Epibiotic traits of the invasive red seaweed Acanthophora spicifera in La Paz Bay, South Baja California (Eastern Pacific)

Abstract

The aim of this study was to analyze the interaction of a non‐native macroalga (Acanthophora spicifera) with native macroalgae (Sargassum spp.) and sponge assemblages in a subtropical embayment of the Mexican Pacific. The intensity of A. spicifera epiphytism on the native seaweed Sargassum varied significantly over time and was inversely related to the Sargassum density and size. The higher intensity (up to 28 individuals per host plant) occurred when Sargassum was smaller and was lower in density (senescence period). The lower intensity was recorded during the growth period of Sargassum and the subsequent increase in intensity was attributed to a high fragmentation period of A. spicifera, which was evidenced by a decrease in its average size and biomass and by the presence of larger free‐floating accumulations on the subtidal zone. The facultative interaction between A. spicifera and Sargassum appears to be neutral, as no negative or positive effects were found for epiphytic or basibiont seaweeds. However, this invasive seaweed characteristically monopolizes almost all types of hard substrate, and its effects on other algae and benthic organisms should be investigated. Moreover, A. spicifera was often epizoic on epilithic sponges. This invasive seaweed was found anchored on the sponge tissue by rhizome‐like structures. In addition, free‐floating fronds of A. spicifera were frequently found carrying small pieces of the basibiont sponge in its basis (60% of them with eggs and embryos), which suggests a novel facilitation mechanism for some sponge species, as the A. spicifera epizoism could favor fragmentation, dispersal and recruitment of these invertebrates. This study shows that A. spicifera is not only a species that adapts rapidly to the new conditions of the receiving environment but, due to its epibiotic traits, it can directly interact with and influence the life histories of some native species.

Records of the non‐native alga Acanthophora spicifera (Rhodophyta) and their colonial epibionts in La Paz Bay, Gulf of California

“…This red macroalga has been considered an invasive alga in Mexico by various authors ( Ávila et al 2012 , Méndez-Trejo et al 2014 , Riosmena-Rodríguez et al 2014 , Schnoller et al 2016 ); however, this term has different interpretations: academic interpretations, based on biological properties ( Richardson et al 2000 ) or pragmatic or political interpretations, which involve environmental affectation ( Blackburn et al 2011 , Iannone et al 2020 ). According to IUCN (2023) , “Invasive alien species are animals, plants, or other organisms introduced by humans, intentionally or accidentally, into places outside their natural range, negatively impacting native biodiversity, ecosystem services, or human economy and well-being”.…”

“… spicifera in La Paz Bay from 2004-2023. This database contains literature, citizen science and field data: presence and size of the macroalga, segment of the thallus with epibionts ( Hydrozoa or Bryozoa ), presence of Hydrozoa , Bryozoa or both, sampling data (year, month, day), place and coordinates of collection or recording, depth, environmental variables in situ (salinity sea surface, temperature), environmental satellite variables Chlo- a , PAR, PIC, POC and SST and anthropogenic activities in the site, such as natural protected area, tourism and local uses, fishing, nutrient supply, metal supply, nautical traffic, runoff water, mining, physical habitat modification, dump, industry and mangrove deforestation ( Méndez et al 2006 , Velasco García 2009 , Mendoza-Salgado et al 2011 , Ávila et al 2012 , Secretaría de Medio Ambiente y Recursos Naturales and Comisión Nacional de Áreas Naturales Protegidas 2014 , Tovar Lee et al 2015 , Secretaría de Medio Ambiente y Recursos Naturales and Recursos Naturales and Comisión Nacional de Áreas Naturales Protegidas 2016 , Roldán-Wong et al 2020 , Mendoza-Becerril et al 2022 , Estrada-González pers. obs.).…”

“…The first published record was from La Paz (south-western Gulf of California) ( Muñoz-Ochoa et al 2010 ). However, Ávila et al (2012) cited material not published before the summer of 2006, growing in a small area in the locality of Costa Baja, near the Port of Pichilingue ( Águila-Ramírez et al 2012 , Aguilar-Rosas et al 2014 ). Norris (2014) did not mention this taxon in his global study of seaweeds from the northern Gulf of California.…”

“…However, the species has been reported in other biological or ecological studies ( Riosmena-Rodríguez et al 2014 , Schnoller et al 2016 , Antonio-Robles et al 2021 ) or others related to its chemical composition or biological activity ( Muñoz-Ochoa et al 2010 , Tenorio-Rodriguez et al 2017 , Di Filippo-Herrera et al 2019 , Schnoller et al 2020 ). One of the most evident effects of its introduction to La Paz Bay is substratum monopolisation, as this alien seaweed forms dense beds colonising almost all types of hard substrata from the intertidal to 5-6 m depth, such as rocks, mussels, sponges and coral rubble ( Ávila et al 2012 ). The success of this species in occupying new habitats has been related to its high morphological plasticity, sexual and asexual reproductive strategies, adaptability to a wide range of hydrological conditions and its successful epiphytism on other algae ( Russell 1992 ).…”

“…Worldwide, A. spicifera has been recorded as a frequent substrate for fouling organisms such as hydroids ( Migotto 1996 , Chiaverini 2002 , Oliveira and Marques 2007 , Ávila et al 2012 ), as well as sponges and seaweeds in records from La Paz Bay ( Ávila et al 2012 , Méndez-Trejo et al 2014 ). Likewise, non-fouling organisms, such as annelids, arthropods, echinoderms and molluscs, use this macroalga as refugia ( Méndez-Trejo et al 2014 ), showing that A.…”