Characteristic Sizes of Life in the Oceans, from Bacteria to Whales

Imagine picking any organism, from bacteria to whales, out of the ocean. Which one trait characterizes the largest part of this organism’s physiology, encounter rate with prey (and predators), abundance of conspecifics, reproductive rate etc.? The body size of the organism has been proposed as the best candidate for such a master trait.

A new paper from a group of researchers with DTU Aquas Centre for Ocean Life shows how body size also determines the organism’s fundamental design and strategy towards life: if it is small (unicellular) it is likely to photosyntheize, while very small bacteria does not photosynthesize. If the organism is large (larger than about a cm) it is likely to be slender and streamlined, while smaller organisms come in odd shapes with appendages necessary for sensing movements of the water to compensate for lack of vision. Larger organisms, such as fish, however, are largely visual predators. The largest organisms in the ocean are warm blooded and breathe air, while all organisms less than about 10 kg are cold blooded and take oxygen from the water.

The authors suggest dividing life in the ocean into seven major realms based on trophic strategy, physiology, and life history strategy. Such a categorization represents a move away from a taxonomically oriented description toward a trait-based description of life in the oceans. Finally, the paper discuss life forms that transgress the simple size-based rules and identify unanswered questions.

Characteristic Sizes of Life in the Oceans, from Bacteria to Whales
K.H. Andersen, T. Berge, R.J. Gonçalves, M. Hartvig, J. Heuschele, S. Hylander, N.S. Jacobsen, C. Lindemann, E.A. Martens, A.B. Neuheimer, K. Olsson, A. Palacz, F. Prowe, J. Sainmont, S.J. Traving, A.W. Visser, N. Wadhwa, and T. Kiørboe
Annual Review of Marine Science, Vol. 8: (Volume publication date January 2016)