Distribution and ecology of cyanobacteria in the rocky littoral of an english lake district water body, devoke water

Abstract

Cyanobacteria were sampled along two vertical and two horizontal transects in the littoral of Devoke Water, English Lake District. Profiles of cyanobacterium diversity and abundance showed that both attained a maximum close to the water line, but declined rapidly 20-40 cm above it. The distribution of individual species with height together with species and site ordinations showed that several taxa occurred in well-defined zones. A narrow "black zone" in the supralittoral was colonised mainly by species of Calothrix, Dichothrix and Gloeocapsa with pigmented sheaths. There was no evidence of lateral variation of species around the lake, but the height of the black zone correlated positively with wind exposure. The flora of Devoke Water is that of a base-poor mountain lake with some elements of a lowland, more alkaline water-body.

Figure 1

View of Devoke Water looking east from Station 1 showing littoral rocks and boulders colonised by cyanobacteria.

Figure 2

Map of Devoke Water showing the eight sampling stations.

Figure 3

Distribution of the main littoral cyanobacteria at Station 1. Left, profile of lake edge; centre, relative abundance of cyanobacteria and green algae; right, distribution of associated bryophytes and lichens. Hymenelia lacustris (HL), Racomitrium aciculare (RA), Xanthoparmelia conspersa (XC).

Figure 4

Distribution of main littoral cyanobacteria at Station 5. Explanation as in Figure 3. Additional bryophytes and lichens: Andreaea rothii (AR), Ochrolechia androgyna (OA), Pertusaria corallina (PC) and Racomitrium aciculare (RA).

Figure 5

Overall diversity and abundance of littoral cyanobacteria in Devoke Water. (a) Species richness at Station 1; (b) species relative abundance at Station 1; (c) species richness at Station 5; (d) species relative abundance at Station 5.

Figure 6

(a) Biplot of cyanobacterium species: af Aphanocapsa fonticola, ag Aphanocapsa grevillei, ae Aphanothece elachista, chp Chroococcus pallidus, cg coccoid green algae, fg filamentous green algae, gl Gloeocapsa compacta, gk G. kuetzingiana, gp G. punctata, gr G. rupestris, hr Hydrococcus rivularis, kc Klebsormidium crenulatum [green alga], mp Merismopedia punctata, an Ammatoidea normanii, hf Homoeothrix fusca, ll Lyngbya lagerheimii s.l., mL Microcoleus lacustris, sf Schizothrix fuscescens, cap Calothrix parietina, do Dichothrix orsiniana, scm Scytonema mirabile, stm Stigonema mamillosum, so Stigonema ocellatum; (b) Biplot of the 90 samples from the eight stations. Open circles represent samples taken below lake level, closed circles sites 0–30 cm above lake level. Crosses represent samples taken >30 cm above lake level.

Figure 7

Height of visible cyanobacterium colonisation above the lake level at the eight sampling stations. Arrow shows prevailing wind direction.

Figure 8

Littoral zone of Devoke Water close to Station 5 showing a dark line on the boulder representing the limit of cyanobacterial colonisation at approximately 40 cm above water level.