139
5 Timing and Location of Aggregation and Spawning in Reef Fishes
among spawning sites; those larvae that become entrained in larger current systems
have a higher chance of being widely dispersed (Domeier 2004 , “Grouper Moon
project” – unpublished data), while those not entrained may be retained more locally
(Colin 1992 ; Heyman et al. 2005 ) . In areas with extensive shallow reefs or large
coastlines it is often not easy for reef fi sh eggs from both aggregating and nonaggregating species to become entrained into oceanic circulation as currents do not
necessarily favour transport off the shelf edge (Appeldoorn et al. 1994 ; Hensley
et al. 1994 ) , however oceanic entrainment may be common for small islands with
narrow shelves and isolated reefs due to differences in water circulation near them
(Fig. 5.10 ).
5.7 Temperature Regimes and Other Physical Parameters
Water temperature determines the rates of many of the metabolic functions of fi shes.
Most reef fi shes live in a fairly narrow range of annual temperatures with water
temperatures in the low latitude tropics typically quite stable over the year, with a
range of only about 1–3°C in the IWP and 3–4°C in the TWA. At higher latitudes
with reefs (e.g. Great Barrier Reef, Hong Kong, southern Japan, Bermuda) summer
high temperatures are similar to equatorial regions but winters are considerably
cooler for greater annual variation.
Many RA species in the equatorial tropics spawn year-round throughout the
limited annual temperature range, but little is known for areas with greater yearly
variation. In most places, TAs are reported to occur seasonally within a particular
temperature regime, usually at locations where there is an annual variation of at
least a few °C (Domeier and Colin 1997 ) . In areas of the IWP where there is little
annual temperature variation, TA species may have lengthy aggregation periods
(Fig. 5.17 ) to as much as year-round (or nearly so), but always with a lunar periodicity (Johannes et al. 1999 , Chap. 12 ). If a species with a broad latitudinal distribution
has its spawning season varying with latitude, this would potentially indicate a close
relationship between temperature and spawning. For Nassau grouper, spawning
occurs at a fairly consistent temperature (see below). Other species may not have
such a close correlation, but often truly defi nitive data are lacking. Camoufl age
grouper aggregation, for example, is reported at different temperatures (between
about 24°C and 29.5°C) over its range (Chap. 12 ).
Temperature determines how fast embryos develop in the egg, when eggs will
hatch, when feeding can begin, the time window a larva has to initiate feeding before
it starves, and how fast it can grow under otherwise suitable conditions. At hatching,
pelagic larvae lack a mouth, formed fi ns and pigmented eyes, and must live off their
yolk for a limited time. After development of functional eyes, fi ns and a complete
digestive system with mouth and anus, the yolk is nearly absorbed. A “critical
period” of limited duration (a few hours?) occurs at this point during which the
larvae must start feeding or starve (Leggett and Dublois 1994 ; Yoseda et al. 2006 )
(Chap. 7 ).
5 Timing and Location of Aggregation and Spawning in Reef Fishes
among spawning sites; those larvae that become entrained in larger current systems
have a higher chance of being widely dispersed (Domeier 2004 , “Grouper Moon
project” – unpublished data), while those not entrained may be retained more locally
(Colin 1992 ; Heyman et al. 2005 ) . In areas with extensive shallow reefs or large
coastlines it is often not easy for reef fi sh eggs from both aggregating and nonaggregating species to become entrained into oceanic circulation as currents do not
necessarily favour transport off the shelf edge (Appeldoorn et al. 1994 ; Hensley
et al. 1994 ) , however oceanic entrainment may be common for small islands with
narrow shelves and isolated reefs due to differences in water circulation near them
(Fig. 5.10 ).
5.7 Temperature Regimes and Other Physical Parameters
Water temperature determines the rates of many of the metabolic functions of fi shes.
Most reef fi shes live in a fairly narrow range of annual temperatures with water
temperatures in the low latitude tropics typically quite stable over the year, with a
range of only about 1–3°C in the IWP and 3–4°C in the TWA. At higher latitudes
with reefs (e.g. Great Barrier Reef, Hong Kong, southern Japan, Bermuda) summer
high temperatures are similar to equatorial regions but winters are considerably
cooler for greater annual variation.
Many RA species in the equatorial tropics spawn year-round throughout the
limited annual temperature range, but little is known for areas with greater yearly
variation. In most places, TAs are reported to occur seasonally within a particular
temperature regime, usually at locations where there is an annual variation of at
least a few °C (Domeier and Colin 1997 ) . In areas of the IWP where there is little
annual temperature variation, TA species may have lengthy aggregation periods
(Fig. 5.17 ) to as much as year-round (or nearly so), but always with a lunar periodicity (Johannes et al. 1999 , Chap. 12 ). If a species with a broad latitudinal distribution
has its spawning season varying with latitude, this would potentially indicate a close
relationship between temperature and spawning. For Nassau grouper, spawning
occurs at a fairly consistent temperature (see below). Other species may not have
such a close correlation, but often truly defi nitive data are lacking. Camoufl age
grouper aggregation, for example, is reported at different temperatures (between
about 24°C and 29.5°C) over its range (Chap. 12 ).
Temperature determines how fast embryos develop in the egg, when eggs will
hatch, when feeding can begin, the time window a larva has to initiate feeding before
it starves, and how fast it can grow under otherwise suitable conditions. At hatching,
pelagic larvae lack a mouth, formed fi ns and pigmented eyes, and must live off their
yolk for a limited time. After development of functional eyes, fi ns and a complete
digestive system with mouth and anus, the yolk is nearly absorbed. A “critical
period” of limited duration (a few hours?) occurs at this point during which the
larvae must start feeding or starve (Leggett and Dublois 1994 ; Yoseda et al. 2006 )
(Chap. 7 ).