Life in the dark Flashcards
Define aphotic
Aphotic - relating to the region of a body of water that is not reached by sunlight and in which photosynthesis is unable to occur
Define disphotic
Disphotic – transition between aphotic and euphotic
Define Euphotic
Euphotic - relating to, or being the uppermost layer of a body of water that receives sufficient light for photosynthesis and the growth of green plants
How much does light intensity decline with depth?
Light intensity declines by approximately 2.6 log units in the first 100 m but less rapidly below that (1.5 orders of magnitude every 100 m) due to increased clarity of the water with depth.
Importance of time in the photic zone squidz
Example: Squid (Teuthida, Cephalopoda)
Capable of jet propulsion, thus capable of fast attack and evade behaviours.
Also, capable of jettisoning ink to temporarily blind positional predators, thus causing distraction and maximising escape time.
The use of ink for blinding is only effective in light environments.
The rates of metabolic processes in animals vary tremendously throughout the biosphere
The origins and scope of this variation are a matter of active debate.
Proposals have been:
- Geometric and environmental constraints
- Resource limitation
- Diversity of ecological roles (energy demands)
Measures of Temperature Influence: Q10
Temperature increases influence oxygen consumption:
A rise of 10°C causes O2 consumption to increase by 2 or 3 fold.
The 10°C generated an increase in rate is called Q10 (unitless coefficient)
If the rate doubles, Q10 = 2, if the rate triples, Q10 = 3 and so on.
If an organism has a wide temperature tolerance, its rate of O2 consumption may accelerate vastly as T increases.
e.g. With a Q10 of 2, starting at 0°C, the rate would double at 10°C and quadruple at 20°C, and 8-fold at 30°C.
This is an exponential relationship.
what do Seibel and Drazen (2007) conclude about the relationship between depth and oxygen consumption?
Temperature alone does NOT explain the patterns of metabolism with depth
2 – Pressure does NOT restrict metabolism in the deep sea
3 – Oxygen does NOT drive the decline in metabolism with depth
4 – Food availability does NOT constrain metabolic rates
5 - Metabolic rate IS correlated with depth only in visually orientating animals
The Visual interactions hypothesis (Childress & Mickel 1985) is the leading hypothesis explaining the observed declines in metabolism with depth.
It suggests that in the absence of light, the distances over which predators and prey interact are reduced resulting in relaxed selection pressure for rapid locomotory capacity for pursuit and evasion.
What colours do mesopelagic fish tend to be?
Mesopelagic area – animals are a different colour
Twilight zone – light changes over course of the day – become black and silver
Black – melanin – hidden at a certain time of day
Silvery guanine – silver – adaptation – less visible in certain light conditions
Summary 1
The visual interactions hypothesis explains the decline in metabolism with depth.
The absence of light can also account for morphological adaptation and behaviour.
Colour, or lack of, is a feature in not just deep-sea animals but those where there is no light.
Red is also an important colour because it attenuates light the quickest.
Relative eye size in demersal fish species in relation to the mean depth of occurrence
Although eye size declines with depth, they are still present
Explain
- Only a slight decline in eye size – most of which in top 1000 – 1500 m
- Bluefish
- Pores around the mouth – electroreception
- Big eyes deep down – bioluminescence
Not all light in the marine environment is solar light
Bioluminescence: “the production and emission of light by a living organism”
What is it used for?
Used for:
•Counter illumination
(camouflage/masquerade)
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•Attracting mates
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•Distraction/Decoy escape
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•Communication
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•Luring prey
How is bioluminescent light created?
Luciferin (pigment) reacts with oxygen to create light
Luciferace (enzyme) acts as a catalyst to speed up the reaction
Oxygen excites the luciferin and luciferase complex
Picture of the uses of bioluminescence.
Picture 2 uses of bioluminescence - offence
Example of camouflage tactic
The Hatchet fish;
The Hatchet fish; Stomiiformes.
One photophore in the eye faces upwards and ‘records’ the downwelling light.
The array of photophore on the ventral surface recreate this intensity thus masking it if viewed from below.
The effect is aided by the body morphology, with the smallest projected area seen from below.
Mass is maintained in large projected area from the side.
What is a photophore?
A photophore is a light-emitting organ which appears as luminous spots on various marine organisms.
The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, colour filters and reflectors.
The light can be produced from compounds during the digestion of prey, from specialized mitochondrial cells in the organism, called photocytes (“light producing” cells), or, similarly, associated with symbiotic bacteria in the organism that is cultured.
