Selection of estuarine habitats by juvenile gags in experimental mesocosms

The degradation and destruction of estuarine habitats threaten the organisms that depend on these habitats for food and shelter. Gags Mycteroperca microlepis reside on rocky reefs for most of their lives but initially settle and rear in estuarine habitats before moving to offshore reefs. Gag populations have declined to the point where some consider them vulnerable to extinction, and the recovery of the species requires an understanding of what habitats these fish use and why they use them. We examined the habitat selection of juvenile gags in North Carolina using experimental mesocosms. We manipulated the shelter characteristics of habitats and compared the foraging rates of gags to determine the specific attributes of habitats that influence habitat selection. Gags selected structured seagrass or oyster reefs over sand and shell hash habitats. While gags did not show a preference between eelgrass Zostera marina and oyster reefs, they did choose oyster reefs over shoal grass Halodule wrightii and selected seagrass habitats with high shoot densities over those with lower densities. The addition of a small shelter to the habitat that the gags did not choose dramatically increased their use of that habitat. Finally, when we provided pinfish Lagodon rhomboides as prey, gag foraging rate did not vary among seagrass habitats with different shoot densities. However, gags consumed penaeid shrimp at much lower rates in seagrass habitats of high shoot density. Our results agree with those of other studies suggesting that seagrass habitats are important to gags. However, our results also emphasize that gags select specific attributes within seagrass landscapes and suggest that oyster reefs may be important habitats for them.