Using benthic communities as a proxy for water quality to elucidate the effects of space and time within two natural harbours

The Water Framework Directive (WFD) is the primary legislative act for the protection of water quality in the European Union (EU). In the Republic of Ireland, the Marine Institute Winter Environmental Survey (WES) fulfils the monitoring requirements of the WFD in coastal and transitional waters and has collected substantial data since its inception in 2011.

As a component of the WES, benthic macroinvertebrate communities have been monitored throughout Ireland. These communities have a well-established relationship with overall ecological status, and therefore have been adopted as a Biological Quality Element throughout the EU under the WFD. Furthermore, several indices have been developed to quantify the status of macroinvertebrate communities, with the Infaunal Quality Index (IQI) being implemented within Irish waters.

Research has taken a novel approach in elucidating trends in the hitherto relatively unexplored benthic macroinvertebrate community dataset. These data have been analysed here to detect changes, both spatially and temporally, within benthic communities to answer the question of whether these communities change over space and time in response to potential pressures?  Additionally, biotope maps indicating the extent of the communities’ present have been created utilizing the pan-European EUNIS habitat classification system.

All analyses were conducted in PRIMER 7 using appropriate multivariate techniques such as cluster analysis, nMDS, and PERMANOVA. ArcGIS Pro was utilised to construct a biotope map for each waterbody.

The benthic communities within two natural harbours were explored to elucidate the effects of space and time. Waterford Harbour, located in the south-east of Ireland within the Celtic Sea, is an industrialised water body that is subject to extensive fine sediment dredging. Cork Harbour, located in the south-west of Ireland within the Celtic Sea is also industrialised and is in addition, classified as a heavily modified water body under the WFD.

Space and time were revealed as being significant factors in PERMANOVA for both Waterford Harbour (Time: df = 3, pseudo-f = 3.1257, p(perm) = 0.003. Space: df = 9, pseudo-f = 1.6239, p(perm) = 0.001) and Cork Harbour (Time: df = 2, pseudo-f = 5.9486, p(perm) = 0.001. Space: df = 14, pseudo-f = 2.8402, p(perm) = 0.001). However, differences exist within the estimated components of variation for Waterford Harbour (Time = 298.93, Space = 221.26) and Cork Harbour (Time = 472.58, Space = 914.45). These results indicate that while the benthic communities in Waterford Harbour are changing more throughout time than space, potentially because of pressures, Cork Harbour demonstrates the inverse, with the observed changes being driven by the spatial factor, despite the presence of pressures. These results are in alignment with the moderate and good IQI statuses for Waterford Harbour and Cork Harbour respectively.

The results here will be used to inform future WFD monitoring activities including the early detection of certain waterbodies that require more frequent monitoring due to changes in benthic community status. Additionally, the biotope maps created for each waterbody have numerous applications including informing restoration and protection of habitats, or to advise marine spatial planning activities.