1. Habitat structure, including vegetation structural complexity, largely
determines invertebrate assemblages in semi-natural grasslands. The importance of
structural complexity to the saltmarsh invertebrate community, where the interplay
between vegetation characteristics and tidal inundation is key, is less well known.
2. It was hypothesised that canopy complexity would be a more important predictor of
spider and beetle assemblages than simple vegetation attributes (e.g. height, community
type) and environmental variables (e.g. elevation) alone, measured in two saltmarsh
regions, south-east (Essex) and north-west (Morecambe Bay) U.K. Canopy complexity
(number of non-vegetated ‘gaps’ in canopy≥1mm wide) was assessed using side-on
photography. Over 1500 spiders and beetles were sampled via suction sampling, winter
and summer combined.
3. In summer, saltmarshes with abundant spider and beetle populations were characterised
by high scores for canopy complexity often associated with tussocky grass
or shrub cover. Simple vegetation attributes (plant cover, height) accounted for 26% of
variation in spider abundance and 14% in spider diversity, rising to 46% and 41%, respectively,
with the addition of canopy complexity score. Overwintering spider assemblages
were associated with elevation and vegetation biomass. Summer beetle abundance, in
particular the predatory and zoophagous group, and diversity were best explained by
elevation and plant species richness.
4. Summer canopy complexity was identified as a positive habitat feature for saltmarsh
spider communities (ground-running hunters and sheet weavers) with significant ‘added
value’ over more commonly measured attributes of vegetation structure.