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Host-microbe interactions are ubiquitous and play important roles in host biology, ecology, and evolution. Yet, host-microbe research has focused on inland species, whereas marine hosts and their associated microbes remain largely unexplored, especially in developing countries in the Southern Hemisphere. Here, we review the current knowledge of marine host microbiomes in the Southern Hemisphere. Our results revealed important biases in marine host species sampling for studies conducted in the Southern Hemisphere, where sponges and marine mammals have received the greatest attention. Sponge-associated microbes vary greatly across geographic regions and species. Nevertheless, besides taxonomic heterogeneity, sponge microbiomes have functional consistency, whereas geography and aging are important drivers of marine mammal microbiomes. Seabird and macroalgal microbiomes in the Southern Hemisphere were also common. Most seabird microbiome has focused on feces, whereas macroalgal microbiome has focused on the epibiotic community. Important drivers of seabird fecal microbiome are aging, sex, and species-specific factors. In contrast, host-derived deterministic factors drive the macroalgal epibiotic microbiome, in a process known as "microbial gardening". In turn, marine invertebrates (especially crustaceans) and fish microbiomes have received less attention in the Southern Hemisphere. In general, the predominant approach to study host marine microbiomes has been the sequencing of the 16S rRNA gene. Interestingly, there are some marine holobiont studies (i.e., studies that simultaneously analyze host (e.g., genomics, transcriptomics) and microbiome (e.g., 16S rRNA gene, metagenome) traits), but only in some marine invertebrates and macroalgae from Africa and Australia. Finally, we introduce an ongoing project on the surface microbiome of key species in the Strait of Magellan. This is an international project that will provide novel microbiome information of several species in the Strait of Magellan. In the short-term, the project will improve our knowledge about microbial diversity in the region, while long-term potential benefits include the use of these data to assess host-microbial responses to the Anthropocene derived climate change. [ABSTRACT FROM AUTHOR]

The benthic infauna of mangrove forests have received little research despite their importance in regulating ecological processes and nutrient cycling. The majority of studies of benthic community in mangrove systems have either focused on the adjacent tidal flats, or areas with high density of pneumatophores without entering within the forest, giving a misleading impression that mangrove infauna community is understood in detail. To fill the knowledge gap we investigated the composition and distribution of benthic taxa across a tidal gradient in two meso-tidal tropical estuarine mangrove forests in north Queensland, Australia. We used a 10-cm corer to sample inside the mangrove forest and on the adjacent tidal flat. Taxonomic composition was vastly different between the tidal flat and the mangrove forest. In fact, although peracarid (e.g. amphipods) characterized the community of tidal flats, they were never recorded within the forest. The contrasting community composition likely denotes contrasting ecological role of the two habitats. In particular, because peracarids are a key component of juvenile fish diets, their absence within the forest probably limits foraging opportunities for many juvenile fish within the forest, while their dominance on adjacent tidal flats suggests that these are likely to be the key feeding areas. [ABSTRACT FROM AUTHOR]

Our knowledge of suitable criteria to determine rarity in most marine invertebrates is lacking, thus hindering targeted impact studies, long-term monitoring programs, and associated conservation strategies. Standardized definitions of rarity are required to enable comparisons of different assemblages and taxa. Gaston (Rarity, Chapman and Hall, Melbourne, 1994) has recommended that rare species are defined as the lowest quartile of species in the assemblage. In this study, the 25% 'cut-off' was applied to intertidal macromolluscs along the Illawarra Coast, Australia from 200 surveys of 13 reefs, using three measures of population structure; (1) local abundance (numerical rarity); (2) number of locations (spatial rarity) and; (3) percent of surveys (temporal rarity). Rare species were consequently defined as those species with no more than; (1) a local abundance of two individuals; (2) a regional occurrence at two reefs and/or; (3) a temporal occurrence in 2% of all surveys. These cut-off values increased when only intertidal specialists were analysed. Using a combination of all three measures, 62 species (42%) were classified as regionally rare, but only four of these were true intertidal specialists. Most species were rare by only one or two definitions of rarity; illustrating the importance of considering multiple measures of rarity and the need to design specifically targeted survey methods for future monitoring. Many species that are rare by all three definitions are likely to be temporary immigrants, as subtidal species were significantly more likely to be classified as rare. Clearly many factors can influence the rarity of marine invertebrates on intertidal reefs, and these must all be considered to set appropriate conservation priorities. [ABSTRACT FROM AUTHOR]