Vogeler, S. | bioRxiv Science

bioRxiv2026

Ontogeny of settlement behaviours in response to Grammatophora marina diatom biofilms in the marine polychaete, Platynereis dumerilii

Settlement, the transition of a swimming planktonic larva to a crawling or sessile benthic juvenile, is a key process in the development of many marine invertebrates. Successful recruitment via larval settlement is critical for the development and maintenance of seafloor ecosystems. Microbial biofilms act as positive cues for larval settlement across diverse taxa, yet the behavioural processes preceding settlement are poorly understood. Here, we investigated age-dependent changes in settlement behaviour in the marine polychaete Platynereis dumerilii larvae in response to Grammatophora marina diatom biofilms. Settlement behaviours (crawling, crawling speed, and track straightness (tortuosity)) were quantified from recordings of larvae at five developmental stages (mid-trochophore to late-nectochaete) in the presence or absence of diatom biofilms, using image segmentation and spot-tracking software. As larvae developed, the proportion of individuals crawling (settlement) over the biofilm increased. Older larvae colonised biofilms more rapidly and showed greater discrimination between G. marina biofilms and non-biofilmed controls. The movement trajectory of older larvae also straightens compared to individuals swimming in the presence of biofilms, or behaviour witnessed in the absence of biofilms. The proportions and magnitudes of these behaviours may reflect changing prioritisation of sensory inputs from physical and chemical cues as larvae develop. Our findings suggest that behavioural traits that are associated with settlement are developmentally programmed in P. dumerilii. Understanding settlement behaviours in P. dumerilii expands on this species behavioural repertoire and sheds light on the evolutionary relationship between marine larvae and microalgal biofilms.

animal behavior and cognition↗

bioRxiv2021

Investigation of vitamin B12 concentrations and tissue distributions in larval and adult Pacific oysters and related bivalves

Vitamin B12 (B12) is an essential micronutrient for all animals, but is not present in plants and is produced de novo only by bacteria or archaea. Accordingly, humans must derive required B12 from eating animal products or vitamin supplements, as deficiencies can lead to severe health issues including neuropathy. An often overlooked source in the human diet of B12 is shellfish, in particular bivalves, which have significantly higher levels of B12 than other animal sources, including all vertebrate meats. Origins and key metabolic processes involving B12 in bivalves remain largely unknown, despite the exceptionally high levels. In this study, we examined in several Australian bivalve species, hypotheses concerning B12 utilisation and uptake through diet or microorganism symbiosis. Vitamin B12 is not distributed evenly across different tissues types of the Pacific oyster, the commercial scallop and Goolwa cockle (pipi), with higher accumulation in the oyster adductor muscle and gill, and mantle and syphons of the Goolwa cockle. Oyster larvae before first feeding already contained high amount of B12; however, a significant decrease in B12 concentration post metamorphosis indicates a higher utilisation of B12 during this life event. We demonstrated that microalgal feed can be supplemented with B12, resulting in an enriched feed, but this did not result in an increase in larval B12 concentrations when oyster larvae were fed with this diet relative to controls, thus supporting the theory that a B12 producing microbiome within bivalves was the potential source of B12 rather than feed. However, B12 concentrations in the digestive tract of adult oysters were low compared to other tissue types, which might challenge this theory, at least in adults. Our findings provide insight into B12 uptake and function in bivalve species, which will aid the promotion of bivalves as suitable B12 source for humans as well as provide crucial information to the aquaculture industry in relation to optimisation of vitamin supplementation in bivalve hatchery production.

ecology↗