Patterns of fish and macro-invertebrate distribution in the upper Laguna Madre: bag seines 1985-2004

摘要

The Laguna Madre is a hypersaline lagoon. Despite harsh conditions, the upperLaguna Madre (ULM) is a highly productive ecosystem and a popular sportfishing area,especially for spotted seatrout and red drum. It is also the most important Texas bay forcommercial fishing of black drum. TPWD?s Coastal Fisheries division beganconducting routine monitoring of coastal fishery resources in 1977 to guidemanagement. The goal of the present study was to improve understanding of spatiotemporaltrends in relative abundance of selected fish and macro-invertebrate species inthe upper Laguna Madre. I used TPWD?s bag-seine and water-quality data from theyears 1985-2004 to examine variation in species? relative abundances and relationshipsto several environmental factors. I hypothesized that one or more of these variables,alone or in combination, were related to spatial and temporal trends in communitycomposition. I used detrended correspondence analysis (DCA) to measure speciesturnover (beta diversity) and to determine which model (linear or unimodal) of speciesresponse along a gradient to apply. I used canonical correspondence analysis to relatespecies abundances directly to explanatory variables. The explanatory variables were tested for significance and the variance partitioned among three groupings: temporal,spatial and environmental.DCA indicated complete species turnover along two dimensions: seasonal andspatial. It also indicated that a unimodal method such as CCA was appropriate forfurther analysis. The CCA model included 39 variables. The included variablesexplained 14% of the variation in species abundance in the data set. Since the first fouraxes explained 67% of the variation contained in the first two DCA axes, the chosenexplanatory variables were sufficient to explain the majority of the tractable variation inspecies abundance. The variance partitioning procedure indicated that temporal effectswere the most important in explaining species variation in the Upper Laguna, followedby the spatial component. The pure environmental component explained the leastamount of variation.In this study, much of the variability in species abundance was due to thespawning patterns of estuary-dependent species, most of which spawn in the spring andsummer months, leading to higher abundances from spring through fall.