Table B1: Larval production and post-settlement parameters for the Meso-American and Philippines/South China Sea instantiations of CORSET (generic recruitment parameters ap- ply to both regions). Details of derivations for these parameters are provided in the text of Appendix B.
Parameter Derived value(s) Sources Meso-American Reef system
Brooding and spawning coral larval production (at 100% cover)
2×109 – 6×109 km-2 yr-1 1, 2, 3
Herbivorous fish larval production 5×103 – 7×103 kg-1 yr-1 3, 4, 5 Small piscivorous fish larval production 3×102 – 5×102 kg-1 yr-1 3, 4, 5 Large piscivorous fish larval production 7×102 – 9×102 kg-1 yr-1 3, 4, 5
Urchin larval production 6×102 – 8×102 kg-1 yr-1 3, 6, 7 Philippines/South China Sea region
Brooding and spawning coral larval production (at 100% cover)
8×108 – 2×109 km-2 yr-1 1, 2, 3
Herbivorous fish larval production 5×103 – 7×103 kg-1 yr-1 3, 4, 5 Small piscivorous fish larval production 1×102 – 4×102 kg-1 yr-1 3, 4, 5
Large piscivorous fish larval production 1×103 – 4×103 kg-1 yr-1 3, 4, 5 Urchin larval production 2×105 – 4×105 kg-1 yr-1 3, 6, 7 Generic
Initial mortality of brooded coral larvae 0.7 – 0.99 8 Mortality of brooding and spawning coral recruits
during the first year following settlement
0.2 – 0.7 yr-1 9
Mortality of fish and urchin recruits during the first year following settlement
density dependent 10, 11, 12, 13
The area of 1yr old coral recruits 2.18 cm2 14 The biomass of 1yr old herbivorous fish recruits 80 g 5 The biomass of 1yr old piscivorous fish recruits 150 g 5 The biomass of 1yr old urchin recruits 10 g 7, 15 Sources: 1Harrison and Wallace (1990),2Richmond (1988),3(see text below),4Cowen et al. (2006,
supplementary material),5Froese and Pauly (2004), 6Levitan (1991), 7Levitan (1988), 8Fadlallah (1983),9Babcock (1985),10Hixon and Webster (2002),11Anderson et al. (2007),12Carr and Hixon
(1995),13Stimson (1990),14Edmunds (2007),15Carpenter (1997)
Appendix B
i.e. varying larval production production (within acceptable ranges derived from the literature) to achieve coral cover and consumer biomasses representative of a healthy reef system. A healthy reef system is defined according to published indicator values (as indicated in Chapters 1 and 4). The practical steps involved in model tuning were to (i) run the model over long time series (50 – 100 years) using broad ranges for larval production parameters, (ii) compare model output with expected values for coral cover and consumer biomasses, and (iii) increase the minimum and decrease the maximum values for larval production parameters before re-running the model. This process was conducted separately for each of brooding and spawning corals, herbivorous, small piscivorous and large piscivorous fish. Larval production estimates derived using this method for the Meso-American Reef system and the Philippines/South China Sea region are reported in Table B1. Production over the course of a year is assumed to be equivalent for brooding and spawning corals (Richmond, 1988; Harrison and Wallace, 1990).
Pre- and post-settlement mortality are represented explicitly for brooded coral larvae. The estimate for pre-settlement mortality is 0.7 – 0.99, assuming that brooded larvae are competent to settle within an average period of 4 days (Fadlallah, 1983) and that average pre-settlement mortality is
between 0.25 day-1 (as for spawned coral larvae; Tables 1.2 and 4.2) and 0.7 day-1 (as for post-
settlement mortality of coral larvae; Table B1). Pre-settlement mortality is implicit in connectivity matrices for spawned coral, fish and urchin larvae.
Post-settlement processes
The post-settlement mortality rate of brooding and spawning coral recruits during the first year
following settlement is 0.2 – 0.7 yr-1 (Babcock, 1985). Mortality of fish and sea urchin recruits
is set at a constant background level with density dependent mortality beyond a threshold of 1
recruit/m2, based on findings from Jones (1990). Hixon and Webster (2002) present a regional-scale
comparison of post-settlement mortality rates for a species of damselfish (Pomacentrus moluccen-
sis) based on studies from the southern (Doherty and Fowler, 1994a,b) and northern (Beukers
and Jones, 1997) Great Barrier Reef (GBR). The former studies reported density-independent post-settlement mortality, while the latter found density dependent mortality. A key difference between these two cases is that the initial density of recruits was much lower on southern than on northern GBR sites. Hence density dependence was observed at high recruit densities only. Sale (pers. comm.) suggests that in most cases on coral reefs, post-settlement mortality of fish recruits is density independent until numbers get extremely large. This is the form of response adopted in the CORSET.
Predation is frequently implicated as a major source of density dependent mortality in coral reef fish recruits (Hixon, 1991; Carr and Hixon, 1995; Forrester, 1995; Hixon and Carr, 1997; Webster, 2002; Anderson et al., 2007). Hixon and Webster’s (2002) literature survey also indicates the role of habitat complexity and the synergistic effects of various groups of predators and interference competitors. Predation and competition may be from con-specifics (Stimson, 1990), other reef species (Beukers and Jones, 1997; Hixon and Carr, 1997; Connell, 1998), or some combination of the two (Anderson et al., 2007). Given that predation and competition pressures may vary between species and reef locations, and are most likely a combination of con- and hetero-specific effects, the implementation of density-dependent mortality in CORSET is as a function of recruit density.
Background mortality of fish recruits in CORSET is 0.2 yr-1, as for damselfish recruits studied by Doherty and Fowler (1994a) and Beukers and Jones (1997) (data summarised in Hixon and Webster, 2002). Background mortality for sea urchin recruits is assumed to be the same as fish
recruit mortality. Mortality of fish and sea urchin recruits increases by 0.1 yr-1for every additional
500 000 recruits/km2 beyond the threshold of 1 000 000 recruits/km2 identified in Jones’ (1990)
study, up to a maximum mortality rate of 0.98 yr-1, i.e. 0.2, 0.3, 0.4, ... , 0.9, 0.98 (complete
mortality of 1.0 yr-1is assumed to be unrealistic). Sensitivity of model behaviour to the maximum
post-settlement mortality rate for fish and sea urchins (explored in Section 2.2, Chapter 2 for the
range 0.9 – 0.99 yr-1) indicates that modelled fish and urchin biomasses tend to be higher when
maximum mortality is equal to 0.9 (the maximum post-settlement mortality rate for fish reported by Russ, 1991), but that this parameter does not influence model behaviour under perturbation scenarios.
CORSET assumes that survival of fish recruits is reduced by 70% in reef cells where coral cover
is≤5%, based on findings from Holbrook et al. (2008) and Feary et al. (2007). Above 5% coral
cover fish recruit survival follows the Shepherd (1982) function: survival = aC/1 + (a/b)Cd
(see Holbrook et al., 2008), whereC is the coral cover in a particular reef cell anda,b anddare
fitted parameters. CORSET usesa= 1,b= 1.11 and d= 1 (i.e. saturating survival).
Coral, fish and sea urchin recruits enter modelled cover/stock after 1 year. From Edmunds’ (2007) review of studies of juvenile coral growth rates, the mean diameter growth rate for juvenile corals
is 1.67 cm/yr, hence the diameter of year old coral recruits is assumed to be 2.18 cm2. Biomasses
of year old fish recruits were estimated using von Bertalanffy growth equation parameters from
FishBase (Froese and Pauly, 2004). From Carpenter (1997),Diadema antillarum recruits reach
a diameter of 25 – 30 mm in a year. Assuming the diameter of a 1-year old sea urchin recruit
is 27.5 mm, and using the allometric equation from Levitan (1988) for D. antillarum, which is
log 10{live weight (g)} = 2.99×log 10{size (mm test diameter)} −3.20, the biomass of a 1-year
old sea urchin recruit was estimated as 12.7 g. This biomass is assumed to apply for Indo-Pacific sea urchin species newly recruited to the 1-year age class.
Appendix C