Tethya californiana de Laubenfels, 1932

Turner, Thomas L., 2020, The order Tethyida (Porifera) in California: taxonomy, systematics, and the first member of the family Hemiasterellidae in the Eastern Pacific, Zootaxa 4861 (2), pp. 211-231 : 219-222

Tethya californiana de Laubenfels, 1932

Synonymy.

Tethya aurantia var. californiana de Laubenfels, 1932

Tethya vacua Austin et al. 2014

Material Examined. CASIZ 235109 , Hopkin's Marine Station , Monterey CA (34.47182, -120.14262), 9/16/19 . CASIZ 235108 , Naples Reef , Santa Barbara CA (34.42212, -119.95154), 7/31/19 . CASIZ 235106 , Elwood Reef , Santa Barbara CA (34.41775, -119.90150) 4/17/19 . CASIZ 235107 , Santa Cruz Island , CA (33.98378, -119.63910), 4/26/19 . TLT 361 , Santa Rosa Island , CA (33.89966, -120.10735) 10/9/19 . CASIZ 184729 , Santa Rosa Island , CA (34.00000, -120.00170), collected by France & Efford , 12/24/81 ( T. vacua paratype) . CNPGG 1199 , Ensenada , Bahia Topolobampo, Baja California, Mexico, 4/8/11 . CNPGG 0012 , Cabo San Miguel , Gulf of California, Mexico, 3/5/85. (For tabular format, see supplemental table 2) .

Description. Macroscopic features. Approximately hemispherical, with broad gutters between tubercles when relaxed. The sponge constricts upon collection, closing the gutters and placing the tubercles in contact. The width and depth of the gutters varies greatly in field photos, as does color (from yellow to orange, but sometimes covered in a dark red growth of apparent algae). As this species has been well described elsewhere ( Austin et al. 2014), I focused on improving our understanding of the quantitative aspects of spicules that have been shown to vary among samples.

Spicules. To assess the possibility of multiple species of Tethya within the study region, I quantified two aspects of spicular morphology found to vary in previous studies ( Austin et al. 2014; Heim & Nickel 2010; Sará et al. 2001). The first concerns the morphology of the megascleres. Austin et al. (2014) divided megascleres into three categories defined as follows:

- anisostrongyles: distal end (foot) smaller diameter than proximal end (head).

- strongyloxeas: fusiform, distal end (foot) a point; sides narrow toward rounded end (head).

- styles: straight sides, distal end (foot) a point; diameter of rounded end (head) equal to that of shaft.

After examining a large number of spicules, I found strongyloxeas and styles to be part of a continuous spectrum. I measured the width of each spicule at the head and the widest point, and some were very fusiform (widest point more than 4 times wider than head), some were clearly styles (widest point equal to head), but most spicules were intermediate. I therefore grouped these two types together. Anisostrongyles were easier to distinguish, as many spicules clearly lacked a sharp point, though once again there were spicules that were intermediate and hard to classify. I therefore present data on all megascleres together, and also present data on anisostrongyles separately (table 1). Regardless of method, the distributions of megasclere dimensions broadly overlapped among samples. ANOVA of all megascleres considered together revealed no significant differences among samples (F=1.73, p=0.13). One sample, from the Gulf of California ( Mexico), was found to lack anisostrongyles almost completely, while anisostrongyles comprised 27–45% of megascleres in all other samples (see remarks).

The other quantitative measure that has been found to vary among Tethya in this region relates to megasters (star-shaped spicules). By dividing the ray length by the centrum diameter, a parameter called R/C can be calculated for each aster ( Austin et al. 2014). I did this for 40–50 asters per sponge, and used ANOVA to determine if there were significant differences among samples (there were, F=12.14, p= 1.81e- 10). Tukey's honest significant differences test was then use to determine which samples were different from others at the 95% family-wide confidence level. Note that the T. californiana sample from Hopkin's Marine Station in Central California (near the type location for T. californiana ) was not significantly different from the T. vacua paratype (table 1).

Remarks. Though Tethya are the best studied sponge in California from an ecological perspective, their taxonomy has remained unresolved. Tethya aurantia var. californiana de Laubenfels was described in 1932, with Carmel Bay, in Central California, as the type location (de Laubenfels 1930). The variety was raised to species status in 1993 ( Sarà & Corriero 1993). Heim and Nickel (2010) then split this taxon, describing those from British Columbia as a separate species, T. leysae . Tethya leysae was synonymized with T. californiana by Austin et al. (2014), who proposed that this species ranged from British Columbia to Central California. In the same monograph, Austin et al. erected T. vacua for Southern California, based on a single collection from Santa Rosa Island (figure 1). They also implied that the sponges described as T. californiana from the Gulf of California, at the Southern range limit, were likely a different species. I wished to confirm or refute the validity of the name T. vacua , and assess the possibility of an additional species in the South.

Genetic data do not support species status for T. vacua . In the same monograph where T. vacua was described, Austin et al. (2014) argued that 0.6% absolute sequence divergence at cox1 was insufficient to support species status for T. leysae . I show that T. vacua are even more similar (0% sequence divergence) to T. californiana at this same locus. The same is true at the 18S nuclear locus.

The spicules of Central and Southern California Tethya are likewise indistinguishable. The only spicule data used to support T. vacua was that the one sample analyzed had asters with a higher R/C value than the T. californiana syntype. No statistical test was used, however, and another T. californiana sample from Monterey Bay (CASIZ 067731, table 14 of Austin et al. 2014) was very similar to the T. vacua sample. Here I show that the R/C values of the T. vacua paratype are not significantly different from another sponge collected in Monterey Bay, near the type location for T. californiana . Though not statistically significant, average values are slightly larger for 2 of the 3 Southern California samples analyzed here vs. the Central California sample, and this is consistent with a geographic cline in R/C value as previously reported ( Austin et al. 2014).Austin et al. show that R/C values are shortest in cold British Columbian waters, and increase towards the South (and again used this cline to argue against species status for T. leysae ). R/C values of the Ensenada sponge analyzed here have the largest values, consistent with this cline.

The only other morphological difference reported for T. vacua are the vacuoles that are its namesake. I compared tissue sections of sponges from Monterey (Central California), Naples Reef (Southern California), and Santa Rosa Island (Southern California, near the holotype location for T. vacua ), to look for these vacuoles (see supplementary data). I failed to find vacuoles in any sponge, but these negative data should not be considered conclusive. I did not have access to the T. vacua holotype as a positive control, so it is possible that my methods were inadequate to see them. In any case, I feel that the lack of any spicular characters, combined with the lack of genetic differentiation, clearly indicates that these taxa should be synonymized.

I was also interested in whether there is an additional species of Tethya at the Southern end of the T. californiana range. Two sponges from Pacific Mexico were graciously shared with me by Patricia Gómez, Porifera Curator at the National Autonomous University of Mexico. One is from Ensenada, just South of the US/ Mexico border, where habitats are similar to California kelp forests. The spicules of this sponge were indistinguishable from those in Southern California (table 1). The other was from Cabo San Miguel, in the Gulf of California; this is beyond the range of the giant kelp Macrocystis pyrifera , in an ecosystem quite different from those on California shores. Sponges from this collection were described as having several morphological differences compared to the T. californiana holotype, the most significant of which was having only strongyloxeas instead of anisostrongyles and strongyloxeas ( Sará et al. 2001). Sará, Gómez, and Sára (2001) did not feel these differences warranted species status. In my reanalysis of one of these sponges, I replicate their finding of (nearly) exclusive strongyloxeas, and find that the R/C values of asters are somewhat anomalous compared to the clinal expectation. I attempted to sequence fragments of cox1 and 18S from these Mexican samples, but was unable to amplify any DNA (I also attempted to sequence DNA from other archived samples of Mexican Tethya species, again without success). Collection of fresh material for sequencing is therefore highly recommended. It remains unconfirmed if the Gulf of California Tethya are T. californiana , but the similarities of the Ensenada sponge to California samples makes it unlikely that this Gulf of California morphotype range into the state of California.

Geographic distribution. Tethya californiana was previously described as ranging from British Columbia in the North to Central California in the South ( Austin et al. 2014). Genetic data now extend this range to Southern California, and morphological comparisons extend it to at least Ensenada, Mexico. Consistent with published reports, this sponge was common in kelp forest habitats in California. I observed it at 19/47 (40%) of kelp forest locations surveyed. There are some indications it may be more abundant in colder waters (because of the nature of the survey, these patterns should be considered hypotheses only; see methods). Water temperatures are colder in Central California than Southern California, and within the Santa Barbara Channel there is a strong gradient, with colder waters in the West ( Claisse et al. 2018). Tethya californiana were present at 2 of 3 sites in Central California, and 4 of 4 sites on the Western-most islands of San Miguel and Santa Rosa. In contrast, it was seen at only 2 of 8 location on Anacapa Island, and 2 of 7 locations in Los Angeles County. It was not present at the two oil platforms surveyed, nor on floating docks in the four harbors surveyed. I did not find it in the 3 intertidal locations checked, but pictures posted by others to the site iNaturalist show that the sponge is sometimes present in the intertidal in Northern and Central California (and the holotype collected in Central California in 1926 was an intertidal sponge).