Bunaken National Park has been surveyed for a fourth time in 14 years, in an attempt to establish the species composition of heterobranch sea slugs in a baseline study for monitoring programs and protection of this special park. These molluscs are potentially good indicators of the health of an ecosystem, as many are species-specific predators on a huge variety of marine benthic and sessile invertebrates from almost every taxonomic group. Additionally, they are known to contain bio-compounds of significance in the pharmaceutical industry. It is therefore of paramount importance not only to document the species composition from a zoogeographic point of view, but to assist in their protection for the future, both in terms of economics and aesthetics. These four surveys have documented more than 200 species, with an approximate 50% of each collection found only on that survey and not re-collected. Many species new to science have also been documented, highlighting the lack of knowledge in this field.

Background: Bunaken National Park (BNP) is one of the most famous marine national parks in Indonesia with an extraordinary diversity in marine life forms. However, this diversity is threatened by an increasing population on the islands, ongoing destructive fishing techniques and lately by an increase in tourism. Protecting and managing the future use of BNP resources will require the assessment of both, local marine biodiversity through monitoring efforts and the identification and subsequent reduction of any threats or changes in the park. A high diversity in marine Heterobranchia indicates a high diversity of metazoan life forms and a diverse habitat structure. Surveying the complete biological diversity across taxonomic groups found in BNP would be an extensive undertaking, so focus on heterobranch diversity as an indicator of coral reef health was initiated and a model group on which future monitoring and conservation efforts can be based is provided. This study follows up the first investigation of marine Heterobranchia in BNP, conducted 12 years ago, while assessing molluscan diversity, and intends to present a base line for future monitoring programs. Results: The diversity of marine heterobranchs around BNP was surveyed with an emphasis on Bunaken Island by diving and snorkeling at nearly 20 sites. Species are listed with photographic documentation (81 species) and results compared with the former study on molluscan species diversity in BNP. Taking these two studies into account 135 species are now recorded from BNP. The low overlap of described species (21) between the two BNP studies illustrates the gap of knowledge about overall species diversity in this particular area. A comparison with other studies from the region and Indo-Pacific also provides evidence for undersampling, but show similar taxa composition except of a somewhat higher cladobranch number in relation to Anthobranchia. Conclusions: BNP is still under-sampled with regard to sea slug diversity. Thus conclusions as to whether or not a shift in species has occurred during the 12 years since the first study cannot be drawn. More and extensive studies are necessary to completely document the species richness in this area.

Nudibranchia, marine soft-bodied organisms, developed, due to the absence of a protective shell, different strategies to protect themselves against putative predators and fouling organisms. One strategy is to use chemical weapons to distract predators, as well as pathogenic microorganisms. Hence, these gastropods take advantage of the incorporation of chemical molecules. Thereby the original source of these natural products varies; it might be the food source, de novo synthesis from the sea slug, or biosynthesis by associated bacteria. These bioactive molecules applied by the slugs can become important drug leads for future medicinal drugs. To test the potential of the associated bacteria, the latter were isolated from their hosts, brought into culture and extracts were prepared and tested for antimicrobial activities. From 49 isolated bacterial strains 35 showed antibiotic activity. The most promising extracts were chosen for further testing against relevant pathogens. In that way three strains showing activity against methicillin resistant Staphylococcus aureus and one strain with activity against enterohemorrhagic Escherichia coli, respectively, were identified. The obtained results indicate that the sea slug associated microbiome is a promising source for bacterial strains, which hold the potential for the biotechnological production of antibiotics.

We describe a new species, Moridilla jobeli sp. nov.