Diving

Marine birds share the problem of breathing whilst hunting for food that has been noted in marine mammals, in that they are secondarily adapted to a marine existence and therefore do not have gills or other adaptations to breathing in water (Kishida et al. 2007). This unique difficulty of having lungs rather than gills is increased by the problems faced when diving that the lungs will be compressed due to increased pressure with increased depth in the water (Chappell et al. 1993). It has been found that, to accomplish maximum dive time penguins have a number of adaptations (Le Vaillant et al. 2012).

Fig. 11. Influence of depth on dive duration (A) and bottom time (B) for foraging Adelie Penguins near Palmer Station, Antarctica. Shadings indicate number of dives at each combination (1 m by 1 s) of depth and duration or depth and bottom time. N = 14 048 dive

Fig. 11. Influence of depth on dive duration (A) and bottom time (B) for foraging Adelie Penguins near Palmer Station,
Antarctica. Shadings indicate number of dives at each combination (1 m by 1 s) of depth and duration or depth and bottom
time. N = 14 048 dive (Chappet et al. 1993)

In the case of Adélie penguins their diving profile is similar to that of other marine diving birds, in that they begin with a rapid descent to a specific depth, remain in and or around that depth for a length of time and then ascend quickly but regularly to the surface (Chappet et al. 1993). This pattern is maintained so as to access demersal prey that are in schools at such depths (Chappet et al. 1993). Fig 11a compares the depth of Adélie penguin dives with the duration of dives, showing that there is a higher frequency of shorter shalloewer dives, but that deeper dives tend to be of a longer duration. Whilst Figure 11b gives the dive depth cotrasted against bottom time, again indicating a preference for shallower dives with relatively short bottom times.

Figure 11 the anatomy of penguin respiration

Figure 12 the anatomy of penguin respiration

Penguins have a very high lung capacity in relation to other marine mammals (Fig 12), this is related to their not diving as some other marine mammals (Adélie penguins have a lung volume of 165ml BTSP/kg compared to 25ml BTSP/kg of a bottlenose whale) (Kooyman et al. 1973). Their lungs are also elasticated and coated in mucus to prevent alveoli sticking together (Kooyman et al. 1973).  Marine vertebrates such as penguins want to maximise dive time for the most efficient use of their hunting time (Le Vaillant et al. 2012).

Myoglobin is a protein used for the storage of oxygen that can also be used in anaerobic conditions for approximately 5 minutes, Gentoo penguins have myoglobin at a concentration of 4.4g/100g tissue (Ponganis et al. 2010) .Haemoglobin? Increased blood volume? Phosphocreatine PCR can also be of use as a phosphate store to rapidly re-synthesise ATP (Williams et al. 2012). PCR will rapidly regenerate ATP by working with the ADP, PCR donates a phosphate to the ADP making it usable again, So that energy can be made quickly (Williams et al. 2012). This is helpful for diving penguins as they need a constant energy supply to maintain diving ability, as with PCR coupled with myoglobin the energy that can be released, can be of real benefit (Williams et al. 2012).

Past studies would use “simulated” or “restrained” diving, this is described in (Kooyman et al. 1973). “They were held in place on an aluminium plate by means of steel hoops… The plate was then fastened… to the wall of the compression chamber… The chamber… was completely filled using a high-speed water pump…” In these studies it was suggested that diving animals functioned mainly anaerobically under the water (Kooyman et al. 1973). However more recent “natural” studies have suggested that diving animals function mostly aerobically, but do have anaerobic function (Chappell et al. 1993). The differences in these data is likely due to the stressful situation of an air breathing animal (even one used to diving for prolonged periods of time) being restrained underwater.

much lower (going into bradycardia) than in dives below the ADL (Meir et al. 2008). This bradycardia is maintained by the vasoconstriction of arteries, reducing blood flow to organs less necessary when diving, but protecting the brain and preventing this from going into an anaerobic state (Meir et al. 2008). Neuroglobin is used to protect the neurones in the brain from damage when oxygen levels are reduced and to heal any damage caused (Zenteno-Savin, Leger & Ponganis 2010). Hence this is thought to be the reason that diving air-breathing vertebrates have higher concentrations of Neuroglobin than their land dwelling counterparts (Zenteno-Savin, Leger & Ponganis 2010).

In total penguins have a vast array of adaptations to reduce the problems associated with diving for food, and can maintain their internal systems when diving and presented with the difficulty of maintaining oxygen levels as well as battling against pressure.

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