Miriam Steinitz-Kannan

The rare endemic brittle star Amphicutis stygobita (Echinodermata: Ophiuroidea: Amphilepididae) is found in Bernier Cave on San Salvador Island in The Bahamas. We report here on the diatom-rich detritus on which the brittle star feeds. The detritus contains a microbial biofilm dominated by a large diatom Campylodiscus neofastuosus Ruck & Nakov that thrives in the cave’s brackish water. The biofilm diatoms and bacteria produce sticky, carbohydrate-rich, extracellular polymeric substances (EPS) that add to the detritus’ nutritional value and help give the detritus a consistency for A. stygobita to pull it into its mouth. Of particular interest is that Campylodiscus neofastuosus has distinct cell wall features that make efficient use of the limited light in the cave. It appears these morphological adaptations might focus light onto the chloroplasts increasing light capture. Furthermore, large, dark, and highly lobed chloroplasts serve as an additional low-light adaptation. This is a rare instance where efficient photosynthetic activity by diatoms produces a complex biofilm that feeds an endemic cave species population.

An undescribed diaptomid copepod probably belonging to a new Mastigodiaptomus species has been discovered and was very abundant in El Junco Lake (San Cristóbal Island, Ecuador) from 1966 until 2004. The species was not found in samples from 2007, 2008 or 2018. The loss of this key species from the lake coincides with the illegal introduction of Nile tilapia to El Junco Lake in 2005 and its subsequent eradication in 2008. The disappearance of this biogeographically and ecologically important copepod population may be explained by direct mechanisms of predation and competition, by a combination of both processes, and by indirect mechanisms linked to alterations in the lake ecosystem. The effects of fish eradication using rotenone may have contributed to the loss of the diaptomid population and to preventing its recovery. This article discusses the search for sources of propagules for recolonization and possible reintroduction scenarios and procedures.

The presence of the rotifer species Brachionus rotundiformis from the B. plicatilis species complex in Lake Arcturo, a saline lake in the Genovesa Island of the Galápagos Islands, is here reported. This is the first record of the species for the rotifer fauna of Ecuador as well as of the species complex to the Galápagos Islands. This finding is consistent with the idea of high dispersion capacity, and of cosmopolitan distribution of this species complex. Because Genovesa Island is uninhabited, passive transport by wind currents and zoochory by migrant birds seem to emerge as the most plausible factors in this process of colonization. Integrative studies on the morphological variations, genetic, molecular, and ecological aspects are still required to further understand the process of dispersion and the ecology of this member of the B. plicatilis species complex in this remote and isolated locality, and the exact taxonomical position of the island’s population to the other members of the complex.

The presence of the rotifer Keratella cochlearis (Gosse, 1851) is reported in El Junco Lake, a freshwater crater lake in San Cristóbal Island, Galápagos Islands. This taxon is a known species aggregate containing both eurytopic cosmopolitans as well as local and regional endemics, but also some insufficiently documented cryptic species. This record is the first of a representative of the aggregate for the rotifer fauna of the Galápagos Islands. Considering that the animal is now being recorded from the lake while earlier surveys did not, and the high dispersal capacity of many rotifers, we hypothesize that the organism recorded is one of the more widespread members of the aggregate, which colonized El Junco Lake only recently.

Patterns that maintain and generate biodiversity of macro‐organisms in the Neotropics are widely discussed in the scientific literature, yet the spatial ecology of micro‐organisms is largely unknown. The unique character of the tropical Andes and adjacent Amazon lowlands generates a wide gradient of environmental conditions to advance our understanding of what drives community assembly and diversity processes. We analysed the distribution patterns of benthic diatoms (unicellular siliceous algae) as a model group of microbial passive dispersers, including predictors that describe limnological and geo‐climatic gradients for a total of 113 waterbodies (0–28°S and 58–80°W), including lakes and streams. Complementary multivariate statistical analyses were performed to correlate (1) community composition and (2) diatom species richness with environmental and spatial factors to infer niche‐based and dispersal‐based assembly processes, respectively. Results showed that two gradients structured both diatom assemblages and waterbodies, namely climate and landscape configuration. Variance partitioning revealed that broadscale spatial variables (distance‐based Moran's Eigenvectors) outperformed the two environmental components (limnological and geo‐climatic), suggesting dispersal‐assembled communities. However, diatom assemblages were structured by geo‐climatic (regional) factors in certain lakes in the northern and central Andes, although their effects were partially manifested via local variables after the geographical distances were factored out. In a similar way, climatic and topographic structuring homogenized lake and stream communities within ecoregions, as indicated by the strong overlap between the two community types and the weak correlation between biota and limnological variables. Notably, a significant increase in diatom species richness was related to increased water connectivity, interpreted to indicate that a decrease in the remoteness of the system increase species number. Synthesis. We emphasize the strength of macroecological gradients (landscape configuration and climatic factors) in affecting both diatom diversity and community composition in the South American tropics. In this context, our results and the commonalities of ecoregion patterning with groups of macro‐organisms (vegetation) suggest the need to integrate microbial ecology into a macroecology framework to unravel mechanisms behind diversity gradients.

Finely laminated sediments within Bainbridge Crater Lake, Galápagos, provide a record of El Niño–Southern Oscillation (ENSO) events over the Holocene. Despite the importance of this sediment record, hypotheses for how climate variability is preserved in the lake sediments have not been tested. Here we present results of long‐term monitoring of the local climate and limnology and a revised interpretation of the sediment record. Brown‐green, organic‐rich, siliciclastic laminae reflect warm, wet conditions typical of El Niño events, whereas carbonate and gypsum precipitate during cool, dry La Niña events and persistent dry periods, respectively. Applying this new interpretation, we find that ENSO events of both phases were generally less frequent during the mid‐Holocene (~6100–4000 calendar years B.P.) relative to the last ~1500 calendar years. Abundant carbonate laminations between 3500 and 3000 calendar years B.P. imply that conditions in the Galápagos region were cool and dry during this period when the tropical Pacific E‐W sea surface temperature (SST) gradient likely strengthened. The frequency of El Niño and La Niña events then intensified dramatically around 1750–2000 calendar years B.P., consistent with a weaker SST gradient and an increased frequency of ENSO events in other regional records. This strong interannual variability persisted until ~700 calendar years B.P., when ENSO‐related variability at the lake decreased as the SST gradient strengthened. Persistent, dry conditions then dominated between 300 and 50 calendar years B.P. (A.D. 1650–1900, ± ~100 years), whereas wetter conditions and frequent El Niño events dominated in the most recent century.