109
4 Spawning Aggregations in Reef Fishes; Ecological and Evolutionary Processes
each region. Moreover the amount of reef habitat per kilometre of coast is 3.5 times
greater in the western Pacifi c than in the Caribbean (Tables 4.4 – 4.7 ). Inter-ocean
differences in spawning behaviour will be important in groupers such as members
of the genus Plectropomus which occur at higher densities than any species of
Caribbean grouper (Chiappone et al. 2000 ; Pears 2005 ) . If so, the catchment area
from which aggregations are drawn and the distances to suitable aggregation sites
will both be smaller in the western Pacifi c. This predicts that (a) the average size of
undisturbed aggregations, and (b) the magnitude of trans-habitat migrations will be
smaller in the western Pacifi c and the number of potential aggregation sites per unit
of coastal habitat will be greater. In this context, details of spawning aggregations in
leopard coralgrouper support the predictions of numerous small sites with resident
aggregation (Chap. 12.9 ).
Moreover, if the association between mass spawning events and clear regional
environmental cues (van Woesik 2010 ) is a general phenomenon, then the timing
and frequency of aggregations is also expected to be a geographically specifi c feature. In addition, Colin (Chap. 9 ) drew attention to the differences in tidal amplitude
between the oceans and this approach needs to be extended to seasonal wind fi elds
that may infl uence the pelagic environment and the extent of deeper reef habitats
that may provide additional spawning sites.
4.7.2 Regional Differences in Body Size
and Transient Spawning
The list of aggregate spawning reef fi shes comprises at least 11 families (78 species). With respect to transient spawning two lineages, groupers and snappers, dominate the present examples with the greatest diversity for these groups occurring in
the Indo-Pacifi c. However for both groups the majority of confi rmed records are
from the Atlantic and East Pacifi c. The PCA analysis (Fig. 4.2 ) demonstrated an
association between mean size and spawning mode. A more comprehensive analysis of size structure for each group was carried out to determine (1) the mean size of
the total species pool in each group, (2) the geographical distribution of size within
each group and (3) mean size of aggregating species in each group (Table 4.9 ).
Analyses of size structure for entire lineages and of the currently recognized aggregating species demonstrated a consistent trend within groupers and snappers of a
greater mean size in the Atlantic and with transient spawning species dominated by
large Atlantic and East Pacifi c species. The geographical and reproductive size
trends observed in the groupers and snappers can be interpreted with respect to the
evolutionary history of each group. For the diverse genus Epinephelus the phylogenetic analysis of Craig and Hastings ( 2007 ) revealed a basal group of very large and
geographically widespread species with a mean size of 105 cm TL and a derived
clade consisting of small species (44 cm TL) confi ned to the IWP. The clade of very
large groupers, presently included in the genus Mycteroperca, is basal to Epinephelus
4 Spawning Aggregations in Reef Fishes; Ecological and Evolutionary Processes
each region. Moreover the amount of reef habitat per kilometre of coast is 3.5 times
greater in the western Pacifi c than in the Caribbean (Tables 4.4 – 4.7 ). Inter-ocean
differences in spawning behaviour will be important in groupers such as members
of the genus Plectropomus which occur at higher densities than any species of
Caribbean grouper (Chiappone et al. 2000 ; Pears 2005 ) . If so, the catchment area
from which aggregations are drawn and the distances to suitable aggregation sites
will both be smaller in the western Pacifi c. This predicts that (a) the average size of
undisturbed aggregations, and (b) the magnitude of trans-habitat migrations will be
smaller in the western Pacifi c and the number of potential aggregation sites per unit
of coastal habitat will be greater. In this context, details of spawning aggregations in
leopard coralgrouper support the predictions of numerous small sites with resident
aggregation (Chap. 12.9 ).
Moreover, if the association between mass spawning events and clear regional
environmental cues (van Woesik 2010 ) is a general phenomenon, then the timing
and frequency of aggregations is also expected to be a geographically specifi c feature. In addition, Colin (Chap. 9 ) drew attention to the differences in tidal amplitude
between the oceans and this approach needs to be extended to seasonal wind fi elds
that may infl uence the pelagic environment and the extent of deeper reef habitats
that may provide additional spawning sites.
4.7.2 Regional Differences in Body Size
and Transient Spawning
The list of aggregate spawning reef fi shes comprises at least 11 families (78 species). With respect to transient spawning two lineages, groupers and snappers, dominate the present examples with the greatest diversity for these groups occurring in
the Indo-Pacifi c. However for both groups the majority of confi rmed records are
from the Atlantic and East Pacifi c. The PCA analysis (Fig. 4.2 ) demonstrated an
association between mean size and spawning mode. A more comprehensive analysis of size structure for each group was carried out to determine (1) the mean size of
the total species pool in each group, (2) the geographical distribution of size within
each group and (3) mean size of aggregating species in each group (Table 4.9 ).
Analyses of size structure for entire lineages and of the currently recognized aggregating species demonstrated a consistent trend within groupers and snappers of a
greater mean size in the Atlantic and with transient spawning species dominated by
large Atlantic and East Pacifi c species. The geographical and reproductive size
trends observed in the groupers and snappers can be interpreted with respect to the
evolutionary history of each group. For the diverse genus Epinephelus the phylogenetic analysis of Craig and Hastings ( 2007 ) revealed a basal group of very large and
geographically widespread species with a mean size of 105 cm TL and a derived
clade consisting of small species (44 cm TL) confi ned to the IWP. The clade of very
large groupers, presently included in the genus Mycteroperca, is basal to Epinephelus