Large scale pattern of recruitment by the labrid, Semicossyphus pulcher: Causes and implications

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Abstract
The pattern of recruitment of sheephead, Semicossyphus pulcher, is described throughout a major portion of its range over a period of 7-9 years. The relative recruitment success was determined uing both field transects and age-structure data. The observed pattern of recruitment was compared to both spatial and year-to-year variations in the current regime within the region using both average flow data (CalCOFI data base) and satellite imagery. It was found that in areas with larval sources to the north and south, recruitment occurred consistently from year-to-year. However, in areas where there was no larval sources "upstream" of the typical current direction, recruitment was highly variable and dependent upon anomalous events in the current flow. These anomalous events are considered on two levels: low-level events, which last from days to weeks, thereby affecting recruitment of only one or a few species, and high-level events, which last from months to years (e.g. El Nino events), affecting recruitment of many species. A positive relationship is found between frequency of recruitment events and density of adult populations. In addition, the persistence of populations is dependent upon recruitment frequency and the longevity of the individuals. The interaction between recruitment frequency, population density and persistence is considered to be important in determining the northern distribution limit of sheephead at Point Conception (also a major break for many other species). In the past, this faunal break has typically been attributed to temperature differences and inferred physiological constraints. It is concluded, from the findings in this study, that the faunal break a Point Conception is heavily influenced by hydrographic constraints on dispersal.