Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Oceanography and Coastal Sciences

First Advisor

Donald M. Baltz


Introductions of exotic aquatic plants raise concerns for the health of assemblages of native species. The possible influence of the establishment of the exotic Eurasian watermilfoil Myriophyllum spicatum on fish and invertebrate assemblages in the Lake Pontchartrain estuary was examined with a microhabitat approach. Fish and invertebrate assemblage structure and population responses were compared among macrophyte species and unvegetated areas. Native macrophytes included wild celery Vallisneria americana and wigeongrass Ruppia maritima. Additionally, the relationships of the common submerged macrophytes to environmental and temporal variables were analyzed. A total of 517 samples, collected with a modified Wegener ring, included 3,564 fishes of 29 species and 53,006 macroinvertebrates of 13 taxa. The distribution and abundance of M. spicatum were positively related to turbidity and depth, whereas for V. americana they were positively related to sandy substrates. Along the northeast shore of Lake Pontchartrain, high wave energy probably limited the distribution of M. spicatum and R. maritima and favored the dominance of V. americana. In the Lake Pontchartrain estuary, R. maritima was probably replaced, in part, by M. spicatum. Most fishes and invertebrates were denser in submerged vegetation, although no significant differences in assemblage structure of fishes and macroinvertebrates were detected among submerged macrophyte species. Three of the common fishes and all of the common invertebrates differed significantly in density among macrophyte species, but overall patterns were not clearly different. Juvenile blue crab Callinectes sapidus, which were analyzed in three size classes, were more abundant in vegetated areas than in unvegetated areas, and all size classes were significantly denser in at least one native macrophyte species than in M. spicatum. Resident fishes were more abundant in spring and summer, whereas transient fishes were more abundant during recruitment events, usually in late winter and early spring. Amphipods and other small invertebrates were generally more common in winter. The use of M. spicatum by blue crab declined with increasing crab size, whereas the use of V. americana increased. Although the apparently benign exotic macrophyte M. spicatum did not measurably affect assemblage structure, it did significantly influence distributions of several littoral fishes and macroinvertebrates.