Matthew Bracken, assis­tant pro­fessor of biology, sur­veys bio­di­ver­sity along a rocky shore in Nahant. Photo by Michael Hutson.

Here’s another reason to cheer for the little guy. A new study co-​​authored by Matthew Bracken, assis­tant pro­fessor of biology in Northeastern’s Col­lege of Sci­ence, has found that rare species from the bottom of the food chain can have a large impact on an ecosystem’s health.

The find­ings were pub­lished in March in the online edi­tion of the sci­en­tific journal Ecology Let­ters.

Bracken and Brown Uni­ver­sity stu­dent Natalie Low con­ducted sev­eral exper­i­ments that ana­lyzed the impact of removing sea­weed and ses­sile ani­mals, such as mus­sels and bar­na­cles, from the rocky shores of Northeastern’s Marine Sci­ence Center in Nahant, Mass. The exper­i­ments were designed to mimic nat­u­rally occur­ring changes in bio­di­ver­sity on rocky shores.

The find­ings were star­tling. “We have shown that the loss of these extremely rare species — which col­lec­tively rep­re­sent less than 10 per­cent of the sea­weed and animal bio­mass at the base of the food web — causes major declines in the abun­dance and diver­sity of ani­mals, such as snails, crabs and other mobile ani­mals,” Bracken said.

Prior research on the extir­pa­tion of rare species from a par­tic­ular ecosystem focused on how the loss of top preda­tors — often referred to as “key­stone” species — affects plants and ani­mals at the bottom of the food chain. Bracken and Low, on the other hand, have shown that the loss of rare species from the base of the food chain, which they call “cor­ner­stone” species, can also reshape marine systems.

A pat­tern of decline emerged after only three weeks of exper­i­ments and per­sisted for the remainder of the five–week study. “Pre­vious work on the effects of rare predator removals took months to years to show strong effects,” Bracken said. “We found strong effects of rare sea­weed removals after only a few weeks.”

Written by Lori Lennon, Col­lege of Science.