Abstract
Microbial symbionts of marine sponges play important roles for the hosts and also for the ecosystems. The unique tolerance of marine sponge to a wide diversity of microbial symbionts allows them to acquire a wide variety of “evolutionary solutions” to environmental challenges. Ice scour is one of the main forces structuring Antarctic benthic communities and its effect is expected to increase as further warming is projected for the Western Antarctic Peninsula (WAP). The interaction of these physical drivers may have a significant impact shaping the microbiome of Antarctic sponges under current and future scenarios of climate change. The aim of this research was to assess how stressors such as warming and injuries produced by ice scour, affect the microbiome of the marine Antarctic sponge Isodictya kerguelenensis. under current and predicted scenarios. Individuals of I. kerguelenensis were sampled in shallow waters (10 m) off the coast of Doumer Island, Palmer Archipelago, WAP. In order to mimic the effect of tissue damage produced by ice scour, tissue samples were taken at day 0 (T0d) and 15 (T15d) from individuals placed in control (0.5 °C) and two temperature treatments (3 and 6°C). Our analysis of 16S libraries from the V4-V5 region revealed two phyla of Archaea and 22 of Bacteria. Proteobacteria and Bacteroidetes were the most representative in terms of both number of OTUs and sequence abundances. The analysis at OTU level showed significant effect of injury and treatment. Principal Coordinates Analysis (PCoA) showed a clear group of uninjured sponges and three other groups of injured sponges according to temperature. Our results also showed a group of OTUs that were only present in injured sponges, being potential markers of sponge damage. Our study suggests that disturbance produced by icebergs may have direct impact on the sponge microbiome. Future climate change scenarios with warming and increases in iceberg impacts may lead to prokaryotic symbiont disruption on sponge species, having potential cascading effects for the host and the functional roles they play in the Antarctic ecosystem; however, the potential effects of this disruption are yet to be further studied.
Highlights
The phylum Porifera, known as sponges, is a highly important metazoan, playing roles in three main areas: (a) impacts on the substrate, (b) bentho-pelagic coupling, and (c) sponge associations with other organisms (Bell, 2008).Sponges are the earliest diverged metazoan group still extant and continue to survive in vast numbers of marine and freshwater habitats, adapting to drastic changes in environmental factors and competing biota (Müller, 2003)
Research on other Antarctic invertebrates has shown the existence of differences in recovering from shell damage and shell thickness in the Antarctic bivalve Laternula elliptica depending on the level of exposure to ice scour (Harper et al, 2012)
The experimental design consisted of three treatments: control (0.5◦C) and two heat-stress treatments at 3◦C and 6◦C, and these same sponges were cut to mimic the effect of ice scour (n = 3 per treatment)
Summary
The phylum Porifera, known as sponges, is a highly important metazoan, playing roles in three main areas: (a) impacts on the substrate (provoking bio-erosion, building and stabilizing reefs, and consolidating and regenerating the benthos substrate), (b) bentho-pelagic coupling (interfering in carbon, silicon, oxygen, and nitrogen cycles and coupling energy from the pelagic to the benthic ecosystem), and (c) sponge associations with other organisms (facilitating primary production, being directly implicated in secondary production, and providing a complex microhabitat from bacteria and archaea to other macroinvertebrates and fish) (Bell, 2008).Sponges are the earliest diverged metazoan group still extant (van Soest et al, 2012) and continue to survive in vast numbers of marine and freshwater habitats, adapting to drastic changes in environmental factors and competing biota (Müller, 2003). Ice scour is considered to be a major force shaping the ecological characteristics of the Antarctic benthos in shallow waters (Gutt and Starmans, 2001; Brown et al, 2004; Barnes, 2017; Barnes et al, 2018; Lo Giudice et al, 2019; Morley et al, 2019). In some areas of the WAP, up to a third of the substrate in shallow waters is disturbed by icebergs within a year (Barnes, 2017). In this regard, some research has assessed the responses of benthic organisms to damage, such as that produced by ice scour. Similar studies on the effect of ice scour on the ecology/physiology of other sessile Antarctic organisms, such as sponges, are yet to be conducted
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