San Diego’s three major attractions — Sea World, San Diego Zoo and the city’s expansive beaches — are gearing their workforces for a summer full of challenges. The lines will grow for those seeking part-time jobs and, in some cases, available positions will be slim. SeaWorld may offer the most opportunities as it plans to expand its number of employees from 2,500 to 4,000 for the three peak summer months, starting on Memorial Day weekend. Lifeguards will take on 160 employees to patrol the sands from Ocean Beach to Black’s Beach. Meanwhile, the zoo will lower the number of general hires from 600 to 300, while putting a greater emphasis on its college educational program.  Interns will assist in key areas, said zoo officials. Peak days will be Memorial Day, Fourth of July and Labor Day — as well as additional demands in the late-evening periods. “Economically, it’s still slow and we’ re not under any illusion that visitations will be anything like it was a number of years ago, but we’re pleased so far in what we’ve seen (during the spring),” said SeaWorld media relations representative Dave Koontz.  “The new Dolphin show, which debuts on Memorial Day, could make a big difference.  “We hire for enthusiasm and attitude,” he said. “These people will have to interface with our visitors in the park. Of course, we have a number of seasonal rehires who might assist with the animals.” SeaWorld job opportunities will be available in ride operations, merchandising, food service, entertainment, ticket selling and guest relations. The San Diego Lifeguard Services provides public safety to users of San Diego’s coastline and ocean waterways from Point Loma to La Jolla. Beach areas include Ocean Beach, Mission Beach, Pacific Beach, Windansea, the Children’s Pool, La Jolla Cove, La Jolla Shores, Black’s Beach, and Mission Bay. Lt. Nick Lerma of the Mission Bay lifeguard base said all the towers are in place and added lifeguards will spring into action on Memorial Day. “El Niño has battered the coastline and rip tides have been prevalent,” Lerma said. “Between 40 and 50 new hires have compensated for vacancies to establish 200 seasonal lifeguards.” “Roughly 160 additional positions will be filled for the summer, including our junior lifeguard program,” he said. “We’re in spring mode and preparing for summer.”  The temporaries will receive a three-day refresher course and be retested for physical skills. Lerma said El Niño has beat up the ocean so rip tides will be a challenge for swimmers    “That represents 80 to 90 percent of our rescues,” he said. “Of course, the ancillary things like the board walks, lacerations, stingrays and jellyfish, surf boarders and some law enforcement issues are all part of the package.” San Diego Zoo community relations representative Tim Mulligan said there are three reasons for the cutback in hiring there: the economy, an effort to give the regular workers more hours and a college training program. “We haven’t had as much turnover and we’ll have some rehires,” Mulligan said. “We’ll have people on board by Memorial Day and remaining  through Labor Day.  Those who do a good job in the summer might be rehired for the Christmas holiday. Usually, we get several hundred applications and I think there will be more than in the past.”   The zoo’s Institute for Conservation Research will offer 130 summer college student fellowships, affording 12-week internships. Mulligan remained optimistic. “If summer is anything like spring break, then we are looking for good numbers.” On an extremely good day, 20,000 people will roam the 107 acres, he said.