L18 - Invertebrates in the Pelagic Zone Flashcards
What ecological roles do marine invertebrates play?
They are often near the bottom of food web, they are pivotal in structuring ecosystem function
Remember…?
97% of animals do not have a backbone
What are the oceanic divisions?
Pelagic (Neritic & Oceanic), Increasing depth - epipelagic, mesopelagic (200m), bathypelagic (700 to 1000m), abyssalpelagic (2000m to 4000m), hadalpelagic (5000m+)
What lives in the pelagic realm?
Nekton, plankton (Holoplankton, meroplankton)
What are zooplankton?
Metazoan zooplankton contains a huge number of very different taxa. Size range from ~100um to a few metres (10s of metres for pyrosomes). Usually capable of some sort of swimming but unable to escape currents. Important groups include ctenophores, cnidarians, crustaceans, molluscs and chordates (although don’t forget meroplankton)
What are gelatinous zooplankton?
Gelatinous body: water content 95% or higher. At least 2000 species. Salps (subphylum Tunicata), comb jellies (phylum cnidaria, class scyphozoa), box jellyfishes (phylum cnidaria, class cubozoa), hydromedusae (phylum cnidaria, class hydrozoa), siphonophores (phylum cnidaria, class hydrozoa)
What can gelata sometimes do?
Form massive blooms
What is the reason for gelatinous zooplankton blooms?
Most gelata taxa have an asexual reproductive mode as well as a sexual one, allowing them to respond rapidly to pulses in food; gelatinous animals can show phenomenal growth rates (24% d-1 in the lab, 9% d-1 in the wild.
What life is at the surface?
Hundreds of species live at the ocean’s surface, drifting in currents and driven by winds.
What happens to plankton below the surface?
Drift in currents but usually able to swim weakly, and especially move vertically in the water.
What does MVBS mean?
Mean volume backscattering strength
What are Diel vertical migration?
Largest migration in terms of biomass on the planet. Freshwater and marine habitats. Animals occur in deeper water during the day (Deep scattering layer, DSL). Move to shallower water at night.
Why do DVM occur?
Animals travel 10 - 100s m in a few hours. There are clear costs to this behaviour - movement at a low reynolds number if energetically expensive. Predator evasion hypothesis, better unfed than dead.
What dominate the zooplankton biomass in the ocean?
Copepods. Believed to be the most abundant metazoans in the ocean and, maybe, on the planet
What are the Holoplanktonic copepods?
Calanoida, cyclopoida. They are free-living.
What are the benthic copepods ?
Harpacticoida, they are free-living.
What are the parasitic/associative copepods?
Gelyelloida, misophrioida, monstrilloida, platycopoida, poecilostomatoida, siphonostomatatoida
What are copepods?
13,000 spp, 10 orders, typically 1-2mm
What is the development of calanoid copepods?
Normally, 12 developmental stages, each separated by a moult. 6 nauplius stages (NI - NVI), 6 copepodite stages (CI - CVI). Sexually mature adult is the last stage CVI
What are pteropods?
Shelled (Thecosomata) and shell-less (Gymnosomata) planktonic molluscs. Foot modified into pair of wings. Thecosomes are suspension (filter) feeders (although fragments of larger prey have been found in their stomachs). Trap food particles in mucous covered parapodia. Secrete mucous nets (up to 2m across)
What do thecosomes have?
Important ecological role
What waters are meroplankton important in?
Temperate waters
What is larval dispersal?
Vast majority of planktonic larvae will die: swept into inhospitable habitats; eaten by predators; starvation. Most recruits will come probably from nearby
What is the position of larvae in the water column?
Larvae will go through one or more stages of photopositive and photonegative behaviour: photopositive - near surface, photonegative - close to bottom. Larvae can show behavioural (depth) changes to take advantages of local currents and tides.
What are invertebrate nekton (active swimmers)?
Able to move independently of water currents. Most nektonic animals are fish. Nektonic marine invertebrates are mainly crustaceans and cephalopods. Invertebrate nekton occupy similar trophic levels to fish
What are nektonic crustaceans?
Swimming crabs, shrimp, krill. Krill occupy the niche of pelagic, schooling fish in the southern ocean. Wasp-waist systems: dominated by a mid trophic-level species that is thought to exert top-down control on its food and bottom-up control on its predators
What Euphausiacea?
Either krill or copepods make up the greatest animal biomass of any species on Earth (copepods more numerous, krill are larger). Generally up to a few cm long. All marine (85spp), large exposed gills ventilated by thoracic appendages
What are the two subclasses of cephalopods?
Nautiloidea and Coleoidea
What are Nautiloidea cephalopods?
Pelagic, external, chambered shell for buoyancy, pinhole eye
What are Coleoidea cephalopods - order Sepioidea?
Cuttlefish; 8 arms + 2 tentacles (decapod). Internal, chambered shell for buoyancy (Sepia, Spirula), mostly benthic, neritic (coastal)
What is the order Octopoda?
8 arms (octopod); internal shell considerably reduced (Cirrata) or absent (Incirrata); Incirrate octopods are all benthic
What are squid?
Common in shallow sea where they can form enormous shoals during breeding migrations. Very important food item for seabirds, marine mammals and fish
What is the Humboldt (jumbo) squid, Dosidicus gigas?
Up to 2.5m in length (mantle length 1.5m), 50kg. Shoals of over 1000 animals. Depths of 200-700m. Mainly feed on micronekton (DSL) - show DVM. Evidence of cooperative hunting. Showing northerly range expansion, risking commerically important fish stocks.
What can respond better to pulses in food?
Gelatinous zooplankton because they can reproduce asexually and show phenomenal growth rates.
What is DVM fundamental in?
It is a fundamental driver in open water ecology, including higher trophic levels.
