Fouling invertebrates from PVC plates at Chahué Marina, Oaxaca, Southern Pacific coast of Mexico

. The port fouling fauna from Mexico has recieved greater study in the last 15 years. By improving our knowledge of fouling invertebrates on artificial substrates on the Southern Pacific coast of Mexico, we can better understand their distribution and prevent bioinvasions. The specimens listed in this present study come from PVC plates that were placed between June 2019 to June 2020 submerged at 1 m depth, on four docks of the Chahué Marina, Oaxaca, Mexico. Forty‑four taxa, representing nine phyla were identi‑ fied: Sipuncula (1 species), Entoprocta (1), Bryozoa (3), Arthropoda (3), Porifera (4), Cnidaria (5), Chordata (6), Mollusca (10) and Annelida (11). Thirty taxa were identified to species, with two still requiring confirmation. Five were identified to genus, two to family, and five to class level. From the 30 identified species, 18 were non‑native species: one entoproct, one mollusk, two bryozoans, three hydrozoans, three barnacles, four polychaetes, and four ascidians. These results include seven new records from the state of Oaxaca: one entoproct, one barnacle, two bryozoans, and three hydrozoans


INTRODUCTION
Marine invertebrates can colonize any type of substrate, including human-made structures (Terlizzi and Faimali 2010).Coastlines, docks, piles, and ship hulls are frequently colonized by invertebrate communities, which is is commonly referred to as biofouling (Carlton 1987;Goldburg and Triplett 1997;Terlizzi and Faimali 2010).These fouled structures are of concern because they can be used as stepping stones by marine fauna, allowing the establishment and spread of both native and introduced species, which can adversely affect the local fauna and disrupt human activities (Okolodkov et al. 2007;Terlizzi and Faimali 2010;Bishop et al. 2017).
Along the coast of Oaxaca, 1,765 marine and estuarine invertebrate species have been recorded in all habitats (mostly natural), belonging to fourteen phyla (Bastida-Zavala et al. 2013;Bastida-Zavala and García-Madrigal 2022).A few studies have been conducted in harbours, marinas, and ports, focusing on few families of polychaetes, hydroids, octocorals and bryozoans, with the goal of identifying the presence of introduced species (Bastida-Zavala et al. 2016;Bastida-Zavala et al. 2017;Humara-Gil and Cruz-Gómez 2018;Humara-Gil and Cruz-Gómez 2019;Bastida-Zavala et al. 2024).Despite these efforts, the knowledge about fouling marine invertebrates associated with artificial structures on the coast of Oaxaca is almost unknown.The main objective of this study is to record the fouling fauna found in artificial marine structures from the Chahué Marina, Oaxaca on the Southern Pacific coast of Mexico, constituting the first faunistic study in the region completely focused on artificial marine structures.

STUDY AREA
The Chahué Marina, which comprises an area of 36,230 m 2 , has a main floating dock with three secondary docks.The marina is part of Chahué Bay, located on the central coast of Oaxaca at the western end of the Gulf of Tehuantepec, Mexico (Figure 1).It is characterized as an euryhaline environment (environments with wide salinity range).In the extreme northwest of the Marina, the Chahué channel allows for the arrival of fresh water, especially in the months of greatest precipitation (June to October), although Chahué Marina receives variable contributions of treated fresh water throughout the year, originating from the wastewater treatment plant located 700 m away.During the sampling period, the water temperature had a maximum value of 31 °C and a minimum value of 26.7 °C, with an annual average of 29.76 °C.Salinity ranged between 23.15 and 34.58, with an average of 29.66.

METHODS
The invertebrate specimens revised in this work came from polyvinyl chloride (PVC) plates, placed on four docks of the Chahué Marina in Chahué Bay, Oaxaca, Mexico (Figure 1).Five PVC plates (15 × 15 cm length and width, and 0.6 cm thick) were deployed at each dock on 1 June 2019.The exposed surface of each plate was previously sanded.A fragment of brick was fixed on the opposite side to prevent the plates from floating.Each plate was tied with rope and secured to the dock with staples.The plates were submerged at 1 m depth, with a minimum horizontal separation between plates of 2 m.After three months, three plates at each location were removed and three new plates were submerged, until one year of study was completed, on 6 June 2020.
The specimens were obtained using a suprabenthic net with a 500 µm mesh opening; subsequently, the brick was removed, and the plates were placed in plastic bags (Ziploc).Due to time constraints, the specimens were not relaxed but rather fixed using a 4% formalin seawater solution inside the bag.The specimens were then washed and removed by scraping the exposed side of the plate, then preserved in 70% ethanol.
All studied material was deposited in the Scientific Collection (OAX-CC-249-11) of the Laboratorio de Sistemática de Invertebrados Marinos (LABSIM), Universidad del Mar (UMAR), Puerto Ángel, Oaxaca, Mexico.The abbreviations used in the material examined for catalogue numbers for each taxon are as follows: Hydrozoa (UMAR-HYDR), Polychaeta (UMAR-POLY), Sipuncula (UMAR-SIPU), Bivalvia (UMAR-BIVA), Branchiomma bairdi (McIntosh, 1885) INT Gulf of California (Tovar-Hernández et al. 2009a, 2009b, 2012, 2014 The polychaete Maldanidae NI (Figure 4A) was identified only to family level due to it being an incomplete specimen, making further identification difficult.The shell of the gastropod mollusk Calyptraeidae NI (Figure 6I) was damaged during extraction, causing it to lose diagnostic morphological features.Another five taxa were left at genus level: a sponge, Cliona sp.(Figure 2F (Figure 8E).These were not able to be identified to species level due to the lack of diagnostic morphological features.
Two taxa still need confirmation, Parasabella cf.lacunosa and Styela cf.canopus, since these have morphological differences pointed out in the remarks of each species.Identification.Erects colony, 6.8 cm high, from a creeping hydrorhiza.Monosiphonic hydrocaulus, alternately branched with terminal hydrants.Dark brown hydrocaulus, thick, straight, becoming slightly curved in upper section closest to the tip, with annulations where the branches arise.Branches more slender than the hydrocaulus with annulations along its entire length, younger branches without cancellations; hydrants distributed along the branch, about five hydrants per branch (Figure 3A).Pear-shaped hydrants, hypostome surrounded by capitate tentacles, below some filiform tentacles (Figure 3B).Oval gonophores with four small bulbous projections (Figure 3C).
Remarks.Pennaria disticha was described from the Gulf of Naples, Italy (Goldfuss 1820).Fraser (1938aFraser ( , 1938b) ) recorded P. disticha as P. tiarella (Ayres, 1854) at several locations in the Eastern Pacific.Humara-Gil and Cruz-Gómez (2018), provided the first record of P. disticha from Oaxaca, describing variations from the redescription of Schuchert (2006), regarding the number of tentacles and position and number of annulations in the pedicel.These variations were also observed in the Chahué Marina colony.Miglietta et al. (2015Miglietta et al. ( , 2018)), after molecular analyzes, concluded that P. disticha is a species complex, with several species morphologically indistinguishable from each other.
Remarks.Although the type locality of Bougainvillia muscus is in Great Britain (Allman 1863), it has been recorded from the Pacific and Indian Oceans.Calder et al. (2019) recorded the species from the Galapagos Islands and stated that the species is part of the fouling community in ports and canals, possibly transported by navigation.Identification.Colony coarse, fascicled, approximately 2 cm high; main stem base 0.5 mm in diameter, irregularly branched, branches more slender than the main stem (Figure 3H).Perisarc tube firm, covering up to hydranth base; terminal hydranth, is elongate and cylindrical, with 17-20 scattered filiform tentacles on its surface (Figure 3I).
Distribution.Pacific of Panama and Mexico (east of Navidad and Isabel Islands, and Tenacatita Bay) (Calder et al. 2022).This constitutes the first record of Corydendrium flabellatum for Oaxaca.Remarks.Corydendrium flabellatum was described from the Pacific of Panama (Fraser 1938a) and is the only Corydendrium species recorded in the Tropical Eastern Pacific.Corydendrium flabellatum is morphologically close to C. parasiticum (Linnaeus, 1767), and since Fraser (1938a) did not describe the gonophores in the original description, morphological differentiation between these two species is unclear.Although the colonies here examined also lack the gonophores, we identified them as C. flabellatum, which is an endemic species from Tropical Eastern Pacific, geographically distant from the distribution of C. parasiticum (Mediterranean Sea).The lack of knowledge of gonophores, however, reinforces the need for further studies to better distinguish these species.In this work, the local name will be retained until morphological and molecular analyzes are carried out between C. flabellatum and C. parasiticum as suggested by Calder et al. (2022).

Distribution.
Western Atlantic; Western and Eastern Pacific (Calder et al. 2019).This constitutes the first record of Obelia oxydentata for the Mexican Pacific and for Oaxaca as an introduced species.
Remarks.Obelia oxydentata was described from Saint Thomas, Lesser Antilles (Stechow 1914).The colonies found in Chahué Marina are morphologically close to Obelia bidentata Clark, 1875, described from Long Island, New York (Clark 1875).It should be noted that according to Calder et al. (2019), O. bidentata is represented by robust, tall colonies, about 15 cm tall, with polysiphonic stems; in comparison with the Chahué Marina specimens, which are smaller, less than 3 cm tall, and have monosiphonic stems and with shorter stolon, even than Stechow′s (1914) O. oxydentata description.
Recently, Calder et al. (2019) recorded Obelia oxydentata from the Galapagos Islands, as an epibiont of Amathia verticillata (delle Chiaje, 1822) and as a common species in the fouling community on float docks.

Identification (UMAR-POLY-993).
Tubes flexible, brownish to dark, with horizontal dark brown to gray stripes.Body olive-green with small brown and white spots.Body length 38 mm long (Figure 4B).Radiolar crown with 10-16 pairs of radioles, with a pattern of white and brown transversal bands, with orange spots, macrostylodes strap-like.Collar lobes subtriangular with rounded ends.Identification (UMAR-POLY-997).Pale yellow body.Spiral radiolar crown, pink to reddish (Figure 4C), radioles lacks subdistal compound eyes and stylodes.Short subtriangular collar.Thoracic notochaetae spatulate, without mucron.Abdominal neurochaetae limbate.Thorax and abdominal uncini avicular with short manubrium, shorter than the distance between the crest and the chest; with companion neurochaetae with needle shape distal membrane.Lacks interramal abdominal eyespots.

Distribution. Only known from Chahué Marina.
Remarks.The specimens from Chahué Marina are morphologically close to Parasabella lacunosa, described from the Western Atlantic (Perkins 1984).The nominal species has not been recorded from any location near to the study area and, precautionarily, the specimens have been left as an unidentified species pending future comparisons with specimens of P. lacunosa from the Western Tropical Atlantic.Remarks.Hydroides brachyacantha was described with specimens from Mazatlán, Sinaloa and Acapulco, Guerrero (Rioja 1941).Sun et al. (2016), revised H. brachyacantha records and molecular analyses comparing with the populations of H. amri Sun, Wong, ten Hove, Hutchings, Williamson & Kupriyanova, 2015 from Australia, and designated a neotype to H. brachyacantha in Mazatlán.The Chahué Marina specimens match morphologically with the nominal species description.This species is considered native from the region, further, this serpulid is very common in natural and man-made substrates along the Mexican Pacific (Bastida-Zavala et al. 2016).Identification.Tube white with visible longitudinal and transverse ridges.Opercular peduncle white and smooth.Opercular funnel with 25-27 radii with pointed tips, verticil with 11-14 spines, straight, flattened T-shaped tip, with one basal internal spinule (Figure 4E).Collar with bayonet chaetae, with two basal teeth pointed.
Identification.Tube white, without longitudinal ridges.White and smooth opercular peduncle.Opercular funnel with 24 radii with blunt tips, verticil with 14-16 spines, all spines similar in shape and size with pointed tips; all the spines with three pairs of lateral spinules (Figure 4F).Collar with bayonet chaetae, with several tiny teeth.
Remarks.Hydroides sanctaecrucis was described from Saint Croix Island, Lesser Antilles (Mörch 1863).It was the most abundant species in this study, whose presence could be of concern in the natural habitat, because this species competes successfully for substrate with other native species.Bastida-Zavala and ten Hove (2002Hove ( , 2003) ) mentioned that the species could be transported by maritime means.Identification (UMAR-POLY-1008).Tube white, with three longitudinal ridges and two rows of alveoli along the tube; transversally circular.Branchial crown with two semicircular lobes.Opercular peduncle insert in the left lobe, with short and smooth wings, with pointed tips, opercular plate with a mid-dorsal slight depression.Operculum conical, smooth, with a pair of lateral circular dark spots, in the mid operculum (Figure 4H).Few collar chaetae limbate.
Remarks.Spirobranchus minutus was described from Acapulco, Guerrero (Rioja 1941b).The specimens revised from Chahué Marina match with the description by Rioja (1941b).Bastida-Zavala et al. (2016) recorded the species on rocks from Chahué Marina and mentioned that the species could colonize both natural and artificial substrates, as was found in this study.Identification.Body light brown, covered with scattered dome-shaped papillae, darker than the body (Figure 5G).With digitiform nuchal tentacles.Unidentate hooks arranged in rings (Figure 5H).With four retractor muscles.

Phylum
Distribution.Tropical Eastern Pacific.From Gulf of California to Panama (Silva-Morales and Gómez-Vásquez 2021).
Remarks.Phascolosoma puntarenae was described from Puntarenas, Costa Rica (Grube 1858).Despite the juvenile condition of the specimen, the diagnostic morphological characters of Phascolosoma puntarenae were observed, mainly the arrangement and conformation of the introvert hooks and the presence of the dome-shaped papillae.According to Cutler (1994), all sipunculan species live exclusively in marine waters, never in brackish waters.Thus, this is the first record of a sipunculan in brackish waters (salinity 27) from the Tropical Eastern Pacific.Identification (UMAR-BIVA-021).Size 14.2 mm.Shell elongated cylindrical, of pale-yellow color with lighter parts, sharp towards the anterior end with rounded termination and the tips between crossed (Figure 6A).With terminal calcareous adhesions.Line pattern on the shell is visible.
Remarks.Leiosolenus aristatus was described from Senegal, Western Africa (Dillwyn 1817).According to the description of Olsson (1961), the specimens have an average length of 32 mm, larger than the Chahué Marina specimens (6-14 mm).However, the termination of the leaflets in long and rounded tips that alternately intersect, resembling a pair of scissors, is diagnostic, even in the smaller specimens, differing only in the prolongation of the tips.Remarks.Ostrea conchaphila was described from Mazatlán, Sinaloa (Carpenter 1857).The specimens from Chahué Marina match with the original description of Carpenter (1857).This native species was previously recorded by Holguín-Quiñones and González-Pedraza (1989) who mentioned it as a common sessile species in artificial substrates.
Identification.Size 1.7 cm on average (n= 15).Shell oval, longer than wide.Slightly pronounced cup-shaped lower valve, upper valve slightly flattened.Outer margin with palmate foliations.Internal color from white to Remarks.Saccostrea palmula was described from Mazatlán, Sinaloa, as a subspecies of Ostrea conchaphila (Carpenter 1857), posteriorly moved to Saccostrea Dollfus & Dautzenberg, 1920 by Harry (1985).The specimens match morphologically with the original description (Carpenter 1857).Identification (UMAR-BIVA-029).Size 1.9 cm.Shell irregularly oval.Flat upper valve.A small recess present under the frequently enlarged ligament area of the left leaflet.Heavily marked, widely spaced chomatas, with five on each side of the ligament area.Dark brown outer surface, strongly iridescent whitish inner surface (Figure 6E).Identification.Size 2 cm.Shell oval.High apex curved and inclined to one side.Oblique spines arranged in generally regular rows, some tubular spines, especially those of greater length.White shell with gray, brown and reddish tones.Crenulated margin.Slender cup-shaped structure on the ventral part of the shell (Figure 6J).
Remarks.Crucibulum spinosum is a native species of spiny cup-and-saucer snail from the Eastern Pacific (Hendrickx et al. 2014).Although the specimens examined here were smaller than the specimens recorded by Keen (1971), they share the diagnostic characters.However, the specimens differ in having lesser definition in the distribution and size of the shell spines.
Identification.Size 2.7 cm. Shell tubular sinuous.The upper part of the shell is light brown with darker patches, and the lower part white, circular opening.Ornate surface with fine lines along the tube (Figure 6G).Inner tube porcelain.(Brusca 1980;Gamboa-Contreras and Tapia-García 1998;González-Villarreal 2005).

Distribution. Mexican Pacific
Remarks.Thylacodes margaritaceus is a vermetid endemic to the Mexican Pacific (Brusca 1980).According to Keen (1971), this species has almost straight tubes and is often ornamented by lines along the tube, as was observed in the specimens examined here; however, the ends are slightly curved (Figure 6G).
Identification.Size 2 cm.Tubular shell, with a very marked spiral in the shape of a tower.Black color with red parts; circular opening.Ornate surface with fine lines along the tube (Figure 6H).Inner tube porcelain.
Remarks.Thylaeodus indentatus was described from Mazatlán, Sinaloa (Carpenter 1857) and endemic to the Mexican Pacific (Brusca 1980;Rodríguez-Palacios et al. 1988).Keen (1961) mentioned that this species exhibit color variations, including the reddish coloration, which can be slightly seen on the edges of the tubular shells (Figure 6H).

Identification (UMAR-THOR-032).
Shell with smooth white plates, with violet-pink or dark to violet-colored longitudinal stripes (Figure 7A).Scutum, internal region slightly concave in the middle part (Figure 7B).Tergum with a slight carinal protrusion and a spur wide as long, rounded (Figure 7C).Labrum multidentate, with 10 teeth on each side decreasing in size, pronounced notch in the middle part (Figure 7E).Mandible with four to six teeth, two upper and four lower, fourth and sixth teeth with additional denticles (Figure 7D).
Remarks.Balanus amphitrite was described by Darwin (1854) from Natal, South Africa (sensu Harding 1962).Posteriorly, the B. amphitrite complex was revised by Henry and MacLaughlin (1975), who confirmed the wide distribution in tropical and subtropical waters.Twenty years ago, Pitombo (2004) performed a phylogenetic analysis of the Balanidae, establishing a new subfamily, the Amphibalaninae, and a new genus Amphibalanus Pitombo, 2004, whose type species is B. amphitrite.
The specimens of Amphibalanus amphitrite from Chahué Marina match the description of Darwin ( 1854) and the redescription by Harding (1962), with some differences regarding the labrum, it was supposed to have 4-13 teeth (Darwin 1854; Harding 1962), whereas the Chahué Marina specimens have 8-18 teeth (Figure 7E); the mandible in the Chahué Marina specimens has three upper teeth and two lower teeth, the last with an irregular shape (Figure 7D), whereas Darwin (1854) and Harding (1962) described it with two upper teeth and three lower teeth, all with an irregular shape.However, these variations fall in the variation range of the redescription of A. amphitrite made by Henry and MacLaughlin (1975).

Identification (UMAR-THOR-036).
White shell conical with smooth ivory white plates (Figure 7F).The scutum has strongly marked growth ridges and teeth at the occlusal margin (Figure 7G).The tergum has a protruding carinal margin and does not have a marked longitudinal groove (Figure 7H).Labrum with 11 teeth on each side, the central part presents a pronounced notch (Figure 7J).Mandible with six teeth, two upper teeth, and four lower teeth; fourth, fifth, and sixth of irregular shape (Figure 7I).

Distribution.
Circum-(sub)tropical. East coast of the United States to Brazil, southwest Europe, Mediterranean, Black and Caspian seas, Western Africa, India, Japan to Hawaii and Eastern Pacific (Henry and MacLaughlin 1975).Eastern Pacific: Gulf of California (Henry and McLaughlin 1975;Salgado-Barragán and Hendrickx 2002), Colima (Henry and McLaughlin 1975), Panama (Matsui et al. 1964) and Colombia (Lozano-Cortés and Londoño-Cruz 2013).This constitutes the first record of Amphibalanus eburneus for Oaxaca as a non-native species.
Remarks.Balanus eburneus was described by Gould (1841) from Boston Bay, Massachusetts (sensu Henry and McLaughlin 1975).Recently, the species was moved to the genus Amphibalanus by Pitombo (2004).The shells of the specimens of the Chahué Marina match morphologically with the redescription provided by Henry and McLaughlin (1975); and some characters reflects the juvenile stage of the specimens studied: The labrum in Chahué Marina specimens has 11 teeth (Figure 7J), while Henry and McLaughlin (1975) mentions 6-32 teeth; the mandible of the examined specimens had six teeth (Figure 7I), while the redescription of Henry and McLaughlin (1975) mention that it has 5-7 teeth.Additionally, the first maxilla of Chahué Marina specimens has 10 spines, while the redescription mention that it has 5-14 spines (Henry and McLaughlin 1975).Identification (UMAR-THOR-030).Shell conical, triangular opening almost equilateral; walls with a pattern of vertical violet-pink lines (Figure 7K).Radii with a white background color, sometimes showing pale pink patches.Scutum is slightly internally concave in the middle part; an ivory white external region with pale pink patches, longitudinal grooves with four rows of deep perforations, more widely spaced at the base of the shield; margin occlude jagged (Figure7L).Tergum wider than long and spur as long as wide and short; straight basal margin; pronounced basi-scudal angle (Figure 7M).
Labrum with three small teeth, notorious notch in the middle (Figure 7O).Mandible with five teeth, fourth and fifth smaller with additional denticles and irregular tip (Figure 7N).
Remarks.Balanus trigonus was described from Java, Indonesia by Darwin (1854).The specimens collected from Chahué Marina match the original description provided by Darwin (1854) and the redescription by Pilsbry (1916).However, these specimens exhibit a deep internal curvature in the scutum and tergum that is not mentioned in either Darwin′s original description or Pilsbry′s redescription.

Identification (UMAR-ENTO-001).
Stolon progressive and thin, with some bifurcations.Basal muscle slightly long, up to ¼ as long as the stem length; slightly transparent and compressible in consistency, inverted elongated cup-shaped.Slender straight peduncle, slightly widening upwards, with perforations in the inner layer; joints not present (Figure 8A).Calyx vase-shaped, terminal lophophore; calyx base separated from the pedicel by a short flexible portion.Lophophore with 12 to 20 filiform tentacles, according to the zooids size (Figure 8B).

Distribution.
Circum-(sub)tropical. Western Atlantic, Japan, India (Osburn 1953).Eastern Pacific: Southern California, Ecuador, Perú and Magallanes Strait (Osburn 1953;Wasson and Mariscal 2007).This constitutes the first record of Barentsia discreta for the Mexican Pacific and for Oaxaca as a non-native species.It is also the first entoproct recorded for Oaxaca.
Remarks.Barentsia discreta was described from Nightingale Island, in the Southern Atlantic Ocean (Busk 1886).The colonies from Chahué Marine morphologically match with the description; however, the zooids have fewer tentacles (12-20) and joints have not been observed, whereas Osburn (1953) recorded 20-24 tentacles and joints may occasionally occur.
Barentsia discreta has a worldwide distribution in both natural and artificial substrates.Owing to its physiological tolerance to environmental conditions, it is considered a non-native species in the Eastern Pacific (Osburn 1953;Emschermann 1993) Identification.Branches erect in a bushy form, with color ranging from reddish-purple to light brown.Branching is dichotomous, with zooids in two alternating rows.Zooids oval, 200-300 µm in length, with a single pointed tip on the outer corner of the zooids; avicularia and spines absent (Figure 8C).Ovicells large, globular with a brittle consistency; white to dark brown in color, located in the middle of the branches in vertical rows (Figure 8D).
Remarks.Savignyella lafontii was described from Egypt (Audouin 1826).The colony matches the redescription of Winston (1982).The species shows a disjunct distribution in the Eastern Pacific, which is more related to inconsistent sampling effort, rather than the natural distribution.It is likely that, by increasing the sampling effort along the Eastern Pacific, the real distribution of the species would be clear, and reveal the continuous distribution of this species.In this work, S. lafontii is considered a non-native species in the Tropical Eastern Pacific.Identification (UMAR-ASCI-070).Colonial.Transparent, soft test with embedded zooids.Zooids brown, grayish or black colored, oral siphon, and abdomen variable, some even have a yellow hue on the thorax (Figure 9A).Atrial siphon lateral to pharynx, runs along it.Male gonad divided in two.Pharynx with two to four rows, each with 7-10 stigmas.Organs in the abdominal region.

Phylum
Larvae oval, embedded in the tunic.Three adhesive papillae in a row, with a thin peduncle.With four pairs of ectodermal suction cups on each side.The tail extends over the middle of the body (Figure 9B).
Remarks.Diplosoma listerianum was described from the La Manche coast, France (Milne-Edwards 1841).The colonies examined from Chahué Marina match with the original description.Ritter and Forsyth (1917) and Van Name (1945)  Identification (UMAR-ASCI-075).Tunic beige, ovoid-shaped and flattened.Muscles visible through skin.Oral siphon with eight lobes, atrial siphon with six lobes; both with pale orange spot between each lobe (Figure 9E).Nerve ganglion at the base of the atrial siphon.With 100-120 tentacles of two sizes, filiform.Dorsal tubercle U-shaped with a rolled edge towards the center; in the center of the dorsal lamina.Symmetrical pharynx with 30-40 longitudinal vessels, 70-75 transverse vessels, and 3-4 stigmata, domeshaped papillae.Digestive tract occupies more than half of the left side of the body, and has a narrow intestinal loop, stomach globose.One portion of the ovary is surrounded by the first intestinal loop and the other portion is on the second intestinal loop.Male follicles are in the stomach and the first intestinal loop.
Remarks.Botrylloides niger was described from Bermuda (Herdman 1886).The specimens examined here match with the original description.The stomach in zooids examined presented 7-9 folds, which may be the result of incomplete folds, being lesser number of folds compared with the ones recorded by Van Name (1921), nine mains with one or two small incomplete folds.Botrylloides niger was first recorded from Oaxaca by Moreno-Dávila (2010).Is a non-native species in the Tropical Eastern Pacific (Tovar-Hernández et al. 2022).Identification (UMAR-ASCI-084).Flattened body, lacking regular shape.Tunic light brown, firm consistency.In the siphons the coloration intensifies in vivo with thin white bands (Figure 9H).Longitudinal muscles arise from the siphons.

Botrylloides violaceus Oka, 1927
Oral and atrial siphons found in the anterior part of the body, with short distance between them, of similar size, both tetralobulated.22-30 simple gill tentacles of three sizes.Very narrow U-shaped orifice of the dorsal tubercle.Pharynx with four longitudinal folds on each side, longitudinal straight stigmata, 20-30 longitudinal vessels (approximately four between each fold) and parastigmatic vessels present.Continuous, smooth, and wavy dorsal lamina.Intestine on the left side of the pharynx.Stomach elongated, with the inner wall with 17-20 longitudinal folds.The anus has undulations.Hermaphroditic gonads, two on each side of the body.Gonad elongated; globular testes follicles surrounding female glands (Figure 9I).

Distribution. Chahué Marina, Oaxaca.
Remarks.The specimens of Styela cf.canopus from Chahué Marina are morphologically close to S. canopus (Savigny 1816); however, there are some differences, Chahué Marina specimens have 17-20 stomach folds, 22-30 tentacles and show a very narrow U-shaped dorsal tubercle, while S. canopus has 18-30 stomach folds, 40-50 tentacles and a wide U-shaped tubercle (Van Name 1945).De Barros and Rocha (2021) suspected that S. canopus is a complex of cryptic species and analyzed 19 populations, using simple locus methods, and concluded that the current S. canopus comprises at least 15 species.For the differences between the redescription of Van Name (1945) and the Chahué Marina specimens, and considering the discovery of de Barros and Rocha (2021), our specimens have precautionarily been left as an unidentified species pending future revision of Styela species from the Eastern Tropical Pacific.(Michaelsen, 1904) Figure 9J Identification (UMAR-ASCI-088).Tunic translucent.Zooids transparent with orange or olive-green pigmented vessels observed in life, endostyle and siphons also pigmented (Figure 9J).Zooids oval and dorsoventrally flattened; 2.5 mm long and 1.5 mm wide.Both siphons located anteriorly.Pharynx, with four longitudinal vessels.Nine rows of stigmata, three stigmata between each vessel.Stomach oval located to the right of the pharynx, with 12-14 folds.Gonads on each side of the pharynx, female gonads between two sets of male gonads.Female gonads circular shaped.Male gonads branched joining at one end, of which five to six come out in each case (Figure 9K).
Remarks.Symplegma brakenhielmi was described from Veracruz, Gulf of Mexico (Michaelsen 1904).The colonies have two colorations of the vessels, orange and olive-green, both were lost by fixation; also, the stomach have slightly fewer folds than those described by Michaelsen (1904) (12-14 versus 14-15), but both agree in the shape of the stomach (oval); however, Monniot and Monniot (1987) mentioned that the stomach has a rectangular shape.Symplegma brakenhielmi was first recorded from Oaxaca by Moreno-Dávila (2010).Is a non-native species in the Eastern Pacific (Lambert and Lambert 2003;Moreno-Dávila 2010).
Fouling is a cause for concern because it is the main conduit for the introduction of non-native species (Karslon and Osman 2012; Okolodkov and García-Escobar 2014).In our study, polychaetes and ascidians had the highest number of non-native species, each with four taxa, followed by barnacles with three species.The entoproct Barentsia discreta was recorded for the first time in the Mexican Pacific, although it is a common fouling organism in bays and ports of California, growing abundantly in sessile communities (Wasson and Mariscal 2007).Introduced species usually represent the highest abundance of organisms in fouling communities of ports and marinas, as was demonstrated in this study, where the three most abundant solitary species (8,233 specimens) represented 63.4% of all specimens, and the three most abundant colonial species (61 colonies) were 41.8% of all colonies.All six species are non-native.
The use of molecular techniques has generated new approaches to examine species that were previously considered non-native, but have since been determined as native or groups of non-distinguishable cryptic species, such as hydrozoans (Miglietta et al. 2018), barnacles (Chen et al. 2014;Kim et al. 2022), bryozoans (Davidson and Haygood 1999) and ascidians (Peréz-Portela et al. 2013;de Barros and Rocha 2021).These molecular tools, coupled with comprehensive morphological studies, could improve our knowledge and clarify the status of non-native species recorded in poorly studied coastal regions such as the Southern Pacific coast of Mexico.
This work provides a baseline that could generate interest to carry on monitoring activities of port-inhabiting fouling fauna in Oaxaca to ensure early detection of non-native species in this highly biodiverse region.
In addition to the lack of studies on marine fouling fauna in the Mexican Pacific many studies of fouling invertebrates (either ecological or taxonomic approaches) are mainly focused on the most abundant species or describing new species.In both cases, studies are mainly focused on the macrofauna, while the rare or smaller species are often overlooked.We suggest more studies looking at biofouling in coastal lagoons, rocky beaches, and coral reefs, along with permanent monitoring programs to detect non-native species in marinas, ports, and ballast waters using multitaxa approaches and molecular analyses.Janeiro) and Andrea de Oliveira Ribeiro Junqueira (Universidade Federal do Rio de Janeiro) were very useful to improve the quality of the information presented in this paper.Thank you to the subject editor, Rafael B. de Moura, for your kind guidance.

Figure 1 .
Figure 1.Location of the Chahué Marina at the Chahué Bay, Bahías de Huatulco, Oaxaca, Mexico.Red points indicate the sampling sites in the docks.