Abstract
BackgroundPhotosynthetic sponges are important components of reef ecosystems around the world, but are poorly understood. It is often assumed that temperate regions have low diversity and abundance of photosynthetic sponges, but to date no studies have investigated this question. The aim of this study was to compare the percentages of photosynthetic sponges in temperate Western Australia (WA) with previously published data on tropical regions, and to determine the abundance and diversity of these associations in a range of temperate environments.ResultsWe sampled sponges on 5 m belt transects to determine the percentage of photosynthetic sponges and identified at least one representative of each group of symbionts using 16S rDNA sequencing together with microscopy techniques. Our results demonstrate that photosynthetic sponges are abundant in temperate WA, with an average of 63% of sponge individuals hosting high levels of photosynthetic symbionts and 11% with low to medium levels. These percentages of photosynthetic sponges are comparable to those found on tropical reefs and may have important implications for ecosystem function on temperate reefs in other areas of the world. A diverse range of symbionts sometimes occurred within a small geographic area, including the three "big" cyanobacterial clades, Oscillatoria spongeliae, "Candidatus Synechococcus spongiarum" and Synechocystis species, and it appears that these clades all occur in a wide range of sponges. Additionally, spongin-permeating red algae occurred in at least 7 sponge species. This study provides the first investigation of the molecular phylogeny of rhodophyte symbionts in sponges.ConclusionPhotosynthetic sponges are abundant and diverse in temperate WA, with comparable percentages of photosynthetic to non-photosynthetic sponges to tropical zones. It appears that there are three common generalist clades of cyanobacterial symbionts of sponges which occur in a wide range of sponges in a wide range of environmental conditions.
Highlights
Photosynthetic sponges are important components of reef ecosystems around the world, but are poorly understood
Photosynthetic sponges are abundant and diverse in temperate Western Australia (WA), with comparable percentages of photosynthetic to non-photosynthetic sponges to tropical zones. It appears that there are three common generalist clades of cyanobacterial symbionts of sponges which occur in a wide range of sponges in a wide range of environmental conditions
The aim of this study was to determine the percentages of photosynthetic sponges in a temperate region and compare this with previous studies of tropical regions, and to explore the biodiversity of photosynthetic symbionts of sponges and their relative abundance in temperate south-western Australian waters. 5 m belt transects with high numbers of sponges were selected
Summary
Photosynthetic sponges are important components of reef ecosystems around the world, but are poorly understood. Photosynthetic sponges are very diverse in terms of the taxonomy of hosts and symbionts and their biogeography, occurring around the world in tropical and temperate oceans. They occupy a similar niche to hard corals, being filter-feeding benthic primary producers that provide food and shelter for a range of reef organisms. Photosynthetic symbionts include cyanobacteria, dinoflagellates, rhodophytes, chlorophytes and diatoms [5,6,7] These symbionts provide photosynthates [8,9,10] and possibly fixed nitrogen [11] to the sponge host. In addition to donating energy and carbon, cyanobacteria may benefit sponges by the production of secondary metabolites that act as antibacterials and deter predators [12,13]
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