Report | October 16, 2017
What is a ‘Sandbank’: A commentary based on a Maltese case study
Abstract
Habitat Type 1110 ‘Sandbanks which are slightly covered by sea water all the time’, listed in Annex I of the EU’s Habitats Directive, is defined in the EU ‘Habitat Interpretation Manual’ as “elevated, elongated, rounded or irregular topographic features, permanently submerged and predominantly surrounded by deeper water”, which “consist mainly of sandy sediments”, and where the water depth above the sandbank “is seldom more than 20 m below chart datum”. It is specified that Mediterranean sandbanks may be characterised by the marine angiosperm Cymodocea nodosa, but also that “on many sandbanks macrophytes do not occur”.
The main objective of the present work was to characterise ‘geomorphological’ sandbanks around the Maltese Islands. Information on the physical characteristics of sandy elevations in Għajn Tuffieħa, Mellieħa Bay, and the Comino Blue Lagoon was collected during the LIFE BaĦAR for N2K project surveys in 2016, while biotic data from the Għajn Tuffieħa and Mellieħa Bay banks was collected in 2013 as part of an ecological survey commissioned by the then Malta Environment and Planning Authority.
The results of these studies indicate that sandbanks in the Maltese Islands tend to be present in very shallow waters, at depths ranging from ca. 0.02 m to 2.00 m. The surveyed sandbanks had variable dimensions, with lengths ranging from ca. 11 m to 180 m, and widths ranging from ca. 1.5 m to 17 m. Samples of infauna collected using core samples in 2013 did not reveal any significant differences in the total number of species or in the total abundance of organisms between the sandbanks and nearby reference sites. No macroflora, and thus no C. nodosa, were recorded on any of the surveyed sandbanks. In the Maltese Islands, associations with C. nodosa are in fact found throughout the infralittoral, down to ca. 45 m. Cymodocea nodosa may occur as a dense meadow or very sparsely, either as almost monospecific stands or in association with other seagrasses (Posidonia oceanica or Halophila stipulacea) and/or macroalgae (e.g. Caulerpa cylindracea or Caulerpa prolifera). Cymodocea nodosa is thus clearly not limited to the environmental conditions created by sandbanks in the Maltese Islands, is not generally present where such conditions occur, and is therefore not a useful indicator species for this habitat type.
Detailed seasonal studies of physical characteristics are required to confirm with certainty that the habitats identified in Malta are indeed true sandbanks in the geomorphological sense. Monitoring of benthic assemblages is also required to ascertain whether there are any biotic assemblages which could serve as biological indicators for this habitat type, and to demonstrate the ecological importance of this habitat.
(Via Research Gate)
