Growth and mortality in successive cohorts of fish larvae within an estuarine nursery

Abstract

The young of many coastal fishes appear on estuarine nursery grounds in a progression of successive cohorts, few of which encounter identical environmental conditions. Using in situ manipulations, I explored the effects of natural environmental variability and use of a nursery habitat by prior cohorts on growth and mortality rates in successive larval cohorts of the mummichog Fundulus heteroclitus, a cyprinodontid fish common in salt marshes along the east coast of North America. Variation in mean daily specific rates of growth ( G = 0.027 to 0.143) and mortality (Z = 0.007 to 0.1 18) within a n d among cohorts was associated with the tidal cycle. Growth rate was positively associated and mortality rate negatively associated with the duration of tidal flooding experienced by groups of fish larvae. Tidal flooding may have affected growth and survival by controlling the renewal rate of prey resources (primarily harpacticoid copepods) in intertidal aquatic microhabitats where the fish larvae are normally found. Overall high survival (up to 90 % after 2 wk) of larvae in experimental cohorts was attributed to the exclusion of predators from field enclosures. Successive cohorts of larvae were not nutritionally independent and use of the nursery habitat by a prior cohort usually had a negative effect on survival of larvae in the next cohort. These findings challenge the general tenet that fish larvae are not foodlimited in nurseries and suggest how variation in the phys~cal environment can restrict food availability even in a highly productive estuarine habitat. The spawnlng pattern of F heteroclitusseems to combine features from along a continuum of reproductive strategies exhibited by other marine fishes and may contribute to maintaining a large and stable population in a fluctuating estuarine environment.

Habitat Use Patterns of Newly Settled Southern Flounder, Paralichthys lethostigma, in Aransas–Copano Bay, Texas

“…Size differences between vegetated and nonvegetated sites may be an indication of differential growth and/or movement between habitat types. Vegetated habitats are structurally complex providing abundant prey and refuge from predators (Rozas and Odum 1988;Sogard 1992;Kneib 1993;Rooker et al 1998). The quality and quantity of complex habitats may lead to faster growth and lower mortality (subsequently better growth and survival) and are important to successful recruitment into adult populations (Houde 1987;Sogard 1992;Kneib 1993;Gibson 1994;Levin 1994).…”

Bioenergetic and landscape considerations for scaling expectations of nekton production from intertidal marshes

“…The high P:B values resulting from the production of the very earliest life stages in tidal wetlands are not considered further here for 2 reasons: (1) Much of the mortality in the youngest age classes of resident species has been connected to consumption by adult residents (Kneib 1987(Kneib , 1993, essentially forming a closed trophic loop (i.e. early larval production is used in situ) and so is unavailable for direct export from the intertidal to the open estuary; (2) Migrant species found in tidal marshes arrive as juveniles because the early stages are generally produced elsewhere (spawned in 285 Fig.…”

Distributions of key exposure factors controlling the uptake of xenobiotic chemicals in an estuarine food web

“…The mummichog is a benthic forage fish that is one of the most abundant and productive fishes in East Coast estuaries from the Gulf of St. Lawrence to Texas [7][8][9][10]. Throughout this range, it inhabits shallow, brackish water coves, inlets, tidal creeks, and associated salt marshes [7].…”