**4. Discussion**

Results showed the lower intertidal zones at Toco, Trinidad, to be dominated by zoantharians, specifically *Palythoa* and *Zoanthus* spp., similarly reported by Rabelo et al. [27] further south from Trinidad and Tobago on flat sandstone reefs in northeastern Brazil. As well, zoantharians were common in shallow-water habitats, and *Palythoa* and *Zoanthus* spp. were most common in shallow waters (<5 m), as reported at sites along the west coast of Curaçao [11]. In fact, Belford and Phillip [9,10,12,28] highlighted zoantharians being more abundant than their Scleractinia counterparts at this study's main sites. Lopez et al. [29] observed extensive zoantharian coverage for species *Zoanthus solanderi* and *Zoanthus sociatus* at a "zoanthid zone" located at Cabo Verde Islands, central eastern Atlantic,. Additionally, Karlson [6] observed similar extensive *Zoanthus* spp. coverage at Discovery Bay, Jamaica. This study reports a similar presence of a zoantharians covering the majority of the benthic lower intertidal zone, dominated by *Palythoa* and *Zoanthus* spp. in the southern-most part of the Caribbean.

Although zoantharian coverage was extensive, identification of zoantharians was difficult, because color morphotypes varied among sites. Similar observations were mentioned by Reimer et al. [20] related to zoantharian identification in the field, and in other studies [30]. Phylogenetic and morphological analyses using the COI marker revealed *Palythoa* brown and green color morphs were specifically *Palythoa caribaeorum* and *Palythoa grandiflora*, respectively, while green, orange, grey, and blue-green were *Zoanthus pulchellus* and *Zoanthus sociatus*, respectively. However, it is worth mentioning that caution should be taken since only the COI marker was used in this study. For instance, Sinniger et al. [31] noted that although the COI marker is easily amplifiable with universal primers, and was hence used in this study, the addition of the mitochondrial 16S ribosomal DNA marker is useful for comparison and further species identification. In fact, the addition of 16S sequences adds distinct advantages as they are slightly more variable in zoantharians than COI, thereby adding useful phylogenetic information [31].

Closed polyps are often observed during extreme low tides, where desiccation plays a factor in distribution; however, Rabelo et al. [27] reported *Z. sociatus* resisting desiccation better than *P. caribaeorum*. However, in this study, the reverse was observed, where *P. caribaeorum* had a significantly higher benthic coverage than *Zoanthus* spp. at lower intertidal zones, nevertheless zoantharian distribution appears to be related to desiccation tolerance [27]. It is not precisely known why the reverse of [27] was observed in this study, however family Zoanthidae, such as *Z. pulchellus* and *Z. sociatus*, have generally been known to adapt to different environments [10,19]. Reimer et al. [20] reported variation in *Palythoa* sp. polyp form and color as a result of variable environments, such as degree of wave action, and benthic type, which were characteristics similarly observed at Toco, Trinidad [9,10,12,28].

Zoantharian color morphotypes were observed in both high and low wave action habitats, especially at the lower intertidal zones where *P. caribaeorum* carpeted much of the lower intertidal zones. However, *Z*. *pulchellus* mainly covered individual rocks, or crevasses, and displayed many colors throughout the intertidal zone. *Z. sociatus* also was found within crevasses, however it was not observed to be found in extensive coverage at sites in this study. It should be noted that extreme caution should be taken while surveying zoantharian coverage using color morphotypes to identify zoantharians since species may be conspecifics [8,19]. This study successfully used molecular analyses to assist with identification of *Zoanthus pulchellus* and *Zoanthus sociatus*. *Zoanthus* spp. display phenotypic plasticity in both oral disk color and polyp height [27]. Additionally, molecular analyses assisted in identifying *P. caribaeorum* and *P. grandiflora*; however it should be noted that these two species can be distinguished from morphological characteristics.

Further phylogenetic analyses of zoantharians confirmed the Symbiodiniaceae genera *Cladocopium* and *Symbiodinium* in *Palythoa* and *Zoanthus* spp., respectively. These results are consistent to past analyses of both species at different locations in the Caribbean Sea and Atlantic [31–33]. Similar results for both *Zoanthus* species mentioned in this study hosting *Cladocopium* and *Symbiodinium* were reported at Cape Verde Archipelagos [30]. As global climate will continue to affect oceanic water temperatures [34], identification and distribution of zooxanthellate zoantharians such as in this study will provide important baseline data for future analyses.

**Funding:** This research was funded by contributors to Martin Methodist College Biology Travel fund by Lou Foster and Emily White. Other funding was received from the American Museum of Natural History Lerner-Gray Fund for marine research.

**Institutional Review Board Statement:** Ethical review and approval were waived for this study, because zoantharians were measured in situ, and genetic analyses on polyps did not require colony destruction.

**Data Availability Statement:** Photographs of zoantharian color morphotypes along the northeastern coast of Toco, Trinidad are available online at the Digital Public Library of America and Martin Methodist College Marine Biology Collection websites: https://dp.la/search?q=martin+methodist+college https: //www.artstor.org/2016/09/26/case-study-going-underwater-with-shared-shelf-commons/ (accessed on 9 June 2021).

**Acknowledgments:** I am grateful to the University of Tennessee Southern for use of laboratory space and equipment. Field equipment was essential in this study, therefore funding by contributors was appreciated. Thanks to all volunteer assistance during data collection from undergraduate research students and local interested citizens of Trinidad and Tobago. I am extremely grateful for advice and laboratory use from Todd LaJeunesse (Pennsylvania State University), Scott Santos (Auburn University), and Jeff Leblond and Dennis Mullen (Middle Tennessee State University). I am extremely grateful for advice on manuscript improvement by James Reimer (University of Ryukyus), and Douglas Dorer (University of Tennessee Southern) for assistance with molecular analyses of sequences.

**Conflicts of Interest:** There were no conflict of interest for this contribution.
