Characterization of settlement patterns of red drum Sciaenops ocellatus larvae to estuarine nursery habitat: a stable isotope approach

Abstract

A novel approach was used to study the settlement of red drum Sciaenops ocellatus larvae from the coastal Gulf of Mexico to a seagrass meadow in the Aransas Estuary, Texas, during an entire recruitment season (September through November 1999). Differences in the δ 13 C and δ 15 N of the food webs supporting red drum while in the planktonic and estuarine habitats were characterized and used to identify post-settlement individuals in the process of completing the isotopic shift between the planktonic and estuarine signatures (transitional larvae). An empirical model was used to estimate the rate of change in the isotopic composition of transitional red drum to back-calculate size at settlement (L sett ; mm standard length: SL) and time since settlement (T sett ; d). During the period of study, there were 4 to 5 ‰ differences in the δ 13 C and δ 15 N of planktonic larvae and 'large' settlers that had equilibrated to estuarine food sources. Red drum captured simultaneously exhibited variability in L sett and T sett values, indicating that they had settled at a range of sizes and over several days. Examination of length-frequency distributions of L sett estimates indicated that the smallest settlers were about 4 mm SL, peak size at settlement was 6 to 8 mm SL, and the largest settlers were 10 to 11 mm SL. Settlement dates derived from T sett indicated that a brief settlement pulse occurred during the latter half of September and that new settlers appeared on a daily basis throughout October and early November. The relatively continuous settlement pattern suggests a consistent supply of potential settlers to the estuary. The approach used in this study provides a fine-scale temporal resolution for the examination of settlement patterns in marine fishes that exhibit a distinct habitat transition and consequent dietary shift during early life. KEY WORDS: Settlement · Fish larvae · Stable isotopes · Sciaenops ocellatus · TurnoverResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 226: 143-156, 2002 also on their ability to respond to the environmental cues that trigger settlement (Victor 1991). Hence, settlement is constrained by the size and/or age at which larvae become competent to settle. Identification of the sizes at which larvae are most likely to settle would be useful when quantifying the abundance of potential settlers (McCormick 1994, Danilowicz 1997.Another critical aspect of estuarine recruitment involves the temporal scales over which settlement occurs. By examining fine-scale temporal patterns of settlement, it is possible to determine whether it occurs periodically, in pulses, or as the result of continuous input of new recruits (Doherty 1991). Such information is crucial for identifying the processes that transport larvae to estuaries and evaluating the relationship between larval supply and settlement (Miller 1988, Milicich et al. 1992, Shenker et al. 1993.This study attempts to characterize the fine-scale temporal settlement patterns of red drum...

Nutritional importance of minor dietary sources for leaping grey mullet Liza saliens (Mugilidae) during settlement: insights from fatty acid δ13C analysis

“…These values are consistent with the bulk δ 13 C signatures of zooplankton (Fig. 3) and are typically planktonic in lagoon and coastal food webs, taking into account a slight 13 C depletion in lipids relative to bulk tissue (Herzka et al 2002, Pepin & Dower 2007. We are therefore confident that the smallest size class was representative of the marine-planktonic phase of Liza saliens juveniles.…”

“…It is believed that the reduced water turbulence in the benthos results in a thicker boundary layer around benthic algae, restricting the diffusion rate of CO 2 or HCO 3 -, with subsequent reduced discrimination against 13 C (France 1995). In coastal environments, this phenomenon may generate a mean δ 13 C enrichment of 5 ‰ or more in benthic algae (including epiphytes) relative to phytoplankton (France 1995, Herzka et al 2002, Jaschinski et al 2008, Vinagre et al 2008. However, the plankton-like FA δ 13 C values of > 200 mm fish were quite surprising, and suggested that young adult L. saliens, which are supposed to have a similar diet to settled juveniles, occupy a distinct isotopic niche.…”

Benthic habitat properties can delay settlement in an estuarine fish (Sciaenops ocellatus)

“…According to stable isotope analysis, larvae switch from a diet of particulate organic matter endmembers (pelagic and detrital) to a diet of marsh plants and macroalgae end-members (benthic) at around 6 to 8 mm SL (Herzka et al 2002). This indicates that larvae change their diet relatively rapidly after entering the estuaries, although our experiments suggest they might not utilize the substrate fully until approximately 12.5 mm SL.…”

Biologging to examine multiple life stages of an estuarine-dependent fish

“…For fishes that use different habitats for each life phase, this 3-phase life cycle decouples reproduction from recruitment of new individuals into the local population. This is especially true for fish taxa with larvae that settle into benthic habitats that are distinct from those of adults (Shulman & Ogden 1987, Eggleston 1995, Peters et al 1998, Herzka et al 2002, Shenker et al 2002, creating 2 stages within the demersal phase of life history. Examination of the processes affecting each of these life stages, and the connections between life stages, is essential to developing a better understanding of ontogenetic habitat requirements of fishes.…”