A recently published scientific report shows the response of macrophyte indicators for the Water Framework Directive to anthropogenic gradients.
Response of macrophyte indicators to natural and anthropogenic gradients in two coastal areas of Sweden
Benthic macrophytes are known to be affected by anthropogenic activity, and therefore these communities are suitable for the assessment of ecological status according to the WFD. The existing assessment method for benthic macrophytes is based on the depth distribution of a few selected species, which only represents one aspect of potential changes in macrophyte communities in response to stress. Moreover, the present method performs poorly in shallow areas and areas dominated by soft substrate. There is therefore a need for new macrophyte indicators for the assessment of ecological status. The aim of the study was to test and evaluate a number of potential macrophyte indicators on a homogenous data set from well-described pressure gradients on both the west and east coast of Sweden.
On the west coast, the study was conducted in five areas along the gradient in the fjord areas inside the islands of Orust and Tjörn. In the Baltic Sea (Swedish east coast), sampling took place in seven areas in three parallel gradients in the county of Östergötland. Surveys of large squares (5×5 m) using SCUBA-technique was chosen as the main method of the studies. To reduce the variation between sampling squares, the squares were sampled on either hard or soft substrate within a limited depth range. On soft bottoms communities on the west coast, depth range of eelgrass (Zostera marina) was surveyed using video. Environmental data such as salinity, Secchi depth, total nitrogen and total phosphorus were sampled at three stations in each of the five and seven areas.
For hard substrate communities, the results show that species richness in macroalgal communities is a promising indicator as it increased with increasing Secchi depth. Cumulative cover and community complexity (the ratio between cumulative and total cover) were also positively related to Secchi depth. The proportion of opportunistic and latesuccesional macroalgal species was only related to Secchi depth on the west coast.
For soft substrate communities on the west coast, the depth distribution of Zostera marina responded strongly in the study gradient and is a promising indicator. In the more speciesrich soft bottom communities on the east coast, the areas with high nutrient concentrations and small Secchi depth had low species richness and dominance of tolerant species. However, this was likely at least in part due to low salinity in these areas. Overall, the tested indicators for soft substrate on the east coast showed a large variation within areas and a large sampling effort is required to reduce uncertainty.
Reference and link
Wikström, S.A., Blomqvist, M., Qvarfordt, S and Nyström Sandman, A. 2016. Response of macrophyte indicators to natural and anthropogenic gradients in two coastal areas of Sweden. Deliverable 3.2-3, WATERS Report no. 2016:1. Havsmiljöinstitutet, Sweden.