The reproductive season of Acropora in Socotra, Yemen.

Determining when corals reproduce has clear management and economic implications. Here we document the reproductive condition of corals in the genus Acropora on the island of Socotra in Yemen during February 2014. Twenty percent of colonies (n = 143) contained mature gametes and 28% had immature gametes indicating that spawning will occur in both February and March in 2014, confirming previous anecdotal reports of coral spawning at this time in Socotra. Acropora typically reproduce in synchrony with many other broadcast spawning scleractinian corals, and we therefore predict that many other species are reproductively active at this time of year.

Observation

Most hermatypic scleractinian corals have an annual gametogenic cycle that culminates in the broadcast spawning of gametes once per year [1]. In most reef regions, numerous species spawn in sychrony following full moons when sea surface temperature is either rising or falling [2, 3]. Determining exactly when spawning takes place has important implications for reef management and clear economic benefits [4]. For example, activities that are likely to limit fertilization success, such as dredging, can be prohibited during these often brief spawning periods [5]. In addition, the diving industry can benefit from public interest in coral spawning.

Here, we document the reproductive condition of Acropora corals on the island of Socotra, Republic of Yemen. The island, located 240 km east of the Horn of Africa and 380 km south of the Arabian Peninsula, supports a diverse scleractinian fauna of over 250 species (including 20 Acropora species) [6], and includes sites with a high cover of Acropora ( Figure 1). Acropora colonies were sampled before the full moon on 15 February 2014 to determine their reproductive condition. Three reproductive conditions were defined based on the appearance of the oocytes as observed with the naked eye in the field [7] (1) mature - oocytes pigmented and therefore likely to spawn within a month (2) immature - oocytes pale but visible indicating that they are close to maturity and likely to spawn within two to three months (3) empty - oocytes too small to see or absent indicating either that the colony has recently spawned, or is unlikely to do so for at least three months.

Figure 1.

The island of Socotra supports diverse assemblages of Acropora species.

A total of 143 Acropora colonies from approximately 14 species were sampled at four sites on the north of Socotra (Samerhur 12°41'40.96"N, 53°29'3.69"E; Qaiso 12°39'58.91"N, 53°24'33.86"E; Dihamri 12°40'20.35"N, 54°11'39.96"E; Hadibo 12°40'0.77"N, 54° 3'7.74"E) between the 31 January and 8 February 2014 ( Table 1). Twenty percent of colonies contained mature oocytes ( Figure 2), 28% contained immature oocytes and no oocytes were visible in the remaining 52% of colonies ( Table 1). Colonies with mature oocytes are highly likely to spawn at some time around the full moon in February 2014, whereas colonies with immature oocytes are likely to spawn in March 2014. The remaining colonies have either spawned recently, or alternatively, there could be a second reproductive season later in the year, similar to Western Australia [8], Singapore [9] and some locations in Indonesia [1]. Ten species had at least one colony with mature gametes ( Table 1) suggesting a multi-species spawning event is likely in February 2014. The Acropora typically reproduce at much the same time as most other broadcast spawning scleractinian corals [10, 11] and therefore we predict that many other species will be spawning in February and March in Socotra. Our results confirm previous anecdotal reports of coral spawning on Socotra in February and March [6].

Table 1.

The percentage of Acropora colonies with mature-, immature- or no oocytes, sampled between 31 January and 8 February 2014 on Socotra Yemen.

n = number of sampled colonies.

Species	Percentage mature	Percentage immature	Percentage empty	n
Acropora appressa	100	0	0	1
Acropora dendrum	100	0	0	2
Acropora downingi	0	7	93	14
Acropora cf humilis	8	46	46	13
Acropora lamarki	33	33	33	3
Acropora cf lutkeni	33	33	33	12
Acropora microphthalma	0	0	100	2
Acropora formosa	0	11	89	18
Acropora nasuta	100	0	0	1
Acropora roseni	0	27	73	11
Acropora cf solitaryensis	67	33	0	3
Acropora cf spicifera	21	38	42	48
Acropora valida	44	33	22	9
Acropora verweyi	50	17	33	6
Total	20	28	52	143

Figure 2.

Mature (colored) oocytes are clearly visible in the branches of Acropora colonies.

The authors followed up on my only recommendation. I have nothing more to add.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

The authors have responded appropriately to my review comments, and to those of Bert Hoeksema. I am satisfied with this version of the article.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

This short publication presents clear results and is well written. I have one comment. The conclusive sentence seems redundant, and may need rephrasing or some additional explanation if the authors want to maintain it. “In addition, these data add to a growing body of evidence indicating that multi-specific spawning synchrony is a feature of all speciose coral assemblages.”

The present results concern a selection of Acropora species. I wonder whether this would be sufficiently representative for a speciose coral assemblage. In theory any assemblage of two coral species can be considered multi-specific. With many Acropora species in a speciose coral assemblage, some degree of spawning synchrony is not surprising. So, in the present context I wonder if there is a minimum number of species for what counts as speciose and if the authors have a minimum number or percentage in mind for what exactly counts as multi-species spawning. If the authors cannot clarify their remark or cannot give more supportive information to this statement, I suggest that this sentence should be removed.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

We have removed the sentence as suggested.

Background information, purpose of study, data, and interpretation are all clearly and concisely presented. Documentation of coral sexual reproductive status at Socotra, Yemen in 14 species of Acropora provides a useful first contribution to improved understanding of global patterns of this reef maintenance and renewal process. Given that more than 250 species of scleractinian corals are supported at the island, it would be interesting and useful to extend these initial studies to additional species at other times of the year, and to confirm inferred spawning period and synchrony with field observations.

That said, I would suggest that the article title, “The reproductive season of scleractinian corals in Socotra, Yemen” is too broad, given that only ~5% of the scleractinian fauna was sampled. A more focused title should indicate that the observations are confined to the genus Acropora. Within the article, it would also be informative to provide the number of species of Acropora reported among the scleractinian fauna, so as to give some perspective on the proportion of Acropora species sampled.

I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

We have changed the title to “The reproductive season of Acropora in Socotra, Yemen”.

We have also provided the number of Acropora species reported to occur in Socotra as listed by Devantier .