For more than 100 years, marine biologists have sought an understanding of how the minute larvae of marine invertebrate animals – cast out into the vast ocean – find and settle in the right ecological settings for survival, growth and reproduction. A grant, totaling more than $870,000, from the Gordon and Betty Moore Foundation to the University of Hawai'i (UH) will support research to understand the mechanisms by which marine biofilm bacteria – bacteria that live in slime films on the surfaces of all objects submerged in the sea – induce the settling of larvae of marine invertebrate animals.
In the last two decades there has been growing recognition that bacteria are likely the factor that causes many free-floating larvae to settle and transform, yet very little is known of the diversity of bacteria that stimulate larvae to settle, and less is known of the mechanisms through which these bacteria act.
With this grant, a UH research team will focus on a small tube worm, Hydroides elegans, that settles onto marine surfaces in warm ocean waters around the world where they form masses of hard, calcified tubes. The team, led by professor Michael Hadfield at the Kewalo Marine Laboratory, Pacific Biosciences Research Center in the School of Ocean and Earth Science and Technology (SOEST) at UH-Mānoa (UHM), includes larval biologist Brian Nedved (Kewalo Marine Laboratory), microbiologist Rosie Alegado (Center for Microbial Oceanography: Research and Education, SOEST, UHM), and natural products chemist Shugeng Cao (Department of Pharmaceutical Sciences, Daniel K. Inouye College of Pharmacy, UH-Hilo).
"We have isolated specific strains of bacteria from marine biofilms that induce the worm's larvae to settle and metamorphose. Using these bacteria, our goals are to determine what factors produced by the bacteria cause the larvae to stop swimming, stick to the surface and undergo the dramatic physical changes that make up the process of metamorphosis," said Hadfield.
During the two-year project, Hadfield and colleagues will also study the larva's receptor or response system. Understanding the relationship between the tube worm and bacteria will shed light on the complex phenomena that lead to the establishment and maintenance of healthy marine seafloor communities throughout the ocean.
Larvae are very particular in selecting surfaces on which they will settle – which is why different communities of invertebrate animals live on sandy beaches, rocky coasts, pilings and other surfaces in enclosed harbors.
"For many – probably most – of these animals, biofilm bacteria are the key. This research holds promise to reveal the basis for differential larval settlement in the sea," said Hadfield.
The current project arose from long-running research in Hadfield's laboratory. In the lab, Hadfield has studied the biology of marine larvae and long ago established Hydroides elegans as a useful model organism for studying larval settlement and "biofouling" – the accumulation of undesirable organisms on marine surfaces.
Larva of barnacles, tube worms, oysters, and other organisms settle on ship hulls, pilings and in the pipes used to draw cooling water into electrical plants and factories resulting in millions of dollars in loss annually in these maritime trades. Knowing why larvae settle in particular places is an important first step in ensuring they do not settle where they are not wanted.
Moreover this work may have real-world application to areas such as mariculture, where the goal is to successfully raise larvae of clams and oysters and have them settle on a particular surface, as well as for the development of methods to deter larval recruitment onto the hulls of ships and other marine surfaces.