A Tropical Eastern Pacific Barnacle, Megabalanus coccopoma (Darwin), in Southern California, following El Nino 1982-83

The Tropical Pacific Ocean experienced “El N iño” in 1982-83. The event was marked by increased water temperatures in the Eastern Pacific and, near shore in Southern California, the appearance of nekton normally found well to the south. The present note records the appearance of waifs of the large, tropical, benthic barnacle, Megabalanus coccopoma, in waters off San Diego, California, following this event. The timing of the appearance of this species, a year or so after El Niño 1982-83 was officially over, and the appearance of the related species, M. californicus, north of its normal range, a year or so prior to the recognition of El Niños 1940-41 and 1982-83, indicate that significant range extensions apparently related to El Niño events may bracket El Niño years designated by physical oceanographers. “ E l N i ñ o ” o f 1982-1983 in Southern Cali­ fornia consisted of 1) anomalously high sea surface temperatures over wide areas (as much as 4°C coastally), 2) reduced nutrient concentrations, 3) a significant rise in sea level (as much as 20 cm in September of 1983), 4) severe winter storms, 5) depression of the thermocline (deep mixed layer), especially off­ shore, 6) a vast reduction in macrozooplankton and kelp beds, and 7) the widespread nearshore occurrence of nekton normally found well to the south, off the coast of cen­ tral Mexico (cf. Dayton and Tegner 1984; McGowan 1985; Gains and Roughgarden 1987). While El Niño was generally con­ sidered over in 1983 in the eastern Pacific, it lasted a year longer in Southern California (M. Tegner, personal communication). Daily sea surface temperatures taken throughout 1983 at the Scripps Institution of Oceanography (SIO) pier showed positive anomalies of several degrees Celsius, except during the period of May through July, and as much as 4°C through the late summer and fall (Dayton and Tegner 1984). Except for three occasions in 1984, sea surface tempera­ tures were uniformly warmer than normal off 1 Manuscript accepted May 1986. 2 Scripps Institution of Oceanography, La Jolla, Cali­ fornia, 92093. the SIO pier, at least 2°C, but with highs of 4°C for a period of several months (M. Tegner, personal communication). Some of the warm­ ing has been attributed to an influx of waters from the west, but the appearance of south­ ern nekton and plankton, as well as physical data, indicate strengthening of the warm, northward-flowing, nearshore counter-current system (Figure 1; cf. Dayton and Tegner 1984, Norten et al. 1985, and Brodeur 1986). An example among the nekton has been the Red Crab, Pleuroncodes planipes Stimpson, juveniles of which are frequently transported north by the California Counter-Current, from approximately 25°N on the Pacific coast of Baja California to Point Conception (35°N). However, juveniles were reported somewhat north of Point Conception in 1983, and as far north as San Francisco in 1984 (38°N; Smith 1985). Furthermore, a sub­ tropical neritic euphausid, Nyctiphanes sim­ plex, became an im portant food of resident predators off Oregon and Washington in 1983 and 1984 (Brodeur 1986). Indeed, the effects of El Niño were felt in Canada (50°N; K abata 1985) and into the Gulf of Alaska (Cannon 1985). Waifs of a Tropical Eastern Pacific large, benthic acorn barnacle, Megabalanus cocco­ poma (Darwin, 1854), became established in intertidal and shallow waters off San Diego,