeast Asia Globe.

Siamese Crocodiles are not considered a threat to Humans, reaching a maximum size of about 4 m and feeding largely on Frogs, small Snakes, and similar prey. There are only four confirmed attacks on Humans by the species, all non-fatal, and in two of these cases the animal was defending itself, while in third it was defending its young. A fatal attack on a child by a Siamese Crocodile in Thailand in 1928 may have been made by a Siamese Crocodile, but this is uncertain. Siamese Crocodiles have historically been hunted extensively, both for their skins and for captive breeding in farms (again for their skins), but today the largest threat to their survival in the wild is considered to be habitat loss, largely to deforestation which changes the nature of the environment around the rivers the species inhabits. The Siamese Crocodiles are also still threatened by poaching.

See also... Crocodiles found dead in ghost net in Queensland.
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Tuesday, 18 February 2020

Fireball meteor over Arizona.

The American Meteor Society has received reports of a bright fireball meteor being seen over Arizona, slightly before 7.20 am local time (slightly after 2.20 pm GMT) on Sunday 16 February 2020. The meteor passed over the central part of the state from west to east. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but may be the result of man-made space-junk burning up on re-entry. It is thought that some material from the meteor may have fallen to Earth in the area south of Prescott.

Heat map of the southwest United States showing areas where sightings of the meteor were reported (warmer colours indicate more sightings), and the apparent path of the object (blue arrow). American Meteor Society.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).
These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.
Witness reports can help astronomers to understand these events. If you witness a fireball-type meteor over the US you can report it to the American Meteor Society here
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Searching for suspended and Salp-ingested microplastic debris in the North Pacific, using epifluorescence microscopy.

Marine debris is a worldwide ocean pollution problem, with plastics found in virtually all aquatic environments. The majority of marine debris analyzed to date has been microplastic, plastic particles less than 5 mm in size. However, findings suggest even smaller plastics (less than 333 μm) are both under-sampled due to the inappropriate mesh size of common sampling nets and far more numerous because plastic particles physically degrade over time into progressively smaller pieces. Such small debris can be consumed by, and deleterious to, suspension-feeding marine organisms, including Salps. Salps are pelagic Tunicates that possess the highest per-individual filtration rates among marine zooplankton, ingesting particles from under 1.0 μm to about 1.0 mm in size. They primarily feed in the upper water column, where microplastics are abundant. Once plastics are ingested by zooplankton, they have the potential to bioaccumulate in the food web into larger organisms, along with adsorbed persistent organic pollutants and harmful chemical additives, with unknown physiological consequences.

In a paper published in the journal Limnology and Oceanography Letters on 27 November 2019, Jennifer Brandon of the Scripps Institution of Oceanography at the University of California San Diego, Alexandra Freibott, also of the Scripps Institution of Oceanography, and of the Pacific Northwest Research Station of the United States Forest Service, and Linsey Sala, again of the Scripps Institution of Oceanography, present the results of a study which aimed to isolate, identify, and quantify microplastics 5–333 μm in size, a subgroup of microplastics which they termed mini-microplastics, from surface seawater samples and salp specimens collected from the North Pacific.

Although many zooplankton species consume microplasticc in a laboratory setting, the ecologically significant question lies in whether they are ingesting such particles in situ. Although the measured abundance of surface seawater microplastics is high, it is 1–3 orders of magnitude below model predictions of plastic inputs. In 2014 a considerable influx of both salp tunics and fecal pellets to about 4000 m depth following a bloom of Salpa spp. in the northeast Pacific. Thus, Salps could be a key link explaining the discrepancy between modeled and measured abundances of buoyant plastics, because fast sinking Salp fecal pellets and carcasses may be a vector moving ingested surface microplastics to the deep sea.

A Salp (plural Salps) is a barrel-shaped, planktic Tunicate. It moves by contracting, thus pumping water through its gelatinous body, one of the most efficient examples of jet propulsion in the Animal Kingdom. The Salp strains the pumped water through its internal feeding filters, feeding on phytoplankton. Wikipedia/Oregon Department of Fish and Wildlife.

Isolating, identifying, and quantifying microplastics 5–333 μm in size is a difficult task in the ocean due to their small size and irregularity. Brandon et al. took advantage of the well-documented autofluorescence of many plastics, and modified an epifluorescence microscopy approach normally used to enumerate planktonic microorganisms, to quantify oceanic mini-microplastics in surface seawater and Salp gut contents. Specifically, they asked: What are the distribution and abundances of these mini-microplastics in surface seawater? Are Salps ingesting mini-microplastics in situ? And, does the size distribution of ingested particles reflect that of available plastic particles?

Surface seawater samples and salp specimens used in this analysis came from the following cruises: SEAPLEX (02–21 August 2009), R/V Falkor (21–30 October 2013), SKrillEx I (26–31 July 2014), and SKrillEx II (11–17 June 2015). Surface seawater samples (1–2 m) were collected in metal buckets, immediately filtered onto 5 μm pore polycarbonate filters, and frozen. Brandon et al. sorted Salps from sodium borate-buffered 1.8% formaldehyde preserved plankton samples. These were collected via a 202 μm mesh bongo net at a tow depth of approximately 200 m or a surface-dwelling 333 μm mesh manta net. They tested for airborne plastic contamination during sample collection on a separate cruise in January 2017 by separately filtering both surface seawater samples and ultra-filtered Milli-Q water.

Maps of sampling locations, for testing of microplastics both in surface seawater and in Salp gut contents via epifluorescence microscopy. Surface seawater samples were taken via bucket tow in the open ocean (A) on the R/V Falkor (yellow, California Current; purple, transition region; mint green, North Pacific Subtropical Gyre; grey, SKrillEx sites), in 2013 and the nearshore (B) on SKrillEx I in July 2014 (blue) and SKrillEx II (green) in June 2015. Salp samples were taken via manta tow in the open ocean (A), on SEAPLEX (red), in August 2009, and in the nearshore environment (C), on SKrillEx I in July 2014. In (C) the bright green dots indicate stations with 10 Salps present, dark green indicate less than ten Salps present, and grey indicate no Salps in the sample. Brandon et al. (2019).

Brandon et al. sorted, measured, and identified Salp species and life history stage from preserved specimens from each sampling location, located in three open ocean regions: North Pacific Subtropical Gyre, California Current, the transition region, and a nearshore region. Life history stage was designated as blastozooid, the sexual chain-forming generation, or oozooid, the asexual solitary generation. Salp guts were dissected; however, any existing mucous nets and gill bars were not analyzed to avoid artifacts of net feeding.

Traditional epifluorescence microscopy techniques add fluorochromes to stain the DNA and proteins of plankton so that identifying features appear under different reflected wavelengths of light. Because Brandon et al.'s target was identification of plastics, not living organisms, they did not add any fluorochromes. Brandon et al. left prepared slides at room temperature for at least 24 hours to diminish chlorophyll a autofluorescence of plankton before visualization. This ensured the most fluorescent particles on microscopy images were likely microplastics, bacteria, or transparent exopolymeric particles. Brandon et al.tested multiple plastic and nonplastic reference materials, such as cotton and wool, under the four light excitation channels of our microscope to determine their autofluorescence. Filtered surface seawater samples and Salp gut contents were prepared for microscopy using an all-glass filtration apparatus.

Brandon et al. created a decision tree to determine if a particle was plastic. Generally, plastics appeared as long, thin fibers or flat fragments with sharp edges. Plastic particles fluoresced uniformly and did not have inner striations, coloration patterns, or features suggestive of biological particles, such as spines, nuclei, or organelles. Not all plastics fluoresce, so this was not used as a diagnostic feature Particles that were invisible under transmitted light but fluoresced under another light channel were determined to be transparent exopolymeric particles. Particles identified as likely diatom frustules, including chain-formers and pennates like Pseudo-nitzschia, were not counted as plastics. When in doubt, particles were not counted as plastic, so Brandon et al.'s estimates are conservative and most likely underestimate total mini-microplastic abundance.

Decision tree for enumerating plastic microdebris on slides, used to determine which particles were plastic and which were biota or other detritus. Brandon et al. (2019).

Particles were categorized as short or long fibers and fragments. The lengths, widths, areas, and fluorescence were recorded for every fragment and short fiber (under 300 μm) in automated images. Long fibers (at least 300 μm) were enumerated in separate, manual visual transects at lesser magnification to eliminate the possibility of double-counting single large fibers that were not visualized in their totality in automated images. Fibers under 200 μm in length were not counted in manual transects; however, there may be some overlap between the short fibers counted in automated images and long fibers counted in manual transects, due to the 200–300 μm overlap. Brandon et al. recorded long fiber color, length, and width with an ocular micrometer.

Brandon et al. analyzed plastic particles in filtered salp gut contents via epifluorescence microscopy. Because Salp gut walls and ingested biogenic material can fluoresce, fluorescence was considered a secondary characteristic of ingested plastic over particle shape and reflectivity under transmitted light. However, fluorescence was checked to visualize inner striations or patterns characteristic of diatom chains. When in doubt, particles were not counted as plastic. The thick gut walls of Salps and ingested biogenic material most likely occluded some plastic, so our data underestimate total plastic ingestion.

To calculate salp ingestion rates of plastic, mini-microplastic counts were divided by gut clearance times for each species identified, which ranged from 2.5 to 6.25 hours.

Brandon et al. found different patterns of fluorescence between plastic and biological materials, and when in doubt, particles were not counted as plastic. Using a controlled test, they determined that the vast majority of mini-microplastic materials in these filtered seawater samples were not from contamination during processing.

Transmitted light and epifluorescence images of microplastics from surface seawater, including a plastic fragment (A), thick and thin short plastic fibers (B), a long fiber and transparent exopolymer particles (C). Column (1) transmitted light; Column (2) Excitation 450-490 nm, Emission greater than 515 nm; Column (3) Excitation 340-380 nm, Emission 435-485 nm; Column (4) Excitation 465-495 nm, Emission 635-685 nm. Brandon et al. (2019).

Brandon et al. detected no significant spatial heterogeneity in seawater plastic concentrations across the Falkor transect (at 12 h intervals) for three open ocean regions: North Pacific Subtropical Gyre, California Current, the transition region. Nearshore samples from SKrillEx I and II were collected at approximate 15 km intervals, and showed no significant spatial heterogeneity possibly due to small sample sizes. Mean open ocean mini-microplastic concentrations compared to nearshore demonstrated significant heterogeneity between regions. Nearshore mini-microplastic concentrations differed from all other regions

Open ocean mini-microplastic concentrations were on the order of 10-100 per litre for short fibers and fragments with lower long fiber concentrations (1-10 per litre). In contrast, the fluorescent long fibers were 3.5–6.5 times more abundant than mean concentrations of nearshore short fibers and fragments on SKrillEx I, and almost eight times more abundant on SKrillEx II.

Almost every open ocean fragment and short fiber was below 333 μm in length and would have been missed by previous studies using larger mesh nets. Long fibers were usually over 333 μm, but thin enough to easily slip through 333 μm mesh. The minimum lengths of fragments and short fibers were between 14 and 50 μm for all locations, approaching the 5-μm pore size of the filters. For long fibers, both surface area and length were significantly different among regions, with significantly shorter fibers in the transition region. Similarly, in the nearshore samples (SKrillEx I and II), every measured fragment and short fiber length was under 333 μm

Individual particle surface area ranged from 0.0 003 to 0.71 mm², compared to earleir studies using a 333 μm net, which detected particles 0.01–565 mm². These earlier studies found plastic particle lengths ranging from 0.34 to 65.7 mm, while Brandon et al found lengths from 0.01 to 16.27 mm (including long fibers). Ultimately, the most pronounced difference between Brandon et al.'s findings and those of earlier studies was not the size range of particles, but rather their concentrations. Mini-microplastics in this study were five orders of magnitude more abundant than the over 333 μm microplastics of earlier studies. However, when concentration was multiplied by surface area Brandon et al. found that the over 333 μm microplastics had significantly higher areal concentrations than the under 333 μm mini-microplastics.

Salps have a very interesting life cycle, known as alternation of generations.  Salps have two different life stages: a solitary asexual stage and a colonial sexual stage.  The solitary stage of Salps (also referred to as the oozooid stage) has a special structure called a stolon.  This stolon develops into chains of the colonial stage.  When a chain of the aggregate stage has grown large enough within the solitary organism the chain will be released.  The chain is the sexual stage of the Salp (also referred to as the blastozooid stage).  In many species, the colonial stage (chain) looks very different from the solitary stage, and in fact when scientists first discovered Salps they often thought that the colonial and solitary stages of the same species were actually different species.  Chains of the colonial stage can extend for several meters in the water, and include hundreds of individuals.  The chains start off as females, and are fertilized by the sperm from older chains.  Once the eggs within a chain are fertilized, an embryo (of the solitary stage) will grow within each individual of the colonial stage.  The colonial stage will then give live birth to the solitary (asexual) stage so that the process can repeat itself.  As the chains matures it will switch from a female to a male. FSU Zooplankton Ecology and Biogeochemistry Lab.

Every single Salp gut analyzed contained plastic. Blastozooids had higher ingestion rates than oozooids. In general, nearshore Salps were larger than open ocean Salps  The California Current Salps were the smallest and had the lowest plastic ingestion rates. Excepting the North Pacific Subtropical Gyre and transition region oozooids, there was no detectable relationship between body length and plastic ingestion rate for dissected Salps. Although Brandon et al found regional differences in mini-microplastic concentrations in the water column, there was no significant effect of region on Salp plastic ingestion rate. Fibers made up 91% of the total ingested particles. The surface area and lengths of fibers and fragments differed significantly between most regions.

Brandon et al. compared the size of ingested mini-microplastics with that of ambient mini-microplastics in surface seawater, both from their data and from earlier studies Most of the net-collected particles from earlier studies fell within the size range of potential Salp food particles. At all sample locations, the average size of particles consumed by Salps was significantly smaller than the size of ambient seawater plastic.

Brandon et al. successfully used epifluorescence microscopy to identify mini-microplastic particles in natural seawater samples and Salp gut contents. This method required careful judgment and expertise to distinguish biotic from plastic materials. Furthermore, autofluorescence of Salp gut walls and biogenic materials made ingested plastic fluorescence only a secondary identification characteristic. This method allowed us to distinguish plastic from nonplastic particles and fluorescent from nonfluorescent plastic, but not to identify specific plastic types. Isolating plastic-type autofluorescence patterns under specific emission wavelengths may permit such differentiation in future work. However, our ultimate goal was to use standard epifluorescence microscopy techniques to differentiate plastics from nonplastic particles in order to obtain accurate bulk measurements of plastics under 333 μm, which the method accomplished.

This study may be one of the first to estimate the abundance of the smallest mini-microplastics in surface seawater, which are consistently under-sampled. Brandon et al. found a mean plastic concentration across all locations of 8277 particles per litre (8 277 000 particles per m³). Their particle concentrations averaged 5–7 orders ofmagnitude higher than previous studies. This highlights the previously unquantified significance ofmini-microplastics inmarine debris counts.

Nearshore samples had higher plastic concentrations than open ocean samples. This agrees with published findings that have recorded similar spikes in plastic concentrations nearshore, close to populated areas, with a decline in plastic moving offshore. The difference in plastic concentrations between SKrillEx I and II may be explained by annual differences in rainfall and watershed input to these nearshore waters.

Many estimates of macro- and microdebris, including modeled debris trajectories agree that the highest concentrations of open ocean marine debris occur in convergence zones of subtropical gyres. However, Brandon et al. did not detect a significant increase in mini-microplastic concentration in the North Pacific Subtropical Gyre and their open ocean samples were not significantly different across regions. Many possible sinks of mini-microplastics could account for this. Plastic below 5 μm in size presumably degrade beyond the detection limit of Brandon et al.'s method. Plastics can also be biofouled and sink out of surface water, or ingested and removed from the water. As plastic accumulates in the North Pacific Subtropical Gyre and breaks down into progressively smaller pieces, Brandon et al.'s data suggest that plastic under 333 μm is removed from the gyre through biofouling, ingestion, or degradation at the same rate it is being supplied. In the nearshore zone, however, mini-microplastics, especially long fibers (in the 200 μm–17 mm range), likely have a higher rate of input than loss. All of these sources and sinks require further research to be better parameterized.

Earlier studies sampled almost no particles smaller than 0.333 mm × 0.333 mm (0.11 mm²), due to the mesh size of the sample collection net, while Brandon et al. detected many particles below that limit (minimum size 0.000 3 mm²). Their results show the majority of plastic concentrations occur between under 333 μm and 0.11 mm². Although the mini-microplastics they measured were more numerically abundant, they did not comprise the majority of the plastic surface area in the water. Organisms that colonize surface substrates in the ocean are more likely to find surface area on micro- and macroplastics rather than mini-microplastics, despite the numerical abundance of mini-microplastics.

This is the first record of Salp ingestion of microplastic in situ. Every Salp dissected had plastic in its gut, regardless of species, life history stage, or region of the ocean sampled. Salp gut clearance times are on the order of 2–7 hours, so Brandon et al. are confident that by only analyzing the gut, they avoided artifacts of net feeding or other contamination. Airborne contamination is a major concern in modern microplastic work, especially when samples are dominated by fibers, as in this study (91% of the Salp-ingested particles). However, our processes of seawater filtration, slide preparation, and salp dissection limited contamination. Compared to filtered control samples, most of the plastics in Brandon et al.'s surface seawater samples were not contamination.

Brandon et al. detected no regional differences in plastic ingestion by Salps, excluding the much lower values of the California Current Salps. This finding is likely attributable to the very small body size of those salps. The California Current Salps had the lowest ingestion rate of any region, whereas for surface seawater, concentrations of mini-microplastics in the nearshore environment were significantly higher than the entire open ocean. Overall, however, both Salp ingestion and surface seawater plastic concentrations had limited regional differences.

Salps are predominantly generalist suspension feeders with ingestion based primarily on particle size, typically from less than 1 μm to 1 mm. All seawater mini-microplastic measured, and almost all the plastic in earlier studies, fall within their possible ingestion range. Yet, the Salps sampled by Brandon et al. ate significantly smaller pieces of plastic than were available in the ambient surface water. This may be explained by the fact that Salps can efficiently collect down to submicron particles and feed throughout a greater area of the water column than the surface, where larger,more buoyant plastic is retained.

Salps are of ecological importance due to several factors: their notoriously rapid growth and opportunistic reproductive rates that can lead to extremely high population densities or 'blooms', higher filtration rates per individual than any other zooplankton grazer, and production of dense fecal pellets that can result in high vertical fluxes of this material to deeper depths. The large fecal pellets of Salps have proven to possess rapid sinking and slow decomposition rates such that they can reach the deep ocean relatively intact, transporting organic carbon and potential microplastics with them. Brandon et al.'s evidence for the widespread and universal consumption of microplastics by Salps leads Brandon et al. to believe that Salps may be an important vector of marine debris transport from the surface ocean to deep-sea communities. The transport of microplastics via Salps may be critical to incorporate into microplastic export calculations as an overlooked output from surface waters.

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