I. Zonation -- Figure 1.22 review
deep sea >200 m deep
dysphotic zone -- still receives some light (no
PS)
aphotic zone -- no light
II. Sampling the deep sea
A. Long cable and sampling gear
B. Dredges - often not 'quantitative'; box cores
or multicores
C. Trawl avoidance by midwater fish
D. New technology – submersibles; ROV; deep sea
cameras; acoustical devices
E. Still poorly sampled
F. Lack of natural history data
III. Environmental Characteristics – temporal constancy
A. Light
B. Pressure
1. increases one atmosphere
for every 10 meters depth
2. difficulties bringing
deep sea organisms to the surface
3. pressure-dependent
physiology
a. deep-sea bacteria
b. enzyme properties in fish
c. homeoviscous adaptation – deep-sea bacteria construct their
membranes
from more fluid lipids
d. protein synthesis
e. solubility of CaCO3 increases at greater pressure
f. fish lack a functional swim bladder in the deep-sea
C. Salinity
D. Temperature
E. Oxygen
1. generally high but does
decrease in the 20 m or so just above the bottom
2. oxygen minimum zone
(500-1,000
m)
F. Food
1. allochthonous
-- comes from elsewhere
(no photosynthesis)
a. some particles (e.g., marine snow and fecal pellets) are not
directly
edible by animals; animals feed on decomposer bacteria
b. patchy and limiting –
i. restrict the abundance and size of most deep-sea organisms
ii. more food available under areas of high surface primary production
or near terrestrial habitats
iii. only about 20% of the epipelagic production makes it to the
mesopelagic
iv. only about 5% makes it to the abyssal
v. typically are 5-10X fewer organisms at 500 m than at the surface,
and
perhaps 10X fewer again at 4,000 m
c. particles accumulate on bottom
2. autochthonous
-- hydrothermal vents
a. chemosynthesis
b. higher abundance and diversity of life than elsewhere in the deep
sea
IV. Adaptations of Deep Sea Organisms
A. Color
1. mesopelagic
a. fish generally silvery-gray or deep black
b. invertebrates purple and bright red
2. deep sea --
a. no countershading
b. often colorless; whitish; black (fish) – lack pigment
B. Eyes/Sensory adaptations
1. mesopelagic
a. (<2000 m) have large eyes
b. some fish have tubular eyes – two part retina; great
sensitivity
to low light; yellow filter to distinguish
between natural light and bioluminescence
c.
bilobed eyes in invertebrates
d. twilight vision -- enhancement of vision of some fish in
mesopelagic
e.
dimorphic eyes – some mesopelagic squids; small eye oriented
downward
and
large eye upward -- match downwelling light with its photophores and is
camouflaged
2. >2000 m -- reduced or
no eyes
3. bottom dwellers -- may
have no eyes
4. mesopelagic fishes often
have well-developed lateral lines
C. Food scarcity --
1. huge mouths
2. backpointing teeth
3. bioluminescent lures
D. Low oxygen
1. problem in oxygen minimum
zone
2. fishes, krills and
shrimps
have large gills
3. tend to be less active
4. some have hemoglobin
that is very efficient at low oxygen
E. Problems finding mates
1. low population densities
2. many deep-sea fishes
are hermaphrodites
3. signals to attract mates
-- bioluminescence, pheromones
4. male parasitism
5. invertebrates aggregate
into breeding groups, although the cues aren't known
F. Body Size --
1. Most deep-sea benthos
and mesopelagic organisms are small
2. Abyssal gigantism
-- some invertebrates
G. Bioluminescence –
1. common
a. in general emits light of 460-480 nm (blue)
b. most prevalent in mesopelagic and upper bathypelagic
2. Structure – light can
be produced by the animal's own tissue or by
bioluminescent
symbiotic bacteria
a. simple – glandular cells or cups with bacteria that produce light
b. may have lenses to focus, color filters, or adjustable diaphragms
c. squids often combine photophores with skin that contains
chromatophores
and can alter the color/intensity of the bioluminescence
3. function
a. counterillumination -- preventing silhouette production
b. luring prey (e.g., angler fish)
c. lighting an area to see prey
d. mate recognition
e. burglar alarm hypothesis -- startles the predator; may
attract
other predators;
deep-sea squids