A quantitative assessment of the cryptobenthic fish assemblage at deep littoral cliffs in the Mediterranean

Abstract

Summary:The present study provides the first quantitative assessment of cryptobenthic fish species diversity and abundance on hard bottoms below 20 m depth by examining Mediterranean underwater reefs with deep vertical cliffs. Quantitative sampling was performed at depths down to about 45 m and yielded 220 cryptobenthic and 61 epibenthic individuals belonging to 21 species, showing that the cryptobenthic fishes highly outnumbered the epibenthic individuals. The study highlights the high diversity and abundance of this unexplored part of the benthic fish community. The cryptobenthic fish assemblage was dominated by the family Gobiidae in terms of both biodiversity (>60% of all species) and abundance (>90% of all specimens). Fish species previously considered rare were present and some of them were even numerous in this assemblage. Three out of fourteen recorded habitat variables (depth, rocky cliff surface area vs. the bottom of the cliff area, and the presence of sand as the bottom substrate) were identified as significant for species occurrence. Species were generalist in their choice of shelters since the size and quantity of semi-caves, caves, cavities and even bio-cover type had no significant influence on the species distribution and abundance.Keywords: cryptobenthic fishes; multivariate analysis; benthos; littoral zone; underwater cliffs; scuba diving. Evaluación cuantitativa de la comunidad de peces criptobenónicos en los acantilados profundos del litoral MediterráneoResumen: Este trabajo presenta una primera evaluación cuantitativa de la diversidad y abundancia de los peces criptobentónicos de fondos duros por debajo de 20 m de profundidad, como ejemplo de acantilados litorales sumergidos del Mediterráneo. Se realizó un muestreo a profundidades cercanas a 45 m de profundidad y se obtuvieron 220 individuos criptobentònicos y 61 epibentónicos pertenecientes a 21 especies. El estudio pone de manifiesto la gran diversidad y abundancia de esta fracción inexplorada de la comunidad de peces bentónicos. La familia Gobiidae domina la comunidad de peces criptobentónicos en biodiversidad y abundancia (>60% y >90% del total de especies respectivamente). Se han observado especies de peces de este grupo consideradas raras, incluso algunas son numerosas. Tres de cada 14 variables registradas del hábitat (profundidad, superficie rocosa del acantilado vs fondo del acantilado y presencia de arena en el sustrato del fondo) fueron significativas para la presencia de las especies. En la elección de los refugios las especies fueron generalistas ya que el tamaño y la cantidad de semicuevas, cuevas, cavidades e incluso tipos de cubierta biológica no tienen influencia significativa en la distribución y abundancia de las especies.Palabras clave: peces criptobentónicos; análisis multivariante; bentos; zona litoral; acantilados sumergidos; submarinismo.

A quantitative assessment of the diel influence on the cryptobenthic fish assemblage of the shallow Mediterranean infralittoral zone

“…C. liechtensteini, M. macrocepha-lus, Z. zebrus and C. zebratus, had exclusively or predominantly cryptobenthic specimens, with no evidence for regular or significant habitat switches between cryptobenthic and epibenthic layers (Table 1). Similar to the findings of comparable studies, more than half the specimens sampled in our study belonged to the three most frequent species, all three gobies (Gobiidae) of minute size (Kovačić et al 2012, Glavičić et al 2016, Goatley et al 2016). Among those five most frequent species, C. liechtensteini, Z. zebrus and Chromogobius zebratus were confirmed to be cryptobenthic and abundant, as found by Kovačić et al (2012) and Glavičić et al (2016), whereas M. macrocephalus was absent or poorly represented in earlier studies due to the deeper depth ranges targeted by Kovačić et al (2012) and Glavičić et al (2016).…”

“…Considering the lack of any data on diel variations in cryptobenthic fish assemblages and the rarity of studies on diel shifts of other littoral benthic fishes in general, the general goal of the present study was to fill this knowledge gap, which might hide important aspects of the dynamics and relationships of coastal inshore fish assemblages. The quantitative assessment of littoral cryptobenthic fish assemblages of the shallow infralittoral (0.5-3 m depth) also complements earlier studies of littoral cryptobenthic fish assemblages performed deeper by Kovačić et al (2012) and Glavičić et al (2016). The present research used the cryptobenthic fish definition of Kovačić et al (2012) based on the fish position at the bottom, so the aim was to study the fish assemblage in the hidden physical space, "inside bottom" (cryptobenthic in this work), and to compare it with the fish assemblage laying on the open bottom (epibenthic in this work).…”

“…Community composition of cryptobenthic fishes was analysed in order to detect explanatory variables (including both the habitat variables and the times of day) that best explain species distribution and abundance patterns. Only cryptobenthic specimens from species with four or more cryptobenthic specimens were included in the analyses (modified from Glavičić et al 2016). Therefore, only the 13 most common species were used for analysis (Table 1).…”

“…Season and year of fieldwork were introduced into the model as covariables to partial out possible confounding effects varying between fieldwork date using partial constrained analysis. The option "down-weight rare species" was not selected (Glavičić et al 2016). The first canonical correspondence analysis was performed with all 17 environmental variables, and after forward selection 14 variables were incorporated in the final model.…”

“…These fishes by definition have an intimate association with the benthos and provide important food web links between the benthos and nekton communities of coral reefs, with their quantitative significance resulting from their exceptional growth rates and mortality (Goatley et al 2016). Most quantitative ecological studies that differentially have targeted microhabitats of cryptobenthic fishes have been performed in coral reef and seagrass meadow ecosystems (Depczynski and Bellwood 2003, Ahmadia et al 2012, Tornabene et al 2013), a few in south temperate reefs (Prochazka 1998, Willis andAnderson 2003), and only a few in northeastern Atlantic (Beldade and Goncalves 2007) and Mediterranean warm temperate reefs (Kovačić et al 2012, Glavičić et al 2016, Thiriet et al 2016. Mainly on the basis of these studies, cryptobenthic reef fishes are now considered to play a globally significant role in temperate and tropical reefs: they are numerically dominant across different cryptic microhabitats, they may serve as a key trophodynamic component between open water and seafloor habitats, and ecologically highly differentiated species assemblages evolve rapidly in different microhabitats and regions and hence may serve as sensitive environmental indicators (Goatley and Brandl 2017).…”