Barnacles go with the flow

Guest speaker talks dispersal methods of invertebrates.

A study led by Claudio DiBacco from the Bedford Institute of Oceanography in Nova Scotia has discovered that barnacle larvae (called cyprids) have a simple, yet effective, behaviour for traveling around the sea.

“Ocean invertebrates typically have a planktonic larval stage,” DiBacco explained. “This is their best chance to disperse across large distances.” However, to reach maturity, the larvae must return to the coast and settle.

The question for years has been how this is possible. Cyprids are microscopic in size; crossing miles of ocean seems like a Herculean task for them. Numerous explanations have been proposed, and the most compelling is the examination of cyprid behaviour in downwelling convergence zones—regions of the ocean where physical conditions cause water to come together and rush downwards.

An earlier study found that cyprids tended to be concentrated in the upper half-meter of these zones, which occur around the world. Thus, it was suggested that cyprids were taking advantage of the currents to minimize their energy expenditures in returning. But how they knew what to do was unclear, with explanations ranging from the innocuous (such as moving towards light) to the convoluted (such as measurement of angles to celestial bodies).

DiBacco’s work, which he discussed in a talk Mount Allison on Friday afternoon, aimed to determine what was driving the cyprid’s behaviour. To do this, he carefully designed and tested a special flume to mimic conditions of a downwelling zone. Pumps drove water from the top of a cylinder to the bottom, with minimal turbulence. A pair of video cameras were set up to observe behaviour of cyprids added to the flumes, and special software analysed the video data, assessing the movement tracks of individual cyprids.

Successful cyrpids tended to show a diversity of strategies to stay in the water column—some hovered, expending energy to remain in one spot, while others alternated between swimming up, then sinking slowly down to rest and recover. All exhibited “positive rheotaxis”—their instincts were to fight the current, letting the convergence zones carry them shoreward.

“These are very simple organisms, hard-wired with a single purpose,” said DiBacco. “Many complex explanations [for their behaviour] have been put forward, and that’s the first indication that you’re probably wrong.”

DiBacco noted that his use of complex techniques in the study of simple behviour is justified by high-quality results. He finished his talk by telling students to be wary of alarmist news articles about “expensive” and “frivolous” research work, saying that, “science for the sake of curiosity is never a bad thing.” He is continuing research at BIO, using new techniques to study the potential effects of climate change on ocean invertebrates.

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