was better in 2003, in part because of better survival during late‐larval to early‐juvenile stages
(from Voss et al. 2012, their figure 9).
3.6.7 Lateolabrax japonicus (Lateolabracidae)
Lateolabrax japonicus is abundant in East Asian coastal waters. In the marine Ariake Bay (Japan) spawning occurs in winter, where eggs hatch and early‐stage larvae develop and grow (Matsumiya et al. 1981, 1982, 1985). Postflexion larvae and small juveniles (≥15 mm SL) migrate to the tidal Chikugo River where their variable growth and mortality rates (to ~25 mm SL) determine recruitment outcomes (Shoji et al. 2006, Shoji & Tanaka 2007a, 2007b). Highly variable growth and survival rates of larvae to 15 mm SL in Ariake Bay (Shoji & Tanaka 2007a, 2008) are density independent and survival increases at higher temperatures (Shoji et al. 2006, Shoji & Tanaka 2007b), which are positively related to Chikugo River freshwater discharge.
After ingressing to the tidal Chikugo River, early‐stage juveniles (15–20 mm SL) of Lateolabrax japonicus find best feeding conditions near the salt front and estuarine turbidity maximum (Islam et al. 2006) where the copepod Sinocalanus sinensis is dominant prey. In this period, weight‐specific growth (G), mortality (M) and an index of recruitment potential (G/M) all become density dependent (Shoji & Tanaka 2007a, 2008) while continuing to be strongly related to temperature (Figure 3.23) (Shoji & Tanaka 2007b). In 11 years of observations, 24‐fold variability in annual abundances of 15 mm larvae declined to 9.4‐fold annual variability at 20 mm SL (Shoji & Tanaka 2008), which suggests that density‐dependent mortality and regulation of recruited abundance occur in the 15–20 mm, earliest juvenile stage. Limited abundance of the dominant prey S. sinensis is the probable factor driving density dependence.
The most important controls and regulators of recruitment variability in Lateolabrax japonicus are (i) density‐independent processes controlling growth and mortality of pre‐immigration larvae in Ariake Bay; (ii) positive effects of temperature on growth and survival of pre‐ingress larvae in Ariake Bay and post‐ingress larvae in the Chikugo River; (iii) positive effects of moderate freshwater discharges in the Chikugo River on survival and growth and (iv) density‐dependent growth and mortality of 15–25 mm SL juveniles during Chikugo River residence.
3.6.8 Fundulus heteroclitus (Fundulidae)
Estuarine shorelines, fringes and adjacent marshes provide habitat for numerous, small, abundant and primarily demersal resident fishes (Able et al. 2022). These fishes reproduce in the estuary and their young recruit to local habitats, often on the fringing shorelines. An example is Fundulus heteroclitus, a small fundulid found along the Atlantic coast of the USA and Canada (Able & Fahay 2010). Adults have limited home ranges and spawn intertidally. Although relatively little is reported on growth and mortality of its eggs and larvae on regional scales, or of recruitment variability, there is considerable knowledge of its dynamics at smaller scales. For example, Kneib (1993) reported fivefold variability in weight‐specific growth rates (0.027–0.143 d−1) and major variability in mortality rates (0.001–0.118 d−1) in enclosure experiments in a Georgia (USA) estuary, indicating that substantial variability in cohort‐specific recruitment levels would be expected. In this case, variability in recruitment was primarily attributed to duration of tidal flooding; longer flood‐tide durations positively influenced growth of larvae and resulted in reduced mortality rates, apparently related to tidal delivery of food. The importance of larval and small juvenile stages was demonstrated in a Delaware (USA) marsh, where production by young‐of‐the‐year individuals contributed 71.6% to the total annual production by this species (Teo & Able 2003).
Figure 3.23 Weight‐specific growth coefficient (G), mortality coefficient (M) and the ratio G/M for Lateolabrax japonicus five‐day larval cohorts in relation to mean daily temperature experienced by each cohort in the Chikugo Estuary, Japan. G/M is an indicator of productive potential and potential to recruit
(from Shoji & Tanaka (2007b, their figure 5)).
3.7 Summary and conclusions
The patterns of reproduction and ontogeny in the taxonomically rich estuary‐associated fishes from around the world, including all the major groups from elasmobranchs to bony fishes, are as diverse as documented for fishes living in other ecosystems. Further, the diversity in the life histories of bony fishes, the dominant group in estuaries, is complex with egg, larval, juvenile and adult stages having different ecologies. Moreover, some stages that use estuaries also use the adjacent, downstream ocean and upstream freshwaters for parts of their life history. Given these complexities in patterns and modes of reproduction, it is not surprising that recruitment processes of estuary‐associated fishes are also diverse. In the Introduction, we listed six broad topic areas that framed the scope of the chapter. We summarise major conclusions in the six areas.
The state of knowledge of fishes that utilise estuaries for reproduction.There is a substantial foundation of knowledge on patterns and modes of reproduction by estuary‐dependent and ‐associated fishes. Resident, anadromous, catadromous and amphidromous species are represented amongst the diverse taxa utilising estuaries for reproductive and recruitment processes. Demersal and pelagic spawning occur, with a relatively high representation of demersal spawning, particularly by small, resident species. Fecundities range from a few to millions of eggs. Larval stages from spawning by resident and anadromous spawning utilise the estuary as a nursery. Larvae of nearshore and offshore spawners and metamorphosing individuals of catadromous and amphidromous fishes ingress to estuaries. While estuaries often are variable environments that challenge reproductive success, they also are rich and productive ecosystems that support successful recruitment in those species that can tolerate such conditions.
Egg, larval and juvenile stages of fishes that occur in or ingress to estuaries, including ecology, dynamics and behaviour, especially regarding the role of estuaries as nurseries.There is considerable knowledge, but also voids in understanding, of processes that assure success in transport or retention of eggs and larvae, processes that promote ingress to estuaries for species that spawn nearshore or offshore and retention of eggs and larvae within estuaries for resident and anadromous species. For offshore‐spawning species, selection of spawning sites by adults and features of ocean circulation that deliver eggs or larvae to the coast and mouths of estuaries are critical to the recruitment process. Ingress to estuaries by larvae can be passive, but more often is promoted by hydrodynamic processes, combined with sensory cues and behavioural mechanisms that allow larvae to successfully enter an estuary by appropriate use of tides, diel vertical migrations and active swimming behaviour. For eggs and early‐stage larvae within estuaries, retention is required to assure recruitment success. Estuarine residence time and numerous hydrographic processes promote successful retention and, in some cases, up‐estuary transport of larvae.During ontogeny, postflexion‐stage larvae of estuary‐associated fishes often develop substantial swimming ability and behaviours that support ingress to estuaries or retention, in addition to supporting trophodynamics (feeding) processes, habitat selection and predator avoidance. Metamorphosis and associated settlement (by demersal species) represent diverse and complex ontogenetic steps in estuary‐associated species and are particularly notable in the pleuronectiform fishes. In estuary‐associated fishes, shifts in habitats often occur with ontogeny. Such shifts are notable for nearshore and offshore spawners, and particularly so for ocean‐spawning catadromous