David G. Lindquist

Top down vs. bottom up control of benthic community composition on an intertidal tideflat

Nutrient enrichment and predation have been shown to have important, though sometimes conflicting, effects on intermediate trophic levels in freshwater communities. Though predation is also important in structuring marine soft-sediment benthic communities, the influence of nutrient enrichment in marine benthic systems is less well understood. We examined the interactive effects of nutrient enrichment and predator exclusion on a benthic community to assess the importance of these factors and to test the bottom-up:top-down theory of trophic control in this habitat. Predator exclusion was associated with increased numbers of surface deposit feeders but had less impact on burrowing deposit feeders. Effects of nutrient addition on abundances were observed only in treatments allowing predator access, but increased size of a benthic polychaete, Streblospio benedicti Webster, was observed in predator exclusion treatments with nutrient addition relative to other exclusion plots. However, responses to nutrient addition and predator exclusion varied between years. These results suggest that nutrient addition may be associated with effects on benthic communities, possibly through increased benthic microalgal production, but that the presence or absence of predation may alter the visible response of benthos to enrichment.

Top-down Versus Bottom-up Limitation in Benthic Infaunal Communities: Direct and Indirect Effects

Top-down effects of predators and bottom-up effects related to resource availability can be important in determining community structure and function through both direct and indirect processes. Their relative influence may vary among habitats. We examined the effects of nutrient enhancement and predation in southeastern North Carolina to determine relative effects on benthic macrofaunal communities. Short-term nutrient additions and predator exclusions were conducted in two estuaries to examine main and interactive effects on benthic microalgae and infauna. This experimental approach was complemented by comparisons of microalgal biomass, infaunal abundance and composition, predator abundance and predator exclusion among four estuarine systems that varied in background nutrient levels. In the short-term experiments, nutrient enhancement induced increased microalgal biomass but had limited effects on abundances or sizes of infauna. Predator exclusion increased the density of sedentary and near-surface dwelling fauna, but we did not observe interactions between predation and responses to nutrient additions as might be predicted from a simple cascade model. General patterns of abundance were explained to a larger extent by interannual and amongestuary pattems. These results indicate a lack of simple trophic cascade responses for this community over a short time scale and little evidence for local interactive effects. The lack of interactive effects may reflect the opportunistic nature of the dominant infaunal species and potentially different time and spatial scales for the effects of predation and resource controls.

Interactive Effects of Nutrient Additions and Predation on Infaunal Communities

Nutrient additions represent an important anthropogenic stress on coastal ecosystems. At moderate levels, increased nutrients may lead to increased primary production and, possibly, to increased biomass of consumers although complex trophic interactions may modify or mask these effects. We examined the influence of nutrient additions and interactive effects of trophic interactions (predation) on benthic infaunal composition and abundances through small-scale field experiments in 2 estuaries that differed in ambient nutrient conditions. A blocked experimental design was used that allowed an assessment of direct nutrient effects in the presence and absence of predation by epibenthic predators as well as an assessment of the independent effects of predation. Benthic microalgal, production increased with experimental nutrient additions and was greater when infaunal abundances were lower, but there were no significant interactions between these factors. Increased abundances of one infaunal taxa,Laeonereis culveri, as well as the grazer feeding guild were observed with nutrient additions and a number of taxa exhibited higher abundances with predator exclusion. In contrast to results from freshwater systems there were no significant interactive effects between nutrient additions and predator exclusion as was predicted. The infaunal responses observed here emphasize the importance of both bottom-up (nutrient addition and primary producer driven) and top-down (predation) controls in structuring benthic communities. These processes may work at different spatial and temporal scales, and affect different taxa, making observation of potential interactive effects difficult.

Spawning and nesting behavior of the waccamaw darter,Etheostoma perlongum

SynopsisThe spawning and nesting behavior ofEtheostoma (Boleosoma) perlongum was investigated in the field and laboratory. Sexual dimorphism is highly developed in such features as genital papillae, first dorsal and paired fins, and nuptial coloration. A reproductive migration from mid-lake to shore occurs in the spring: males precede females to select nest sites under submerged sticks and other debris. The male excavates a depression beneath the submerged object. Gonad analysis indicates a single spawning season extending from March through June. Nests were found from late April to mid-June and were guarded by a single male for periods of 13 to 36 days. Males initiate courtship by lateral display, lead the female to the nest site and show the nest by inverting. The female responds by tail up, tail wag and circle; males also tail wag and circle. Spawning pairs invert, usually in unison, and orient head to head or, less often, head to tail. The female deposits eggs while holding her body in a weak ‘S’ or ‘J’ shape with the caudal peduncle held away from the spawning substrate while vibrating.

Trophic morphology of four western Atlantic blennies (Pisces: Blenniidae)

Etude de la morphologie de la dentition et des maxillaires de Hypsoblennius ionthas, H. hentzi, Hypleurochilus germinatus et Parablennius marmoreus en fonction du regime alimentaire

Breeding behavior and early life history of the waccamaw killifish,Fundulus waccamensis

SynopsisThe territorial, courtship and spawning behavior ofFundulus waccamensis was investigated in the field and laboratory. Spawning occurs from April to August. Sexual dimorphism is manifested through dichromatism, genitalia, morphometric differences and contact structures. In nature, nuptial males vigorously defend circular territories and court entering females by circling them, sidling, ‘J’ shaping and spawning in the sand substrate. In the aquarium, males perform eight advertisement motor patterns during courtship, of which dipping and flashing are most frequent. The female is relatively inactive, performing only two basic acts. The maximum number of mature eggs per ovary is 120. Both mature egg numbers and total egg numbers are highly correlated with standard length. Recently fertilized eggs are colorless and adhesive. The newly hatched young is well developed and relatively large in size.

Selection of sites for egg deposition and spawning dynamics in the waccamaw darter

We provided 93 experimental spawning covers for the waccamaw darter. We grouped the covers (3 sizes of slate and one of concave tile) in three arrangements at six Lake Waccamaw locations to separate the variables of water depth, distance from shore, cover density and cover type. Tag returns of marked males suggest low fidelity for nest sites. Egg production under the 3 different sizes of slate was not significantly different. Egg production under the tile was significantly less than that under the slates. Egg production was significantly higher off the undeveloped southeastern shore in 2 m of water and lowest at the shallowest location with the highest experimental cover density. The number of eggs in nest is positively correlated with male size. We conclude that medium size slate covers placed in a linear arrangement in 2 m of water on a mixed sand bottom result in the highest egg production for the waccamaw darter.