Consumptive Effects of Fish Reduce Wetland Crayfish Recruitment and Drive Species Turnover

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Consumptive Effects of Fish Reduce Wetland Crayfish Recruitment and Drive Species Turnover

Kellogg CM and Dorn NJ

Corresponding author: Nathan J. Dorn

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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 2-5 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Loxahatchee National Wildlife Refuge) ranged from undetectable densities (0-0.2 m-2) up to 2 m-2 in 2006-2011 (N. Dorn, unpublished data, means of n = 5 traps).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

Chick JH, Coyne S, Trexler JC (1999) Effectiveness of airboat electrofishing for sampling fishes in shallow, vegetated habitats. N Am J Fish Manag 19:957-967

Chick JH, Ruetz III CR, Trexler JC (2004) Spatial scale and abundance patterns of large fish communities in freshwater marshes of the Florida Everglades. Wetlands 24:652-664

Dorn NJ (2008) Colonization and reproduction of large macroinvertebrates are enhanced by drought-related fish reductions. Hydrobiol 605:209-218

Dorn NJ, Trexler JC, Gaiser EE (2006) Exploring the role of large predators in marsh food webs: evidence for a behaviorally-mediated trophic cascade. Hydrobiol 596:375-386

Jordan F, Coyne S, Trexler JC (1997) Sampling fishes in vegetated habitats: effects of habitat structure on sampling characteristics of the 1-m2 throw trap. Trans Am Fish Soc 126:1012-1020

Loftus WF (2000) Accumulation and fate of mercury in an Everglades aquatic food web. Ph.D. Dissertation, Florida International Univ., Miami, FL USA

Loftus WF, Eklund AM (1994) Long-term dynamics of an Everglades small-fish assemblage. Pages 461-483. In S.M. Davis and J.C. Ogden, editors. Everglades: the ecosystem and its restoration. St Lucie Press, Boca Raton, Fla. USA

Loftus WF, Kushlan JA (1987) Freshwater fishes of southern Florida. Bull Fla State Mus Biol Sci 31:147-344

Mittelbach GG, Persson L (1998) The ontogeny of piscivory and its ecological consequences. Can J Fish Aquat Sci 55:1454-1465

Nilsson PA, Bronmark C (2000) Prey vulnerability to a gape-size limited predator: Behavioural and morphological impacts on northern pike piscivory. Oikos 88:539-546

Parkos JJ, Ruetz CR, Trexler JC (2011) Disturbance regime and limits on benefits of refuge use for fishes in a fluctuating hydroscape. Oikos doi: 10.1111/j.1600-0706.2011.19178.x

Persson L, Andersson J, Wahlstrom E, Eklov P (1996) Size-specific interactions in lake systems: Predator gape limitation and prey growth rate and mortality. Ecology 77:900-911

Trexler JC, Loftus WF, Jordan F, Chick JH, Kandl KL, McElroy TC, Bass Jr OL (2002) Ecological scale and its implications for freshwater fishes in the Florida Everglades. Pages 153-181. In J.W. Porter and K.G. Porter, editors. The Florida Everglades, Florida Bay, and Coral Reefs of the Florida Keys: and Ecosystem Sourcebook. CRC Press, New York, NY USA

Trexler JC, Loftus WF, Perry S (2005) Disturbance frequency and community structure in a twenty-five year intervention study. Oecologia 145:140-152

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 log10-transformed 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