Biofilms: The missing link in understanding the effects of ocean acidification on Settlement Selection?

Chair: Jean-Pierre Gattuso

Katie S Nelson1, Miles D Lamare1

 

1 Department of Marine Science, University of Otago, Dunedin, Otago, 9016, New

Zealand

 

Background:

Settlement and recruitment is a complex and critical juncture in the life history of benthic marine invertebrates. Over the course of the settlement process, marine invertebrate larvae move from a relatively stable pH condition in the pelagic environment to a more variable pH condition in the benthos. Additionally, biofilms cover all marine substrates and play a critical role in mediating the physiological and molecular level cues that induce settlement in benthic marine invertebrates. The polychaete tubeworm, Galeolaria hystrix, was used as a model species to determine if changes in biofilms reared at IPCC predicted levels of pH 7.8 (near future), pH 7.4 (extreme) would effect settlement selection and metamorphosis.

Methods:

Overall biofilm community composition was quantified using multiple methods including 1) r16S DNA analysis, 2) chlorophyll extractions and 3) diatom, ciliate and invertebrate  analysis  by  light  microscopy.     Larvae  were  reared  through  to competency at ambient pH and settled out onto biofilms in settlement assays that were scored at 24hrs, 48hrs and 5 days post introduction.

Findings:

Biofilm chlorophyll content and diatom coverage deceased with pH, regardless of biofilm age, along with expected shifts in microbial community composition. Successful settlement and metamorphosis was associated with pH treatment and biofilm  age;  larvae  preferred  old  (60  day)  pH  7.8  biofilms  and  young  (23  day) ambient biofilms that shared the most similar chlorophyll and diatom profiles.

Conclusions:

Ocean acidification can cause significant shifts in biofilm community composition that effect settlement selection. As with settlement selectivity, responses are likely species-specific and potentially related to feeding strategy and bacterial mediation of metamorphosis. If settlement patterns are altered, ocean acidification may cause shifts in the population distribution of benthic marine invertebrates in the inter-tidal and sub-tidal zones.