Growth of newly settled red drum Sciaenops ocellatus in different estuarine habitat types
Stunz, G. W.
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We examined growth of recently settled juvenile red drum in salt marsh, seagrass, oyster reef, and on nonvegetated bottom areas in the Galveston Bay system of Texas (USA). We estimated growth using otolith microstructure from free-ranging fish collected in different habitat types and also measured growth of red drum in experimental enclosures where fish movement was restricted. Otolith growth was closely related to somatic growth in fish of 13 to 33 mm SL, and we used daily otolith increments from the last 10 d before capture as an indicator of growth following settlement into estuarine habitats. Growth rates of red drum captured at marsh, nonvegetated, and seagrass sites were not significantly different; no fish were collected on oyster reef. While reducing potential problems of a lagged response between otolith growth and somatic growth, the use of a 10 d growth period may have increased the likelihood of fish movement among habitats affecting our comparisons. The overall post-settlement growth rate of 0.45 mm d-1 was similar to rates reported in the literature. Movement among habitat types was eliminated in experiments employing 24 solid-walled enclosures (60 cm diameter). Growth rates in enclosures over the 7 d experiment were 0.12 mm d-1 in oyster reef, 0.21 mm d-1 on nonvegetated bottom, 0.40 mm d-1 in salt marsh, and 0.42 mm d-1 in seagrass; rates in vegetated enclosures approximated natural growth rates. Significantly higher growth in marsh and seagrass enclosures suggests that growth potential for red drum may be highest in these vegetated areas. However, growth results in enclosures need to be evaluated carefully, because fish movement among habitat types may be important in these shallow estuarine systems.