Perspective Chapter: Remarks on the Relationship of Mangrove Recruitment and Thrombolithic Development in Coastal Lagoons

Thrombolithic formations are sedimentary structures generated by precipitation, consolidation, and lithification of sediments and caused by the evolution of cyanophyte mats that promote coastal ground formation. These, and unlithified thrombolithic platforms or pro-thrombolites, are closely associated with mangrove trees and forests that use them as an anchoring substrate. So, in contrast with the suggested role of mangroves as coastal ground formers, here, evidence is provided that supports the hypothesis that mangroves are actually opportunists that eventually colonize various phases of the evolution of thrombolites. Photographs of mangrove specimens found affixed on various pro-thrombolithic structures, including the first thrombolite platform described in 2005, constitute palpability for the above. Also, lithified structures have been identified as rhizoliths belonging to mangrove trees as evidence that colonization on thrombolite platforms has occurred also during earlier geological events. It is desirable that specialists on mangrove ecology consider analyzing and assessing this theory from their own perspective

Nuevos registros florísticos de diatomeas bentónicas (Bacillariophyceae) del golfo de California

Background. Most studies on benthic diatoms found in northwestern Mexico have been done along the western coast of the Baja California peninsula. Thus, few studies exist for the Gulf of California. Goals. To gather new records of benthic diatoms found in the Gulf of California. Methods. Diatom samples from sediments and rocks of the coast of Santa Rosalía, Baja California Sur, were observed under a light microscope (LM). Results. Three taxa were recorded and depicted: Caloneis liber var. bicuneata (common), Gyrosigma naja (scarce), and the new combination Entomoneis pulchra var. pulchella (scarce). Conclusions. These three taxa were recorded for the first time in northwestern Mexico.  Antecedentes. Los estudios sobre diatomeas bentónicas para el No­roeste mexicano se han hecho principalmente para la costa occidental de la península de Baja California, pero son pocos para el golfo de Cali­fornia. Objetivos. Presentar nuevos registros de diatomeas bentónicas para el golfo de California. Métodos. Se observaron muestras de diato­meas de sedimentos y rocas de la costa de Santa Rosalía, Baja Califor­nia Sur, México bajo el microscopio de luz. Resultados. Se registraron tres nuevos taxa: Caloneis liber var. bicuneata (común) y Gyrosigma naja (raro), y la nueva combinación Entomoneis pulchra var. pulchella (raro). Conclusiones. Estos tres taxa son registrados por primera vez para la región Noroeste de México

Variaciones en la Estructura de Asociaciones de Diatomeas Epifitas de Macroalgas en una Zona Subtropical

Epiphytic diatom samples of various macroalgae from a subtropical bed taxa were analyzed in order to determine if they belonged to a single assemblage, and whether they exhibited time variations. The analysis was based on community structure, i.e. relative abundances, biological value (BVI), species diversity, dominance, and equitability. The macroalgae hosts were collected from a bed located in a beach known as El Caimancito, B. C. S. Specifically five macroalgae taxa were chosen: Laurencia pacifica, L. johnstonii, Padina mexicana, P. caulescens and Hydroclathrus clathratus. The most abundant diatom taxa, out of 211 species and varieties were Cocconeis disculus and C. dirupta. However, according to the BVI the taxa determining the assemblage structure were Navicula incerta, Nitzschia frustulum, C. disculus and N. frustulum var. perminuta. Diversity (H) values of the epiphytic diatom assemblages varied according to macroalgae host genus. The highest diversity value was for P. mexicana (H = 5), whilst the lowest value (H = 1.48) was for L. pacifica. The estimated species diversity and richness are among the highest measured for epiphytic diatom assemblages. Time variations in the diatom assemblages of the whole macroalgae bed followed the seasonal variation proposed for Bahía de La Paz based on temperature.Se analizaron muestras de diatomeas epifitas de distintos taxa de macroalgas recolectadas en una zona subtropical, con el objetivo de determinar si conformaban una misma asociación y si ésta variaba temporalmente. Para ello se examinó su estructura en términos de abundancias relativas, valor biológico (IVB) de los taxa, diversidad, dominancia y equidad. Las macroalgas se recolectaron en un manchón de la playa El Caimancito, B. C. S. en junio y diciembre de 2001, y abril, mayo y julio del 2002. Específicamente talos de 5 especies: Laurencia pacifica, L. johnstonii, Padina mexicana, P. caulescens e Hydroclathrus clathratus. Sobre estos hospederos se identificaron 211 taxa (especies y variedades) de diatomeas; las más abundantes fueron Cocconeis disculus y C. dirupta. Sin embargo, según el IVB Navicula incerta, Nitzschia frustulum, C. disculus y N. frustulum var. perminuta, determinaron la estructura de las asociaciones. El valor máximo de diversidad (H = 5) se registró en P. mexicana; el mínimo (H = 1.48) en Laurencia pacifica. De acuerdo con lo anterior, se discriminaron varias asociaciones de diatomeas epifitas según el género de la macroalga hospedera. La riqueza y diversidad de especies promedio del manchón de macroalgas están entre los más altos medidos para asociaciones de diatomeas epifitas. Los cambios temporales de todo el manchón coincidieron con el cambio estacional propuesto para la bahía en otros estudios, según su temperatura

Influencia del sustrato y las condiciones ambientales sobre la estructura de asociaciones de diatomeas bentónicas en una laguna costera tropical

Background. The structure of benthic diatom assemblages (BDA) is related to the type of substrate where they flourish. Goals. assess the degree of variation shown by BDA growing on live and non-living substrata from a tropical coastal lagoon (Terminos lagoon). We tested the hypothesis that substrate influence would deem significantly distinct BDA. Methods. diatom samples were collected from live and non-living substrata from four sites within Terminos lagoon, México, where physicochemical variables were also measured. Diatom taxa were identified, and their relative abundances were estimated and used to compute community parameters (species diversity, equitability, dominance), along with the indicator value (IndVal). Also, similarity between the BDA from the four sites was measured and values were then compared using ANOSIM. Results. Although the IndVal showed a clear separation based on the dominant/constant taxa, ANOSIM indicated that differences between the sites were not significant. This may be related to the characteristic patchy distribution of BDA along environmental gradients. Conclusions. in coastal ecosystems the structure of BDA could be mainly influenced by environmental variables.Antecedentes. Las diatomeas bentónicas son uno de los principales componentes del microfitobentos y la estructura de sus asociaciones está relacionada al tipo de sustrato sobre el que se desarrollan. Objetivo. Determinar el grado de diferencia que existe entre asociaciones de diatomeas bentónicas que se presentan sobre sustratos vivos e inertes en cuatro sitios de una laguna costera tropical (Terminos lagoon). Se contrastó la hipótesis de que existen diferencias en la estructura de las asociaciones de diatomeas pertenecientes a cada sustrato. Métodos. Se recolectaron muestras de diatomeas de sustrato vivo e inerte con las que se caracterizó la estructura de las asociaciones de diatomeas. Las asociaciones de diatomeas se contrastaron mediante la prueba ANOSIM. Resultados. En análisis mostró que no existen diferencias significativas entre las estructuras de las comunidades de ambos sustratos, sugiriendo que la influencia de los sustratos no es suficiente para establecer cambios significativos sobre las asociaciones de diatomeas en la laguna, no obstante valores calculados de IndVal mostraron claramente la separación de los taxones dominantes/constantes para cada tipo de sustrato. Esto concuerda con la característica distribución en parches descrita para asociaciones de diatomeas bentónicas a lo largo de gradientes ambientales. Conclusiones. los resultados muestran que las asociaciones de diatomeas bentónicas pueden estar influenciadas, principalmente, por las variables ambientales

Further remarks on the role of pro-thrombolites in the origin of coastal lagoons for Northwestern Mexico

Along the margins of coastal lagoons in Baja California Sur, Mexico, cyanobacteria-dominated communities form thick mats that eventually generate consolidated mud platforms or pro-thrombolites (unlithified thrombolites). Pro-thrombolite platforms grow seaward and form spits that alter water flow and promote sand deposition that develop into barriers, thus influencing coastal geomorphology, promoting lagoon formation. In this paper we provide evidences on the role of pro-thrombolites in the generation of coastal lagoons that includes different regions of NW Mexico where pro-thrombolite and/or thrombolithic platforms are common. In Bahía Magdalena, desiccating microbial mats are dominated by Microcoleus chthonoplastes Thuret ex Gomont and their remaining empty sheats occur together with lithified structures (thrombolites) cemented with micrite, considered of biotic origin. Previously proposed as a lacunar process, it is now suggested that pro-thrombolithic development leading to coastal lagoon formation actually occurs in non-lacunar environments with similar hidrological conditions. Likewise, this process is further enhanced once the coastal lagoon has been formed. We also suggest that the establishment of mangrove forests is indeed preceded by the formation of prothrombolithic platforms that provide a stabilized substrate for these plants in tropical and subtropical coastal lagoons

Recent observations supporting the hypothesis of the colonization of thrombolite platforms by mangroves

Antecedentes. Los trombolitos son estructuras sedimentarias formadas por precipitación, consolidación y litificación de sedimentos debido a la actividad y crecimiento de tapetes de cianofitas y son considerados responsables de la formación de suelo costero; mientras que los mangles son oportunistas que colonizan las plataformas trombolíticas. Objetivos. Proporcionar evidencias de que ocurre colonización de plataformas trombolíticas por mangles. Métodos. Se tomaron imágenes fotográficas de especímenes de mangle presentes en la primera plataforma trombolítica descrita en 2005. Se examinó la plataforma y se tomaron muestras para analizar su composición mineralógica. Resultados. Se reunieron evidencias de colonización de una plataforma trombolítica por mangles. Los especímenes observados sobre la plataforma trombolítica son juveniles saludables con alturas notables. Las muestras de plataforma resultaron estructuras sedimentarias conocidas como rizolitos de raíces de mangle. Conclusiones. Se presentan evidencias de que, además de este evento de colonización, existió una colonización anterior en una plataforma localizada en un estrato inferior. Mediante el análisis mineralógico se probó la hipótesis de que la micrita sería un componente significativo de la estructura de los rizolitos.Background. Thrombolites are sedimentary structures formed by precipitation, consolidation, and lithification of sediments generated by the evolution of cyanophyte mats that are responsible for coastal ground formation. Mangroves, however, are opportunist that colonize said substratum, in this case thrombolite platforms. Goals. To provide recent evidence of mangrove colonization of thrombolite platforms. Methods. Photographic images were taken of specimens of mangroves found fixed on the first thrombolite platform described in 2005. The platform was examined and samples were collected to analyze their mineralogical composition. Results. Evidence was gathered of two mangrove species colonizing a thrombolite platform. Specimens that had reached significant heights, indicating healthy juveniles, were found fixed on the first thrombolite platform. Collected platform structures were identified as rhizoliths belonging to mangrove trees. Conclusions. Evidence is presented that, besides this colonizing event, an earlier colonization on a thrombolite platform occurred at an inferior level. A secondary hypothesis that micrite would be a significant component of the rhizolith structure was proven through the mineralogical analysis of rhizolith fragments

Composición de especies de diatomeas en la dieta in situ del ostión de placer Crassostrea corteziensis en un sistema estuarino

Background: The feeding of cultured mollusks has been based on a few strains of diatoms and green algae; however, it has been shown that these have low nutritional value. Therefore, alternatives have been searched as in this case by resorting to the study of in situ feeding of these mollusks. Goals: To elaborate a floristic list of diatoms that are part of the in-situ diet of Crassostrea corteziensis, both wild and in extensive culture at the aestuarine wetlands of Nayarit, Mexico. Methods: A total of 130 oysters were sampled from three sites and three distinct substrates, i.e., string, sediment, and mangrove roots of the estuarine system, during November 2013, and March and June 2014. Their digestive systems were dissected and their gut contents examined, oxydized and mounted in synthetic resin for the identification of the diatoms ingested in-situ. Results: We identified 212 species and varieties of diatoms. Benthic forms composed 72.6% of the species richness, out of which 50% are of marine affinity, 16% are freshwater forms, and 14% were brackish water forms. The size of pennate diatoms varied between 7.4-230 μm long and 2.82-50.61 μm wide; while the diameter of centric diatoms varied between 4.89-123 μm. Conclusions: The in-situ diet of C. corteziensis showed a high species richness and a benthic origin. The species richness and composition of diatoms in the gut contents of C. corteziensis is characteristic of estuarine sediments and represents an approximate description of the benthic diatom taxocenosis of estero Camichin, Nayarit and similar environments in the region. According to their frecuency, taxa such as Cyclotella striata, Cymatotheca weissflogii, Neodelphineis silenda, Shionodiscus oestrupii and Thalassionema nitzschioides var. capitulatum represent alternatives for the in vitro culture of placer oyster.  Antecedentes: La alimentación de moluscos bivalvos en cultivo in vitro ha tenido como base unas cuantas cepas de diatomeas y algas verdes; empero, se ha observado que dichas cepas tienen bajo valor nutricional. Por ello, se han buscado otras especies de microalgas como alternativa; como en este caso recurriendo al estudio de la alimentación in situ de estos moluscos. Objetivos: Determinar la composición de especies de diatomeas que forman parte de la dieta in situ del ostión de placer Crassostrea corteziensis, tanto silvestres, como de cultivos extensivos que se desarrollan en humedales estuarinos de Nayarit, México. Métodos: Se recolectaron 130 especímenes de C. corteziensis en tres sitios y tres sustratos, i.e., sartas, sedimentos y raíces de mangle, durante (noviembre 2013) y (marzo y junio 2014). Se disectaron sus tractos digestivos y se revisaron sus contenidos intestinales estos se oxidaron y se montaron en resina sintética para identificar las diatomeas consumidas. Resultados: La dieta in situ de C. corteziensis incluyo 212 especies y variedades de diatomeas. El 72.6% fueron formas bentónicas, 50% fueron de afinidad marina, 16% dulceacuícola y 14% de agua salobre. El tamaño de las diatomeas pennadas vario entre 7.4-230 μm de largo y 2.82-50.61 μm de ancho; el diámetro de las céntricas vario entre 4.89-123 μm. Conclusiones. De acuerdo con los resultados, C. corteziensis se alimenta de un alto número de especies de diatomeas cuyo hábitat es predominantemente bentónico. La composición específica y riqueza de las diatomeas en el contenido intestinal de C. corteziensis es propia de sedimentos de zonas estuarinas y representan una primera descripción de la taxocenosis de diatomeas bentónicas del estero Camichín, Nayarit y de ambientes similares de la región. La frecuencia espacial y temporal de taxones como Cyclotella striata, Cymatotheca weissflogii, Neodelphineis silenda, Shionodiscus oestrupii y Thalassionema nitzschioides var. capitulatum en contenidos intestinales, representan alternativas para la dieta de C. corteziensis en cultivos de laboratorio