Download Ichthyology Fish Ecology 1

Oceanic Zone
 Oceanic Zone – The ocean NOT over the
continental shelves.
Stratified over the abyssal plain @
approximately 6000m.
LAYERS (Relationship to Surface)
 Photic Zone = Epipelagic – to 200m
 “Twilight” Zone = Mesopelagic – 200m-1000m
 Deep Lightless Zones = Bathypelagic
(1000m-2000m) & Abyssopelagic (>2000m);
4ºC and less
Oceans
Surface & Intermediate Waters
 Most of the Oceanic Zone has a permanent
thermocline between 500-800m
(Mesopelagic).
Above this = affected by wave action and
considered the surface waters.
Temporary thermocline may form @
approximately 30-50m in the temperate zone
in summer.
 Under 800m but well above the Abyssal
Plain = intermediate waters (many water
masses and, potentially, thermoclines & haloclines)
Bottom Waters
 Waters slowly flowing above the Abyssal
Plain = bottom waters.
 Antarctic Bottom Water (AABW) is slowly
flowing over the bottom in most of the
ocean.
 North Atlantic Deep Water (NADW) is
slowly flowing over the bottom in the
northern part of the North Atlantic.
 These water masses are usually very well
oxygenated.
Oceanic Upwelling and Downwelling
 Upwelling due to:
-diverging currents (from air circulation)
-deep currents encountering physical barrier
-“deep current” upwelling
Ocean “Conveyor Belt”
Primary Production
Abyssal Plain Sediments
Ocean Floor
Epipelagic
 To 200 m
 If nutrients sufficient
then much phytoplankton
& zooplankton.
 Epipelagic fishes usually streamlined and
counter shaded or reflective (constant swimming).
 Other organisms often transparent.
Epipelagic Food Web
phytoplankton
dissolved organic
compounds (DOC)
phytobacteria
microzooplankton
phytoplanktivorous grazing zooplankton
fishes
predatory zooplankton
“predatory” fishes, mollusks, etc.
bacteria
larger
“predatory”
fishes, mammals, etc.
Mesopelagic
 200-1000m; “Twilight Zone”
 Effectively no primary productivity
 Most mesopelagic organisms rise into the
epipelagic to feed at night.
 Fishes black or silvery, others transparent.
 Photophores = light generating “organs”
 Lanternfishes = most common fishes.
Mesopelagic
 Deep Scattering Layer.
Mesopelagic fishes & other animals migrate
toward the surface at night to feed.
This mobile deepwater community is dense
enough that it reflects sonar.
 Mesopelagic fishes usually have
swimbladders.
Deep Scattering Layer - Day
Deep Scattering Layer
Deep Scattering Layer - Night
Deep Scattering Layer
Bathy- & Abyssopelagic
 approx. 1000-6000m; no light, no primary
productivity, cold
 Fishes and most other animals are
sedentary and wait for food to arrive from
above (usually big mouths and long teeth)
 Fishes and crustaceans are black or
bright red and may have a few
photophores.
 No swimbladders & “flabby”
Bathy- & Abyssopelagic Food Web
particulate organic
matter (POM)
collecting/scavenging animals
(mollusks, crustaceans, fishes, etc.)
predatory/scavenging animals
(cnidarians, mollusks, crustaceans, fishes, etc.)
Bathy- & Abyssopelagic
Oceanic Benthic (Abyssal Plain)
 No light, no primary productivity, cold
 Fishes and other organisms usually black,
transparent, or silvery (few photophores).
 Usually less “flabby.”
 Many echinoderms.
Abyssal Benthic Food Web
particulate organic
matter (POM)
dissolved organic
compounds (DOC)
bacteria
collecting/scavenging animals
(annelid worms, echinoderms, mollusks
crustaceans, fishes, etc.)
predatory animals
(echinoderms, mollusks, crustaceans, fishes, etc.)
larger predatory animals
(mollusks, crustaceans, fishes, etc.)
Oceanic Benthic
Hydrothermal (Hot) Vents
 Ocean floor primary production via bacteria.
6CO2 + 6H2O + 3H2S → C6H12O6 + 3H2SO4
Free living and symbiotic with annelids
(Pacific) or bivalve mollusks (Atlantic).
 Vents ephemeral (communities temporary).
Methane (Cold) Seeps
 Ocean floor primary production via bacteria
that use CH4 in chemoautotrophy.
 Many free living and others symbiotic (often
involving tube worms and/or bivalves).
 Methane seeps more constant.
Vertical Migration
 Most mesopelagic organisms migrate
vertically every day.
 Most/many larvae enter the epipelagic or
upper mesopelagic for early development.
 Some abyssal plain organism larvae only
enter the abyssopelagic until they find a
place to settle.
El Niño/La Niña
 Pacific equatorial winds
(to west = “normal”/niña; to east = el niño).
El Niño/La Niña
Human Impacts
 Difficult to define or even address.
 Oceanic Zone enormous
Fishing activities significant in epipelagic),
over fished in many places.
Oceanic plastic trash of greater concern.
Collects in centers of oceanic gyres.
Microplastics.
 Climate Change – carbon sink (?) and
carbon saturation; ocean conveyor belt;
climate regulation