Wider Reading

Question 1

Hypoxia influences on biofouling

Answer 1

Hypoxia induces abnormal larval development and affects biofilm–larval interaction in the serpulid polychaete Hydroides elegans

Shin et al 2013-

• Investigated how hypoxia effects development and settlement of H. elegans larvae.
• Recruitment rates of H. elegans is reduced when hypoxia levels increase.
• There was a higher proportion of deformed larvae when oxygen levels were at 1mg/l due to a reduction In clearance rate. Deformed larvae were characterized by a change in shape, unclear segmentation, or an enlarged hyposphere.
• Despite the type of biofilm (developed either under hypoxia or normoxia conditions) the larvae were given to settle on, the settlement rate was still reduced in hypoxic conditions. There was not one type of biofilm that enhanced settlement compared to another.
• Settlement rate was increased significantly after the resumption of DO (from 1mg/l to 6mg/l) after 24 hours. However, if the DO was kept at 1mg/l, the settlement rate was still incredibly low even after 48h.
• When the biofilm was developed under hypoxic conditions, only 5% of the larvae would settle on it.
• The effect that hypoxia has on the development of larvae, and how it affects the biofilm formation explains why recruitment of H. elegans declines in the summer.
• Under hypoxic conditions, larvae use their energy to escape hypoxic stress. The action of ciliary movement uses less energy than digestion, food assimilation and growth, so these processes are put on hold.
• When oxygen becomes more readily available, they resume growing and feeding.

Question 2

Innovative approaches for the development of new copper-free marine antifouling paints.
Facts – the importance of innovative appraches

Answer 2

Trepos et al 2014- Innovative approaches for the development of new copper-free marine antifouling paints.

Facts – the importance of innovative approaches

• Marine biofouling = “undesirable adhesion to surfaces and further growth of organisms, mainly biofilm-forming microbes, macro-algae and invertebrates that are defined as foulers”
• International Maritime Organization = world trading fleet is responsible for 90% of global trade.
• Fuel consumption in 2007 = approx. 370 million tonnes.
• Antifouling protection could save governments and companies $150billion per year and prevent about 450 million tons of CO2 from being emitted.
• Biofouling can be the main cause of gain in weight of static structures in aquaculture and can often lead to mechanical failure.
• TBT was widely used until around 2008 when it was banned due to its detrimental effects on marine life. Due to this, modern AF paints rely on copper oxide which is soluble in seawater, as well as different organic booster biocides.
• In 2020 in Washington copper-based paints will be banned and owners will have to buy and apply paints that contain less than 0.5% copper.
• Biofouling also occurs on living organisms such as seaweed and shellfish which can affect aquaculture businesses. People have therefore started to look at biomimetic approaches, and copy the natural defences of organisms against fouling organisms to develop new paints and initiatives for use on vessels.
• Organisms are able to prevent biofouling by epibionts by producing secondary metabolites, which are not involved in life supporting systems, but are mostly involved in defence mechanisms.
• Compounds that have lead traces in are powerful antifoulants, but it can often be challenging to scale up these natural products for use in the coating market. There are four main ways this Is done:

1) natural products collected from the field.
2) natural products collected from cultured organisms.
3) culture recombinant microorganisms to synthesise the natural product.
4) produce the natural product through chemical synthesis.

Question 3

Innovative approaches for the development of new copper-free marine antifouling paints.

PAF

Answer 3

PAF

(trepos et al 2014)

• Platelet Activating Factor (PAF) is an natural example of research and development of antifouling products. PAF is found in sponges and is a bioactive glycerophospholipid. A similar compound was synthesised which was structurally similar to PAF, and was proven to be more effective against marine bacteria than the paint which contained a commercial halogenated biocide called ECONEA.

Question 4

Innovative approaches for the development of new copper-free marine antifouling paints.

Texture

Answer 4

Trepos et al 2014

Texture

Alternatively, another solution is to exploit the physical defence mechanisms shown by marine organisms, and some studies have tried to copy the hostile surfaces such as shark teeth. One focus has been microtextured surfaces, but this has limitations, as the scale of the texture is effective against different types of organisms. E.G microtopographies (1 to≤1000μm) provide a more efficient antifoulant effect, but it does depend on the species in the fouling community. There is use of multi-scale textures which uses different sized waves and peaks in conjunction, which was successful against barnacle and mussel settlement. The only issue is the build-up of biofilm which could hide the original topographical features. Another concern is that these features cannot be too textured as they will contribute towards drag.

Question 5

Innovative approaches for the development of new copper-free marine antifouling paints.

LEAF

Answer 5

Trepos et al 2014

LEAF

Its important to consider synergy. A study combined chemical and topographical methods to prevent fouling. This study took defence mechanisms from Sacccharina latissimi and Fucus guiryi and produced a natural product.

Low-Emission Antifouling Coatings- a New concept not based on biocide emission. Bring foulers to into contact with the coating without releasing loads into the surrounding medium. 0.1% of biocide Ivermectin was embedded into a soft coating and prevented adult barnacles from establishing themselves on the surface. This was not the case for harder coatings. Intoxication Is caused by the organism itself as it tries to settle on the surface.

LEAF had a 3 year testing period with stations in the UK, Sweden, Italy and Brazil, all places where the fouling communities and water differences. These tests finished at the end of December 2015 and a LEAF prototype paint was produced. This was tested on boats in European, Mediterranean and Caribbean waters and was successful. After 4/5 months of testing, 44.4% of the boat owners reported no slime on their boat. 97.1% reported no tube worms and 94.3% reported no barnacles.

Question 6

Bioinspiration

What is the paper about?

Answer 6

Ralston & Swain 2009- Bioinspiration- the solution for biofouling control?

What is the paper about?

• A review paper looking at natural antifouling methods and potential future bioinspired approached for prevention of hull fouling for the US Navy.
• Important to prevent fouling on ships as it increases running costs and can aid transportation of invasive species.
• Biomimicry looks at copying living organisms and their fouling prevention methods and using this on a commercial scale to prevent biofouling of ships hulls.
• Bioinspiration expands upon biomimicry, and attempts to improve on the natural biological concepts for a simple engineering solution against biofouling.
• The antifouling needs of the navy are challenging from that of normal commercial ships, as navy ships spend a lot of time in port.

Question 7

• Bioinspiration- the solution for biofouling control?

Natural chemical

Answer 7

Natural chemicals

Ralston & Swain 2009

• Natural chemicals against biofouling work by lowering the pH, acting as a deterrent or anaesthetic, or inhibiting attachment/metamorphosis.
• Red algae species Delisea pulchra prevents fouling by producing chemicals which are formed at the surface and interfere with cell signalling in bacteria and therefore prevent attachment of barnacles.
• Some barnacle larvae wont settle in the trail of a whelk (due to kairomones), and many fish and coral eggs are protected by antimicrobials.
• Some biofilms prevent settlement of macrofoulants due to the toxic nature of the microfoulers which make up the biofilm. Holmstrom et al 1992 found that 5/40 bacterial stains produced toxic chemicals which prevented attachment of barnacle and tunicate larvae.
• Natural paints often have a shorter life span which isn’t ideal. This is as they have shorter half lives than biocides which contain copper. Its also expensive to produce new chemicals. Additionally, there are lots of unknowns with the use of new natural chemicals (cost, durability, repairability, environmentally friendly).
• Surface energy can affect the initial colonisation of fouling organisms. This is specific to different species.

Question 8

Mechanical Cleaning

Answer 8

Ralston & Swain 2009

Mechanical cleaning

• Mechanical cleaning in organisms is often gentle and is described as grooming. This can occur using specialist appendages which physically remove epibionts, or through symbiotic relationships. For example, crayfish have a type of annelid in the gill chambers which feed on epibionts.
• In man made structures, cleaning is a very effective method to remove foulants when it is used in combination with a hard-durable coating. It is often the case that the apparatus used in cleaning may damage the coating and can release a large concentration of biocide into the environment.
• Another mechanical method is ecdysis, or moulting.
• Organisms use behavioural mechanisms to remove epibionts. This includes burrowing into the sediment dislodge foulants. Organisms with a high salinity tolerance can move between fresh and saltwater pools and remove epibionts which cannot tolerate these extreme changes. This can be used on smaller boats as actions such as moving them out of the water when they are not being used can prevent biofouling. These sorts of activities are not practical for large ships.A gentler method for cleaning the hull of navy ships has been developed called the HullBUG which is hull bioinspired underwater grooming. This is an autonomous underwater robot that slowly moves over the surface of the hull whilst the ship is in port, and gently brushes away at the surface, to prevent microfoulers from permanently attaching.
• Overall = combination of approaches is the most effective method to prevent biofouling.

Question 9

The bigger the better? Volume measurements of parasites and hosts: Parasitic barnacles (Cirripedia, Rhizocephala) and their decapod hosts

Answer 9

Nagler et al 2017- The bigger the better? Volume measurements of parasites and hosts: Parasitic barnacles (Cirripedia, Rhizocephala) and their decapod hosts

• Rhizocephala = castrate other crustaceans such as crabs.
• They are able to carry out castration by absorbing the entire reproductive system of their host.
• Even though these parasites are crustaceans, they lack a lot of the common morphology that crustaceans have. These parasites have a number of different structures, including the externa, interna, egg mass, egg number and visceral mass.
• Its important to understand the ratio of the host and parasite size to understand the energetic cost involved with absorbing a reproductive system.
• They measured the volume of the parasite and the host and found a positive correlation between the size of the parasite and the size of the host.
• Animals which have a high reproductive effort and are long lived are preferred host choice of parasites, as they can consume the reproductive system and live In the space it occupied. This is why a lot of decapods are targeted by parasites.
• This study looked at four species of Peltogaster which is a parasite on hermic crabs, and 5 specimens of Sylon hippolytes which is a parasite on shrimps. This study was one of the first to use micro-CT to quantify the size and volumes of the parasites.
• They measured different parts of anatomy, including surface model of the host, volume of the interna, volume and surface model of the externa, volume of an average egg and number of eggs.
• Concluded that the body size of the parasite in relation to the body size of the host can be used to differentiate different types of host-parasite interactions. Depending on species, castrators tend to occupy 3-50% of the volume of the host.
• Female caridean shrimps have a reproductive system which occupy 6.9-30% of their body mass, and in this study they found the volume of the parasite S. hippolytes to be 18.07% when it was infesting inside caridean shrimps.
• Conclude that the bigger the host, the bigger the rhizocephalan. This is known as Harrisons rule. This is driven by the reproductive effort of the host, as this space is what facilitates growth of the parasite.

Question 10

Effects on food availability on growth and reproduction of the deep-sea pedunculate barnacle Heteralepas canci

Answer 10

Yasuda et al 2015

Effects on food availability on growth and reproduction of the deep-sea pedunculate barnacle Heteralepas canci

• Investigated the effect of food availability on deep sea barnacle species H. canci collected from a depth of 229m of Cape Nomamisaki in S Japan.
• In the deep sea there is high fluctuations in food availability. Animals need to be able to adapt to these fluctuations and do so by exhibiting highly plastic life history traits. This study hypothesises that these organisms may grow rapidly when food is readily available, and then delay growth and reproduction when it is scarce. They also explore the idea of starvation tolerance.
• Collected 136 specimens which were all small. They were reared in the lab where they were randomly allocated one of three food levels: low, middle and high.
• Survival rate = many individuals died when food was high. After 100 days, 44.2% in the low food level survived, 26.1% in the middle level and 8.5% at the high food level.
• The survival rate within the first 73 days was influenced by the food level, and there was a significant difference between survival rate of middle (67.4%) and high (19.1%) food levels.
• Growth= initial mean capitulum length was 2.8±0.1mm (n=136). There were changes seen between the three food groups as early as 31 days. After 73 days, the low food group were 4.0±1.7mm, the middle was 4.7±0.15mm and the high were 5.9±0.29mm. There was a significant difference between the low and middle, and between the middle and high food levels.
• No significant difference in ovary development.
• One individual lived for 167 days without food before it died. Struggled to do this with a larger group of barnacles due to biofilm formation which was an indirect food source for the barnacles.

Question 11

• The influence of interspecific competition and other factors on the distribution of the barnacle Cthamalus Stellatus

Answer 11

Connell 1961- The influence of interspecific competition and other factors on the distribution of the barnacle Cthamalus Stellatus

• Study done in Millport.
• All Dogwhelks were removed from the area as they are predators.
• Found C. montagui was found on higher shores whereas S. balanoides was not present.
• S. balanoides physically overgrew C. montagui
• S. balanoides doesn’t always outcompete C. montagui, it depends on the area.
• Eg, south coast of Ireland its harder for the S. balanoides to outcompete C. montagui. The paper states that this is because C. montagui are thought to feed on the larvae of S. balanoides which are dispersed between March and April. However, in Millport the lower limits of zonation of C. montagui are set by interspecific competition for space. S. balanoides grow faster than C. montagui and so can take up more space. C. montagui can exist on the higher shore due to its evolutionary ability to withstand desiccation.

Question 12

Effect of biofilm on mussel settlement

Answer 12

Yang et al (2014)

looked at the effect of biofilm on the settlement of plantigrade larvae of mussel Mytilus coruscus. They investigated age-related characteristics, such as thickness, chlorophyll a conc and densities of bacteria. They used a control with no biofilm, then biofilm which increased in week increments from 7-28 days. In the control, only 10% of the plantigrades settled. The percentage of settled larvae increased with age of biofilm. The age of the biofilm significantly effected the thickness, and it increased with age. This highlights that natural biofilms promote the settlement of M. coruscus. Settlement was directly positively correlated to biofilm thickness.

Question 13

Biofouling species damages

Answer 13

E.G Forrest & Atalah (2017)

There is a persistent issue of biofouling of mussel Mytilus galloprovincialis on the green lipped mussel Perna canaliculus aquaculture plants in New Zealand. Some of the fouling is so bad (up to 99% cover) which has resulted in an average economic loss of $11.4 million per year.

Question 14

Bioilm

Answer 14

Romero-Lopez et al (2016)

formation of biofilms blocks reverse osmosis membranes, which decreases the permeability and reduces the rate at which water can be desalinated.

Question 15

UV

Answer 15

Zhang et al (2019)

explored the possibility of using long-wave UV photolysis to prevent biofilm formation on membranes in bioreactors, as it prevents quorum sensing from occurring. They found that continuous UV radiation significantly mitigated biofouling on the membrane (0.14mg/cm2) and was more effective than use of a quorum quenching bacteria Rhodococcus. Intermittent UV photolysis was less effective than continuous (0.24mg/cm2) but had a similar effect as using the bacteria. This UV photolysis works as its believed that it interferes with and inactivates signal molecules such as AHLs. This works in the presence of nitrates as the presence of reactive oxygen species generated from the presence of nitrate ions aid in destruction of signalling molecules.

• Long-wave UV quorum quenching (QQ) was explored for anti-biofouling possibility.

•

UV photolysis had fouling mitigation effects greater than QQ bacteria.

•

UV photolysis inhibited biofilm growth on the membrane surface.

•

Intermittent but proper UV dose was comparable to bacterial QQ in fouling control.

•

Nitrate-mediated UV photolysis was responsible for degrading signal molecules.

Question 16

biofouling on finfish aquaculture

Answer 16

Martell et al (2018)

looked at the successional biofouling of a finfish aquaculture facility caused by hydroids. They carried out two experiments each with 36 panels to test the colonisation and succession of the hydroids. The panels were placed at 3 depth intervals of 0.2, 3 and 6m depth. They were left for a year, but every 3 months a panel was brought out for analysis to test for succession. In the succession experiment they found a general increase in species richness (3 species after 3 months, 9 after 12), but there was considerable variation in the mean surface covered by fouling hydroids. They found 11 hydrozoan taxa on the fouling communities. The number of species increased as they have the ability to settle and grow on their competitors and capitalise on increased surface area generated by biofoulers such as mussels and sponges.

Question 17

Surface Exploration: Cyprid Temporary Adhesion

Answer 17

Biochemistry of Barnacle Adhesion: An Updated Review

(Liang et al 2019) Marine and molecular biology and ecology

Surface Exploration: Cyprid Temporary Adhesion
• The cyprid uses its attachment organ – the two attachment discs on the third segment of the paired antennules – to adhere to the substrate.
• Cyprid attachment discs are flat and covered by a carpet of cuticular villi (revealed with SEM). Among species, they vary markedly.
o During surface exploration, the two attachment discs attach and detach from the surface alternatively, allowing the cyprid to “walk” bipedally on the surface.
• Simultaneously, the cyprid is capable of precisely sensing the biochemical, physicochemical, and topological characteristics of the substrate using an array of antennular setae and chooses to either settle or leave.
• Adult barnacle pheromones present on the substrate can greatly promote surface colonization of conspecific cyprids, even when the clear substratum is not satisfactory.

Question 18

Biochemistry of Barnacle Adhesion: An Updated Review
Marine and molecular biology and ecology

Cyprid Temporary Adhesion

Answer 18

Cyprid Temporary Adhesion

(Liang et al 2019)

• Cyprid temporary adhesion exhibits three primary properties: tenacity, speed, and reversibility
o Regarding tenacity, cyprid adhesion strength varies between approximately 100–300 kPa on different substrates as measured by a microbalance.
o In terms of speed, it is estimated to take only several seconds to form a secure bond between cyprid adhesive disks and a substrate by measuring the time gap between two adjacent paces.
o As for reversibility, a cyprid can not only walk on the substrate by alternatively attaching each of its two adhesive disks, but also leave the substrate entirely by detaching both disks.
• After surface exploration, the residual footprints on the substrate are believed to be cyprid temporary adhesives which were first detected by Walker and Yule using a protein dye (Walker and Yule, 1984). Over two decades later, cyprid footprints deposited on various substrates were directly observed with atomic force microscopy (AFM) and imaging surface plasmon resonance, thus adding conclusive evidence to the idea that cyprids secrete adhesives for temporary adhesion.
• By using AFM-based force spectroscopy, Phang et al. (2008) detected the adhesion strength of cyprid footprints, which was only about 1/3 that of the measured adhesion strength of the cyprid.
o Accordingly, they speculated that the microvilli on cyprid attachment discs might play a similar physical adhesion role to that of fly pulvilli and gecko spatula to promote temporary cyprid adhesion when boundary water was displaced by temporary adhesives but, this requires further confirmation.
• By employing high-speed photography, Aldred et al. (2013b) discovered that cyprid temporary adhesion was also regulated by its behaviors.
o For example, during rapid walking, cyprid adhesion is compromised by minimizing contact time and contact area of the attachment discs, while, during careful inspection, cyprid adhesion is enhanced by behaviorally pushing the attachment discs toward the substrate.
o To achieve reversible adhesion, the cyprid tugs the antennules parallel to the surface and peels the attachment discs from the substrate.

Question 19

Biochemistry of Barnacle Adhesion: An Updated Review
Marine and molecular biology and ecology

Settlement-Inducing Protein Complex (SIPC)

Answer 19

Settlement-Inducing Protein Complex (SIPC)

(Liang et al 2019)

• The size and adhesion strength of cyprid footprints increase on more hydrophobic substrates, probably implying that cyprid footprints are abundant in hydrophobic proteins and they experience conformational changes leading to exposure of hydrophobic domains.
• Cyprid footprints are also rich in basic proteins that have an average isoelectric point (pI) of 9.6–9.7, consistent with the observation that more cyprids choose to settle on negatively charged carboxyl self-assembled monolayers (SAMs).
• Through immunoblotting (a type of rapid assay), a glycoprotein called the settlement-inducing protein complex (SIPC) originally isolated from adult barnacles is also identified within cyprid.
• SIPC in Amphibalanus amphitrite has three subunits with apparent molecular weights (MW) of approximately 98 kDa, 88 kDa, and 76 kDa.
o Each of them is glycosylated (a carbohydrate is attached) and can be recognized by lentil lectin.
o Based on this, the acidic pI (The isoelectric point (pI) is the pH value at which the molecule carries no electrical charge) of A. amphitrite SIPC is not in agreement with the latest discovery that A. amphitrite cyprid footprints mainly comprise basic proteins, which probably suggests that the SIPC is only one among many unknown footprint proteins.
o Sequence alignment reveals that A. amphitrite SIPC shares approximately 30% identity with members of the α2-macroglobulin (A2M).
• So far, the SIPC is the only characterized protein in cyprid footprints and it plays multiple roles.
o First, it acts as a conspecific biochemical cue to mediate larvae-adult and larvae-larvae interactions to induce the gregarious settlement of cyprids.
o Settlement assays found that even a low density of surface-bound SIPC can attract significantly more conspecific cyprids to colonize while the homologous A2M protein fails.
o An SIPC homolog named MULTIFUNCin has also been isolated from Balanus glandula. Interestingly, it not only plays the same role as SIPC in promoting gregarious attachment of cyprids, but also functions as a feeding stimulus that induces barnacle predators hunting for barnacles.
o Another main purpose of the SIPC is functioning as an adhesive protein to facilitate the temporary adhesion of cyprids. By using surface plasmon resonance, Petrone et al. (2015) found that the SIPC of A. amphitrite shows comparable adsorption on various SAMs to that of fibrinogen, a well-known adhesive protein in the extracellular matrix.
o In contrast, homologous A2M only has weak to no adsorption on the same substrates.

Question 20

Biochemistry of Barnacle Adhesion: An Updated Review
Marine and molecular biology and ecology

Surface Settlement: Cyprid Permanent Adhesion

Answer 20

(Liang et al 2019)

Surface Settlement: Cyprid Permanent Adhesion

• The cyprid permanent adhesive, also called cyprid cement, is synthesized and secreted by the cyprid cement apparatus which includes cement glands and accessory ducts.
• Notably, the glands used to produce cyprid permanent and temporary adhesives are different.

o In acorn barnacle cyprids, the permanent cement gland is kidney-shaped, distributed at the posterior of the compound eyes, and contains two types of cells while the unicellular temporary adhesive gland is located in the second segment of the antennules.

o In the cyprid of the stalked barnacle, O. angulata, the permanent adhesive gland is rod-shaped and located at the back of the compound eyes, while the temporary adhesive gland is oval and buried in the mantle of the body.

• In the 1970s, Walker first examined the permanent adhesive gland of the Balanus balanoides cyprid.

o He categorized these gland cells into columnar α and round β cells based on their morphological differences.

o The two types of cells were located at the apex and the basal area of the gland, respectively.

o In addition, he detected phenols and poly phenolase in the α cells but neither of these were found in the β cells.

o The permanent adhesive of the A. amphitrite cyprid was later discovered to be a a dual-phase bioadhesive comprising a protein and a lipid phase which are separately stored in the α and β cells before secretion.

o An in vitro study using isolated permanent adhesive glands of the Megabalanus rosa cyprid found that cyprid cement is secreted when the cyprid glands are stimulated by neurotransmitters such as dopamine and noradrenaline. The cytoplasmic vesicles containing cyprid cement migrate to specific regions of the cell to release the glue into the extracellular ducts through exocytosis.

o After secretion from these glands, cyprid cement is transported via extracellular ducts to the muscular sac for temporary storage. When needed, it is delivered by long cement ducts in the antennules to the attachment discs where it is released through the openings

Question 21

Biochemistry of Barnacle Adhesion: An Updated Review
Marine and molecular biology and ecology

Cyprid permanent adhesive
Biochemical composition

Answer 21

(Liang et al 2019)

Cyprid permanent adhesive

• Biochemical Composition of Cyprid Cement
• For instance, by employing AFM-based force spectroscopy to stretch cyprid cement proteins adhered on the substrate, Phang et al. (2006) observed gradually decreasing stretching events and maximum extension length. This particular result was attributed to the curing of cyprid cement and allowed researchers to estimate curing time to be within several hours (Phang et al., 2006). Via synchrotron radiation based μ-X-ray fluorescence analysis, Senkbeil et al. (2016) detected a large amount of halogen elements as well as low-content metal ions (e.g., Ca2+, Mg2+, and Fe3+) in the permanent adhesive of A. amphitrite and Balanus improvisus cyprids. However, their possible roles have not been discussed
• By using laser scanning confocal microscopy to observe cyprid cement deposited on different SAMs, Aldred et al. (2013a) found that a layer of non-protein substance enclosed the proteinaceous bulk glue.
• Via a combination of chemistry-specific fluorescent probes and Raman microscopy, Gohad et al. (2014) further demonstrated that the non-protein interfacial layer is lipidaceous and the internal bulk glue is phospho proteinaceous.
• The protein and lipid phases are separately stored in the α and β cells and the lipid phase is released ahead of the protein phase upon secretion.
• The interfacial location and prior secretion of the lipid phase probably indicates that it plays the key role in removing boundary water layers and keeping microbes away from the proteinaceous bulk glue.
• This discovery shed light on the important roles of non-protein components in underwater adhesion for the first time. Likewise, He et al. (2018) noted that lipids, as integral components, also assist in mussel underwater adhesion and function similarly as they do in cyprid permanent adhesion. Therefore, secreting water-repelling lipids to prepare the substrate and create an adhesion-friendly local environment ahead of depositing multi-protein holdfasts may be a general strategy for underwater adhesion.

Question 22

Biochemistry of Barnacle Adhesion: An Updated Review
Marine and molecular biology and ecology
Adult barnacle Underwater adhesion

Answer 22

Adult Barnacle Underwater Adhesion

(Liang et al 2019)

• laboratory studies have revealed that barnacles dislodged from substrates (e.g., silicones) where they have weak adhesion can also secrete secondary cement and attach to a new substrate if their bases are intact.
o Accordingly, adult barnacle cement is classified into primary and secondary cement. Generally, primary cement refers to the cement used for natural attachment while secondary cement is only employed during reattachment.
• Comparative studies confirm that the two types of barnacle cement are identical because they have similar micro- and nano-morphologies, biochemical compositions, and secondary structures.

Question 23

Biochemistry of Barnacle Adhesion: An Updated Review
Marine and molecular biology and ecology

Nanofibrils

Answer 23

(Liang et al, 2019)

Nanofibrils

• It was noted that remnants of fibrillar barnacle cement on several substrates could be stained by amyloid fiber dyes – Thioflavin T and Congo Red – indicating that barnacle cement fibers probably contain amyloid.
• Amyloid fibers are nanofibers that self-assemble through non-covalent interactions of building blocks rich in β-sheet secondary structures.
• Amyloid fibers are considered functional in biohesives.

Question 24

Cephalopods adhesion mechanisms

Answer 24

• Liquid glue is an ancestral trait, more advanced cephalopods rely on suction
• Some octopus use intricate surface texture to increase frictional forces during attachment
• Sepia - found in windswept rocky intertidal regions, and is exposed to turbulent water - strong and fast adhesion is required by mechanical attachment such as suction
• Sepia typica - South Africa - adhere to hard substrata
  
  • settles at low tide
  • mantle contractions to form a sucker
  • *

Question 25

Suction Cephalopods

Answer 25

In the cephalopods, use of a liquid glue is an ancestral trait. More advanced cephalopods rely more on suction.

4 genera (Nautilus sp., Sepia sp., Euprymna sp. and Idiosepius sp.) use liquid adhesives.

One genus, Euprymna, also uses a deadhesive – i.e. produces one material to attach and another to detach!

Question 26

Limpets

Answer 26

• Modern-day limpets also rely on suction for adhesion, using it for attachment during locomotion in addition to capillary/Stefan adhesion.

When exposed by the tide, however, limpets secrete a true adhesive hydrogel, containing:

o <97% water and several polar proteins,

o A 140 kDa glycoprotein complex for adhesion,

o Gives a tenacity of <500 kPa.

(all that’s known about marine gastropods)

Question 27

Suction remora

Answer 27

The remora’s ‘sucker’ is a modified dorsal fin.

The fin is flattened into a pad and surrounded by a thick lip of connective tissue that creates the suction seal.

The lip encloses rows of plate-like structures called lamellae, from which rows of tooth-like spinules emerge for mechanical grip.

Mucus may help the edge of the disc to conform to irregularities in the substrate

presence of mucous increases the viscous forces associated with Stefan adhesion - increasing the forces needed to overcome suction.

• Attachment to challenging substrates – fouling, roughness and limits of adhesion in the northern clingfish (Gobiesox maeandricus) (Ditsche, et ak 2014)
• Northern clingfish use a ventral suction disc to stick to rough substrates in the intertidal zone. Bacteria, algae and invertebrates grow on these surfaces (fouling) and change the surface properties of the primary substrate, and therefore the attachment conditions for benthic organisms. In this study, we investigate the influence of fouling and surface roughness on the adhesive strength of northern clingfish, Gobiesox maeandricus.
• Nevertheless, even on fouled surfaces the adhesive forces are approximately 150 times the body weight of the fish. To identify the upper threshold of surface roughness the fish can cling to, we tested seven unfouled substrates of increasing surface roughness. The threshold roughness at which northern clingfish failed increased with specimen size. We hypothesize that because of the elastic properties of the disc margin, a larger disc can adapt to larger surface irregularities. The largest specimens (length 10–12 cm) were able to cling to surfaces with 2–4 mm grain size. The fish can attach to surfaces with roughness between 2 and 9% of the suction disc width.
  *