Explaining diversity patterns in dark waters – a study of aquatic caves in Yucatán, Mexico

Abstract

In the tropics, limestone caves in karstic areas are known for their unique biodiversity. However, many caves remain unstudied and little is known about underlying gradients that determine diversity and biomass in aquatic microhabitats. Here, we sampled zooplankton and benthos in a set of 12 aquatic caves, locally called closed cenotes in Yucatán, Mexico. Our aim was to explain diversity patterns and differences in biomass with particular attention for correlations between bat colony characteristics and other biota. Compared with caves that support photosynthesis, diversity was low with an average of four planktonic and two benthic species in these dark caves. Undetectable phosphorus concentrations in the water suggest this nutrient is limiting. Several associations hint at a potential link between bat abundance and functional guild composition, water quality and aquatic biota. As such, more bats were linked to higher nitrate concentrations. Yet this was not translated to higher invertebrate biomass, probably since phosphorus is limiting. Overall, the trends found in this survey suggest that bats could be important as fertilizers of the caves although mechanistic links that mediate the flux of nutrients need to be confirmed experimentally.

Changes in the sediment microbial community structure of coastal and inland sinkholes of a karst ecosystem from the Yucatan peninsula

“…The high levels of nitrate concentration in the water column from the three sediment zones at the inland sinkhole and at the WM from the coastal sinkhole may influence the abundance of AOB, AOA and NOB in the sediments from these zones, while NH 4 + and nitrite values were below detection limit (< 0.2 mg/L and < 1.5 mg/L, respectively) in all sediment zones at both sinkholes, suggesting an oxidation ammonium pathway with N 2 and 2H 2 O as products 35 , and a rapid cycling of ammonia and nitrite in the sinkhole sediments. Nitrite oxidation could also be responsible for the high NO 3 − concentrations in the water column from the sinkholes, however, we do not discard other sources of NO 3 − including the agricultural and wastewater infiltration into the groundwater aquifer ecosystem 4 , or the presence of abundant bat population which has been previously associated with higher nitrate concentrations in caves from the Yucatan peninsula 8 . Lower concentrations of nitrate (< 1.5 mg/L) in the sediments from caverns and caves correlate with low abundance of NOB.…”

“…In the central region of the peninsula, most of these inland sinkholes are exclusively freshwater systems and, in contrast, those close to the coast have a marked vertical stratification of surface freshwater and deeper saltwater 3 , 7 . Differences in physicochemical variables between sinkholes have been correlated with variation in ichthyofauna 5 , and bat populations 8 , in addition to other organisms. For example, the ichthyofauna and invertebrate diversity of the coastal sinkholes are more similar to the marine environment than that found at inland sinkholes 3 , 9 .…”

“…The microbial communities found in the karst cave systems around the world have been associated with important roles in biogeochemical cycles 10 , 11 , alternative primary production 12 , trophic interactions that impact food webs 13 , as indicators of the health of the ecosystem 6 , 14 , and as a source of new products of biotechnological importance 15 . However, despite the potential essential roles of microorganisms in the Yucatan groundwater ecosystem, most studies regarding these cave systems have focused on cave morphology and hydrology 1 , 3 , macrofaunal diversity 8 , 16 , and pollution 14 , 17 , 18 . The microbial communities associated with these unique environments remain largely unexplored.…”

Principales Aportaciones Científicas De La FMVZ-Uady Al Conocimiento De Los Vertebrados Terrestres De La Península De Yucatán, México

“…Considerando que los cenotes y cavernas constituyen refugios importantes para los murciélagos, se llevó a cabo un estudio con el fin de explicar los patrones de diversidad y diferencias en biomasa de zooplancton y bentos y su relación con la composición y tamaño de las colonias de murciélagos en 12 cuevas con cenotes en Yucatán, basados en el supuesto que los murciélagos incrementan la materia orgánica y otros nutrientes en los refugios por acumulación de las excretas o guano. Los resultados no indicaron una relación directa entre los murciélagos y la comunidad de invertebrados en las cuevas, sin embargo, se observó una tendencia que sugiere la importancia de los murciélagos como fertilizadores de las cuevas, aunque aún falta más esfuerzo para comprender el flujo de nutrientes y las interacciones ecológicas en los cuerpos de agua presentes en las cuevas de Yucatán (Hendus et al, 2019).…”

Benthic species assemblages change through a freshwater cavern-type cenote in the Yucatán Peninsula, Mexico

“…The general view of the aquatic biodiversity structure in subterranean waters suggests that abundance and diversity of organisms progressively decrease from the highly populated and energy-rich well illuminated zones to the energy-deprived and poorly populated deeper zones (Mammola 2019). This assumption is supported by the fact that well-illuminated zones of the cenotes, usually known as "windows to the surface", are the regions where primary production by photosynthetic organisms happens and where allochthonous organic material enter to the subterranean system (MacSwiney et al 2007;Hendus et al 2019). However, there is increasing evidence that food sources originated from bacterial communities and nutrient transport are relevant for supporting trophic web chains in zones where sun light is limited or totally lacking (Brankovits et al 2017;Chávez-Solís et al 2020).…”