Les Ecrevisses sont un constituant majeur de la production des invertebres benthiques dans les habitats lentiques et lotiques. Elles representent aussi une importante ressource nutritive pour nombre de Poissons. En raison de leur abondance et de la taille relativement elevee de leur corps, les interactions entre les Poissons et les Ecrevisses peuvent avoir de profonds effets sur le reste de la communaute benthique. Nous presentons ici 1) une synthese a propos des relations trophiques et ecologiques deja bien connues entre les Poissons et les Ecrevisses, 2) d'autres interactions potentiellement importantes mais moins bien etudiees. Les Poissons et les Ecrevisses ont ete generalement percus comme predateurs-proies. Les Ecrevisses ne sont pas des proies faciles pour de nombreux Poissons a cause de leur forte taille et de leur armement defensif, et nombre d'etudes ont montre que la taille relative Poisson-Ecrevisse est un facteur majeur affectant l'interaction predateur-proie entre ces especes. Les Ecrevisses peuvent aussi entrer en competition avec de petits Poissons benthiques pour la nouriture et l'abri. En outre, elles ont ete impliquees dans le declin des populations de Poissons en raison de la predation directe sur les oeufs de Poissons qu'elles exercent et elles peuvent affecter indirectement les populations de Poissons par la destruction des herbiers de macrophytes qu'elles provoquent, ces derniers constituant des habitats importants pour les Poissons juveniles. Nombre de ces interactions subtiles entre Poissons et Ecrevisses ont ete tout d'abord observees lorsque des especes exotiques d'Ecrevisses ont ete introduites dans un nouveau systeme (intentionnellement ou accidentellement). De nouveaux travaux experimentaux et des donnees a long terme sont necessaires pour decouvrir l'importance de ces interactions Ecrevisses-Poissons peu etudiees. Une attention particuliere devrait etre accordee aux multiples possibilites d'interactions en ce qui concerne l'amenagement, l'elevage, l'introduction ou les etudes de ces macro-consommateurs aquatiques.
Asian swamp eels ( Monopterus albus / javanensis ) were first reported as introduced to Florida waterbodies in 1997 near Tampa and Miami; a third population was recorded by 1999 in Homestead. Initial assessments, published soon after swamp eels in southern Florida were first recorded in wetlands beyond canals and ponds (in 2007), concluded there was little threat to Florida’s aquatic ecosystems. Long-term data now suggest they precipitated population crashes of crayfishes and small fishes in the eastern Everglades. We used records from continuous long-term monitoring programs, sporadic monitoring studies, and online databases to reconstruct swamp eel presence across Florida. Monitoring studies provided wetland hydrologic variables to assess limits for swamp eels. From 1997–2007, populations in southern Florida remained restricted to canals; initial spread from 2007–2017 across southern Everglades National Park proceeded slowly and the two populations covered ~1500 km 2 of southern Florida. From 2017–2022, the rate of spread increased as they spread west and north (~5800 km 2 range). Through 2014, the Tampa population occurred only along southern/eastern Tampa Bay (~60 km 2 ) but has since spread south along the Gulf Coast, east into central Florida, and south along the Lake Wales Ridge (~11,000 km 2 ). We found evidence of two potentially new introductions, in Palm Beach County and Orlando. There was no clear evidence of limitation of wetland drying on swamp eel occurrence in the Everglades; they were captured in marshes that dried for 1–5 months during the previous dry season, but short-hydroperiod wetlands may have slowed spread. In the Everglades, evidence suggests swamp eels may have been inadvertently spread into marshes from canals used to deliver water for flood control and hydrologic restoration. Swamp eels are currently spreading unchecked across Florida, and there should be great concern about continued spread in this region and their establishment and spread elsewhere.
A mysterious parthenogenetic cambarid crayfish (the Marmorkrebs) has been spreading across the globe for the past decade. We compare this crayfish directly to two other cambarids, Procambarus fallax and P. alleni , that have been suggested to be related or even identical to the Marmorkrebs. Using external morphology and sequences of two mitochondrial genes we show clear correspondences between Marmorkrebs and P. fallax , a species found natively throughout peninsular Florida, USA. Based on these congruent results we suggest that the Marmorkrebs is the parthenogenetic form of P. fallax . This finding has potential evolutionary and ecological implications at several levels. The Marmorkrebs might be a type of geographical parthenogenesis, but a natural population in the wild is so far unknown. Furthermore, challenges arise in regard to the respective species status of the Marmorkrebs. Taxonomically we suggest that the Marmorkrebs is treated as ‘parthenogenetic form’ of P. fallax . Last but not least, the identity of this animal and its ecology has an impact for considering potential spread and effects of this species across the globe.
We investigated the use of crayfish gastroliths and exoskeleton pieces for quantifying crayfish abundance and size-structure in diets of White Ibis (Eudocimus albus) chicks in the Everglades. We then quantified crayfish and fish abundance from various small hard parts and intact fish heads in 23 boluses, taken from two nesting colonies in Water Conservation Area 3 (WCA 3) and Arthur R. Marshall Loxahatchee National Wildlife Refuge (Lox) in the Florida Everglades during May 2006. We determined that using gastroliths to estimate crayfish numbers in boluses had significant drawbacks; only a small fraction of field-caught crayfish bear gastroliths and the two crayfish species in the Everglades differ in percentage bearing gastroliths. In contrast, counts of crayfish rostrums and chelae pairs gave simple and similar estimates of crayfish in the boluses. The two colonies had strikingly different diets in May 2006; New Colony 3 (Lox) boluses were dominated by crayfish while birds from the Alley North (WCA 3) boluses were fish-dominated and had few crayfish. Using measurements of the crayfish rostrums we determined the size-structure of crayfish found in the diets of the New Colony 3 birds, and determined that the crayfish in the diet were relatively large (mean = 19 mm carapace length) when compared to the available crayfish in the marsh. These crayfish were also large relative to previous reports of crayfish found in White Ibis diets in the Everglades.
Mortality (e.g. predation, disturbance) is often thought to lower the intensity of interspecific competition and thereby promote the coexistence of competing species. However, surprisingly few tests of this idea exist, especially for metazoans feeding on a self‐renewing resource. Here we examined the effect of density‐independent mortality on the coexistence of four species of pond zooplankton (microcrustacean grazers) in a series of laboratory microcosms. Across the experimental mortality gradient, consumer biomass decreased and resource abundance increased with an increase in mortality. Thus, the treatments resulted in an increase in resource availability per consumer (one measure of reduced competitive intensity). There was no significant effect of mortality treatment on species relative abundances or species evenness, and the zooplankter Diaphanosoma dominated community biomass at all mortality levels. Mortality rate did have a marginally significant effect on species richness (p<0.07), but richness did not increase monotonically with mortality level. Instead, richness tended to be highest in the low‐ and no‐mortality treatments.
Summary For aquatic herpetofaunal species, two of the possible determinants of density and local species composition are fish presence or absence and hydroperiod; factors which are sometimes, but not always, correlated. We quantified wetland herpetofaunal assemblages in 20 wetlands that varied in both attributes (in south‐eastern Florida, U.S.A.) to examine the effects of fish, wetland permanence and their potential interaction. Fish presence significantly reduced the density of five anuran species and reduced overall species richness. Wetland permanence had no measured effect on composition or richness of herpetofaunal assemblages. Three anuran species (including the imperilled Gopher Frog, Rana capito ) were absent from most of the wetlands with fish and capture rates of two larger generalist ranids ( Rana grylio , R. s phenocephala ) were significantly lower in the presence of fish. No species of anuran was captured more frequently when fish were present. Non‐permanent wetlands are often perceived to be quality anuran habitat, but such a perception may be incorrect for wetlands that rapidly recolonise with fish. Dredging and ditching of otherwise temporary wetlands, and fish stocking, may lead to local, and potentially regional, reductions in anuran breeding habitats, especially for faunal assemblages that lack anurans that thrive when fish are present.
