The effect of environmental and anthropogenic factors on the microbiome of the sponge, Halichondria panicea, at three coastal sites with different bathing water quality in North east England

Abstract The breadcrumb sponge, Halichondria panicea , is a cosmopolitan marine species. Life functions, such as feeding, metabolism and defence, are maintained through microbial symbiosis. As such, perturbations to the symbiotic balance can be expected to affect the health and survival of the sponge. Although generally tolerant of environmental variables, such as temperature, pH and salinity, responses to anthropogenic factors are poorly understood. In this study, the microbial community of the H . panicea was examined over the course of 1 year. Sponge and seawater samples were collected in January, April, July and October 2022, from three locations with different levels of bathing water quality, according to the UK’s Environment Agency. Samples were sequenced using the 16S ribosomal RNA (rRNA) gene, and amplicon sequence variants (ASVs) were inferred from the generated data. Differences in bacterial diversity and abundance among sponge samples from the three locations were examined. A correlation test was used to study the effect of physical and chemical environmental factors along with faecal indicator bacteria on the abundance of the top ten most abundant bacterial phyla. Environmental factors (determined from seawater physicochemical properties) and pollution (determined from trace metals, nutrients and faecal bacteria levels) were found to play an important role in shaping the microbial community of this sponge. The sponge microbiome showed a noticeable seasonal shift, with some species flourishing in January and others emerging in April, notably the faecal and coliform bacteria. Sponge microbiomes from sites with poor-quality bathing water were generally less diverse and had lower microbial abundance, resulting in a greater range of intra-species dispersion than those of sponges living in excellent–good quality waters.