Light sensitivity in larval fishes: Implications for vertical zonation in the pelagic zone

Abstract

Larval fishes exhibit marked vertical zonation patterns that are important in planktonic predator-prey interactions. This zonation has been related to both proximate physical (e.g., light intensity) and ultimate biological factors (e.g., predator risk, prey availability). We hypothesize that changes in visual sensitivity and feeding performance in larval fishes provide a constraint on depth distributions and that this constraint may represent the major determinant of vertical distribution patterns. To test the generality of the relationship between larval age and visual sensitivity, larvae were obtained from captive breeding adults of seven species (three Apogonidae and four Pomacentridae). The lowest light intensity at which feeding behavior occurred was measured using infrared video techniques with natural prey items. The visual sensitivity of the larvae, measured as initiation of feeding, increased by about 3 orders-of-magnitude during the larval phase. The abilities of the larvae were broadly similar within families, but there were marked differences between families. Pomacentrids were about an order-of-magnitude less light-sensitive than apogonids. Larval apogonids are potentially capable of feeding at a depth of about 100 m in clear tropical waters at 4 mm standard length (SL) and to 200 m at 12 mm SL. The patterns of ontogenetic and phylogenetic differences in light sensitivity are consistent with field observations on the vertical distributions of larvae in these taxa.

Vertical migrations of reef fish larvae in the Straits of Florida and effects on larval transport

“…One hypothesis for the prevalence of downward OVM is that poorly developed eyes prevent young larvae from feeding effectively at deeper, darker depths (Job and Bellwood 2000). Our data are mostly consistent with this hypothesis.…”

“…Larval vertical distributions-The majority of reef fish taxa had mean depths in the range of 20-50 m. Most fish larvae in most marine environments tend to accumulate in this depth range (Heath 1992), possibly because too little light for feeding is available at deeper depths (Job and Bellwood 2000), and dangerously high levels of ultraviolet radiation are present closer to the surface (Browman 2003). Small holocentrids, small Pristipomoides spp., and sphyraenids had mean depths , 20 m. Additionally, mullids and tetraodontids aggregated in the neuston layer during the daytime but dispersed during the night.…”

Development of swimming abilities in reef fish larvae

“…9 d. Adult brood stock were kept in >1000 l aquaria and were fed a diet of chopped pilchards, prawns and Ascetes twice a day. Rearing methods follow Job & Bellwood (2000). Larvae were reared in 200 l aquaria at 27.5 to 29°C, under a 14:10 h light:dark photoperiod, throughout the study period.…”

Detection and quantification of marine larvae orientation in the pelagic environment

“…The enclosure also limits the vertical movement of larvae. In consequence, vertical swimming behavior and cues that would trigger a response by vertical positioning, such as light intensity, water density, or concentration of chlorophyll (Job and Bellwood 2000;Cowen et al 2003), cannot be investigated with this device. Its purpose is to explore the horizontal (i.e., cardinal) orientation of larvae.…”