Online Resources for:
Consumptive Effects of Fish Reduce Wetland Crayfish Recruitment and Drive Species Turnover
Kellogg CM and Dorn NJ
Corresponding author: Nathan J. Dorn
Email: ndorn1@fau.edu
Phone: 954-235-1315
Online Resource 1
Picture of experimental wetlands in Davie, FL.
Fig. 1 Experimental Wetlands at University of Florida’s I.F.A.S. Station, Davie, FL. The mesh
cages were used in the 2010 experiment.
Online Resource 2
Rationale for Sunfish Species selection and experimental Stocking Densities
The Everglades fish community is dominated by small killifishes (Cyprinodontidae),
livebearers (Poeciliidae), and small sunfishes (Centrarchidae) (Loftus and Kushlan 1987).
Sunfish (Lepomis spp.) are known to make up ~38% by number of the total large-bodied fish (>8
cm standard length, SL) assemblage in the Everglades (Chick et al. 1999). The trophic
importance of large-bodied predatory fish on prey in the Everglades has been debated (Kushlan
1976, Loftus and Eklund 1994, Trexler et al. 2005, Dorn et al. 2006) and the influence of
piscivorous species on small fish is generally believed to be less than the effect of drying in
marshes that have dried in the last 4-6 years (Trexler et al. 2005). However, field experiments
and observations suggest that larger-bodied (> 6 cm SL) predatory fishes likely have strong
effects on crustaceans and other invertebrates in south Florida wetlands (Dorn et al. 2006, Dorn
2008). While large-bodied fish abundances rise with longer hydroperiods (i.e., average length of
wetland inundation) (Trexler et al. 2002, Chick et al. 2004, Parkos et al. 2011), determining the
total densities of medium and large sunfish (> 4 cm standard length, SL) is challenging because
1-m2 throw traps probably underestimate their numbers (Jordan et al. 1996) while other sampling
techniques, like electrofishing (Chick et al. 1999, 2004, Parkos et al. 2011) do not provide exact
density estimates and primarily capture fish > 7-8 cm. Mean densities of smaller (mostly fish 25 cm SL) sunfishes in 1-m-2 throw traps taken from long hydroperiod sloughs (Water
Conservation Area 3A and Loxahatchee National Wildlife Refuge) ranged from undetectable
densities (0-0.2 m-2) up to 2 m-2 in 2006-2011 (N. Dorn, unpublished data, means of n = 5 traps).
Chick et al. (1999) sampled large size classes of sunfish and other predatory species from similar
slough habitats with block-nets; from their data the densities of the largest size classes of sunfish
(≥8 cm SL) appear to range up to ~0.03 m-2 and total large predatory fish densities including
yellow bullheads (Amieurus natalis) largemouth bass (Micropterus salmoides) and non-native
cichlids (Cichlasoma spp.) ranged up to ~0.05 m-2 or 1 fish per 20 m-2. Those numbers are
somewhat irrelevant for our stocking levels because we did not work with predatory fish that
large (all sunfish stocked into our wetlands were 3.3-7.1 cm SL) but serves as a reminder that
larger predatory fishes also exist in the sloughs. Furthermore, the sunfish densities listed by
Chick et al. (1999) did not include smaller species of sunfish like the dollar sunfish (L.
marginatus, mostly < 8 cm SL in the Everglades) that was one of the species stocked into our
experiment. Considering the clearing efficiency of the throw traps (Jordan et al. 1997, 63%
accuracy for all small marsh fishes), variation in hydrology and the various size-classes of
sunfishes in the Everglades we estimate that total small sunfish (Lepomis spp. and Eannacanthus
gloriosus) wet season densities can range up to at least 3 m-2 in the Everglades and surrounding
wetlands with some unknown fraction of those fish being > 4 cm SL. The sunfish stocking
densities in our experiments in 2009 were 4, 8, 16, and 32 sunfish tank-1 or 0.22, 0.43, 0.86, and
1.72 sunfish m-2 respectively and in 2010 were 4 and 24 sunfish tank-1 or 0.24 and 1.45 m-2
respectively. Stocking densities for the 2010 experiment were calculated after adjusting for the
addition of two 1 m2 cages that excluded sunfish in each wetland. These stocking densities were
therefore meant to include realistic values for densities of smaller sunfish found in the
Everglades and other Florida wetlands. The two species used were chosen to represent a range
of predator morphologies (i.e., gape sizes) as gape size is an important morphological trait in
predator-prey interactions in freshwater (Persson et al. 1996, Mittelbach and Persson 1998,
Nilsson and Bronmark 2000). Dollar sunfish (Lepomis marginatus) representing the more
numerous Lepomis sunfishes (14-100% of all sunfish in 2007 throw traps taken from the
conservation areas) with smaller gape sizes and the warmouth (Lepomis gulosus), representing
the less common species (0-20% of catch) caught in throw traps. The dollar sunfish is one of the
most common Lepomis species in the Everglades, is a small-mouthed Lepomis sunfish and it
preys on small aquatic invertebrates, including crayfish (Loftus 2000). The warmouth is
generally less common in throw trap samples, but is the most abundant larger-bodied (adults
growing > 10 cm SL) sunfish predator in the Everglades (Parkos et al. 2011), has a relatively
large gape diameter for a sunfish and feeds on small fish, aquatic insects, benthic crustaceans and
is known to prey extensively on crayfish (Loftus 2000). The warmouth’s larger proportional
gape diameter will allow it to feed on a wider range of crayfish sizes. Warmouth grow larger
than dollar sunfish and are generally caught in the Everglades at larger sizes than the dollar
sunfish (C. Kellogg, pers. obs.). The experiments are restricted to studying smaller size-classes
of sunfish however larger sunfish size classes and other species of large-bodied fishes (e.g.,
bullheads (Ameirus natalis), bowfin (Amia calva), and Florida gar (Lepisosteus platyrhincus) are
known to eat crayfish (Loftus 2000) and larger adult killifishes (Fundulus spp.) may be
important predators as well, therefore these experiments probably represent a conservative study
of predatory fish effects on crayfish recruitment.
References
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Online Resource 3
Species-specific length-mass regressions used to calculate crayfish biomass
Table 1. Regression statistics for converting log10-transformed carapace length (mm) to log10transformed dry mass (g) for Procambarus fallax and Procambarus alleni.
Species
Slope
Intercept
R2
N
Smallest
CL
Largest
CL
Procambarus fallax
3.2274
-4.6578
0.98
87
5.3
33.5
Procambarus alleni
3.2697
-4.6057
0.98
75
5
53