Heteractis magnifica Sea Anemone Population Dynamics at Village Reef, Perhentian Kecil, Malaysia: Monitoring of Growth, Formations, and Hosting Status

The coastal waters of Malaysia have been known to allow proliferation of sea anemone assemblages, which are resident species of tropical coral reefs. Along the Perhentian Islands of Terengganu, no efforts have been made thus far to investigate the presence and population dynamics of sea anemone assemblages locally. In this study, Heteractis magnifica assemblages at Village Reef at Perhentian Kecil were monitored during May, July, and August of 2020, thus providing a first assessment of their abundance. Sea anemone formation size, individual size, habitat location, and hosting status of anemonefish were assessed. Results demonstrate significantly larger counts of individuals within aggregated formations in the patch reef as compared to the fringe reef, without the presence of larger individual sizes. In addition, Heteractis magnifica specimens that were actively hosting anemonefish had significantly larger cover, larger individual sizes, and demonstrated higher individual counts within their aggregated formations compared to non-hosting specimens. There was no significant overall effect of time on sea anemone growth throughout the monitoring period, nor were there any significant changes in abundance levels regarding formation make-up throughout the monitoring phase. However, time related effects where present upon data inspection per assessment period. The restricted time frame of the monitoring period could play a role in explaining the absence of overall time related effects. A prolonged monitoring will help to further understand Heteractis magnifica population dynamics at this location, which can increase knowledge capacity for reef management and conservation strategies.


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The sea anemones' (Actiniaria) ability to reproduce asexually, and their lack of skeletal structure 35 allows rapid formation and community expansion in suitable environments (Steinberg et al. 2020). Sea 36 anemones can continually produce viable nodules for colonisation of neighbouring patches, where, 37 given favourable environmental factors, sexual reproduction is actively suppressed in favour of rapid, 38 asexual colonisation (Brace & Quicke 1986). Environmental parameters that influence sea anemone 39 abundance and growth include temperature, seasonal effects, radiance and nutrient loadings,

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Government departments, local businesses, and social enterprises alike engage in reef restorative 61 activities such as coral planting projects, promotion of 'reef friendly' tourism techniques, removal of 62 toxic or smothering materials, and educational outreach. Despite these efforts, large-scale effectiveness 63 is significantly impacted by restraints in staff capacity, lack of adequate financial resources, and 64 logistical limitations (Islam et al. 2013    anemones are reported to constitute clones (Allen 1975;Dunn 1977).

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Sea anemones with hosting capacity additionally undertake an obligatory symbiosis with anemonefish 109 (Amphiprion spp.) for nutrient intake, including a direct transfer from symbiont to host (Cleveland et       Between May and August of 2020, abundance, size, hosting status, and formation markers of hosting 182 sea anemone species Heteractis magnifica were monitored using SCUBA. All data collection sessions 183 took place between 8.30am and 11.59am, and visibility had to be over five meters as a prerequisite to 184 diving. Within the survey area, ten 20 meter transects were laid out in parallel using a 225° south-west 185 bearing, in addition to cross-referencing from a stable landmark (see    formations when a fully expanded individual's tentacles could touch a neighbouring sea anemone 235 (Allen 1975). In the event of ambiguity, video recordings were made for ex-situ examination by both 236 researchers.

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To estimate size, a long and short axis measurement of the oral disc was taken, using a tailor's tape, 240 and subsequently used to conduct calculations (Hirose 1985). If the Heteractis magnifica was 241 retracted, time was given for the animal to resume expansion before resuming measuring. For sea 242 anemones present as clustered formations, the same method was applied, but using the centre of the 243 cluster as a mid-point for axial measurements. In the event that clusters did not fully cover the 244 substrate, or if clusters did not assume a circular or elliptical shape, an area cover estimate was 245 recorded to adjust calculation (0-100%, estimated in increments of 10).

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To calculate individual size estimates for clustered sea anemones, cluster categories were marked 248 (Allen 1975). Categories include solitary, less than 5, less than 10, less than 15, with subsequent 249 increments of 5 until less than 35, which was the largest cluster formation category encountered at

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The maximum clustered formation within this reef region consisted of 12 individuals.

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During May, the collective cover of the sea anemones located in the fringing region at 294 Village Reef was 1.80m 2 , which increased to 3.64m 2 by July, and came to 2.39m 2 by August.   Table 3.

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To test for significant effects of time on Heteractis magnifica abundance levels at Village Reef,

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Kruskal-Wallis analyses were run for formation size differences, individual sea anemone size differences, and cluster make-up differences over time. Results indicate no significant effect of time on 307 sea anemone growth, including formation size, individual size and the counts of individuals clustered 308 within a formation (p = .095, p = .290, and p = .309 respectively).

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Moreover, to test for differences in formation size, individual size, and cluster makeup between the 311 two reef habitats at Village Reef, Mann-Whitney U tests were performed. Results indicate that 312 throughout the entire period of monitoring, a significant difference exists in the number of clustered 313 individuals present within a formation between fringe and patch reef regions, where clustered 314 formations contained significantly more individual specimens in the patch reef (see Table 4). No 315 significant results were found for formation or individual sea anemone size throughout the monitoring 316 period. Results did reveal a significant difference in cluster counts for May between the patch and 317 fringe reef, with a mean count of 1.80 specimens per formation at the fringe reef, and a mean count of 318 3.71 in the patch reef (see Table 4). Formation cover was significantly different between reef habitats 319 in July (see Table 4), with an average formation cover of .151m 2 in the fringe reef, and .174m 2 in the 320 patch reef. The results provide partial support for our hypothesis of significant differences in 321 Heteractis magnifica cover, size, and cluster make-up over time, as formation cove, and cluster counts 322 did differ significantly between reef habitats within specific monitoring periods, although individual 323 size estimates did not.

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Mann-Whitney U tests were performed to examine effects of hosting status on sea anemone formation 326 cover, individual size, and cluster counts within the patch reef. Throughout the entire monitoring 327 period, those Heteractis magnifica formations actively hosting anemonefish were larger than their 328 non-hosting counterparts in formation cover, individual size, and cluster counts: U = 37181.500, p <

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.001 for formation cover; U = 31776.500, p =.044 for individual size; and U = 36596.500, p < .001 for 330 cluster counts. When testing these effects for the individual monitoring periods, results remained 331 significant for May: U = 5061.000, p < .001 for formation cover; U = 4208.000, p < .001 for 332 individual size; and U = 4627.500, p < .001 for cluster counts. In July, only cluster counts had 333 significant differences in hosting status: U = 3558.000, p =.040.

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For August, no significant differences related to hosting status were detected.

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Individual sizes were larger for actively hosting by .015m 2 compared to non-hosting sea anemones.

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Finally, to test for time effects on clustered versus solitary sea anemones, a ChiSquare test was run.

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Results revealed no significant effects of formation make-up over time, indicating that abundance 346 levels of solitary or clustered formations did not differ significantly between the monitoring periods (p 347 = .130), a result that contrasts our study hypothesis.