LIFE IN THE OCEAN’S TWILIGHT ZONE HAS LONG FASCINATED SCIENTISTS. But even though there are gigatons of fish in the twilight zone, surprisingly little is known about them. WHOI scientists are building the first long-term observation network focused on life in the twilight zone. “It’s going to be a huge advance.”Sound sources anchored at the network’s four corners will send out acoustic signals that can be “heard” by tiny receivers in tags attached to bigeye tuna and swordfish, two commercially important species known to dive into the twilight zone for prey. Their movements fast-track atmospheric carbon from surface waters to the deep ocean, helping to regulate global climate.