15m BT

Bottom Temperature Records (15 m) from the Point Loma Kelp Forest

Mia J. Tegner and Kristin L. Riser
Marine Life Research Group
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, California 92093-0201

Introduction

The Point Loma kelp forest, located offshore of San Diego, California, is one of the largest giant kelp (Macrocystispyrifera) forests in the world. The productivity and health of Macrocystis is very sensitive to nutrient availability, which is expensive to monitor on a regular basis. Temperature is inversely related to the concentration of nitrate, the nutrient that limits kelp growth; nitrate is not detectable above about 16°C in this region (reviewed in references below). Although there is some interannual variability in the curve, this strong inverse relationship allows use of temperature as a surrogate for nitrate-nitrogen availability or stress. Thus, we began measuring bottom temperatures during the 1982-84 El Niño on a grid of stations representing long- and cross-shore gradients of the forest. Here we present the data from a site at 15 m depth in the center of the forest (32°41.995’ N, 117° 16.111 W), our longest and most complete record. There are significant temperature differences between depths across the center of the forest (e.g., Dayton et al. 1992, 1999) as well as longitudinally at the same depth (Tegner and Dayton 1991), but the general patterns are very similar.

Methods

Insitu bottom temperatures were recorded with TempMentors (Ryan Instruments, Redmond, WA) and Hobo-Temp Temperature Loggers (Onset Computer Corporation, Pocasset, MA). One of the Hobo-Temps is pictured in Figure 1 (click on image to enlarge).

Figure 1. Although this instrument is attached off the bottom, the image illustrates a Hobo-Temp Temperature Logger as deployed underwater.

Temperatures were determined every three hours from the continuous record (eight values per day) and averaged by day (Figure 2) and by month.

Figure 2. Daily average bottom temperatures for the center of the Point Loma kelp forest, 1984-1998.

The annual curve (averaged by month plus and minus one standard deviation) for 1984-1998 is presented in Figure 3. The diving quarantine during the 1992 sewage outfall break (Tegner et al. 1995) and occasional equipment failures caused some gaps in the record.

Figure 3. The annual average curve for the center of the Point Loma Kelp forest,1984-1998, based on monthly averages plus and minus one standard deviation.

Citation Information

We would appreciate an acknowledgement of K. L. Riser and M. J. Tegner if you use these data. One of the references below may be cited for methods.

References

Dayton, P. K., M. J. Tegner, P. E. Parnell, and P. B. Edwards. 1992. Temporal and spatial patterns of disturbance and recovery in a kelp forest community. Ecological Monographs 62: 421-445.

Dayton, P. K., M. J. Tegner, P. B. Edwards, and K. L. Riser. 1999. Temporal and spatial scales of kelp demography: The role of oceanographic climate. Ecological Monographs 69: 219-250.

Tegner, M. J. and P. K. Dayton. 1991. Sea urchins, El Niños, and the long-term stability of Southern California kelp forest communities. Marine Ecology Progress Series 77: 49-63.

Tegner, M. J., P. K. Dayton, P. B. Edwards, K. L. Riser, D. B. Chadwick, T. A. Dean, and L. Deysher. 1995. Effects of a large sewage spill on a kelp forest community: Catastrophe or disturbance? Marine Environmental Research 40: 181-224.

Tegner, M. J., P. K. Dayton, P. B. Edwards, and K. L. Riser. 1996. Is there evidence for long-term climatic change in southern California kelp forests? California Cooperative Oceanic Fisheries Investigations Reports 37: 111-126.

Tegner, M. J., P. K. Dayton, P. B. Edwards, and K. L. Riser. 1997. Large-scale, low-frequency oceanographic effects on kelp forest succession: a tale of two cohorts. Marine Ecology Progress Series 146: 117-134.

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