WR Buoyancy, Colour and Micro plastics Flashcards
Use of colour - mimicry and colour change
Intro
LECTURE 21 - USE OF COLOUR
Mimicry & colour-change to enhance effectiveness
→ Cortesi F., Musilova Z., Stieb S.M., Hart N.S., Siebeck U.E., Cheney K.L., Salzburger W., Marshall J. (2016) From crypsis to mimicry: changes in colour and the configuration of the visual system during ontogenetic habitat transitions in a coral reef fish. Journal of Experimental Biology, 219: 2545—2558,
[Cortesi et al., 2016]
Introduction
- Dusky dottybacks (Pseudochromis fuscus) are native to the south-western Pacific & eastern Indian Ocean -> they are enigmatic mimics that can imitate differently coloured model species in its surroundings
- study conducted at Lizard and Heron Island, Great Barrier Reef, Austrailia (March 2007-November 2013)
LECTURE 21 - USE OF COLOUR
Mimicry & colour-change to enhance effectiveness
→ Cortesi F., Musilova Z., Stieb S.M., Hart N.S., Siebeck U.E., Cheney K.L., Salzburger W., Marshall J. (2016) From crypsis to mimicry: changes in colour and the configuration of the visual system during ontogenetic habitat transitions in a coral reef fish. Journal of Experimental Biology, 219: 2545—2558,
[Cortesi et al., 2016]
Study
Study
- multidisciplinary approach: developmental time series to study the ontogenetic change in colouration AND spectral absorbance
- adults and juveniles were collected by hand from shallow reefs (2-5m) using an aesthetic clove oil solution (10% clove oil, 40% ethanol, 50% seawater), also collection at night using light traps during the summer recruitment pulses
- juveniles and adults were differentiated by their colouration by eye, then their categorisation was reviewed based on the shape of their spectral reflectance curves (reduce subjectivity of categorisation)
- larval holding tanks: seawater directly from the ocean, tanks were in daylight with 1cm of sand substrate at the bottom of each tank with a live coral colony (= reef mesocosm)
- single larval dottybacks in holding tanks with either yellow or brown juvenile damselfish (adult dottybacks are known to change their body colouration to imitate yellow or brown damselfish) – four replicates per colour with five individuals in each
- used MSP to measure the spectral absorbance of different photoreceptor types in the retina of larval and adult dottybacks & coral trout, analysed raw absorbance spectra and used to make theoretical fish visual models
- models were used to determine:
- > whether an adult expression profile would change the ability of dottybacks to discriminate between damselfishes compared with a juvenile expression profile
- > perception of adult and juvenile dottybacks by predatory coral trout
LECTURE 21 - USE OF COLOUR
Mimicry & colour-change to enhance effectiveness
→ Cortesi F., Musilova Z., Stieb S.M., Hart N.S., Siebeck U.E., Cheney K.L., Salzburger W., Marshall J. (2016) From crypsis to mimicry: changes in colour and the configuration of the visual system during ontogenetic habitat transitions in a coral reef fish. Journal of Experimental Biology, 219: 2545—2558,
[Cortesi et al., 2016]
Findings
- Findings
- Dottybacks have an ontogenetic shift in colour pattern after their pelagic larval stage
- two major ontogenetic habitat shifts that were associated with developmental modifications -> start as translucent larvae = well camouflaged within open water then become pigmented that appears cryptic to background to predators
- mimic colouration of damselfishes to gain fitness benefits in terms of deceiving and capturing prey as well as cryptic benefits
- pelagic larval stage = translucent & only have a few pigmented chromatophore cells (dorsal axis and cranial plate)
- 2-3 days post-settlement (dps) = pigments rapidly start to form & disperse over the whole body
- 7-9 dps = overall grey to light-brown colouration & this colour is maintained until they change to either dark brown or yellow colour morphs as adults with feeding and habitat specialisations
- 34 dps (end of developmental time series) juveniles possessed a mixture of melanophores, erythrophores and xanthophores (the latter two first accumulate along the dorsal axis) BUT erythrophores were absent in the skin of larger juveniles and adult dottybacks & instead found ‘mosaic’ cells (<1% of overall chromatophores) – can change their pigment content
- in concordance with their change in colour pattern, these fish also undergo major morphological changes when the fish metamorphose into their juvenile phenotypes
- > early stage = pure cone retina & sensitive to shorter wavelengths (ideal for well-lit epipelagic environment)
- > later life stages & movement down the water column is accompanied by a fully-developed retina with all photoreceptor types (single cones, twin cones & rods) that are present in all sampled adults w/ 3 longer-wavelength cone opsins which theoretically allow settlement-stage fish with the ability to see colours needed for survival on the reef
- > this change in visual system from juveniles to adults was found to occur when the fish reached ~25mm – before the juvenile to adult colour change (~43 mm)
- visual models showed that adult dottybacks have an increased ability to distinguish between colourations of their model (damselfish) compared to juveniles – this colour discrimination may be important to determine between the fish they’re going to mimic which gives an explanation for why juvenile dottybacks switch their visual system before the ontogenetic colour change occurs
LECTURE 21 - USE OF COLOUR
Mimicry & colour-change to enhance effectiveness
→ Cortesi F., Musilova Z., Stieb S.M., Hart N.S., Siebeck U.E., Cheney K.L., Salzburger W., Marshall J. (2016) From crypsis to mimicry: changes in colour and the configuration of the visual system during ontogenetic habitat transitions in a coral reef fish. Journal of Experimental Biology, 219: 2545—2558,
[Cortesi et al., 2016]
Critical analysis
Critical analysis
- difficult to determine between chromatophore types and pigments contents
Use of colour - accuracy of deception
Intro
→ Cheney K.L. and Marshall J. (2009) Mimicry in coral reef fish: how accurate is this deception in terms of colour and luminance? Behavioural Ecology 20, 459—468
Intro
- batesian and aggressive mimics are formed under a selection pressure to resemble their models, but signal receivers are under pressure to be able to discriminate between mimics and models
Mimicry – accuracy of deception
→ Cheney K.L. and Marshall J. (2009) Mimicry in coral reef fish: how accurate is this deception in terms of colour and luminance? Behavioural Ecology 20, 459—468
Study
Study
- investigated the potential ability of fish with various visual systems to discriminate between model and mimic colours using theoretical vision models
- examined 15 model-mimic coral reef fish pairs (collected from the same locality)
> not always able to collect more than one pair (model-mimic) due to rarity of some species
- 10 = aggressive mimics 4 = batesian 1 = aggressive, batesian
- collected by divers (2005-2007) from 2-18m from southeast Indonesia & Lizard and Heron Island, GBR, used hand and barrier nets
- fish were housed in tanks with running seawater for 1-3 days until their spectral reflectance could be measured, then fish were released to their point of capture
- spectral reflectance measurements were obtained using an Ocean Optics -> fish were taken out of water for a short amount of time and skin was kept moist during measurements which produces results similar to measuring fish in water & allows a more accurate colour quantification
- spectral reflectance measurements were taken within each coloured body match > 4mm2 & considered the effects of signal transmission through water to be negligible as most coral reef fish would view models and mimics from a relatively close distance (ca. 1—2m)
- all fish that were measured had been screened with a UV camera, which ensured that coloured areas were not ignored & took averages from at least 10 samples of each coloured area of the fish taken in rapid succession
- also measured illumination underwater using a spectrometer from 1—2m from reed and pointing horizontally at the reef = more accurate estimate of light striking the side of a fish than vertical hemispherical irradiance which is often used
- assessed the discriminatory ability of signal receivers to distinguish between mimic and model spectral reflectance (mimic—model) & mimic similarity to other non-model coral fish (mimic—general fish) with the same colour patches from the same location -> used spectral reflectance data of fish species that had previously been measured with a spectrophotometer with the same methodology
Mimicry – accuracy of deception
→ Cheney K.L. and Marshall J. (2009) Mimicry in coral reef fish: how accurate is this deception in terms of colour and luminance? Behavioural Ecology 20, 459—468
Findings
Findings
- majority of mimics closely resembled models in terms of colour and luminance from a non-subjective perspective
BUT fish with trichromatic visual systems (3 distinct cone photoreceptors) with ultraviolet sensitivity had a better capacity to discriminate between models and mimics compared to fish with dichromatic visual systems (poorest discriminative ability)
- the spectral reflectance of colour patches reflected by models and mimics became more similar with increasing depth, which indicates that signal receivers are more likely to distinguish mimics in habitats in shallower depths … the selection pressure on mimics to resemble their model is dependent on the visual system of the receiver & the light environment
- the spectral reflectance of colour patches on coral reef fish mimics were qualitatively similar to their models for the majority of model—mimic pairs
- mimics resembled the colours of their models more accurately than the general fish from the same habitat but the ability of receivers to discriminate between models and mimics varied depending on their visual system
- fish with sensitivity in the UV region (e.g. Abudefduf abdominalis) had a greater capacity to discriminate between mimics and models based on colour signals, compared to trichromat or dichromat species
- as depth increased, model and mimic colours became more similar … mimics may resemble their models more closely in deeper habitats
- there was no significant trend for the difference in luminance between model and mimic signals to increase or decrease with depth, therefore mimics appear to accurately resemble their models at all depths (in terms of luminescence)
Mimicry – accuracy of deception
→ Cheney K.L. and Marshall J. (2009) Mimicry in coral reef fish: how accurate is this deception in terms of colour and luminance? Behavioural Ecology 20, 459—468
Critical analysis
Critical analysis
+ they considered how the fish is perceived by the signal receiver, rather than just human perspective
+ release of fish to their capture site
- the threshold at which 2 colours become distinguishable for fish remains to be tested
Lecture 22: Plastics & POPs
Deep-sea amphipods
Study
Lecture 22: Plastics & POPs
Microplastics and synthetic particles ingested by deep-sea amphipods in six of the deepest marine ecosystems on earth.
(Jamieson et al, 2019)
Study:
Collected amphipods (Lysianassoidea) at hadal depths (7000 m to 10 890 m) in six of the deep ocean trenches around the Pacific Rim (Japan, Izu-Bonin, Mariana, Kermadec, New Hebrides and the Peru-Chile trenches), and sampled the hindguts for plastic.
Lecture 22: Plastics & POPs
Deep-sea amphipods
Findings
Findings:
- Detected the presence of ingested microplastics in the hindguts of Lysianassoidea amphipods populations (one of the most important and dominant scavenging fauna in the deep sea at a similar frequency (72%) to crustaceans in coastal water habitats.
- Over 72% of individuals examined (65 of 90) contained at least one microparticle.
- Fibres were more common than fragments (84% and 16% of amphipods).
- A total of 122 ingested microparticles were identified.
- The study concludes that there are likely to be no marine ecosystems left without plastic pollution.
Lecture 22: Plastics & POPs
Deep-sea amphipods
Possible critical anaysis
Possible critical analysis:
- Usual deep-sea sampling problems
- Total sample size of 90 individuals split between different species – few repeats.
- Funnel traps were used which may catch the courageous, courageous amphipods may be more likely to consume plastic fibres.
Indian Ocean = 555 debris items per km2 (Woodall et al., 2015)
Galgani F., Hanke G. and Maes T. (2015) Global distribution, composition and abundance of marine litter. In: Bergmann M., Gutow L., Klages M (eds), Marine Anthropogenic Litter (pp. 29—56) Springer.
[Galgani et al., 2015]
- “plastic bags, fishing equipment, food and beverage containers are the most common items and constitute more than 80% of litter stranded on beaches”
- “plastics typically constitute the most important part of marine litter” – consistent with LtO findings
- -> “plastic, the main component of litter, has become ubiquitous and forms sometimes up to 95% of the waste that accumulates on shorelines, the sea surface and the seafloor”
- “humans generate considerable amounts of waste and global quantities are continuously increasing, although waste production varies between countries”
- “plastic bags, fishing equipment, food and beverage containers are the most common items and constitute more than 80% of litter stranded on beaches”
- “accumulation rates vary widely and are influenced by many factors such as the presence of large cities, shore use, hydrodynamics, and maritime activities”
- “analysis of the composition of marine litter is important as it provides vital information on individual litter items, which, in most cases, can be traced back to their sources”
- Classifying marine litter -> land-based or ocean-based (where the litter entered the sea) = important for developing reduction methods
- land-based sources = “recreational use of the coast”, litter, industrial waste, landfills/dump sites,
- ocean-based sources = commercial shipping, commercial & recreational fishing vessels, pleasure boats, offshore installations, e.g. aquaculture, rigs, etc
- “factors such as ocean current patters, climate and tides, the proximity to urban, industrial and recreational areas, shipping lanes and fishing grounds also influence the types and amount of litter that are found in the open ocean or along beaches”
- Plastics: “some take hundreds of years to break down or may never truly degrade”
- “marine debris is commonly found at the sea surface or washed up on shorelines”
- Marine litter on beaches = “has become a permanent reason for concern”
- “past studies may have vastly underestimated the quantity of available debris because sampling was too infrequent”
- “factors influencing the accumulation of debris in coastal areas include the shape of the beach, location and the nature of debris”
- “most sediment-surface counts do not take buried litter into account and clearly underestimate abundance, which biases composition studies”
- BUT “raking of beach sediments for litter may disturb the resident fauna”
- “most sediment-surface counts do not take buried litter into account and clearly underestimate abundance, which biases composition studies”
- “similar to large debris, there is growing concern about the implications of the diverse microparticles in the marine environment” = ≤1 μm
Read through the rest of microplastics
Buoyancy - Buoyancy of gas-filled bladders at great depth.
The study -
(Priede, 2018) Buoyancy of gas-filled bladders at great depth.
• The weight of compressed gases at great depths limits the buoyancy gas bladder systems can provide
- At high hydrostatic pressures (excceding 20 MPa, equivalent to deoth exceeding ca.2000m) the behaviour of gases deviates significantly from the predictions of standard equations (such as Byloe’s Law, the Ideal Gas Law and Van der Waals equation).
• Gas-filled swim bladders or air bags can provide buoyancy at full depth
- Owing to reduced compressibility of gases at high pressures, gas-filled bladders at full ocean depth provide potentially useful buoyancy comparable with that available from man-made materials.
• This explains why some of the deepest living fishes have gas-filled swim bladders (ca. 7000m depth)
Buoyancy - Buoyancy of gas-filled bladders at great depth.
The results
Results:
- Temperature has a significant effect; as expected, density is lower at 15°C than at 0°C
- The buoyancy obtained depends on the density of the surrounding seawater which is itself influenced by salinity, temperature and pressure
- The salinity of oceanic deep water is generally ~35%, higher salinities occur in Mediterranean Sea, ~39% in deep eastern basins
- This results in a 0.5-0.7% increase in buoyancy at the maximum depth of ca. 5000m in Mediterranean Sea
- Compression of seawater at high pressures at great depths has a larger effect on buoyancy
Lecture 17. Buoyancy
(Priede, 2018) Buoyancy of gas-filled bladders at great depth.
Discussion:
- Results confirm that gas-filled bladders can provide positive buoyancy over the full range of ocean depths
- Even the heaviest of the gases, oxygen has a lower density than squalene oil (commonly found accumulated by sharks in their livers as buoyancy material)
- There are fish species that live a depths of 5000-7000m that do use swim bladders, and in this depth range the density of gases are significantly lower than any other buoyancy materials available to fishes such as fats, oils and dilute watery body fluids.
- In the deep sea, fishes swim bladders are predominantly filled with oxygen gas
