Evidence of novel symbiotic relationships between Christmas tree worms and coral reef blennies and gobies

Morgan F. Bennett-Smith, Catheline Y.M. Froehlich, Lili F. Vizer, Peter M. Buston (2025). Symbiosis https://doi.org/10.1007/s13199-025-01067

In Kimbe Bay, Papua New Guinea, I set out to investigate a curious behavior I’d noticed during years of diving: occasionally, a small reef fish would perch directly on top of a Christmas tree worm—or even nestle within its delicate feeding structures. If you’ve seen these worms in the wild, you know they are famously skittish, disappearing instantly at the slightest disturbance. So why do some fish seem to get a free pass?

To explore this question, we spent several weeks observing patches of Porites coral inhabited by Christmas tree worms, recording every interaction between fish and worms. What we found was remarkable: certain species—particularly a small goby and a blenny—were regularly tolerated, while others triggered an immediate defensive retreat.

Is this a newly recognized mutualism? Or a subtle form of kleptoparasitism, where the fish cleverly exploit the worm’s feeding structure? Our paper dives into the details and explores what these surprising relationships might mean for life on the reef.

Link to paper: https://link.springer.com/article/10.1007/s13199-025-01067-w

Links to select press coverage:

BBC Wildlife Magazine: https://www.discoverwildlife.com/animal-facts/marine-animals/christmas-tree-worms-and-fish-papua-new-guinea

Near complete local extinction of iconic anemonefish and their anemone hosts following a heat stress event

Near complete local extinction of iconic anemonefish and their anemone hosts following a heat stress event
npj Biodiversity 4:35 (2025) Bennett-Smith et al.

This study documents the catastrophic impact of the 2023 marine heatwave in the central Red Sea, where anemonefish (Amphiprion bicinctus) and their host sea anemones (Radianthus magnifica) suffered near-complete collapse. Across three surveyed reefs, we recorded 100% bleaching of host anemones, 94–100% mortality of anemonefish, and up to 94% mortality of anemones following extreme thermal stress reaching 22 °C-weeks. By comparing these findings to other Indo-Pacific sites where such declines were not observed, the study reveals how mutualistic reef species can face local—or even regional—extinction under intensifying climate stress.

The work was featured by National Geographic in September 2025, accompanied by original photography from the Red Sea, and has since been cited in discussions of reef ecosystem collapse and climate resilience.

Link to paper: https://www.nature.com/articles/s44185-025-00107-4

Links to select press coverage:

National Geographic: https://www.nationalgeographic.com/animals/article/heatwave-wipes-out-clownfish-in-red-sea-reefs

MongaBay: https://news.mongabay.com/2025/10/losing-nemo-in-the-red-sea-clownfish-vanish-as-anemones-bleach/

Individual clown anemonefish shrink to survive heat stress and social conflict

Heatwaves cause clownfish to shrink — a surprising survival strategy
Science Advances (2025) — Melissa Versteeg, Chancey MacDonald, Morgan Bennett-Smith, Peter Buston, and Theresa Rueger

This study revealed that clownfish (Amphiprion percula) can shrink in size to survive extreme marine heatwaves — the first documented case of shrinkage in a coral reef fish.

Conducted at the Mahonia Na Dari Research and Conservation Centre in Papua New Guinea, the team monitored 134 individually marked clownfish through a 2023 heatwave and found that 75% of them became shorter as temperatures rose. Shrinking increased their likelihood of survival by up to 78%, suggesting that this physiological flexibility may provide a short-term buffer against warming oceans, albeit with reproductive tradeoffs. The work was widely covered by international media, including CNN, Washington Post, and NPR, and has been featured in over 200 news outlets worldwide.

Link to paper: https://www.science.org/doi/10.1126/sciadv.adt7079

Links to media coverage:

Washington Post: https://www.washingtonpost.com/climate-solutions/2025/05/21/clownfish-shrink-climate-warming-water/

npr: https://www.npr.org/2025/06/02/nx-s1-5407527/clownfish-climate-change-heat-stress

The clownfish-hosting sea anemones (Anthozoa: Actiniaria): updated nomenclature, biogeography, and practical field guide

The clownfish-hosting sea anemones (Anthozoa: Actiniaria): updated nomenclature, biogeography, and practical field guide
Zootaxa 5506 (1): 1–34 (2024)

This study provides the first comprehensive update in decades to the taxonomy and biogeography of the ten known sea anemone species that host clownfishes across the Indo-West Pacific. Combining historical literature, modern nomenclatural revisions, and extensive underwater photography, we produced a practical field guide to improve species-level identifications.

The paper also explores the limitations of using machine learning for anemone recognition, emphasizing the continued importance of organismal expertise. By clarifying valid species names and documenting their phenotypic variation and global ranges, this work aims to strengthen ecological and evolutionary studies of the anemone–anemonefish symbiosis.

Link to paper: https://mapress.com/zt/article/view/zootaxa.5506.1.1

Novel in situ observations of asexual reproduction in the carpet sea anemone, Stichodactyla mertensii

Morgan F. Bennett-Smith, Micaela S. Justo, Michael L. Berumen, Raquel Peixoto, Benjamin M.Titus (2022). ZooKeys, 1103, 57–63. 

Abstract

Merten’s carpet sea anemone, Stichodactyla mertensii Brandt, 1835, is the largest known sea anemone species in the world, regularly exceeding one meter in oral disc diameter. A tropical species from the Indo-Pacific, S. mertensii drapes prominently over coral reef substrates and is a common host to numerous species of clownfishes and other symbionts throughout its range, which extends from the Red Sea through the Central Pacific Ocean. Long thought to reproduce via sexual reproduction only, recent genetic evidence suggests it may rarely reproduce asexually as well, although this process had never been confirmed through direct observation and the mechanism was yet to be described. Here, we directly observed and documented in situ asexual fragmentation via budding, in real time, by a Red Sea S. mertensii in a turbid inshore reef environment. While asexual reproduction is not unusual in sea anemones as a group, it is typically expected to be uncommon for large-bodied species. Herein, we describe S. mertensii fragmentation, provide high resolution images of the event from the Saudi Arabian coastline at multiple time points, and confirm asexual reproduction for this species.

Link to paper: https://zookeys.pensoft.net/article/84415/

Contrasting Effects of Local Environmental and Biogeographic Factors on the Composition and Structure of Bacterial Communities in Arid Monospecific Mangrove Soils

T. Thomson, M. Fusi, M. F. Bennett-Smith, N. Prinz, E. Aylagas, S. Carvalho, C. E. Lovelock, B. H. Jones, and J. I. Ellis 

Abstract

Mangrove forests are important biotic sinks of atmospheric CO2 and play an integral role in nutrient-cycling and decontamination of coastal waters, thereby mitigating climatic and anthropogenic stressors. These services are primarily regulated by the activity of the soil microbiome. To understand how environmental changes may affect this vital part of the ecosystem, it is key to understand the patterns that drive microbial community assembly in mangrove forest soils. High-throughput amplicon sequencing (16S rRNA) was applied on samples from arid Avicennia marina forests across different spatial scales from local to regional. Alongside conventional analyses of community ecology, microbial co-occurrence networks were assessed to investigate differences in composition and structure of the bacterial community. The bacterial community composition varied more strongly along an intertidal gradient within each mangrove forest, than between forests in different geographic regions (Australia/Saudi Arabia). In contrast, co-occurrence networks differed primarily between geographic regions, illustrating that the structure of the bacterial community is not necessarily linked to its composition. The local diversity in mangrove forest soils may have important implications for the quantification of biogeochemical processes and is important to consider when planning restoration activities.

Link to paper: https://journals.asm.org/doi/10.1128/spectrum.00903-21

Clownfish hosting anemones (Anthozoa, Actiniaria) of the Red Sea: new associations and distributions, historical misidentifications, and morphological variability

Bennett-Smith, M. F., Majoris, J., Titus, B., & Berumen, M. (2021). Marine Biodiversity Records, 14(1), 1-15.

Background

The Red Sea contains thousands of kilometers of fringing reef systems inhabited by clownfish and sea anemones, yet there is no consensus regarding the diversity of host anemone species that inhabit this region. We sought to clarify a historical record and recent literature sources that disagree on the diversity of host anemone species in the Red Sea, which contains one endemic anemonefish, Amphiprion bicinctus Rüppell 1830.

Results

We conducted 73 surveys spanning ~ 1600 km of coastline from the northern Saudi Arabian Red Sea to the Gulf of Aden and encountered seven species of host anemones, six of which hosted A. bicinctus. We revise the list of symbionts for A. bicinctus to include Stichodactyla haddoni (Saville-Kent, 1893) and Stichodactyla mertensii Brandt, 1835 which were both observed in multiple regions. We describe Red Sea phenotypic variability in Heteractis crispa(Hemprich & Ehrenberg in Ehrenberg, 1834) and Heteractis aurora (Quoy & Gaimard, 1833), which may indicate that these species hybridize in this region. We did not encounter Stichodactyla gigantea (Forsskål, 1775), although the Red Sea is the type locality for this species. Further, a thorough review of peer-reviewed literature, occurrence records, and misidentified basis of record reports dating back to the early twentieth century indicate that it is unlikely that S. gigantea occurs in the Red Sea.

Conclusions

In sum, we present a new guide for the host anemones of the Red Sea, revise the host specificity of A. bicinctus, and question whether S. gigantea occurs in the central and western Indian Ocean.

Link to paper: https://link.springer.com/article/10.1186/s41200-021-00216-6

Hidden Gems of the Middle East

My thoughts on diving and photographing some of the habitats of the Eastern Red Sea, for housingcamera.com.

Shooting Split Shots with a Small Dome Port

One piece of advice in capturing split shots is often, “use a giant dome port.” But most people shooting underwater don’t have giant dome ports. They’re hard to travel with, expensive, and usually reserved for larger-sensor cameras.

So, can you shoot split shots with a small dome, on a smaller camera? 

Yes - and in this article I describe my experiences shooting splits with a relatively small dome on a micro 4/3 camera. For housing camera.com.

https://www.housingcamera.com/blog/underwater-photography/shooting-split-shots-with-a-small-dome-port