Behind anemone lines: determining the environmental drivers influencing lagoonal benthic communities, with special reference to the anemone Nematostella vectensis.

Abstract

Climate change induced sea level rise and increase in associated storms is impacting the coastal zone worldwide. Lagoons are a transitional ecosystem on the coast that are threatened with habitat loss due to ingress of seawater, though conversely this also represents an opportunity for lagoon habitat creation. It is important to quantify the spatio-temporal trends of macrozoobenthic communities and abiotic factors to determine the ecological health of lagoon sites. Such information will ensure optimal and adaptive management of these rare and protected ecosystems. This thesis examines the spatial distribution of macrozoobenthic assemblages and the abiotic and biotic factors that may determine their abundance, richness and distribution at tidally restricted urban lagoon at Poole Park on the south coast of England. The macrozoobenthic assemblages were sampled using a suction corer during a spatially comprehensive survey in November 2017, in addition to aquatic and sediment variables such as salinity, temperature, organic matter content and silt content. Species richness and density were significantly lower in areas of high organic matter and silt content, indicative of hostile conditions. There were no correlations between pelagic fauna and macrozoobenthic fauna which suggests that top-down control of macrozoobenthic species is not significant enough to influence their distribution. Salinity and temperature were spatially homogenous but macrozoobenthic assemblages indicate longer term variability; the euryhaline annelid Hediste diversicolor dominates at sample sites adjacent to surface water outflow pipes. The non-native protected Starlet Sea Anemone Nematostella vectensis was also significantly negatively correlated with organic matter and silt content. It is known to be sensitive to hypoxic-sulfidic conditions associated with high organic matter sediments. The anemone’s indiscriminate and efficient method of prey capture in high macrozoobenthic densities may disproportionately affect prey species, limiting their availability to native predators and negatively affect higher trophic levels. The anemone’s effect on native communities should be subject to further study. This thesis will serve as a baseline to compare subsequent surveys to, particularly post dredging and island construction works planned to commence in Poole Park lagoon in the late autumn of 2018.