192
P.L. Colin
7.1 Introduction
During their early life history (ELH), which covers the period between spawning
and settlement as juvenile fi shes from the water column, reef fi sh larvae must
survive and grow in the pelagic environment in order to successfully recruit to the
benthic stage. Chap. 6 examined the physical and biological environment impacting
the dispersal and retention of reef fi sh larvae, emphasising those with aggregation
spawning. This chapter examines the biology of reef fi sh larvae from spawning
through metamorphosis to try to (1) discern any intrinsic differences between aggregation spawned and other reef fi sh larvae, and (2) determine the common features
of larval development across those families with at least some members engaged in
aggregation spawning. Basic information is fi rst provided on the morphology of
larvae, the probable critical periods in ELH, then examines what differences and
similarities exist between species in their spawning behaviour and initial dispersal,
and how predators might affect success of spawning. Comparisons are made with
potentially similar broadcast spawners and future research directions are indicated.
The larvae and the juveniles/adults of reef fi shes occupy very different habitats,
the former generally in open water “pelagic” environments and the latter in benthic
or near benthic habitats (Fig. 7.1 ). On an individual basis the ELH of aggregation
spawning reef fi shes seems essentially identical to those reef fi shes lacking aggregation spawning. The same determinants of survival (feeding, predation, transport,
water quality) operate on all larvae. If differences do exist, they might provide some
insight into the reasons why some fi shes engage in aggregation spawning. While
considerable progress has been made in understanding the early life history of reef
fi shes in general (reviews include Cowen and Sponaugle 2009 ; Leis and McCormick
2002 ; Cowen 2002 ) , attention has been focused more on species with demersal eggs
and short larval lives. Settlement-stage fi shes can be captured in good condition
using light traps and other means. Some studies utilize cultured larvae, again mostly
from families with demersal eggs, which are easier to culture. The understandable
attention paid towards the more easily studied species has resulted in a tendency to
consider all larvae to behave similarly and to not appreciate the vast differences
between early and late stage larvae.
While it is often feasible to investigate ELH at its start (spawning or hatching)
and its conclusion (settlement), when fi shes are near reefs or other shelf areas, the
period of weeks between is not easily examined. The numbers of larvae in the open
ocean are generally low relative to the water volume, and deciphering the pelagic
life of reef fi shes is not easy, usually requiring costly shipboard work followed by
tedious sorting and identifi cation. Our rudimentary knowledge severely limits the
understanding of what affects success of a given cohort of fi shes.
Questions about whether eggs/larvae from a large mass spawn stay together for
extended periods of time (until at least time of fi rst feeding) have been examined in the
previous chapter, and the initial answer seems to be a qualifi ed “no”. The physical
mechanisms operating at these early stages generally favour gradual dispersal away
from the location of spawning, with perhaps only the slight buoyancy and later vertical
movement ability of yolk sac larvae to promote concentration along oceanic fronts.
P.L. Colin
7.1 Introduction
During their early life history (ELH), which covers the period between spawning
and settlement as juvenile fi shes from the water column, reef fi sh larvae must
survive and grow in the pelagic environment in order to successfully recruit to the
benthic stage. Chap. 6 examined the physical and biological environment impacting
the dispersal and retention of reef fi sh larvae, emphasising those with aggregation
spawning. This chapter examines the biology of reef fi sh larvae from spawning
through metamorphosis to try to (1) discern any intrinsic differences between aggregation spawned and other reef fi sh larvae, and (2) determine the common features
of larval development across those families with at least some members engaged in
aggregation spawning. Basic information is fi rst provided on the morphology of
larvae, the probable critical periods in ELH, then examines what differences and
similarities exist between species in their spawning behaviour and initial dispersal,
and how predators might affect success of spawning. Comparisons are made with
potentially similar broadcast spawners and future research directions are indicated.
The larvae and the juveniles/adults of reef fi shes occupy very different habitats,
the former generally in open water “pelagic” environments and the latter in benthic
or near benthic habitats (Fig. 7.1 ). On an individual basis the ELH of aggregation
spawning reef fi shes seems essentially identical to those reef fi shes lacking aggregation spawning. The same determinants of survival (feeding, predation, transport,
water quality) operate on all larvae. If differences do exist, they might provide some
insight into the reasons why some fi shes engage in aggregation spawning. While
considerable progress has been made in understanding the early life history of reef
fi shes in general (reviews include Cowen and Sponaugle 2009 ; Leis and McCormick
2002 ; Cowen 2002 ) , attention has been focused more on species with demersal eggs
and short larval lives. Settlement-stage fi shes can be captured in good condition
using light traps and other means. Some studies utilize cultured larvae, again mostly
from families with demersal eggs, which are easier to culture. The understandable
attention paid towards the more easily studied species has resulted in a tendency to
consider all larvae to behave similarly and to not appreciate the vast differences
between early and late stage larvae.
While it is often feasible to investigate ELH at its start (spawning or hatching)
and its conclusion (settlement), when fi shes are near reefs or other shelf areas, the
period of weeks between is not easily examined. The numbers of larvae in the open
ocean are generally low relative to the water volume, and deciphering the pelagic
life of reef fi shes is not easy, usually requiring costly shipboard work followed by
tedious sorting and identifi cation. Our rudimentary knowledge severely limits the
understanding of what affects success of a given cohort of fi shes.
Questions about whether eggs/larvae from a large mass spawn stay together for
extended periods of time (until at least time of fi rst feeding) have been examined in the
previous chapter, and the initial answer seems to be a qualifi ed “no”. The physical
mechanisms operating at these early stages generally favour gradual dispersal away
from the location of spawning, with perhaps only the slight buoyancy and later vertical
movement ability of yolk sac larvae to promote concentration along oceanic fronts.