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Revista mexicana de biodiversidad

versión On-line ISSN 2007-8706versión impresa ISSN 1870-3453

Rev. Mex. Biodiv. vol.94  México  2023  Epub 26-Jun-2024

https://doi.org/10.22201/ib.20078706e.2023.94.4968 

Ecology

Diversity of planktonic gastropods from western Baja California Peninsula assessed by 18S rDNA sequences

Diversidad de gasterópodos planctónicos del oeste de la Península de Baja California evaluada mediante secuencias de 18S ADNr

Ricardo Pérez-Enríqueza  * 
http://orcid.org/0000-0001-7770-9155

Alejandra Arciniegab 

Noé Díaz-Viloriac 
http://orcid.org/0000-0001-8964-4184

Salvador E. Lluch-Cotaa 
http://orcid.org/0000-0003-1832-1200

aCentro de Investigaciones Biológicas del Noroeste, S.C., Ave. Inst. Politécnico Nacional No. 195, 23096 La Paz, Baja California Sur, Mexico

bUniversidad de La Rioja, Ave. de La Paz No. 93-10, Logroño, La Rioja , Spain

cInstituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Ave. Inst. Politécnico Nacional s/n, 23096 La Paz, Baja California Sur, Mexico


Abstract

The study of planktonic mollusks is a relevant element to understand the dynamics of the benthic communities under present and future environmental conditions. We present the description of the biodiversity of planktonic gastropods at 2 sampling sites on the Pacific coast of the Baja California Peninsula, Mexico. Organisms collected from plankton tows at 2 locations (Cabo Tosco, n = 89 and La Bocana, n = 213) were sequenced for a portion of the 18S rDNA gene. High diversity was registered, with 71 Molecular Operational Taxonomic Units (MOTUs), which contrasts with the low phenotypic diversity of stereoscopic images. Differences in community composition between and within sampling sites indicate that planktonic gastropod distribution is not random but probably modulated by micro-environmental processes such as currents or biological events. The presence of non-gastropod sequences within some shells (n = 6) suggests their use as carriers of eggs or larvae of other taxa.

Keywords: Larval dispersal; Mollusca; Meroplankton; GenBank

Resumen

El estudio de moluscos planctónicos es un elemento relevante para la comprensión de la dinámica de la comunidad bentónica bajo las condiciones ambientales actuales y futuras. Se presenta la descripción de la biodiversidad de gasterópodos planctónicos en 2 sitios de la costa del Pacífico de la península de Baja California, México. Organismos recolectados en arrastres planctónicos en 2 localidades (Cabo Tosco, n = 89 y La Bocana, n = 213) se secuenciaron para una fracción del gen 18S ADNr. Se registró una alta diversidad con 71 unidades taxonómicas moleculares operativas (MOTU), que contrasta con la baja diversidad fenotípica observada en imágenes de estereoscopio. Las diferencias en la composición de la comunidad entre y dentro de los sitios de muestreo, indican que la distribución de gasterópodos planctónicos no es aleatoria, sino que se encuentra, probablemente, modulada por procesos microambientales tales como corrientes o eventos biológicos. La presencia de secuencias de organismos que no son gasterópodos dentro de algunas conchas (n = 6) sugiere que son utilizadas por organismos de otros taxones como portadores de huevos o larvas.

Palabras clave: Dispersión larvaria; Mollusca; Meroplancton; GenBank

Introduction

Planktonic dispersal in the marine environment is one of the leading connectivity processes among populations of meroplanktonic and holoplanktonic gastropods (Crocetta et al., 2020; Roegner, 2000), and is a relevant element of the trophic dynamics of ecosystems and indirect indicators of the health of adult populations (Campos & Landaeta, 2016; Chávez-Villegas et al., 2014). Planktonic dispersal study will aid in a better understanding of the molluskan community’s behavior under present and future environmental conditions (e.g., Aceves-Medina et al., 2020; Molina-González et al., 2018). For this purpose, baseline studies on the species composition that rely on the use of genetic markers are a starting point.

Planktonic gastropod identification is usually made using their morphology through microscope observation. The use of genetic markers (the Cytochrome Oxidase Subunit I of the mitochondrial DNA, COI) for this purpose is more recent. It has been used to study the genetic connectivity of the marine caenogastropod Bursa scrobilator (Crocetta et al., 2020). Due to its high conservation, the 18S ribosomal nuclear DNA (18S rDNA) gene has been proposed for biodiversity studies (Ranjithkumar et al., 2018).

Planktonic gastropods have been quite extensively studied worldwide (Bandel et al., 1997; Campos & Landaeta, 2016; Chávez-Villegas et al., 2014; Oliva-Rivera & Navarrete, 2007). However, in northwestern Mexico, the main efforts have been in the study of the species composition of holoplanktonic mollusks in the Gulf of California (Angulo-Campillo et al., 2011) and the western coast of the Baja California Peninsula (BCP) (Aceves-Medina et al., 2020; Molina-González et al., 2018; Moreno-Alcántara et al., 2020; Sánchez-Hidalgo y Anda, 1989), characterizing these regions as highly diverse. However, there is no available information about meroplanktonic gastropods in the region. Therefore, this work presents the first record of the planktonic gastropod biodiversity at 2 sites of the western coast of the BCP obtained by genetic markers.

Materials and methods

The sampling design originally intended to evaluate the presence of abalone larvae at 2 sites on the western coast of the Baja California Peninsula: La Bocana (LB: 26°45’1.9” N, 113°42’20.9” W) and Cabo Tosco (CT: 24°18’26.2” N, 111°42’36.6” W) (Fig. 1). However, we focused our study on other mollusks, as abalone larvae were not found. Sampling was done on December 1st, and 3rd, 2009 for LB and CT, respectively. At LB, the sampling area was located about 4.5 km southward, with an average depth of 10 m (Fig. 1). The rocky bottom floor is mostly flat with several small stone promontories composed of boulders, crevices, and a high abundance of macroalgae, mainly Eisenia arborea (Areschoug, 1876). CT is located at the southernmost part of Isla Margarita, and the sampling site was just 150 m off the coastline (Fig. 1), with a depth of approximately 3 m. The bottom is composed of large rocks with abundant crevices, surrounded by soft bottom but low macroalgae coverage. These sites were selected because they represent a high abalone productive area (LB) and the southern extreme of abalone species distribution (CT) (León-Carballo & Muciño-Díaz, 1996). The 8-day mean surface temperature in the first week of December 2009 at each site, which includes the sampling period and was obtained from the Aqua MODIS satellite -NPP, 0.0125°, West U.S., day time (11 microns), Simons (2022)- was 21 °C and 24 °C, respectively (Fig. 1).

Figure 1 Sampling sites at La Bocana (LB) and Cabo Tosco (CT) on the Baja California Peninsula. Color scale represents the 8-day sea surface temperature (°C) data from Aqua MODIS satellite (Simons, 2022). 

At LB, there were 3 towing stations: 1) surface and 2) at 3-4 m depth at the same geographical position (LB-01 and LB-10, respectively), and 3) at the surface, approximately 1 km to the west (LB-07) of the previous position. At CT, there was one towing station (CT-01) at the surface, in a semi-protected area on the southwestern side of Isla Margarita. Tows followed a circular trajectory at a speed of 2.5 knots for 5 min. The plankton net was conical (0.45 m mouth diameter and 180 μm mesh size), with a calibrated flowmeter and a collection cup also with a 180 μm mesh size. Samples were transferred to a 500 mL plastic flask and preserved in 80% ethanol.

The biomass from the plankton tows was estimated by displaced volume (Beers, 1976) and standardized to mL of biovolume per 1,000 m3 of filtered seawater (Smith & Richardson, 1979). Due to high biomass at each towing station, the samples were fractionated to ¼ with a Folsom splitter. Using a stereoscope at 35×, following the description of Courtois de Viçose et al. (2007) for Haliotis tuberculata abalone larvae, gastropod mollusks with egg or globular shapes were separated (Bandel et al., 1997). A total of 384 individuals were separated, set in slides with wells (1 individual per well), and photo-documented (Leica Application Suite EZ, ver. 1.5.0). Individuals were transferred to 96-well PCR plates containing 70% ethanol.

DNA extraction was done following the protocol of Selvamani et al. (2001) , with slight modifications. Before extraction, individuals were crushed with a plastic pestle and dried at ambient temperature. Samples were incubated in 18 μL of lysis buffer (Tris-HCl 10 mM, pH 8.3, KCl 50 mM, Tween-20 0.05%) and 2 μL de Proteinase-K (Sigma®, 2.5 mg/mL) at 55 °C for 24 h. After this time, the proteinase was inactivated by incubating the samples at 95 °C for 10 min. The plates were preserved at -20 °C until the PCR was performed.

A fragment of the 18S rDNA gene was amplified with primers 18SHal2F (5’-TTGGATAACTGTGGTAATTCT AGAGC) and 18SHal2R (5’-CCGGAATCGAACCCT GAT) (Aranceta-Garza et al., 2011). The reactions contained 0.2 mM de dNTPs (Invitrogen), 0.5 μM of each primer, PCR buffer 1× (Invitrogen), 1.5 mM MgCl2, 0.05 U Platinum® Taq DNA polymerase (Invitrogen), 2 μL of DNA and completed to 30 μL with MilliQ® water. PCR conditions were: 1 cycle at 94 °C for 4 min, 30 cycles at 94 °C for 45 s, 57 °C for 45 s, 72 °C for 45 s, and a final extension at 72 °C for 10 min in a thermal cycler (C1000, Bio-Rad). PCR products were verified in a 1.5% agarose gel stained with SYBR gold (Promega), visualized in a UV transilluminator (UVP BioDoc-it Imaging System).

PCR products of approximately 220 bp were individually sequenced either in forward and reverse (LB-7) or in forward only (LB-01, LB-10, CT-01) (Macrogen,Korea). The sequences were manually revised for quality and edited with ChromasPro v. 2.1.9 (Technelysium Pty Ltd). The edited sequences were analyzed to determine the number of similar genotypes with the software DnaSP v. 6.12.03 (Rozas et al., 2017). Identical sequences (100% match) were organized into Molecular Operational Taxonomical Units (MOTUs), for which the putative identity was obtained by a local alignment analysis with BLAST (Altschul et al., 1990). MOTUs were identified either to family, genus, or species level based on the hits with the highest similarity percentage (> 95%) and lowest E value (probability of the sequence match being random < 1 × 10-90). Nomenclature follows the NCBI (National Center for Biotechnology Information) Taxonomy database (Schoch, 2011).

The MOTUs sequences were analyzed as haplotypes (most sequences were homozygotes) to construct a minimum spanning network (Bandelt et al., 1999). The software PopArt (Leigh & Bryant, 2015) was used to visualize genealogical relationships among towing stations and obtain genetic diversity estimators (nucleotide diversity and number of segregating and parsimony-informative sites). The MOTUs’ diversity among towing stations was estimated by the Shannon-Weaver index using the natural logarithm with the vegan package (Oksanen et al., 2020) in R ver. 4.1.1 (R Core Team, 2013), using MOTUs as putatively non-identified species.

Results

At LB, the plankton biomass at the mid-water tow was more than twice as high (LB-10, 1,222 mL 1,000 m-3) as at the 2 surface stations (LB-01 and LB-07, 491 and 557 mL 1,000 m-3, respectively). Surface biomass at CT (CT-01) was 883 mL 1,000 m-3. Planktonic gastropods, similar in shape, varied between 200 - 500 μm in width. As shells were translucent, it was possible to assess the presence of tissue within (Fig. 2).

Figure 2 Gastropod mollusks obtained from a plankton tow from La Bocana. Scale = approx. 200 μm. 

Of a total of 384 individuals analyzed, 302 resulted in reliable DNA sequences matching gastropod mollusks (phylum Mollusca, class Gastropoda). The rest of the sequences were of low quality (n = 75) or matched other taxonomic groups (phylum Cnidaria, order Bivalvulida, and phylum Arthropoda, orders Euphausiacea and Calanoidea, n = 6) or showed no significant match to any species (n = 1). A total of 71 MOTUs were distinguished with matching identities higher than 95% and E-values lower than 1 × 10-100 in most sequences, putatively belonging to several families and orders of 5 subclasses (Tables 1, 2).

Table 1 Number of MOTUs and individuals per taxonomic group of the Class Gastropoda* at the 2 sampling sites. 

Subclass Order MOTU Individuals
Caenogastropoda Caenogastropoda incertae sedis 2 3
Littorinimorpha 16 126
Neogastropoda 5 8
Ptenoglossa (suborder) 1 2
Heterobranchia Aplysiida 3 16
Cephalaspidea 6 11
Ellobiida 1 2
Euthyneura (clade) 1 1
Nudibranchia 9 16
Pleurobranchida 1 4
Pteropoda 5 14
Heterostropha 1 1
Sacoglossa 9 34
Neritimorpha Cycloneritida 5 35
Patellogastropoda Patellogastropoda 1 1
Vetigastropoda Lepetellida 2 2
Trochida 2 5
Unclassified gastropod 1 21
Total 71 302

Nomenclature from the Taxonomy browser of the NCBI database (Schoch, 2011).

Table 2 Individuals per sampling station, organized in Molecular Operational Taxonomic Units (MOTU) from the genetic identity analysis (BLAST) of the 18S rDNA gene sequences in the GenBank database. Genbank accession numbers are shown only for the MOTUs of highest identity percentage and lowest E-value hits. CT-01: Cabo Tosco; LB: La Bocana. BCP: Baja California Peninsula. Proporcionar tabla. 

Sampling stations Taxonomy of hits GenBank hits characteristics Notes on possible species in the study region (the Pacific coast of the BCP) based on the Global Biodiversity Information Facility web [https://www.gbif.org- Consulted: Jan, 14 2022]
Superfamily Family Genera and species (GenBank accession number) E % Identity
MOTU CT-01 LB-01 LB-10 LB-07 Subclass Order
01 2 - - - Caenogastropoda incertae sedis Abyssochry-soidea Abyssochrysidae Provannidae Abyssochrysos melanioides (AB930376) 5×10-99 99.1 There are no records of the genera Abyssochrysos or Rubyspira in the BCP
02 - - 1 - Caenogastropoda incertae sedis Epitonioidea Epitoniidae Alexania inawazai (AB930380) 4×10-106 100 There are no records of Alexania or other species of the genus in the BCP
03 5 - - - Littorinoidea Calyptraeoidea Vermetoidea Lacunidae Calyptraeidae Vermetidae Lacuna pallidula (AJ488686) Crepidula fornicata (AY377660) Thylacodes adamsii (HQ833992) 3×10-102 100 The species Lacuna unifasciata (One-band lacuna) has been registered in the BCP. Several species of the genus Crepidula (American slipper limpet) have been registered in the BCP. Thylacodes adamsii (Scaly worm shell) has been registered in the north of the BCP
04 1 5 8 51 Cypraeoidea Cypraeidae Erosaria erosa (KT753625) Erronea erones (HQ833998) 5×10-125 100 Erosaria erosa and Erronea errones (Mistaken cowrie) are not registered in the BCP
05 - 1 - - Caenogastropoda Littorinimorpha Pterotra-cheoidea Atlantidae Atlanta sp. (MW203647) 3×10-101 100 Several species of the genus Atlanta have been registered in the Gulf of California (Angulo-Campillo et al., 2011), and the BCP (Aceves-Medina et al., 2020; Molina-González et al., 2018; Moreno-Alcántara et al., 2020).
06 - - - 1 Caenogastropoda Littorinimorpha Pterotra-cheoidea Atlanta sp. (MW204226) 2×10-123 99.6
07 - 1 - - Pterotra-cheoidea Pterotracheidae Firoloida desmarestia (MW204031) 4×10-88 95.3 The species Firoloida desmarestia have been registered in the Gulf of California (Angulo-Campillo et al., 2011), and the BCP ((Molina-González et al., 2018)
08 2 - - - Rissooidea Truncate-lloidea Rissoinidae Hydrobiidae Phosinella clathrata (AB930392) 1×10-106 100 No genera of families Rissoinidae or Hydrobiidae are registered in the BCP
09 - 11 2 - Truncate-lloidea Tateidae Trochidrobia punicea (KT313223) 5×10-99 99.1 No genera of family Tateidae are registered in the BCP
10 - 1 - - Novacaledonia numee (KT313210) Kanakyella gentilsiana (KT313209) and others Trochidrobia punicea (KT313223) Novacaledonia numee (KT313210) Kanakyella gentilsiana (KT313209) and others 9×10-102 100 No genera of family Tateidae are registered in the BCP
16 - - 1 - Caenogastropoda Littorinimorpha Tateidae Hydrobiidae Phrantela daveyensis (KT313215) 3×10-97 97.7 No genus of Truncatelloidea is registered in the BCP
11 - - 1 - Caenogastropoda Littorinimorpha Tateidae Hydrobiidae Phrantela daveyensis (KT313215) Bythiospeum sp. (AF367664) 1×10-93 7.7 No genera of family Tateidae or Hydrobiidae are registered in the BCP
12 1 - - - Vanikoroidea Eulimidae Pyramidelloides angustus (AB930386) Hemiliostraca sp. (AB930383) 6×10-104 100 No species of Pyramidelloides or Hemiliostraca have been registered in the BCP
13 - 8 6 - Balcis eburnea (AF120519) 3×10-108 100 The genus Balcis has been registered in the Gulf of California
14 - 1 6 - Melanella acicula (AB930381) 1×10-101 98.2 Several species of the genus Mellanela have been registered in the Gulf of California, and the BCP
15 5 - - - Hipponicidae Cheilea pileopsis (AB930397) Hipponicidae sp (MW204059) 3×10-102 100 The species Cheilea cepacea has been registered in the BCP
18 7 - - - Littorinimorpha Vanikoridae Vanikoro helicoidea (AB930395) 2×10-100 97.7 The species Vanikoro aperta has been registered in the Gulf of California but not in the BCP
70 - 1 - - Littorinimorpha Naticoidea Naticidae Sinum haliotoideum (FJ623466) 8×10-99 98.1 Several species of the genus Sinum have been registered in the BCP
17 - - - 1 Caenogastropoda Neogastropoda Conoidea Several families Several species 2×10-125 99.6 No information available
19 - 1 - - Caenogastropoda Neogastropoda Buccinoidea Several families Several species 4×10-100 99.5 No information available
20 - - 2 - Caenogastropoda Neogastropoda Several families Several species 5×10-105 100 No information available
21 2 - - - Caenogastropoda Neogastropoda Muricoidea Muricidae Coralliophila caribaea (MW204229) 2×10-103 99.5 Several species of the genus Coralliophila have been registered in the Gulf of California, and the BCP
22 - - - 2 Neogastropoda Muricoidea Muricidae Several species 6×10-124 100 Several families of the genus Coralliophila have been registered in the Gulf of California, and the BCP
23 - - - 2 Caenogastropoda Ptenoglossa Triphoroidea Cerithiopsidae Unclassified Cerithiopsidae 3×10-122 99.6 Several genera of family Cerithiopsidae are found in the BCP
24 7 3 1 - Akeroidea Akeridae Akera bullata (AY427502) 3×10-113 99.6 The species Akera maga has been registered in the BCP
25 3 - - - Aplysioidea Aplysiidae Stylocheilus longicauda (DQ093439) Dolabrifera dolabrifera (DQ237960) 3×10-112 100 The species Stylocheilus ricketsii has been registered in the BCP and the Gulf of California. The species Dolabrifera dolabrifera has been registered in the Gulf of California
26 - 1 1 - Aplysiida Aplysia californica (XR_004859253) 6×10-115 99.6 The species Aplysia californica has been registered in the BCP
27 2 - 1 - Aplysiida Bulloidea Bullidae Bulla vernicosa (DQ923452) 6×10-105 97.8 Several species of the genus Bulla are registered in the BCP
28 - - 1 - Haminoeidae Liloa mongii (MH933263) Atys curta (DQ923459) 9×10-113 100 There are no records of Liloa or Atys for the BCP
29 - - 1 - Heterobranchia Cephalaspidea Diaphanoidea Diaphanidae Diaphana globosa (MH933321) 1×10-107 98.2 Diaphana californica has been registered in the BCP
30 1 - - - Heterobranchia Cephalaspidea Philinoidea Cylichnidae Acteocina lepta (MH933295) 6×10-110 99.1 Several species of the genus Acteocina have been registered in the BCP
31 3 - - - Cephalaspidea Philinoidea Cylichnidae Acteocina lepta (MH933295) 7×10-90 99.5 Several species of the genus Acteocina have been registered in the BCP
32 1 - 1 - Cephalaspidea Laonidae Laona confusa (MH933303) 6×10-90 94.3 Laona californica has been registered in a northern region of the BCP
33 - 1 1 - Ellobiida Ellobioidea Ellobiidae Melampus bullaoides (KM280980) 7×10-114 100 Several species of the genus Melampus have been registered in the BCP
35 - 1 - - Euthyneura Pyramide-lloidea Pyramidellidae Turbonilla elegantissima (GU331941) 3×10-92 96.7 Several species of the genus Turbonilla have been registered in the BCP
36 - 2 - - Anadoridoidea Polyceridae Plocamopherus aurantinodulosa (EF534011) 8×10-94 93.7 There are no records of Plocamopherus for the BCP
37 - - 1 - Fionoidea Trinchesiidae Phestilla sp. (MK088224) 2×10-104 97.4 Phestilla lugubris has been registered in the Gulf of California
43 - - 1 - Fionoidea Eubranchidae Eubranchus sanjuanensis (GQ326909) 2×10-100 96.5 Several species of the genus Eubranchus have been registered in the BCP
38 - 1 - - Dendrono-toidea Dotidae Doto columbiana (GQ326881) 1×10-122 98.8 Doto columbiana has been registered in a northern region of the BCP
39 - - 1 - Doto columbiana (GQ326881) 3×10-118 97.6 Doto columbiana have been registered in a northern region of the BCP
40 - 1 - - Heterobranchia Nudibranchia Anadoridoidea Onchidorididae Corambe pacifica (KP340341) 1×10-106 97.8 Corambe pacifica has been registered in the BCP
41 - - 1 - Heterobranchia Nudibranchia Eudoridoidea Chromodorididae Mexichromis porterae (EF534014) 3×10-108 97.8 Two species of Mexichromis (M. antonii, M. tura) have been registered in the Gulf of California
42 - - 1 2 Nudibranchia Eudoridoidea Chromodorididae Diversidoris aurantinodulosa (EF534011) 5×10-111 94.1 There are no records of Diversidoris for the BCP
44 1 - 4 - Nudibranchia Diversidoris aurantinodulosa (EF534011) 4×10-92 94 There are no records of Diversidoris for the BCP
45 - 2 3 - Pleurobranchida Pleurobran-choidea Pleurobranchidae Berthella stellata (AY427495) 9×10-73 90.5 Berthella idiomorpha has been registered in the BCP
46 - 2 - - Thecosomata (Suborder) Desmopteridae Desmopterus papilio (GU969171) 3×10-112 99.6 Desmopterus papilio and D. pacificus have been registered in the Gulf of California (Angulo-Campillo et al., 2011) and the BCP (Molina-González et al., 2018; Sánchez-Hidalgo y Anda, 1994).
47 - 2 - 1 Desmopterus papilio (GU969171) 2×10-135 99.6
48 - 3 - - Desmopterus sp. (MW203406) 2×10-115 100
49 - 2 3 - Pteropoda Desmopterus sp. (MW203406) 2×10-103 99.1
50 - - - 1 Pteropoda Desmopterus papilio (GU969171) 9×10-134 9.3
51 - 1 - - Heterobranchia Heterostropha Pyramide-lloidea Pyramidellidae Hinemoa sp. (GU331936) 2×10-105 97.8 The genus Hinemoa has not been registered in the BCP
52 1 - - - Limapontioidea Caliphyllidae Polybranchia sp. (MH375070) 1×10-111 99.6 Polybranchia mexicana has been registered in the BCP
53 - 1 - - Polybranchia sp. (MH375067) 2×10-109 99.1 Polybranchia mexicana has been registered in the BCP
54 1 - 1 - Polybranchia sp. (MH375070) 4×10-96 96 Polybranchia mexicana has been registered in the BCP
55 - 1 - - Mourgona sp. (MH375064) 1×10-96 96.4 The genus Mourgona has not been registered in the BCP
56 - - 1 - Mourgona sp. (MH375064) 3×10-97 96.4 The genus Mourgona has not been registered in the BCP
57 1 7 10 2 Limapontiidae Aplysiopsis minor (AB501328) 1×10-127 98.9 Aplysiopsis enteromorphae has been registered in the BCP
58 - - 1 - Aplysiopsis minor (AB501328) 1×10-127 98.9 Aplysiopsis enteromorphae has been registered in the BCP
34 5 - 1 - Heterobranchia Sacoglossa Stiliger smaragdinus (AB501324) 3×10-97 96.4 Stiliger fuscovittatus have been registered in the BCP
59 1 - - - Heterobranchia Sacoglossa Oxynooidea Oxynoeidae Oxynoe viridis (AB501318) Oxynoe antillarum (FJ917441) 1×10-121 100 Oxynoe aliciae, O. viridis and O. panamensis have been registered in the Gulf of California
60 17 - - - Neritimorpha Cycloneritida Neritoidea Neritidae Nerita tessellata (FJ977654) Nerita funiculata (DQ093429) 7×10-104 99.1 Nerita funiculata and Nerita tessellata have not been registered in the BCP
61 13 - - - Neritimorpha Cycloneritida Nerita funiculata (DQ093429) 4×10-106 100 Nerita funiculata and Nerita tessellata have not been registered in the BCP
62 2 - - - Neritoidea Neritidae Nerita tessellata (FJ977654) 4×10-106 100 Nerita funiculata and Nerita tessellata have not been registered in the BCP
63 1 - - - Neritimorpha Cycloneritida Neritidae Nerita funiculata (DQ093429) 5×10-105 99.5 Nerita funiculata and Nerita tessellata have not been registered in the BCP
64 - - - 1 Neritimorpha Cycloneritida Phenacole-padidae Phenacolepas osculans (AY923890) 1×10-105 100 Phenacolepas osculans has been registered in the Gulf of California
65 - - - 1 Patellogastropoda Lottioidea Lottiidae Lottia gigantea (KP274858) Lottia scabra (GQ160769) Lottia jamaicensis (FJ977633) 6×10-151 100 Several species of the genus Lottia have been registered in the BCP
66 - - - 1 Fissurelloidea Fissurellidae Fissurella sp. (MK331687) Fissurella virescens (MK322194) Fissurella volcano (HM775293) 2×10-129 100 Fissurella volcano and other Fissurella species have been registered in the BCP
67 - 1 - - Lepetellida Haliotoidea Haliotidae Haliotis corrugata (HM775288) Haliotis fulgens (HM775289) 3×10-102 100 Haliotis corrugata and Haliotis fulgens have been registered in the BCP
68 4 - - - Vetigastropoda Trochida Trochoidea Turbinidae Megastrea undosa (KY766259) Turbo sp. (KY766259) Lunella sp. (EU530105) 1×10-95 100 Several genera of family Turbinidae are found in the BCP
69 - 1 - - Vetigastropoda Trochida Trochoidea Phasianellidae Tricolia pullus (AM048661) 6×10-85 94.1 There are no species of the genus Tricolia registered in the BCP
71 - 15 6 - Gastropoda unclassified (MW203299) 3×10-101 99.1
Σ 89 78 70 65

From the similarity analysis to GenBank sequences by BLAST, 23 MOTUs gave 100% identity. Identification to the species level was likely for 7 MOTUs (i.e., MOTUs 02, 05, 13, 33, 48, 61, and 62; Table 2). The remaining 16 are not certain as some of these MOTUs showed matching hits either to several genera (i.e., MOTUs 01, 03, 08, 10, 12, 15, 20, 22, 25, 28, 64, and 68; Table 2) or several species of a certain genus (i.e., MOTUs 29, 65, 66, and 67; Table 2).

When individual images were organized per MOTU (Supplementary material: Fig. S1[https://doi.org/10.5281/zenodo.7685921]), it was observed that there are many similarities among individuals at distinct taxonomic levels, including subclasses. In contrast, a high genetic diversity was found (nucleotide diversity π = 0.045, with 72 segregating sites and 55 parsimony-informative sites; Supplementary material: Table S1. The phylogenetic analysis inferred from the Minimum Spanning Network indicated that most identified subclasses were represented in all locations (Fig. 3). One exception was Neritimorpha, which was mainly observed in CT.

Figure 3 Minimum spanning network from 18S rDNA sequences per MOTUs. Background shades represent gastropod subclasses. 

The MOTUs’ diversity (Shannon index) varied among towing stations with the highest at LB-10 and the lowest at (LB-07) (Fig. 4). This large difference can be inferred by the presence of many MOTU 04 (family Cypraeidae) individuals at LB-07 (Table 2). Even though the diversity was rather similar among CT-01, LB-01, and LB-10 (Fig. 4), the MOTU composition was different with several MOTUs found only in a single towing station (CT-01: 17; LB-01: 16; LB-10: 14; LB-07: 7), i.e., 54 of the 71 MOTUs found were unique (Table 2).

Figure 4 MOTUs’ Shannon-Weaver diversity index, using the natural logarithm, per towing station. 

Discussion

A relatively high planktonic gastropod diversity was observed in the present study as compared to that found in 2 sites of the Caribbean Sea: 31 species (Oliva-Rivera & Navarrete, 2007) and 34 species (Chávez-Villegas et al., 2014), but lower than the 62 holoplanktonic species from the Gulf of California (Angulo-Campillo et al., 2011), the 6 species of the order Thecosomata (Sánchez-Hidalgo y Anda, 1989), and the 18 species of the family Atlantidae off the BCP (Aceves-Medina et al., 2020; Moreno-Alcántara et al., 2020). Nevertheless, according to a preliminary rarefaction analysis (results not shown due to reduced sample size) the actual species diversity in our study region is probably under-represented. To overcome the sample size issue, which is mainly due to budget constraints, new research technologies such as environmental DNA (eDNA) metabarcoding are broadening the sampling possibilities (Mychek-Londer et al., 2020).

Differences in community composition between the sampling sites of CT and LB (Fig. 1) would be expected as environmental conditions are usually distinct. Personal observations indicated that both sites are mainly composed of rocky bottoms and a few sandy flats, with a higher abundance of macroalgae at LB than at CT, and clearer waters at CT than LB. These differences, which are probably due to a higher productivity at LB, are explained by the position of the sites relative to the Magdalena Biological Activity Center (MBAC) (Lluch-Belda, 2000), with year-round cooler waters at LB (north of MBAC) than at CT (south of MBAC) (Jerónimo & Gómez-Valdés, 2006). In contrast, the differences in MOTUs composition among stations within LB let us hypothesize that planktonic gastropod distribution within a specific area is probably modulated by micro-environmental processes such as currents and biological events (Hernández-Trujillo et al., 2001). For example, many Cypraeidae individuals at LB-07 points to a massive spawning event in that area.

Even though 18S rDNA has been proposed for biodiversity studies (Ranjithkumar et al., 2018), it generally fails to separate species (Aranceta-Garza et al., 2011; Wu et al., 2015). In addition, the lack of a comprehensive database of gastropod 18S rDNA sequences from the western coast of the Baja California Peninsula limits the capacity of proper species identification. For example, the report of Angulo-Campillo et al. (2011) indicates the presence of several Atlantidae or Desmopteridae species, which in our case could not be distinguished (Table 2). Thus, future studies will require additional genetic markers, such as the 16S rRNA or COI genes (e.g., Crocetta et al., 2020).

The putative presence of molluskan MOTUs not recorded in the study region can be explained by either the low number of 18S rDNA sequences in the public databases, the lack of differences among species in this gene sequence of the same genus or family, and the lack of physical records of those specimens in the study region. In any case, efforts should be devoted to increase the number of gastropod 18S rDNA sequences and other genes in the databases and to promote frequent survey campaigns to detect previously undescribed species in this region. This is particularly relevant because mollusks are gaining attention within climate change research, not only to study phenotypic plasticity and genetic variation (Matoo & Neiman, 2021), but also because of their utility to act as indicators of climatic variability (Molina-González et al., 2018). Also, eDNA metabarcoding, which can be used to detect diverse ecological phenomena such as potential species invasions (e.g., Mychek-Londer et al., 2020), requires solid supporting information.

The presence of non-gastropod sequences within the analyzed individuals is a phenomenon that requires further attention. Even though we cannot rule out the possibility of cross-contamination, these individuals were visualized as planktonic gastropods (Supplementary material: Fig. S1), so it is unlikely that individuals of Cnidaria (order Bivalvulida), and Arthropoda (orders Euphausiacea, and Calanoida) were mistakenly put into the PCR tubes. We also consider that their presence as stomach content or as epibionts was unlikely because when mixed DNA is individually sequenced, it is not possible to separate the signature of each species. Rather, we hypothesize that these sequences might come from eggs or larvae of those other taxa that use gastropod shells as a substratum.

Acknowledgements

Sampling was done under “Pesca de Fomento” permit No. DGOPA.03182.290410.-1591. A. Arciniega received a scholarship from Conacyt (No. 41832). Conacyt provided funds for the project “Conectividad entre poblaciones de moluscos bentónicos marinos, estudio de caso: abulón Haliotis spp.” No. 2007-79482 to R.P.E. Fishermen cooperatives “Meliton Albañez” and “Progreso” supported sampling facilities. J. Cruz Hernández provided technical support during plankton tows. M. C. Rodríguez Jaramillo and R. Inohuye-Rivera provided technical assistance for planktonic gastropod photographic documentation. S. Avila gave technical support with genetic analyses. R. Llera-Herrera provided useful comments.

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Received: February 01, 2022; Accepted: December 02, 2022

*Corresponding author: rperez@cibnor.mx(R. Pérez-Enríquez)

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