Research Findings


Population Replenishment of Reef Fish

As part of PISCO’s kelp forest monitoring program, led by PISCO/UCSC principal investigator Mark Carr and PISCO/UCSB science coordinator Jenn Caselle, divers count young rockfish and kelp bass each year at sites from Monterey Bay to the Channel Islands. These summer surveys of ecologically and economically important species provide scientists and managers with a large-scale, long-term perspective on the distribution and year-to-year changes in population replenishment.

Conducted since 1999, the surveys reveal interesting geographic patterns and changes over time (see figure, below). Kelp forests located near each other, such as the Hopkins and MacAbee sites in Monterey Bay, tended to have similar trends in their numbers of young rockfish (red and pink lines on graphs). More distant sites, such as Sandhill Bluff (purple lines), had different trends.

On a regional scale, kelp forests located at, above, and below Point Conception displayed distinct trends in fish population replenishment. For example, young kelp bass occurred only at southern sites, but these sites had few young rockfish. Conversely, sites north of Point Conception had greater number of young rockfish, but young kelp bass have not been encountered during surveys at these sites.

These findings suggest that coastal currents strongly influence patterns of reef fish population replenishment. To understand these local- and regional-scale linkages, PISCO is conducting ongoing studies using oceanographic instruments and devices that collect young fish. Information from this research informs the design and evaluation of marine reserves and other management efforts.

Dramatic Local Changes in Kelp

In 1999, PISCO initiated an intensive program to monitor kelp forests along the West Coast. Initially the effort was concentrated in California (Monterey Bay and Santa Barbara). After establishing reliable protocols, PISCO expanded the large-scale, long-term monitoring program to the Channel Islands, Big Sur, and Oregon. PISCO scientists are generating new insights into the population dynamics of the kelp that form these rich habitats.

Kelp forest surveys from 1999 to 2002 showed regional changes in kelp abundance, as well as strong differences between nearby sites. Historically, scientists have been well aware of fluctuations through time. For example, kelp tends to decline along the coast during El Niño and increase during La Niña. However, PISCO’s intensive sampling has revealed dramatic local variability, even when large-scale climatic shifts are not a factor. Even between sites separated by only a few kilometers, such as along the Monterey Peninsula, trends in kelp abundance can differ markedly.

PISCO is investigating why this variability occurs and how it differs along the entire West Coast. Over the next five years, the monitoring program will grow to include more studies of the ecological processes that shape the trends in kelp abundance. Ultimately, PISCO seeks to identify the consequences of these kelp dynamics for invertebrate and fish populations, many of which are ecologically, economically, and recreationally important.

Kelp forests are not all alike. This figure shows the average abundance of seaweed species at six sites over four years. The percentages of bull kelp (Nereocystis) and giant kelp (Macrocystis) in the kelp-forest canopy are represented by the line drawings. On a regional scale, bull kelp becomes less predominant from north to south, and giant kelp increases. The colored bars indicate the relative abundances of understory seaweed species, which vary within and among regions. Sea spatula (Pleurophycus), for example, was recorded only in Oregon, and its abundance varies markedly (50% to 4% cover) between sites separated by only a few kilometers. Illustrations by Diana Steller.

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