The use of otolith morphology to indicate the stock structure of common coral trout (Plectropomus leopardus) on the Great Barrier Reef, Australia

We investigated the use of otolith morphology to indicate the stock structure of an exploited serranid coral reef fish, Plectropomus leopardus, on the Great Barrier Reef (GBR), Australia. Otoliths were measured by traditional one-and two-dimensional measures (otolith length, width, area, perimeter, circularity, and rectangularity), as well as by Fourier analysis to capture the finer details of otolith shape. Variables were compared among four regions of the GBR separated by hundreds of kilometers, as well as among three reefs within each region, hundreds of meters to tens of kilometers apart. The temporal stability in otolith structure was examined by comparing two cohorts of fully recruited four-year-old P. leopardus collected two years before and two years after a signif icant disturbance in the southern parts of the GBR caused by a large tropical cyclone in March 1997. Results indicated the presence of at least two stocks of P. leopardus, although the structure of each stock varied depending on the cohort considered. The results highlight the importance of incorporating data from several years in studies using otolith morphology to discriminate temporary and possibly misleading signals from those that indicate persistent spatial structure in stocks. We conclude that otolith morphology can be used as an initial step to direct further research on groups of P. leopardus that have lived at least a part of their life in different environments.

Some physiological effects of two algal epiphytes on the surfgrass Phyllospadix torreyi Wats.

Measurement of the physiological effects of the red algal epiphytes Smithora naiadum (Anders.) Hollenberg and Melobesia mediocris (Fosl.) Setch. and Mason on Phyllospadix torreyi Wats. were made near Hopkins Marine Station, Pacific Grove, California. Field studies revealed a significant influence of these epiphytes on both the breakage incidence and length, with that of Melobesia being the most pronounced. Analysis of the photosynthetic rate of the seagrass shows a decrease in the photosynthetic maxima in both epiphytized samples at a light saturating intensity. Under light limiting conditions, an increase in photosynthetic efficiency and a change in chlorophyll a composition in both epiphytized sample types suggest an adaptive mechanism similiar to those found in terrestrial and aquatic shade plants.