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Alternate Title

Diurnal Fish Density in Relation to Seagrass and Drift Algae Cover in Tampa Bay, Florida

Abstract

To assess the relationship between fish density and seagrass and drift algae cover on a small geographic scale, we collected quantitative data on fish and vegetation communities during daylight hours near the mouth of the Little Manatee River, Tampa Bay, Florida. In 1991, fish were collected with two types of sampling gear, a 120-m long-haul seine and 1-m2 roving dropnets. Seagrass and drift algae cover in each sampled area was categorized as none, sparse, moderate, or dense. Despite evident gear bias, sampling with both types of gear produced similar overall fish densities. Anchoa mitchilli, Lagodon rhomboides, and Syngnathus scovelli were the most abundant or frequently collected species, regardless of gear type. Densities of 12 of the 20 most abundant species were significantly related to either seagrass or drift algae cover or both. When fish density-vegetation cover relationships were significant, the greatest fish densities always occurred in either dense or moderate covers of seagrass or drift algae. Densities of L. rhomboides and Orthopristis chrysoptera were positively related to the level of seagrass and drift algae cover in samples collected with both types of gear, but significant relationships between the densities of other species and the level of vegetation cover generally varied by vegetation or gear type (or both). Density of Eucinostomus gula peaked in moderate seagrass and declined at higher and lower levels of cover. Total fish density was similar at sites dominated by either drift algae or seagrass but was significantly reduced at sites with little cover from either vegetation type. We conclude that both seagrass and drift algae are essential habitats for juvenile and small adult fish in Tampa Bay and that fish density on a small geographic scale is strongly related to vegetation cover. Drift algae may form an important alternate habitat for fish during winter months, when levels of seagrass cover are lowest and those of drift algae are highest.

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