New Records of Marine Diatoms for the American Continent Found on Stone Scorpionfish Scorpaena mystes (Scorpaenidae) in Mexican Shores

The survey of new benthic substrata is expected to yield new records of diatom taxa. A particular type of substratum is the skin of the Stone scorpionfish Scorpaena mystes Jordan & Starks, 1895 that, because of its benthic form of life, represents a potential colonizing surface for various organisms, including epizoic and opportunistic diatom taxa (epibiotic community). Thus, a floristic survey of diatoms was carried out by sampling the epibiotic community from S. mystes specimens collected in the east coast of Baja California Sur (Gulf of California). Thirty diatoms are new records for Mexican littorals. Twelve of these taxa had not been hitherto recorded for American coasts. Micrographs, and morphometric and distribution data on these taxa are provided.


Introduction
A recent surge of floristic studies reviews on benthic diatoms from Mexican littorals has yielded an extensive species list [1] that has kept on growing on the The body form of scorpaenids fishes provides them with camouflage, which is enhanced by skin ornaments, and a brown layer over the skin made from hydrozoans, filamentous algae, diatoms and other organisms that grow mainly on the cephalic region [12]. Thus, the benthic habit of the stone fish Scorpaena mystes Jordan & Starks, 1895, and its idleness, make it an ideal live substratum for testing various hypothesis on the relation animal host/epizoic diatom, but the scarcity of basic studies such as diatom floristics limits the spectrum of said hypotheses. However, several benefits have been noted for these epizoic diatoms, such as protection against grazing, availability of growing nutritional supplements, and an elevated position that also reduces the risk of being resuspended when growing on sediments [13] [14] [15].
Current observations by the first author of a rich diatom flora found within the epibiotic community growing on S. mystes suggested that new taxa could be found on this poorly explored substrate. Thus, the objective of this paper is to report new records of diatom taxa for Mexican waters and the American continent from the epibiotic community of S. mystes specimens collected in the central zone of the east coast of the Gulf of California (Santa Rosalia, Baja California Sur).

Materials and Methods
Twenty scorpion-fish specimens were captured during April 2016 off the coast of Santa Rosalia, Baja California Sur, Mexico which is located at 27˚19'N, 112˚15'W ( Figure 1). Fish specimens were caught manually with hand-held spears using semi-autonomous diving equipment (hookah) at an approximate depth of 20 m. Specimens were identified as S. mystes following Grove and Lavenberg [16].
Diatoms and other organisms (macroalgae mainly) were separated from the skin of the fishes using a tooth-brush to generate a compound sample from the twenty specimens. The brushed-off material was placed in a 250 mL flask and preserved in commercial 70% ethanol. Afterwards, in order to eliminate organic matter which would preclude visibility of the diatom frustules, the compound sample was oxidized by adding 3 mL of 70% nitric acid to 2 mL of sample, heating with a burner to boiling point and until emission of gas subsided indicating end of Canon EOS Rebel T5i camera (Canon, Japan). Identification of the taxa was done specifically using the reference that appears in its corresponding description. A formal list of the diatom taxa was constructed following Round et al. [17], and including information on synonymy, references, distribution, and morphometrics, which in several taxa refer to a single found specimen. Nomenclatural updates were done according to AlgaeBase [18], the Catalogue of Diatom Names, California Academy of Sciences

Results
Thirty benthic diatom taxa, including species and varieties, are presented here as new records for the Mexican littorals, along with twelve taxa not recorded before for the American continent. These taxa belong to the Bacillariophyceae (21 species), Coscinodiscophyceae (6 species), and Fragilariophyceae (3 species), that comprise nine orders, 14 families and 20 genera, with 30% of the species belonging to Amphora (6) and Navicula (3).
In what follows, taxonomic data, reference, synonymy, basionym, distribution, morphometric information, and illustrations are provided. Taxa without a previous record in the American continent are designated with an asterisk (*).
Distribution. Africa (Atlantic coast of Namibia).
Comments. Although only the cingular bands are depicted in the plates, complete valves were observed and measured, but could not be found again for photographic recording.

Discussion
The relative high number of new records for Mexican littorals and those that are new for the whole American continent (12), indicate that much work is yet to be done on floristics of benthic marine diatom. Thus, further surveys that include new substrata where these microalgae may thrive will eventually yield a reliable basis to undertake related studies on ecology and biogeography, both at regional and at worldwide scale. A balance between these findings and an analysis of the overall species richness currently underway, will surely permit addressing questions such as, are exclusively epizoic diatom aggregations lacking on these fish?
What characteristics favor the establishment of unique epizoic diatom aggregations? And, how do these rich diatom aggregations compare floristically with hosts from other localities?
Due to the relevance currently recognized on biodiversity data in terms of conservation policy and potential anthropogenic impact in Mexico and worldwide, species inventories are regaining attention. Studies on benthic diatoms, and in particular those on benthic forms, exhibit an underestimation of their geographic distribution, both regionally and worldwide, that is a function of the lack of research, which undermines the reliability of biogeographical analyses [34]. For example, Biddulphia juncta (A. Schmidt) A. Mann ( Figure 2M), Achnanthes apiculata (Greville) Riaux-Gobin, Compère, Hinz & Ector ( Figure 3A, Figure 3B), Diploneis ingens (Mann) Van Landingham ( Figure 4A), Amphora compacta A. Mann ( Figure 4G), and Navicula permulsa Hustedt ( Figure 4J) had been recorded for a single continent. Several of these for the Philippine Islands, bringing into mind the observation by Mann [29] on the striking similarity between the diatom flora of these islands and the coasts of Campeche, Mexico.
His main concern was the remoteness and isolation between these localities. Our study poses similar questions which require ex-professo biogeographical theory.
Derived from this and other recent efforts on the floristics of benthic diatoms from Mexican coasts, the list of new records incorporated to the overall checklist

Conclusion
The new records of taxa collected from the skin of the stonefish in this study are more indicative of scarce floristic research than as representatives of an epizoic relation, i.e. a product of an increasing survey comprising many more substrates and regions. Also, they inhabit a compound substrate where the main component is the skin of the fish, but other forms such as macroalgae and invertebrates are surely attached to it and diatoms to them, thus making up an epibiotic community. Moreover, many of the recorded taxa have been observed on other substrata elsewhere and may not be considered epizoic sensu stricto but are opportunistic as are the general natures of benthic diatoms. Notwithstanding the later, said taxa have not hitherto been recorded elsewhere for Mexican littorals and constitute new additions to the benthic diatom flora of the region, inasmuch as many of the recorded taxa have been observed on other substrata found elsewhere.