Timothy Lee Ichthyoplankton Ecology Spring 2010 1 Characterizing Mid-summer Ichthyoplankton Assemblage in Gulf of Alaska: Analyzing Density and Distribution Gradients across Continental Shelf Timothy Seung-chul Lee ABSTRACT Ichthyoplankton play critical role in maintaining and characterizing complex marine ecosystems. Gulf of Alaska (GOA) encompasses one of most diverse ichthyoplankton assemblages in northern Pacific. This study assessed mid-summer distribution and density patterns of six species in larval stage across GOA’s continental shelf, and assessed patterns of density gradients with three environmental variables, (temperature, salinity, attenuation). The chosen taxa are Theragra chalcogramma, Hippoglossoides elassodon, Atheresthes stomias, Lepidopsetta bilineata, Bathyagonus alascanus, and Gadus macrocephalus. I hypothesized that densities for all six taxa will be greatest in coastal waters and in parts of shelf with many islands, because these regions have greater proportion of shorelines. The study region was stratified to three shelf regions to compare ichthyoplankton densities between coastal and open waters. It was also stratified to six alongshore regions to compare densities between regions of low and high shoreline proportions. One-way ANOVA and post-hoc pairwise comparisons were used to test density significance across shelf and alongshore strata. Most species exhibited highest densities in costal shelf strata but most did not concentrate heavily in alongshore strata with islands. Linear regression and correlation tests were used to measure responses of densities against attenuation, salinity, and temperature. Two taxa had positive relationship with temperature, four taxa had inverse relationship with salinity, and five taxa had declining densities with increasing attenuation. Further research is needed to determine which environmental factor determines ichthyoplankton assemblage variations in GOA’s continental shelf. KEYWORDS Ichthyoplankton, Density, Temperature, Attenuation, Salinity Timothy Lee Ichthyoplankton Ecology Spring 2010 2 INTRODUCTION Marine fish habitats are among the most fascinating and complex environments; interwoven with dynamic physical factors, they contain some of most biologically diverse communities (Hollowed et al. 2009). Physical factors including climate, bathymetry, salinity, current type, and nutrient transport alter organism biomasses (Doyle et al. 2009), thereby contributing to incredible biodiversity. These factors affect fishes’ spatial and temporal distributions seasonally and annually (Brodeur et al. 1995). The distribution, density, and community structure of marine fish differ not only between species but also between life stages (Matarese et al. 1989). Detailed knowledge of marine fishes’ early life histories is essential to understand fish recruitment; recruitment is defined as the distinct effects of physical and biological factors between different life stages (Doyle et al. 2009). Understanding early life history helps determine species-specific and life stage-specific patterns of densities and distributions based on physical environment (Brodeur et al. 1995). However, little is known about early life histories of fishes throughout marine ecosystems globally (Doyle et al. 2009). Ichthyoplankton are fish in egg, larval, and juvenile stages (Southwest Fisheries Science Center 2007). They depend on nutrients, zooplankton, and phytoplankton for survival; ichthyoplankton concentrations differ between seasons and regions (Brodeur et al. 1995). Early life history studies determine species’ distribution, spawning grounds, stock sizes, and habitat shifts through life stage progression (Matarese et al. 2003). Many ichthyoplankton in Gulf of Alaska for example, once mature, are considered ecologically vital for biomass studies and stock assessment; they are also important for bottom trawls and long-line fisheries (Mueter & Norcross 2002). Because many marine organisms are highly dependent on ichthyoplankton for survival, early life history research can characterize marine ecosystems over time (Matarese et al. 2003). Studying the association of ichthyoplankton with with physical environmental factors is important for several reasons. Larval fish play essential role in marine ecosystems because they are staple diet for many higher trophic level organisms including large fish, mammals, and seabirds (Mueter & Norcross 2002). Ichthyoplankton ecology also helps to determine adult spawning populations (Recruitment Processes Program 2009). Marine habitats encompass dynamic range of environmental forces, and understanding the affect of these variables’ early stage abundance and distribution of species help predict population and distribution patterns through time (Mundy 2005). Fisheries-Oceanography Coordinated Investigations (FOCI)Timothy Lee Ichthyoplankton Ecology Spring 2010 3 conducted over three decades of ichthyoplankton study during groundfish assessment research cruises in Gulf of Alaska (Ichthyoplankton Information System 2009); past research found that larval stage densities and distributions have close correlations with marine abiotic environmental factors. A study of larval flatfish distribution found that densities of larval Arrowtooth flounder (Atheresthes stomias) and Pacific Halibut (Hippoglossus stenolepis) were greater with increasing water column heights and increasing transport pathways (Bailey & Picquelle 2002). Study of capelin showed that the larvae preferred cool and high-salinity waters (Logerwell et al. 2007). Past research has shown that Pacific cod larvae have higher concentrations in warmer waters (Hurst et al. 2009). My objective is to analyze summer larval fish densities’ association with three physical environmental variables –salinity, temperature, and attenuation (the average loss of light through water) - during mid-summer (Pacific Marine Environmental Laboratory 2007). This study is focused in Gulf of Alaska (GOA), one of the most productive and diverse marine habitats in Northern Pacific (Mundy 2005). This study analyzes six most abundant and widespread fish taxa (Walleye Pollock-Theragra chalcogramma, Pacific Cod-Gadus Macrocephalus, Flathead Sole-Hippoglossus elassodon, Southern Rock Sole-Lepidopsetta bilineata, Arrowtooth Flounder-Atheresthes stomias, and Gray Starsnout-Bathyagonus alascanus) in late larval stage across GOA’s continental shelf along southern
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