Using biological traits to understand ecosystem health

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Biological traits analysis is a valuable tool for measuring ecosystem function.

Based on the characteristics of individual organisms, it is also a powerful way to measure ecosystem vulnerability to human activities, between widely separate locations.

The issue

Globally, soft seafloor habitats are seriously affected by human activities like pollution, mining, dredging and trawling.

Many people may not see this as an issue, thinking that these habitats are uniform plains of sand or mud. However, these places are complex, species-rich ecosystems that also contribute substantially to how the greater ecosystem functions. This means they are important to the goods and services that marine ecosystems provide humans.

For example, organisms living in these areas can:

The biological traits of organisms – e.g. having a large, fragile body and limited mobility, or feeding on algae in the water - can also make them sensitive to specific human activities.

The approach

Until recently, decreases in biodiversity were simply seen as loss of species. Now, there is a shift towards the concept of functional diversity - the number, type and distribution of functions performed by an ecosystem’s organisms - as a complement to species diversity.

If an ecosystem has two or more species performing the same function, the loss of one might not have an effect. However, if all the species performing that function are lost, the function itself is lost. This is often followed by a loss of ecosystem services. 

For example, the switch from coral- to algal-dominated reefs in Jamaica in the 1980s was likely caused by a drop in the number of herbivorous fish (fishing) followed by the mass deaths of herbivorous sea urchins.

Biological traits analysis allows us to compare the composition of, and biodiversity between, widely separate locations, independent of regional species pools.

In another example, a study compared two locations in New Zealand likely to have different species pools: Northern Hauraki Gulf and Tonga Island Marine Reserve. It found that both locations had similar biological traits, even though the two sites only had 112 of the 374 observed taxa in common.

The study also highlighted the importance of maintaining habitat variety to support ecosystem functioning. It found differences in the specific traits important for ecosystem function across the habitats studied.

Read the study "Predicting the effect of habitat homogenization on marine biodiversity"

Generally-used traits

Table 1: Biological traits that are generally used to reflect ecosystem processes and sensitivity to human activities in soft sediment environments.

General Category Trait
Motility Sedentary (not moving), or only moving within a fixed structure
  Limited movement
  Freely motile
  Semi-pelagic (spends time in/on sediment, and time in the water column)
Feeding Suspension
Habitat structure Permanent burrow
  Simple hole or pit
  Trampling across sediment surface
Moving sediment Surface (top 2 cm) mixing
  Deep (>2cm) mixing
Size Small (0.5 – 5mm longest dimension)
  Medium (5 – 20mm)
  Large (>20mm)
Form Vermiform (length much greater than width)
  Globulose (length similar or equal to width)
  Contains calcium carbonate (has a shell)
Living position in sediment Sticks out above sediment surface
  Attached to other animals or small hard surfaces
  Top 2 cm
  Deeper than 2 cm

Future applications

Increasing our understanding of the relationships between:

  • species and functional diversity
  • functional diversity and ecosystem functioning

will provide guidance for the conservation and restoration of marine communities.

This approach may also help:

  •  identify vulnerable functional groups, e.g. those which are more sensitive to a particular type of physical disturbance
  • understand their roles in maintaining ecosystem function
  • highlight what species and levels of diversity are needed to maintain function in different marine ecosystems.


  • Bremner, J., Rogers, S.I., Frid, C.L.J., 2003. Assessing functional diversity in marine benthic ecosystems: a comparison of approaches. Marine Ecology Progress Series 254, 11-25.
  • Hewitt, J.E., Thrush, S.F., Dayton, P.D., 2008. Habitat variation, species diversity and ecological functioning in a marine system. Journal of Experimental Marine Biology and Ecology 366, 116-122.
  • Hewitt, J.E., Julian, K., Bone, E.K., 2011. Chatham-Challenger Ocean Survey 20/20 Post-Voyage Analyses: Objective 10 – Biotic habitats and their sensitivity to physical disturbances. New Zealand Aquatic Environment and Biodiversity Report No. 81.
  • Micheli, F., Halpern, B.S., 2005. Low functional redundancy in coastal marine assemblages. Ecology Letters 8, 391-400.
  • Thrush, S.F., Gray, J.S., Hewitt, J.E., Ugland, K.I., 2006. Predicting the effects of habitat homogenization on marine biodiversity. Ecological Applications 16 (5), 1636-1642.
  • Petchey, O.L., Gaston, K.J., 2006. Functional diversity: back to basics and looking forward. Ecology Letters 9, 741-758.
Page last updated: 
4 October 2016


Figure 1: example of how horse mussels (Atrina zelandica) can alter the structure of a muddy habitat by providing a hard surface for other organisms to grow on. [NIWA]


Figure 2: reworked sediment from the burrowing activity of heart urchins (Echinocardium cordatum). [Drew Lohrer, NIWA]


Figure 3: seafloor chamber with a stirrer motor and associated water intake / output (top and bottom), and an oxygen meter (left). [Drew Lohrer, NIWA]


Figure 4: non-metric MDS plot showing that trait differences between habitats (represented by different shapes) within a location are greater than the differences between two locations (filled vs non-filled). [Hewitt et al, 2008].