Recruitment

Standard monitoring unit for the recruitment of reef fishes (SMURF)

PISCO researcher Jenn Caselle collects a standard monitoring unit for the recruitment   of reef fishes (SMURF) used to determine spatial and temporal patterns of reef fish recruitment. Photo credit: Michael Sheehy.

Recruitment is the process that describes the settlement of planktonic larvae or spores to suitable habitat.

Most marine organisms, from rockfish and giant kelp to seastars and barnacles have a multi-stage life cycle. This means that while juveniles and adults are fairly stationary on a rocky reef or intertidal area, 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 ocean circulation affects the dispersal of early life stages.

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 disturbances such as pollution, habitat loss, and the spread of 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.
 

Large-scale recruitment studies

Large-scale recruitment studies are part of PISCO’s core monitoring program.  These studies spans three biogeographic provinces that range from Point Conception in the south to Point Reyes in the north. This area represents a sizable fraction of the entire geographic range of many of the focal species and provides an unprecedented look at the large-scale patterns of recruitment variability. No comparable data set exists for any marine species.

 Barnacle recruitment plates

Barnacle recruitment plates used to quantify number of recruits.
Photo credit: Peter Taylor.

PISCO monitors recruitment at our core sites in the rocky intertidal and kelp forests using a variety of artificial collectors as well as visual surveys. We measure the rates of input of key shallow-water species (including mussels, barnacles, sea stars, crabs, sea urchins, fishes, limpets, hermit crabs and macroalgae). and detect if these rates change over time and space. These samples are typically collected at monthly or biweekly intervals, however many of the processes that may determine successful recruitment can operate on finer time scales. To address this issue of scale, we periodically perform fine temporal-scale recruitment studies, measuring recruitment weekly or even daily.

PISCO’s study has yielded vital information on the relationship between recruitment of marine organisms and nearshore circulation, climatic events such as El Niño and La Niña and coastal upwelling patterns. Moving towards a predictive capability for recruitment along the West coast will be vital for managers in design of MPAs and Ecosystem based management.

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