Monitoring seagrass ecosystem health - The role of perception in defining health and indicators

Thirty-four seagrass researchers/managers were asked to identify seagrass s ites in Cockburn Sound, Western Australia, which they perceived to be healt hy or unhealthy, and indicate the basis for these perceptions. The average respondent based their perception on three variables, ranging from ecosyste m features to plant attributes. Four variables were considered very importa nt in developing perceptions: canopy cover, shoot density, epiphyte biomass , and the proportion of calcareous epiphytes. Three sites perceived to be h ealthy and three perceived to be unhealthy were then compared to determine if features indicated as important in developing perceptions about health d iffered between the sites. None of the four variables considered important by respondents differed statistically between "healthy" and "unhealthy" sit es in winter, but shoot length and above ground biomass were different. In summer, two of the important variables (canopy cover and shoot density) dif fered, along with shoot height, productivity, and leaf area index. Despite their perceived importance, epiphyte features were not different between pe rceived healthy and unhealthy sites. The study suggests that shoot density, canopy cover, shoot height, above ground biomass, productivity, and leaf a rea index of P. angustifolia ecosystems differ statistically between sites perceived to be healthy and unhealthy. However, the usefulness of these var iables as indicators of seagrass health varies seasonally. Health was clear ly a respondent-dependent concept. The basis of perceptions about health am ong a group of expert scientists did not correspond strongly to measurable differences between sites. The unwarranted importance placed on epiphytes m ay be due to previous studies that have reinforced their importance. These observations highlight the role of personal perspective and scientific prec onditioning in forming concepts of health, and raise the question of the ro le that "experts" should be playing in formulating those concepts.