INTRODUCTION

The Veracruz Reef System (VRS) is the largest coral reef system on the continental shores of the southwest Gulf of Mexico (^{Tunnell et al. 2010}). Located off the coast of the Port of Veracruz, Mexico, the VRS comprises 50 reefs and 6 islands (^{Liaño-Carrera et al. 2019}). The VRS was declared a Marine Protected Area in 1992, now covering an area of approximately 65,000 ha (^{DOF 2012}). Although interest in the ecology of the VRS has increased in the past decades (^{Granados-Barba et al. 2007}), the reefs making up this system have been little explored in comparison with those in the northern Gulf of Mexico and Greater Caribbean. Currently the VRS fish assemblage includes 477 species (^{del Moral-Flores et al. 2013}, ²⁰²⁰; ^{Robertson et al. 2019}), including 3 invasive species: the lionfish Pterois sp. (^{Santander-Monsalvo et al. 2012}), the damselfish Neopomacentrus cyanomos (^{González-Gándara and de la Cruz-Francisco 2014}), and the tube blenny Protemblemaria punctata (^{Argüelles-Jiménez et al. 2021}).

As the largest continental reef system in the southwestern Gulf of Mexico, the VRS is an important coral reef outpost and the center of an ecological reef corridor in the southwestern Gulf of Mexico that connects the Sistema Arrecifal Lobos Tuxpan in the north of the state of Veracruz and Arrecifes de los Tuxtlas in the south (^{Ortiz-Lozano et al. 2013}). However, the limited connectivity of these reef tracts with other reefs in the Gulf of Mexico and Greater Caribbean has led to the establishment of a fairly unique assemblage of reef fishes at the VRS (^{Rangel-Avalos et al. 2007}), which comprises several endemic species, such as the jarocho goby, Elacatinus jarocho (^{Taylor and Akins 2007}); the cinta goby, Tigrigobius redimiculus (^{Taylor and Akins 2007}); and the serranids Hypoplectrus castroaguirrei (^{del Moral-Flores et al. 2011}) and Hypoplectrus atlahua (^{Tavera and Acero 2013}).

The majority of biodiversity assessments in the VRS have been performed visually. However, visual censuses tend to overlook a substantial number of small-bodied, bottom-dwelling species (^{Brandl et al. 2018}). Thus, it is likely that increased scrutiny of fish assemblages in the VRS will reveal predominantly cryptic species (^{Rangel-Avalos et al. 2007}). As a consequence of increased scrutiny during surveys of reef fish communities and adjacent habitat in 2020, we recorded and visually documented 2 species of resident cryptic fish that had not been previously recorded in the VRS. With these reports the Veracruz fish assemblage increases to 479 species.

MATERIALS AND METHODS

The VRS has been considered a marine protected area since 1992, and it comprises around ~65,000 ha, with approximately 50 reefs on the continental shelf and <50-m depths (^{Liaño-Carrera et al. 2019}). The VRS is divided in 2 subareas by the outflow of the Jamapa river: (1) the northern reefs, directly off the coast of Veracruz, and (2) the southern reefs, off the coast of Antón Lizardo (Fig. 1). In the southern area of the VRS, visual, photographic, and videographic censuses of fishes in the reef lagoon and coral reef areas were carried out using scuba diving equipment to maximum depths of 25 m in 2020. All species encountered during those surveys were identified and described in this study using the Smithsonian Tropical Research Institute’s Atlantic fish taxonomic photographic database (https://biogeodb.stri.si.edu/caribbean/es/pages; accessed March 2021) and the guide by ^{Humann and DeLoach (2002)}.

Figure 1 Veracruz Reef System, located in the southwest of the Gulf of Mexico. Top right triangle: Liopropoma rubre at Santiaguillo reef (19°08ʹ30.7ʺ N, 95°48ʹ33.5ʺ W). Bottom right triangle: Ptereleotris calliura at Cabezo reef (19°04ʹ47.1ʺ N, 95°52ʹ02.1ʺ W). Green shade: emerged reefs. 

RESULTS

During our surveys we found 2 reef fish species that were not previously recorded in the VRS: Ptereleotris calliura (Jordan y Gilbert, 1882) and Liopropoma rubre Poey, 1861. With their record the taxonomic checklist of fishes in the VRS increased to 479 species.

The species P. calliura can be identified by the following characteristics, which are visible to divers: very elongated body, compressed; head strongly compressed; mouth very oblique, opens above, lower jaw projecting; 2 separate pelvic fins; and caudal fin long and pointed. Its color pattern was as follows: bluish gray to pale lavender on the head, body, and caudal fin; yellowish anal and dorsal fins; the dorsal fins present a black stripe along the outer edge; and the caudal fin sometimes shows dark upper and lower margins. Figure 2a shows a photographic image of one P. calliura individual that confirms the morphological features described for this species.

Figure 2 Ptereleotris spp. (a) Ptereleotris calliura (total length: 12 cm) in the Cabezo Reef lagoon in the Veracruz Reef System, Mexico; photograph by MRH. (b) Ptereleotris helenae; photograph by Graham Edgar. 

Two Ptereleotris species are known to occur in the southwest Gulf of Mexico: P. calliura and Ptereleotris helenae. Morphologically, the biggest differences between the two are the shape of the caudal fin and coloration. Ptereleotris calliura has a long, pointed caudal fin, while that of P. helenae is oval and shorter (Fig. 2b). In addition, the dorsal and anal fins of P. helenae are greenish yellow, while P. calliura has red borders along the second dorsal fin, the anal fin, and the upper and lower edges of the caudal fin (Fig. 2).

During our surveys we found 4 individuals of P. calliura at a depth of 3 m in the reef lagoon of Cabezo Reef in December of 2020, at around 11:30 AM. These individuals were found in an area dominated by sand and coral rubble, in the vicinity of a seagrass meadow. Each individual measured approximately 12 cm in total length, and all of them sheltered in individual burrows.

The second previously unrecorded species we found was L. rubre, which can be identified by the following visible characteristics: moderately elongate and compressed body; pointed head, with a nearly horizontal upper profile; dorsal fin divided to its base between the spines and rays; and caudal fin slightly concave. The head, body, and tail fin were yellow brown, with 5 dark red-brown stripes. The tail had 2 joined black, white edged blotches on the rear edges of the upper and lower lobes, and the rear end of the second dorsal fin and the anal fin had a black, white-edged blotch. The white edging of the black blotches in the caudal, dorsal, and anal fins were confined to the outer part of each blotch and does not completely encircle the blotches.

Another species in the same genus that has been previously reported in the taxonomic inventory of Veracruz is Liopropoma carmabi. The 2 species, L. rubre and L. carmabi, differ in their coloration. Liopropoma carmabi has yellow head, body, and caudal fin, with 4-5 purple, red-edged stripes along the body; the caudal fin has 2 separate black, blue-ringed ocelli at the rear end of the upper and lower lobes; the second dorsal fin has a black, blue-edged ocellus. These 2 species can be easily distinguished by divers as follows: the white-edged black blotches on the tail of L. rubre are joined, while blotches in L. carmabi form a discrete blue-ringed ocellus on each caudal lobe. In addition, L. rubre has a large, white-tipped black blotch at the end of the anal fin, which is absent in L. carmabi (Fig. 3).

Figure 3 Liopropoma spp. (a) Liopropoma rubre (total length: 5 cm) in the Santiaguillo Reef in Veracruz Reef System, Mexico; photograph by MRH. (b) Liopropoma carmabi; photograph by Ross Robertson. 

We found a single L. rubre individual, approximately 5 cm long, at a depth of 9 m on the reef slope of Santiaguillo Reef in November of 2020 at around 10:30 AM. The fish sheltered behind a plate-shaped brain coral, Colpophilia natans (Houttuyn, 1772), and promptly retreated into the cave formed underneath the plate coral. However, the fish reappeared from the cave on 2 occasions, enabling us to examine, record, and photograph the individual clearly to determine that it was indeed L. rubre and not L. carmabi (Fig. 3).

DISCUSSION

The taxonomic fish inventory in the VRS is extensive and has increased substantially in the last years (^{Taylor and Akins 2007}; ^{del Moral-Flores et al. 2011}, ²⁰¹³, ²⁰²⁰; ^{Tavera and Acero 2013}; ^{Robertson et al. 2019}), mainly due to the report of cryptic species, which go undetected by traditional survey techniques (^{Smith-Vaniz et al. 2006}). Visual census is the most used technique for the assessment of the reef fish community in Veracruz (^{González-Gándara et al. 2012}, ²⁰¹³; ^{del Moral-Flores et al. 2013}; ^{Pérez-España et al. 2015}; ^{de la Cruz-Francisco and Franco-Mejía 2017}). Using a different technique, ^{Robertson et al. (2019)} performed a survey that included the collection of cryptic species using clove oil, but L. rubre and P. calliura were not reported.

The 2 species reported here have been poorly documented in Veracruz reefs. Of the 2 species, L. rubre is the least documented. It was officially reported in the Sistema Arrecifal Lobos Tuxpan, northern reefs of Veracruz, in 2009 and anecdotally in Arrecifes de los Tuxtlas in 2014 (^{González-Gándara et al. 2014}). It has been suggested that L. rubre is highly associated with mesophotic reefs (e.g., ^{Bejarano et al. 2014}), yet it has been reported in depths as shallow as 3 m (^{Baldwin and Robertson 2014}). In this document, we recorded L. rubre in a large coral structure at 9 m depth, which is congruent with previous studies (^{Baldwin and Robertson 2014}). Additionally, the finding of this species in a shallow range could indicate that the knowledge on the species in this depth range is scarce or that the influence of the VRS turbid waters, which reduce the levels of solar irradiance (^{Carricart-Ganivet et al. 2011}), on the behavior of the coral reef fish community has not been widely explored.

Unlike L. rubre, P. calliura has been reported more widely, and it has been documented to occur at different depths in natural reefs in the Gulf of Mexico (^{Zarco-Perello et al. 2014}, ^{Streich et al. 2017}) such as reefs on the coast of Texas and the Madagascar Reef in the Campeche Bank. In Veracruz P. calliura was officially reported in the Sistema Arrecifal Lobos Tuxpan (^{González-Gándara et al. 2012}, ²⁰¹³) and recently in Arrecifes de los Tuxtlas (^{González-Gándara 2020}); however, it had not been reported in the VRS. With the addition of P. calliura to the VRS fish inventory, the distribution of this species can be confirmed along the Veracruz reef ecological corridor.

The continuous update of the fish inventory in the VRS highlights the need to perform different survey techniques focused on cryptic species to better understand the coral reef ecological dynamics (^{Smith-Vaniz et al. 2006}). This necessity is stressed by the perturbations that take place in the VRS, mainly because it is located next to the second most important trading port in Mexico, which has been responsible for most of the deteriorating conditions of the reef (^{Ortiz-Lozano et al. 2013}). However, other important perturbations that affect not only the fish community in the VRS but also the reef system include harvesting (^{Jiménez-Badillo 2008}, ^{Escamilla-Pérez et al. 2021}); biological invasions (^{Santander-Monsalvo et al. 2012}, ^{González-Gándara and de la Cruz-Francisco 2014}, ^{Argüelles-Jiménez et al. 2021}), as L. rubre is a lionfish prey (^{Morris and Akins 2009}, ^{Bejarano et al. 2015}); pollution (^{Horta-Puga and Carriquiry 2014}); climate change in a minor way, since the turbid waters likely reduce the levels of solar irradiance (^{Carricart-Ganivet et al. 2011}); and habitat change (^{Horta-Puga 2003}). Given the ongoing changes in coral reefs, a more complete document of the biodiversity and ecological contributions of the cryptic reef fishes in the VRS is fundamental. Therefore, we suggest that future studies use a variety of sampling strategies to survey the reef fish community more broadly and include approaches that enlighten the secretive biology of cryptic reef fish species in the area.