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RESEARCH recruitment Motivation MotivationMost marine organisms, from rockfish and giant kelp to seastars and barnacles have a multi-stage life cycle. In other words, juveniles and adults are fairly sedentary on a rocky reef or intertidal area while the early life stages (larvae or spores) are planktonic and travel through the ocean currents for weeks to months before settling or recruiting to the juvenile or adult habitat. The potential scales of movement by offspring away from the site of their parents are enormous. At present, we have only a limited understanding of the extent to which marine populations are controlled by variable recruitment rates and even less about how how ocean circulation affects the dispersal of early life stages. As a consequence, some fundamental questions are unknown for any marine species with a juvenile phase that disperses for more than a few minutes. What proportion of young arriving into a local population are products of local adults? What is the source of recruits for any local population? Where do the young produced in a local population go? A core part of our program is a large-scale recruitment monitoring effort. These studies continue and expand on existing recruitment monitoring programs at OSU (begun in 1989), UCSC (begun in 1994) and UCSB (begun in 1995), and resume and stabilize intermittent monitoring programs carried out at Hopkins Marine Station (begun in 1982). Recruitment monitoring quantifies the onshore consequence of patterns of larval transport in nearshore coastal environments. Long-term quantification of recruitment is essential if we are to distinguish long-term trends from natural annual and seasonal variability. Research Questions
Approach We sample recruitment collectors at monthly or biweekly intervals, but many of the processes that may determine successful recruitment can operate on finer time scales. For this reason, in some areas at certain times of the year, we monitor recruitment at the scale of 1-2 days. Also, to address this issue of scale, we are working to develop automated recruitment collectors for the moorings in order to increase the temporal resolution in larval sampling. This technology will allow sampling on daily or other short-term time scales. The sampling region also spans three biogeographic provinces. The core recruitment monitoring program includes a sizable fraction of the entire geographic range of many of the focal species. This will provide an unprecedented look at the large-scale patterns of recruitment variability. No comparable data set exists for any marine species. Research FindingsPatterns of recruitment along the West Coast PISCO has learned that transition points along the West Coast are more biologically abrupt than previously thought. In Oregon, we observe periodic current reversals that are associated with wind reversals. We have documented that these reversals are usually associated with barnacle recruitment events on the shore. Recruitment then drops sharply, not gradually, at Cape Blanco. In PISCO also has documented that recruitment of many species drops precipitously near Point Conception. Here southern species often do not recruit north of the point and, similarly, northern species do not recruit south of the point. Our surveys indicate that, in the south, low levels of larval input is correlated with very slow rates of recovery from disturbances. Thus, when disturbed (either by natural or human occurrences), these communities likely will take much longer to recover relative to communities elsewhere. Correlations between recruitment events and climate-related oceanographic eventsSeveral geographical patterns have emerged from our annual surveys of subtidal communities. The onset of PISCO in 1999 coincided with a period of strongly contrasting climatic events known as "El Niño" (1998), "La Niña" (1999) and more benign conditions typical of our coastal environment, "La Nada" (2000-2001). These climatic events can have dramatic effects on nearshore ocean circulation, nutrients, and water temperatures, which can influence the degree to which larvae or algal propagules are retained nearshore or advected offshore. Our research correlates strong differences in recruitment of young rockfishes with changes in climatic conditions. Species that spend long periods of time (3-4 months) in the plankton (and thus occur many kilometers offshore) exhibited greater recruitment during the La Niña year. In contrast, species that have shorter pelagic durations (= 1 month) recruited in Despite the year-to-year variation in abiotic conditions and macroalgal cover, many species appear resilient. Macroinvertebrate abundance varied little over the 3-year sampling period. The abundance of adults of most fish species also varied little from year to year. Changes that did occur were restricted to fishes less than two years old. This result indicates that while certain year classes are highly susceptible to episodic events, adult populations of both fishes and many macroinvertebrates are more resistant to year-to-year variability. Further monitoring is necessary to determine whether these species can withstand chronic changes in climate, larval supply, or other perturbations. By Jenn Caselle, Science Coordinator, and Renee Davis-Born, and Lydia Bergen, Policy Coordinators |
This fundamental gap in our knowledge about marine populations limits advances on many fronts. Managing fisheries, understanding the dynamics and evolution of marine populations and communities, and predicting the responses of coastal ecosystems to perturbations such as pollution, habitat loss, and the spread of exotic introduced species all await breakthroughs in this area. For example, the effectiveness of any marine reserve design is highly dependent on the degree to which populations within the reserve both are sustained by recruitment from other populations and supply recruits to other populations. 
To quantify rates of input of new individuals and detect temporal trends in these rates, we measure recruitment of key shallow-water species (including mussels, barnacles, sea stars, crabs, sea urchins, fishes, limpets, hermit crabs and macroalgae). We use a variety of tried-and-tested methods successfully employed by PISCO PIs and their students and post-docs. At all of our core sites in the rocky intertidal we have recruitment collectors. To extend the spatial scale of recruitment estimates of dominant organisms, partial sets of collectors have been deployed at other sites more distant from the campuses. In some areas, we also have collectors on instrumented moorings anchored in the nearshore ocean. In addition, we do visual recruitment surveys using SCUBA for organisms such as fishes. 
the Santa Barbara Channel, a persistent mid-channel eddy retains rockfish larvae. This oceanographic feature may also prevent pre-settlement invertebrate larvae from moving beyond Point Conception. Such eddies may be an important large-scale transport mechanism that moves water masses out of the local area and, as a result, prevents retention. Eddies also drive significant cross-channel and along-channel transport, which may lead to chaotic dispersal within the channel. 
greater numbers during the El Niño year. These relationships explain year-to-year variation in the relative recruitment of different kelp forest rockfishes.