Perfectly circular patches bare of vegetation in otherwise continuous swards of seagrass, and perfect circles of seagrass with lush fringes of shoots on the outer margins but with virtually bare centres, have both attracted popular attention as ‘fairy circles’ or ‘fairy rings’ in view of the folklore surrounding the supernatural origins of their terrestrial fungal counterparts. Aerial photographic and satellite surveys show that, on the Isles of Scilly, circles of Zostera marina of the second type occur sporadically, with exceptionally prolific clusters in specific localities associated with the colonization of bare substratum after disturbance, gradually disappearing over the period of this study at one site and appearing at another. Their abundance is the highest recorded anywhere in the world. Early suggestions that they represent seaweed growth on the stones of ancient hut-circles, submerged for centuries as a result of sea-level rise, are refuted. It is argued that they result from the unrestricted clonal growth of genets arising from individual Zostera seedlings, expanding equally in two dimensions and colonizing vacant habitat, with the older central shoots senescing and dying. Diameters of the circles constitute a stepwise increase in size, and the growth increments may represent a similar rate of seasonal growth in consecutive years, implying a linear rhizome growth rate of ~2.5 m year−1, which would be exceptional for Zostera marina, but which is supported by an observation on circles exposed on a low spring tide and would be an evolutionary adaptation for rapid recolonization in such a physically disturbed environment.

To investigate the response of the fish community structure to a natural disturbance in their habitat, fish abundance, biomass and species composition were analysed in relation to temporal variability of environmental conditions in a seagrass Zostera marina bed. A total of 3024 fishes belonging to 46 taxa (22 families) were collected by quantitative sampling for 10 years from 2007 to 2016 in the Seto Inland Sea, south-western Japan. Seagrass shoot density decreased to less than 1/20 of its original density after disappearance of vegetation caused by heavy rain in the autumn of 2011 and the area did not recover for the next five years. In order to analyse temporal changes of fish community, the fishes were divided into three groups depending on their habitats or lifestyles: pelagic or migratory species (PM), sand or mud bottom-associated species (SM) and seagrass (Z. marina) – or substrate (rocky bottom including macrophytes) – associated species (ZS). Multiple regression analysis showed seagrass shoot density had the most significant effect on biomass of ZS among the three groups, with higher fish biomass under higher seagrass shoot density. Fish community composition changed after the disappearance of the seagrass vegetation coverage with an increase in abundance of SM during the five years of the post-disturbance period. Seagrass vegetation was concluded to affect temporal change of fish community structure through a stronger influence on fish species that are more dependent on seagrass beds as habitat.

Long-term population dynamics of three-spined stickleback Gasterosteus aculeatus in the White Sea during the 20th century has patterns similar to that of eelgrass Zostera marina. In this study we address possible mechanisms of such association through analysis of spatial distribution of juvenile stickleback in the wild and their substrate preferences in experimental conditions. Samples from different habitats (Z. marina, Fucus spp.) in 13 localities of Kandalaksha Bay have shown that the juvenile sticklebacks occurred mainly in the eelgrass beds. Their density was significantly lower in fucoids. In the experiments, carried out in August 2008–2009, the juveniles were offered the following types of substrates: brown macroalgae (dense and scarce), eelgrass and control (no substrate). In the experiments sticklebacks also showed a tendency to prefer eelgrass to fucoids, even if the density of the latter was higher. This may explain their higher densities associated with eelgrass in the wild.

From the 8th/9th centuries onwards the former peat land area in the northwestern part of the Netherlands was drained and reclaimed. Drainage, peat digging and marine erosion of peat deposits created an extension of shallow marine habitats into which Zostera marina (Eel-grass) expanded. Modern publications do not note the use of Eel-grass as starting material for salt-making. Archaeological evidence, however, indicates salt-making activities by using Zostera in medieval times. We postulate that, after salt-containing peat had become difficult to obtain, Eel-grass was used for salt production.

Stable carbon and nitrogen isotope ratios of benthic invertebrates and their potential food sources, such as suspended particulate organic matter (POM), benthic microalgae, attached algae and seagrass, were identified in Dong-dae Bay during the winter. The carbon stable isotope ratios demonstrate that filter feeders, such as oysters (−19.5 ± 1.0‰), use benthic microalgae (−21.2 ± 0.2‰) as a major food, and polychaetes such as Glycera spp. (−14.0 ± 0.6 ‰) preferentially use meiofauna, such as nematodes (−14.0 ± 0.4‰) and copepods (−13.3 ± 1.0‰). These meiofauna may feed on mixed resources (including bacteria) with the isotope ratios between benthic microalgae (−21.2 ± 0.2‰) and seagrass (−9.3 ± 01.0‰). These findings are consistent with the trophic enrichment in the nitrogen isotope ratios (by 3–4‰) between consumers and food sources. Moreover, the results of the MixSIR model based on the observed isotope ratios suggest a large seagrass contribution to the food sources of benthic organisms such as meiofauna (~53.7–62.6%) and macrobenthos (~41.1–68%) through the food web. This model additionally suggests a relatively large contribution of benthic microalgae to the food sources of filter feeders (i.e. 26.4% for oysters).

Studland Bay contains an extensive seagrass (Zostera marina) bed and two species of seahorse: spiny (Hippocampus guttulatus) and short snouted (H. hippocampus). All are protected under UK and international legislation. Five H. guttulatus have been tagged and all re-sighted several times within the seagrass bed. Home ranges of 30–400m2 were found. The three tagged males have all been observed to be pregnant throughout the summer months suggesting up to five broods per year. On one occasion the courtship display was recorded. This study has demonstrated the value of volunteer divers in monitoring which would not have been so successful without them. This project arose from concerns over negative impacts of boat anchoring and mooring on the seagrass habitat. It is hoped that the insights gained into site fidelity, territory size and breeding ecology of the seahorses will contribute to management plans for this unique site.