In September 2001 BBC broadcast first episode of its new documentary series – Blue Planet. This series of 8 TV shows will try to explain the complexity of ocean life and the incredible connections between all constituents of ocean world.
In this first episode, David Attenborough narrates about how the seas and ocean life are influenced by currents, storms, daily cycle of the Sun, lunar cycle and seasonal cycles.
Everything is shown using stunning case studies from Pacific Island, South Africa and Falklands.
One of the sequences is really helpful to understand the foraging behaviour of Hawaiian spinner dolphins and the whole life chain behind it.
Specifically, the daily cycle of the Sun “produces great migrations in creatures living in the depths of the seas” [Samuel Walters, DauntlessMedia.net].
Hawaiian spinner dolphin are a top link of the whole chain of migratory events driven by Sun daily cycle. The cycle begins with phytoplankton – a microscopic plants floating in the ocean and thriving during daylight. When the Sun sets, the scene changes. From the deeper layers emerges zooplankton to feed on phytoplankton richness that grew over the day [Pearre 1997; Ringelberg 1995]. Zooplankton are microscopic animals – larval stages of fish, molluscs, corals etc. They spent day in deeper layers when the risk of predation from visual predators is lower. Unfortunately, the same strategy show bigger micronektonic animals like, small fishes, squids. They also spent day time in the deep layers up to 700 meters deep where is too dark for fish, visual predators to forage. After sunset, those organisms migrate to the surface as shallow as 400 meters. This is quite a journey for those organisms as they are not bigger than 10 cm. During night, in the shallower layers, micronektonic organisms feed on zooplanktonic animals under the curtain of darkness that protects them from most predators like tuna. Still, there is one predator that those organisms can’t run away from. Spinner dolphins after spending day in the shallow bays of Hawaiian islands resting and avoiding predators [Norris Dohl, 1980] swim offshore and feed on micronektonic fauna. At the end of the night, micronektonic animals travels back into the depths and dolphins go back to Hawaiian bays for rest. Also zooplankton travels down the water column looking refuge from daylight predators. During the day, phytoplanktonic plants thrive again rebuilding biomass completing the cycle.
For more information see in this time line:
– Norris, K.; Dohl, T.; (1980): Behaviour of the Hawaiian Spinner Dolphin, Stenellia longirostris.
– Kelly J. Benoit- Bird, Whitlow W. L.Au., (2003) Prey Dynamics Affect Foraging by a Pelagic Predator (Stenella Longirostris) over a Range of Spatial and Temporal Scales., Behavioural Ecology and Sociobiology, Vol. 53, No. 6 (May, 2003), pp.364-373
- Samuel Walters, DauntlessMedia.net at http://dauntlessmedia.net/bbc/the-blue-planet/01-ocean-world-review.html on 10.08.2012
- Pearr S. (1979), Problems of detection and interpretation of vertical migration. J. Plankton Res., 1:29-44
- Ringelberg J. (1995) Changes in light intensity and diel vertical migration: a comparison of marine and freshwater environments. J Mar Biol Assoc UK., 75:15 – 25
- Norris K.S., Dohl T/P/ (1980) Behaviour if the Hawaiian spinner dolphin. University of California Press, Berkeley
Photo Credit: http://www.google.com/imgres?q=blue+planet+dvd&num=10&hl=en&sa=X&as_st=y&biw=1208&bih=539&tbs=isz:l&tbm=isch&tbnid=fCfbq3dO3noPuM:&imgrefurl=http://funsavingmoney.net/celebrate-earth-day-with-bbc-planet-earth-dvd-collection-giveaway/&imgurl=http://funsavingmoney.net/wp-content/uploads/2012/04/E4136_BluePlanet_US_3d.jpg&w=1329&h=1772&ei=LWQ-UIObLI_Y8gSysID4CQ&zoom=1&iact=hc&vpx=705&vpy=118&dur=1210&hovh=259&hovw=194&tx=114&ty=130&sig=113098644814215731344&page=1&tbnh=93&tbnw=72&start=0&ndsp=18&ved=1t:429,r:5,s:0,i:97