Description of a new marine diatom, Cocconeis caulerpacola sp. nov. (Bacillariophyceae), epiphytic on invasive Caulerpa species

Figures & data

Fig. 1. The study areas and the locations of sampling sites.

Table 1. List of samples from the Adriatic Sea checked for the presence of Cocconeis caulerpacola. Occurrence of C. caulerpacola estimated as + to +++ (+ present in moderate quantities, ++ abundant, +++ extremely abundant) or T (trace); – indicates that the species was not observed in the sample.

Slide	Date	Locality	Substratum	Cocconeis caulerpacola
12944	September 2008	Hvar	Caulerpa taxifolia	++
13084	October 2008	Hvar	Caulerpa taxifolia	++
13086	October 2008	Hvar	Brown algae	T
7	November 2008	Hvar	Caulerpa taxifolia	++
8	November 2008	Hvar	Brown algae	–
36	December 2008	Hvar	Caulerpa taxifolia	++
37	December 2008	Hvar	Brown algae	–
41	January 2009	Hvar	Caulerpa taxifolia	++
42	January 2009	Hvar	Brown algae	–
55	February 2009	Hvar	Caulerpa taxifolia	T
56	February 2009	Hvar	Brown algae	–
14356	March 2009	Hvar	Caulerpa taxifolia	+
14357	March 2009	Hvar	Brown algae	–
14361	April 2009	Hvar	Caulerpa taxifolia	–
14362	April 2009	Hvar	Brown algae	–
14369	May 2009	Hvar	Caulerpa taxifolia	–
14370	May 2009	Hvar	Brown algae	–
14385	June 2009	Hvar	Brown algae	–
14404	July 2009	Hvar	Caulerpa taxifolia	+
14405	July 2009	Hvar	Brown algae	T
14413	August 2009	Hvar	Caulerpa taxifolia	++
14415	August 2009	Hvar	Brown algae	–
15342	September 2009	Hvar	Caulerpa taxifolia	+++
14435	September 2009	Hvar	Padina pavonica	–
14438	September 2009	Hvar	Dictyota dichotoma	–
14439	September 2009	Hvar	Halimeda tuna	–
14440	September 2009	Hvar	Ulva sp.	–
14441	September 2009	Hvar	Codium sp.	–
15368	October 2009	Hvar	Caulerpa taxifolia	+++
15369	October 2009	Hvar	Brown algae	–
15372	October 2009	Hvar	Dictyota dichotoma	–
15373	October 2009	Hvar	Halimeda tuna	T
15374	October 2009	Hvar	Cladophora sp.	–
15375	October 2009	Hvar	Ulva sp.	–
15376	October 2009	Hvar	Codium sp.	–
15378	October 2009	Mljet	Caulerpa racemosa	+
15379	October 2009	Mljet	Padina pavonica	–
15383	October 2009	Mljet	Posidonia oceanica	–
15360	October 2009	Dubrovnik	Caulerpa racemosa	+
15393	November 2009	Hvar	Caulerpa taxifolia	+++
15394	November 2009	Hvar	Padina pavonica	–
15397	November 2009	Hvar	Halimeda tuna	–
15398	November 2009	Hvar	Dictyota dichotoma	–
15399	November 2009	Hvar	Codium sp.	–
15400	November 2009	Hvar	Ulva sp.	–
15401	November 2009	Mljet	Caulerpa racemosa	+
15386	November 2009	Dubrovnik	Caulerpa racemosa	+
15405	December 2010	Dubrovnik	Caulerpa racemosa	+
15422	January 2010	Hvar	Caulerpa taxifolia	T
15423	January 2010	Hvar	Padina pavonica	–
15426	January 2010	Hvar	Halimeda tuna	–
15427	January 2010	Hvar	Dictyota dichotoma	–
15434	February 2010	Hvar	Caulerpa taxifolia	T
15435	February 2010	Hvar	Padina pavonica	–
15438	February 2010	Hvar	Halimeda tuna	–
16772	March 2010	Hvar	Caulerpa taxifolia	–
16773	March 2010	Hvar	Padina pavonica	–
16774	March 2010	Hvar	Dictyota dichotoma	–
16755	March 2010	Mljet	Caulerpa racemosa	T
16778	April 2010	Hvar	Caulerpa taxifolia	T
16779	April 2010	Hvar	Padina pavonica	–
16780	April 2010	Hvar	Dictyota dichotoma	–
16789	April 2010	Mljet	Caulerpa racemosa	+
16790	April 2010	Mljet	Halimeda tuna	–
16785	May 2010	Hvar	Padina pavonica	–
16786	May 2010	Hvar	Dictyota dichotoma	–
16822	June 2010	Hvar	Caulerpa taxifolia	+
16825	June 2010	Hvar	Padina pavonica	–
16826	June 2010	Hvar	Halimeda tuna	–
16799	June 2010	Mljet	Padina pavonica	–
16800	June 2010	Mljet	Halimeda tuna	–
16829	July 2010	Hvar	Caulerpa taxifolia	++
16832	July 2010	Hvar	Padina pavonica	–
16833	July 2010	Hvar	Halimeda tuna	–
16803	July 2010	Mljet	Caulerpa racemosa	T
16813	July 2010	Dubrovnik	Posidonia oceanica	–
16836	August 2010	Hvar	Caulerpa taxifolia	++
16839	August 2010	Hvar	Padina pavonica	–
16817	August 2010	Dubrovnik	Caulerpa racemosa	T
16852	September 2010	Hvar	Caulerpa taxifolia	++
16855	September 2010	Hvar	Padina pavonica	–
16856	September 2010	Hvar	Halimeda tuna	–
16847	September 2010	Mljet	Caulerpa racemosa	+
16859	September 2010	Dubrovnik	Caulerpa racemosa	T
16860	September 2010	Dubrovnik	Posidonia oceanica	–
16877	October 2010	Hvar	Caulerpa taxifolia	++
16880	October 2010	Hvar	Padina pavonica	–
16881	October 2010	Hvar	Dictyota dichotoma	–
16866	October 2010	Mljet	Caulerpa racemosa	+++
16871	October 2010	Dubrovnik	Caulerpa racemosa	+
16874	October 2010	Dubrovnik	Posidonia oceanica	–
19326	February 2012	Hvar	Posidonia oceanica	–
19327	February 2012	Hvar	Caulerpa taxifolia	T

Figs 2–13. Cocconeis caulerpacola, LM. Specimens from the holotype slide. Figs 2–4 are micrographs taken by means of an advanced photomicrography method (kindly provided by Wulf Herwig); Figs 5–7 are phase contrast; Figs 8–13 are differential interference contrast. 2. Holotype specimen, comprising raphe (left) and sternum (right) valves. 3–13. Selected raphe (Figs 3–5, 8–10) and sternum (Figs 6, 7, 11–13) valves. Scale bar = 10 µm.

Figs 14–18. Cocconeis caulerpacola, TEM. 14. Raphe valve showing the striation and raphe branches with terminal and central endings. Note that the raphe endings are slightly bent towards opposite sides. 15. Sternum valve with longitudinal ribs and transapically elongate areolae. 16. Detail of raphe valve apex and part of valvocopula with very shallow undulations on one margin (arrow). 17. Centre of raphe valve. 18. Apex of sternum valve. Note the rudiment of a raphe (arrow). Scale bars = 5 µm (Fig. 14), 4 µm (Figs 15, 16); and 1 µm (Figs 17, 18).

Figs 19–26. Cocconeis caulerpacola, SEM, from the holotype sample, Croatia. 19, 20. Raphe valve exterior, general view. Note sigmoid raphe with external central and terminal endings slightly expanded. 21. Internal view of raphe valve apex. Note the terminal raphe ending. 22. Close up of the centre of the interior of the raphe valve. 23. Sternum valve, external view. 24. Internal view of the sternum valve apex. 25. Sternum valve interior. 26. Close up of sternum valve interior. Note the areolae occlusions (arrow) containing apically oriented slits. Scale bars = 5 µm (Figs 19 and 25); 3 µm (Fig. 23); 2 µm (Fig. 20); 1 µm (Figs 21, 24); and 500 nm (Figs 22, 26).

Figs 27–31. Cocconeis caulerpacola, SEM, from France. 27, 28. Specimens photographed in situ on Caulerpa taxifolia. 29, 30. External and internal views of cleaned sample. 31. Raphe valves, internal view. Note the internal central and apical raphe endings. Scale bars = 10 µm (Fig. 27); 6 µm (Fig. 29); 4 µm (Fig. 30); and 3 µm (Figs 28, 31).

Figs 32–36. Cocconeis caulerpacola from France, SEM. Figs 32, 33 show cells in situ on Caulerpa taxifolia. 32, 33. Cells with sternum valve uppermost, showing generally convex surface along the margins then becoming flat with a slightly depressed sternum. Note that the transapical striae are parallel in the middle, becoming radiate towards the apices. 34–36. Close up and whole (Fig. 36) of sternum valve interior showing transapically elongate areolae. The areolae contain the same type of hymenate occlusions as in the raphe valve. Scale bars = 6 µm (Fig. 32); 4 µm (Fig. 36); 3 µm (Fig. 33); and 500 nm (Figs 34, 35).

Figs 37–41. Cocconeis caulerpacola from France, SEM. 37. Frustule in oblique view. 38. Valvocopulae detached from frustules of C. caulerpacola. 39, 40. Close ups of valvocopulae: the pars interior has an undulate margin fitting over the valve interstriae. 41. Whole frustule with detached valvocopula. Scale bars = 4 µm (Fig. 41); 3 µm (Figs 37, 38); and 500 nm (Figs 39, 40).

Figs 42–49. Cocconeis caulerpacola from Australia, SEM. 42. Raphe valve, external view. Note the sigmoid raphe and the areola pattern typical for C. caulerpacola from the type habitat. 43–45. Raphe valve internal view. Note the hymenate areolae occlusions. 46, 47. Sternum valve external view. 48, 49. Sternum valve internal view. Note the structure of the areolae hymenate occlusions. Scale bars = 5 µm (Fig. 43); 4 µm (Figs 46–48); 3 µm (Fig. 42); 1 µm (Figs 44, 49); and 500 nm (Fig. 45).

Table 2. Major morphometric characteristics of Cocconeis caulerpacola and similar taxa, with diagnostic information.

	Length	Breadth	RV striae	SV striae	Diagnostic characters	Habitat and distribution	References
	µm	µm	in 10 µm	in 10 µm
C. caulerpacola	10–18	3–4	40	44–46	RV: raphe sigmoid, fascia reaching the valve margins; SV striae radiate only at apex; transapical striae not resolvable in LM without special optics on either RV or SV	Epiphyte on Caulerpa sp.: Mediterranean Sea and E coast of Australia (Moreton Bay)	Present study
C. borbonica	8–12	3–4.2	42–60	50–62	RV: raphe straight, fascia (one shorter stria); SV striae radiate only at apex	Marine coral sands and brackish sediments: Réunion Island, western Indian Ocean	Riaux-Gobin & Compère, 2008
C. diruptoides	19–22	9–11	26–30	26–29 at the centre; 34 at the margin	RV: raphe sigmoid, the central area wide, stauros-like, variable but not exceeding half the valve width; several SV striae dichotomize at the valve face margin leading to an increase in stria density from the centre	Wide distribution in temperate and warm seas: Adriatic Sea at Rovinj and Vis (Hustedt Diatom Collection, E74)	De Stefano & Marino, 2001
C. pseudodiruptoides	15–22	8–12	26–28	18	RV: raphe strongly sigmoid, the central area stauros like reaching the valve margin. SV: sternum strongly sigmoid, central area very narrow, in the form of an indistinct stauros. The striae easily recognizable in LM on both valves	Indian Ocean, Tanzania, Coll. Foged (1975)	Witkowski et al., 2000

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