Seagrass-Watch Magazine Issue 47 - March 2013 | Page 4

Temperate North Atlantic
1. agricultural runoff
2. urban/industrial runoff
3. sea level rise

Temperate North Pacific
1. urban/port infrastructure development
2. changes in sea surface temperature
3. sea level rise

Mediterranean
1. urban/port infrastructure development
2. urban/industrial runoff
3. trawling

Tropical Indo-Pacific
1. urban/industrial runoff
2. urban/port infrastructure development
3. dredging

Tropical Atlantic
1. urban/industrial runoff
2. dredging
3. agricultural runoff

Temperate Southern Oceans
1. urban/industrial runoff
2. agricultural runoff
3. dredging

geographic bioregions from Short et al. (2007) JEMBE 350: 3-20

Vulnerability assessment
Using SurveyMonkey®(a free online questionnaire and survey
tool) we were able to apply a more quantitative, scientific
approach. We know many human activities have the potential to
act as a threat to the ecological integrity of seagrass ecosystems.
However these threats have different impacts depending on the
ecological context of where they occur. For instance, ecological
recovery from a propeller scar in a Halophila meadow will usually
be faster than a Thalassia meadow due to the slow growth rates of
Thalassia, making Thalassia meadows more vulnerable to
propeller scars than Halophila meadows. Therefore, we defined
vulnerability as a combination of exposure and sensitivity and
resilience, in a suite of five criteria related to vulnerability to make
basic characterisations of how activities impact seagrass
communities and habitats differently(8). We surveyed 59 scientists
from around the world and the five criteria we used were: scale how big an area of seagrass would be impacted by the human
activity; frequency - how often does the activity occur, rare or

regularly occurring; functional impact - will the activity damage
just one or many seagrass species; resistance - how resistant is a
meadow to the risk; and recovery time - how long would it take
for a meadow to recover after the activity was removed. We also
asked scientists how certain they were of their answers. This
produced a slightly different ranking of risks to seagrass than the
expert workshop approach, but one which is more scientifically
based (see Table below & Figure above).
Globally, using the vulnerability assessment approach, we found
that the greatest threat to seagrass meadows was urban/industrial
runoff, urban/port infrastructure development and agricultural
runoff, in that order. However, differences existed across the
seagrass bioregions.
In each of the seagrass bioregions, differences were also
apparent between the expert workshop and the vulnerability
assessment. In the Indo-Pacific for example, the top two threats
are identical, but at position three was dredging (see Grech et al.
2012). An alternative approach, was to use cumulative impact
mapping.

Rankings of the relative impact of multiple human
activities on seagrasses globally derived from
vulnerability assessment (1 = most threatening activity).
Ranking

Threatening human activity

1

Urban/industrial runoff

2

Urban/port infrastructure development

3

Boat damage (commercial)

8

Boat damage (recreational)

9

Shipping accidents (e.g. oil spills)

10

WWW.SEAGRASSWA
TCH.ORG

Aquaculture

7

4

Trawling

6

LM

Dredging

5

Coastal development along Far North Queensland coast

Agricultural runoff

4

Changes in sea surface temperature
from Grech et al (2012) Environ. Res. Lett. 7, 024006