Although invasive grazing organisms have been introduced throughout the globe, little is understood about the effects of exotic grazers on nutrient cycling and other key ecosystem processes. The major objectives of this doctoral dissertation enhancement project are to examine whether exotic armored catfish alter nutrient cycling and primary productivity, decrease food quality and quantity for native species, and reduce native biodiversity of invertebrates and fishes in invaded tropical ecosystems. Graduate student Krista Capps, under the mentorship of Dr. Alexander Flecker, will study the impacts of armored catfishes on rivers systems in the Grijalva-Usumacinta watershed, a biologically and culturally diverse region in southern Mexico. The research will be done in collaboration with Dr. RocÃo Rodiles-Hernández of the Colegio de la Frontera Sur (ECOSUR) in San Cristobal de las Casas, Mexico. The products generated by this study will include: 1) an experimental framework to assess the effects of invasive grazing organisms, 2) an understanding of how exotic armored catfish retain and process nutrients, 3) biological and chemical surveys of armored catfish invasion sites, and 4) enhanced biodiversity knowledge of the Grijalva-Usumacinta watershed through the creation and enhancement of biological collections.
The introduction of non-native species is one of the greatest threats to species diversity and ecosystem function throughout the world. This study will directly contribute to the general understanding of exotic grazing organisms and their effects on ecosystem health. Since armored catfish invasion has been linked to the collapse of freshwater fisheries in the Usumacinta watershed region, knowledge derived from this study will also have extensive management implications. The research team will collaborate with the Mexican National Institute of Anthropology and History to promote management of exotic armored catfish populations, and will enhance the biodiversity knowledge of freshwater organisms in and around Palenque National Park, a UNESCO World Heritage Site.
Suckermouth armored catfish (family: Loricariidae), also known as "plecos" and "algae eaters" in the aquarium trade, are a diverse family of tropical fish. More than 700 species of armored catfish have been identified and are native to tropical South America, Costa Rica, and Panama. Several species of armored catfish have been widely introduced and large invasive populations have been established in streams, lakes, and reservoirs in the United States, Mexico, tropical Asia, and islands in the Pacific and Caribbean. There is growing concern that exotic populations can have serious negative effects on water quality and native fish populations. Armored catfish have numerous qualities that make them potent invaders in many systems. They are covered in bony armor and spines that make their consumption difficult. Local predators are typically not able to consume mature armored catfish. Additionally, various armored catfishes provide parental care with the male fish excavating nests in stream banks and actively guarding the eggs and fry. Many armored catfish species also have the ability to breathe air through a modified stomach; therefore, they can thrive in low-oxygen environments. The impacts of invading armored catfish in developing countries can be especially severe on local human populations. Freshwater fishes are the primary protein sources of many people in developing areas of Latin America and Asia. The explosion of armored catfish populations in Mexico has destroyed many local fisheries. Armored catfish become entangled in fishing nets and destroy them with their spines. Additionally, as armored catfish populations increase, Mexican fishers have seen a concurrent reduction in the populations of other fishes. This doctoral dissertation research project investigated the impacts of invasive armored catfish on nutrient cycling and on native aquatic communities in Chiapas, Mexico. The research had three primary objectives: (1) examine whether armored catfish are important in sequestering nutrients (i.e. nutrient "sinks") in invaded stream ecosystems, (2) assess the degree to which armored catfish modify food resources and native species diversity and abundance in invaded ecosystems, and (3) assess the effects of invasive armored catfish on primary productivity, which is important for sustaining stream food webs. To assess whether armored catfish are important nutrient sinks, we compared nutrient distributions among major ecosystem compartments, algae, detritus (dead organic material), invertebrates, and fishes, in invaded and uninvaded sites in the Chacamax River. We estimated effects of armored catfish on nutrient recycling by quantifying rates of nutrient excretion. To evaluate the influence of armored catfish grazing on food resources, primary productivity, and invertebrate biodiversity and abundance, we conducted field experiments in the Chacamax River comparing community structure and ecosystem processes in the presence versus absence of armored catfish. We found that armored catfish sequester a large amount of nutrients in river systems where they have invaded. Experimental studies and comparative site surveys revealed that armored catfish graze down algae thereby reducing algal biomass, yet at the same time they can stimulate algal production by recycling nutrients. At high population densities, armored catfish have the potential to modify the availability of nutrients that can limit river productivity. In sum, changes induced by armored catfish appear to have strong ecosystem consequences that can potentially compromise native invertebrate and fish biodiversity.
