nena masthead
NENA Home Staff & Editors For Readers For Authors

Winter Quiescence, Growth Rate, and the Release from Competition in the Temperate Scleractinian Coral Astrangia poculata (Ellis & Solander 1786)
Sean Grace

Northeastern Naturalist,Volume 24, Special Issue 7 (2017): B119–B134

Full-text pdf (Accessible only to subscribers.To subscribe click here.)


Access Journal Content

Open access browsing of table of contents and abstract pages. Full text pdfs available for download for subscribers.

Issue-in-Progress: Vol.30 (1) ... early view

Current Issue: Vol. 29 (4)
NENA 29(4)

All Regular Issues


Special Issues






JSTOR logoClarivate logoWeb of science logoBioOne logo EbscoHOST logoProQuest logo

Northeastern Naturalist B119 S. Grace 2017 Vol. 24, Special Issue 7 Winter Quiescence, Growth Rate, and the Release from Competition in the Temperate Scleractinian Coral Astrangia poculata (Ellis & Solander 1786) Sean Grace* Abstract - I examined winter quiescence (dormancy), growth rate, and competition in the scleractinian coral Astrangia poculata (Northern Star-coral) at an intertidal and a subtidal site in Rhode Island. I observed the onset, duration, and cessation of quiescence from November 2013 to May 2014 and noted when coral tentacles no longer exhibited tactile responses, which I used as a proxy for quiescence. Results demonstrated that intertidal corals entered quiescence in December 2013, when air/water temperatures ranged from 0.71 °C to 5.7 °C, whereas subtidal populations entered quiescence in January when water temperatures ranged from 3.4 °C to 4.3 °C. Corals exited quiescence at similar temperatures (6.0–8.5 °C), again doing so earlier in the intertidal than subtidal populations (April and May 2014, respectively). Corals at both sites grew (added polyps) over the course of the study, but during quiescence, growth ceased in subtidal corals, and intertidal corals lost peripheral polyps. Competitive interactions between Northern Star-coral and the tunicate Didemnum vexillum (Carpet Tunicate) decreased during quiescence with a corresponding increase in “halo” width around each coral. I observed no change in halo-width between coral and the sponge Cliona celata (Red Boring Sponge). All corals examined exhibited winter quiescence, grew during the course of the study, and were released from competition with Carpet Sea-squirt Tunicate; no change in competition with Red Boring Sponge was observed. Introduction The winters in New England create environmental conditions that induce a quiescent state in many organisms. This quiescence may serve as a way to avoid the costs associated with winter’s unfavorable conditions (Cáceres 1997). Quiescence occurs when the basic physiological processes in marine invertebrates are halted due to decreasing or increasing temperatures (Betti et al. 2012, Caceres 1997, Coma and Ribes 2003, López-Legentil et al. 2013, Teixidó et al. 2015). The costs and benefits of quiescence to the biology and ecology of organisms remain understudied. During quiescence, organisms can cease growing, be outcompeted for space, and overgrown, or depredated upon, and they may be exposed to severe environmental conditions (freezing, dessication) that may ultimately affect their survival, distribution, and abundance (Caceres 1997, Comeau et al. 2012, Dimond et al. 2012). Southern New England intertidal and subtidal communities are comprised of many invertebrate species (Dimond et al. 2012, Grace 2004, Harlin and Rines 1993). One conspicuous organism in these habitats is the temperate scleractinian *Department of Biology, Southern Connecticut State University, New Haven, CT 06515; Manuscript Editor: Jay Dimond Winter Ecology: Insights from Biology and History 2017 Northeastern Naturalist 24(Special Issue 7):B119–B134 Northeastern Naturalist S. Grace 2017 B120 Vol. 24, Special Issue 7 coral Astrangia poculata Ellis & Solander (Northern Star-coral), which is typically found in the shallow subtidal from Cape Cod south through the northernmost reef tracts of Florida and throughout the Gulf of Mexico (Cummings 1983, Dimond and Carrington 2007, Dimond et al. 2012, Grace 2004, Peters et al. 1988). This coral is abundantly distributed on hard-bottom substrate in subtidal (depths of 0–30 m) areas of southern New England where it competes for space with other invertebrate species and macroalgae (Grace 2004). The morphology of Northern Star Coral ranges from encrusting to finger-like, with more finger-like colonies found on vertical substrates (Grace 2004); small populations of this coral can be found in the intertidal. Intertidal populations of scleractinian corals are rare worldwide. Those coral species that do exist in the intertidal are typically limited in distribution to the tropics (Anthony and Kerswell 2007, Brown et. al. 2002). Although some temperate and subtropical intertidal-coral species exist (Hellberg 1994, Scott 1984), the presence of intertidal corals in such northerly lattitudes as southern New England is intriguing. The presence of intertidal Northern Star-coral raises questions as to how corals can withstand the abiotic (wave-exposure, salinity changes, temperature extremes, desiccation, UV stress, and mid-day irradiances) and biotic factors (competition and predation) known to affect other intertidal taxa like barnacles, mussels, snails, and several divisions of the macroalgae in temperate regions (Carrington 2002, Helmuth 1998, Menge and Branch 2001). Northern Star-coral is also one of several species of Cnidaria (Betti et al. 2012, Caceres 1997) that experience quiescence during the winter months when temperatures decrease (Grace 1996, Dimond and Carrington 2007). The onset of quiescence appears to begin when coral tentacles become unresponsive to touch, at which time the body and tentacles retract into the calcium carbonate theca and the oral plate puffs out, resulting in a characteristic ring inside the polyp. With polyp retraction, active feeding may cease during quiescence and coral growth can be negative. Jacques et al. (1983) found negligible calcification rates in colonies acclimated at 6.5 °C in comparison to those acclimated at higher temperatures. Moreover, Dimond and Carrington (2007) found that corals exhibited a decline in live-polyp number due to tissue loss during the winter and early spring, and they hypothesized that during this time of inactivity corals were more likely to be over-grown by other species. The biological and ecological significance of quiescence in intertidal and subtidal colonies of Northern Star-coral is unknown. Quiescence may allow intertidal corals to over-winter and survive adverse environmental conditions. Didemnum vellixum Kott (Carpet Tunicate) is a non-native invasive species introduced in Narragansett Bay in the 1980s (Bullard et al. 2007), and it competes with Northern Star-coral by growing to the edges of the coral. This growth creates a “halo effect” around the coral ccolony. Growth of the tunicate is then inhibited by an unknown mechanism that might involve the production of allelochemicals (Hoeksema and Voogd 2012), nematocysts present in coral’s tentacles that come in contact with the tunicate, or, as has been demonstrated in other temperate anthozoans, presence of sweeper tentacles (Sebens and Miles 1988). Although the effects Northeastern Naturalist B121 S. Grace 2017 Vol. 24, Special Issue 7 of some tunicates on tropical reefs have been detrimental (e.g., Diplosoma simile (Sluiter) smothers both coral and coralline algae; Littler and Littler 1995), little research has been done on temperate reefs to examine coral–tunicate interactions or how these interactions may change community structure over time. Cliona celata Grant (Red Boring Sponge) is often observed in direct competition with Northern Star-coral. This competition often presents itself subtidally as a coral colony surrounded by sponge tissue. Given the limestone bio-eroding nature of this sponge’s ecology (Brusca and Brusca 1990, Duckworth and Peterson 2013, Wisshak et al. 2012), it often erodes under the coral, possibly decreasing the coral’s attachment strength, thus affecting community structure. It is possible that both Carpet Tunicate and Red Boring Sponge may overgrow colonies during coral quiescence. The goal of my study was to determine in both intertidal and subtidal populations of Northern Star-coral, the onset, duration, and cessation of quiescence; examine growth rate; and describe interactions between this coral and 2 competing invertebrates—Carpet Tunicate and Red Boring Sponge—during quiescence. Methods Field-site description I studied 2 locations with known coral populations within lower Narragansett Bay and Rhode Island Sound (Fig. 1). The intertidal site, Bass Rock (41°48'21"N, 71°58'21"W), adjacent to Rhode Island Sound in Narragansett, RI, is a moderately wave-exposed rocky shore (Carrington 2002). It is a typical New England intertidal habitat with large granite boulders with seasonal populations of sessile barnacles, mussels, tunicates, sponges, and macroalgae, as well as mobile snails and crabs. The subtidal site, at Fort Wetherill State Park (41°28'40"N, 7121'24"W) in Jamestown, RI, has several coves with subtidal bedrock walls extending from 5 m to 40 m in depth (Grace 2004). Consistent with observations from other subtidal studies, the shallow horizontal substrates in this area are dominated by macroalgae (Grace 2004, Harlin and Rines 1993), and vertical substrates are covered with epifaunal invertebrates such as corals, hydroids, tunicates, sponges, and several mobile fauna (Dimond and Carrington 2007, Grace 2004, Velimirov and Griffiths 1979, Witman and Grange 1998, Witman and Sebens 1988). Quiescence and growth I established one 50-m transect line at the Bass Rock intertidal site, 0.1 m above mean lower low water (MLLW) and tagged the first 30 corals encountered. I scraped areas of substrate near the corals with a wire brush and attached aluminum tree-tags to the substrate using Z-spar epoxy splash-zone compound (Pettit-A788, available in marine hardware stores). Using SCUBA, I established one 50-m transect line at at the Fort Wetherill subtidal site at a depth of 14 m depth and tagged 30 corals as described above. Only aposymbiotic corals (those lacking dinoflagellate symbionts and which appear white) were used in the study because they were most common at both sites. Northeastern Naturalist S. Grace 2017 B122 Vol. 24, Special Issue 7 Figure 1. Map of the 2 Rhode Island sites: Bass Rock (BR) intertidal in Narragansett, RI, and Fort Wetherill (FW) subtidal in Jamestown, RI. Top map:. Rhode Island (author unknown) Bottom map: Available online at countrys/namerica/usstates/outline/ ri.gif. Accessed 8 July 2016, reproduced with permission from World Atlas). To determine the initiation and cessation of quiescence, beginning in November 2013, I touched each tagged colony monthly with a blunt probe to examine polyp behavior. The initiation of quiescence was indicated by a lack of tentacle retraction (non-responsive to touch), observation of a retracted polyp body with full or partial retraction of the tentacles into the calcium carbonate theca, and a puffed or inflated oral plate. Cessation of quiescence was determined when touch resulted in a tentacle contraction. I measured the growth of tagged colonies at 3-month intervals for 1 year beginning in September 2013. As in Dimond and Carrington (2007), I counted the numbers of polyps per monitoring date (September 2013, December 2013, March 2014, June 2014, and September 2014). Growth rate for each colony was analyzed Northeastern Naturalist B123 S. Grace 2017 Vol. 24, Special Issue 7 by 2-way repeated measures ANOVA with site (Bass Rock and Fort Wetherill) and date (September 2013, December 2103, March 2014, June 2014, and September 2014) as fixed factors; the repeating factor was polyp number per coral. I conducted post hoc comparisons with Holm-Sidak tests. To correct for unequal variances, α was adjusted to 0.025 (Keppel and Wickens 2004). All statistical tests were completed in Systat 13.0 (SPSS, Inc., Chicago, IL). Competition Coral–tunicate and coral–sponge assemblages were defined as situations in which either invertebrate was present around a coral (encroaching it), with the interaction forming a characteristic halo-effect. In these cases, the Northern Starcoral was surrounded by a halo of either Carpet Tunicate or Red Boring Sponge. At each site, I noted the frequency of corals alone, coral–tunicate, and coral–sponge assemblages during transect and swath surveys. At the Bass Rock intertidal site, I established one 50-m transect line 0.1 m above MLLW and counted all corals (growing separately), coral–tunicate, and coral–sponge assemblages within a 0.25- m–wide swath centered on the transect line. I used SCUBA to set up transects at the subtidal site. Due to greater coral abundance, I established three 30-m transect lines at a depth of 14 m and counted all corals (growing separately) and coral– other invertebrate assemblages by swimming along each transect within a 0.25- m–wide transect-centered swath. I employed a chi-square test for independence to determine if the observed proportion of coral–tunicate associations, coral–sponge associations, or corals found alone were independent of site. To examine the changes in competition, defined as change in halo-width (cm), I tagged coral–tunicate assemblages (n = 20 intertidall, n = 20 subtidal) and coral– sponge assemblages (n = 5 intertidal, n = 20 subtidal) along the transects described above. I included only aposymbiotic corals because they were most common at the site. At both sites, I used calipers to make monthly measurements of halo-width for 1 year beginning in September 2013. I analyzed the change in halo-width for each coral–tunicate and coral–sponge assemblage by conducting 2-way repeated measures ANOVA with site (Bass Rock and Fort Wetherill) and date as fixed factors and halo-width per coral–competitor assemblage as the repeating factor. I conducted post hoc comparisons with Holm-Sidak tests and adjusted α to 0.025 to correct for unequal variances (Keppel and Wickens 2004). In situ temperature was measured and recorded throughout the monitoring period by data loggers (Stowaway Hobo-Temp TidBit, Onset Computer, Bourne, MA) attached to the substrate adjacent to transects in both intertidal and subtidal habitats. I set the loggers to measure temperature every 8 min once deployed. After 6 months, the recorders were collected, downloaded, relaunched, and placed back in situ; thus, I obtained 1 year of continuous temperature data from the intertidal and subtidal habitats. I calculated average temperature per monitoring day from the continuous recordings. Northeastern Naturalist S. Grace 2017 B124 Vol. 24, Special Issue 7 Results Quiescence and growth All corals experienced quiescence, but the initiation and cessation of quiescence was dependent on habitat and temperature (Fig. 2). I first observed quiescence in the intertidal population in December 2013 and it lasted through April 2014. In the subtidal population, I first observed quiescence in January 2014 and it ended May 2014. Temperature recordings from both sites suggested a lag between temperature and the initiation of quiescence in subtidal populations (Fig. 2). The data suggest that intertidal corals enter quiescence when air/water temperatures range from 0.71 °C to 5.7 °C and exit quiescence when temperatures range from 6.0 °C to 8.9 °C, whereas subtidal populations enter quiescence when water temperatures range from 3.4 °C to 4.3 °C and exit when the water temperatures range from 6.1 °C to 8.5 °C. All corals grew during the course of the 1-year study (Fig. 3); however, growth slowed for subtidal colonies, and was negative for intertidal corals, which exhibited a loss in polyp number during the December to March timeframe only. Results of the 2-way repeated measures ANOVA demonstrate that coral growth was significantly Figure 2. Average temperature (°C ± SD) on monitoring dates taken from continuous temperature measurements per site. Temperature profile for Bass Rock (open circles) and Fort Wetherill (closed circles). Solid and dashed lines indicate the period of quiescence in intertidal corals (solid) and subtidal corals (dashed). Northeastern Naturalist B125 S. Grace 2017 Vol. 24, Special Issue 7 dependent on date (F4,116 = 557.52, P < 0.001; Table 1A), but not on site or on site x date interactions. Holm-Sidak post hoc tests demonstrated that coral-growth rate was different between the 2 sites in June 2014 (Table 1B). Competition Coral–tunicate and coral–sponge interactions occurred at both intertidal and subtidal sites, albeit coral–sponge interactions happened less frequently in the intertidal (Fig. 4). At Bass Rock, 55.3% (67) out of 121 of corals examined were in an interaction with Carpet Tunicates, 4.1% (5) with Red Boring Sponges, and 40.5% (49) had no interactions. At Fort Wetherill, out of a total of 2761 corals examined, 41.8% (1154) were with Carpet Tunicates, 23.1% (639) were with Red Boring Sponges, and 35.4% (978) had no interactions at the time examined. Results of the chi-square analysis (Table 2) show that the proportion of assemblages was significantly different between sites (df = 2, χ2 =24.51, P < 0.05). Coral–sponge assemblages were more likely to be found in subtidal than intertidal habitats and coral–tunicate assemblages were common in both (Fig. 4). Figure 3. Mean (± SE) number of polyps per colony (n = 30) for intertidal Bass Rock (open circles) and subtidal Fort Wetherill (closed circles). Growth was significantly dependent on date (F 4,116 = 557.52, P < 0.001; Table 1A) but not site or site by date interactions. All corals added polyps from the beginning to the end of the study, but growth slowed for subtidal colonies and was negative for intertidal corals exhibiting a loss in polyp number during the December–March timeframe only. Northeastern Naturalist S. Grace 2017 B126 Vol. 24, Special Issue 7 Table 1. (A) 2-way repeated measures ANOVA. Coral (n = 30) growth-rate comparisons at 2 sites (BR = intertidal, FW = subtidal) on 5 dates (13 September, 13 December, 14 March, 14 June, 14 September). (B) Post hoc Holm-Sidak tests demonstrating between-site comparisons by date (significance level = 0.025). df = degrees of freedom, SS = sum of squares, and MS = mean square. (A) Source of variation df SS MS F P Subject 29 1.776 0.0612 1.116 0.385 Site 1 0.199 0.1990 3.691 0.065 Site x coral 29 1.587 0.0547 Date 4 18.311 4.5780 557.597 less than 0.001 Date x coral 116 0.953 0.0082 Site x date 4 0.071 0.0176 2.184 0.076 Residual 109 0.880 0.0081 Total 292 24.623 0.0843 (B) Comparison Difference of means t P P < 0.025 September 2013 0.0071 0.198 0.844 No December 2013 0.0260 0.752 0.455 No March 2014 0.0642 1.860 0.067 No June 2014 0.0922 2.611 0.011 Yes September 2014 0.0768 2.035 0.046 No Figure 4. The percent of interactions noted in both subtidal (black bars) and intertidal habitats (gray bars). The percent occurrence of coral–tunicate interactions was higher in both intertidal and subtidal habitats than coral–sponge interactions, but the percent of coral– sponge interactions was higher in the subtidal than intertidal (df = 2, χ2 = 24.51, P < 0.05). Corals without interactions were common in both habitats. Northeastern Naturalist B127 S. Grace 2017 Vol. 24, Special Issue 7 Halo-width increased with decreasing temperature at both sites for the coral–tunicate assemblages but the difference was more pronounced in the intertidal than subtidal habitat (Fig. 5). The halo-width in the intertidal habitat increased from an average of 0.23 (± 0.09) cm in warmer conditions (September–November) to 0.82 (± 0.14) cm in colder conditions (December-April). Subtidal coral–tunicate assemblages had an average halo-width of 0.44 (± 0.07) cm in warmer months (September–December) and 0.61 (± 0.09) cm in colder months (January–May). Results of the 2-way repeated measures ANOVA indicated a significant site-by-date interaction (F11,209 = 50.405, P < 0.001; Table 3A). The results of Holm-Sidak post hoc tests demonstrate that halo-width was similar between sites in October through December 2013, but then differed significantly between the sites from January through September 2014 (Table 3B). No change in halo-width for coral–sponge assemblages was found throughout the study. Discussion Quiescence and growth All corals entered quiescence in both habitats, though at different times based on temperature (Fig. 2). The first observation of a non-response to touch was noted for intertidal corals on 18 December 2013, when daily intertidal temperatures ranged from 0.71 °C to 5.7 °C. It is likely the intertidal corals entered quiescence prior to that date because intertidal temperatures dropped from a November average of 10.9 (±2.2) °C to 4.7 (± 1.4) °C in December. Subtidal corals exhibited no response to touch on 12 January 2014 when subtidal temperatures ranged from 3.4 °C to Table 2. Results of chi-square analysis, (df = 2, χ2 = 24.51, P < 0.05). The frequency of coral–tunicate, coral–sponge assemblages, and corals alone were different. Subjects Intertidal Subtidal Coral alone Counts 49 978 Expected counts 43.11 983.88 Row % 4.77 95.23 Column % 40.49 35.42 Total % 1.7 33.93 Coral–tunicate Counts 67 1154 Expected counts 51.26 1169.7 Row % 5.48 94.52 Column % 55.37 41.79 Total % 2.32 40.04 Coral–sponge Counts 5 629 Expected counts 26.62 607.38 Row % 0.78 99.22 Column % 4.13 22.78 Total % 0.17 21.83 Northeastern Naturalist S. Grace 2017 B128 Vol. 24, Special Issue 7 4.3 °C. The exact dates of initiating and exiting quiescence is unknown because sampling occurred only monthly. Colder temperatures were documented earlier at the intertidal than at the subtidal site, and this temperature difference corresponded with an earlier onset of quiescence at the intertidal site. Likewise, intertidal colonies experienced warmer temperatures sooner than subtidal colonies and thus exited quiescence earlier (April versus May). It is noteworthy that individual polyps sometimes exhibited activity before the whole colony, suggesting incomplete cessation of quiescence. This intra-colony difference in response occurred in April 2014 at the subtidal site, 1 month before complete cessation of quiescence. Besides becoming non-responsive to touch, Northern Star-coral demonstrates quiescence by pulling in its tentacles, puffing out its oral plate, and remaining inactive until water temperatures rise. Other temperate anthozoans exhibit quiescence similarly. Betti et al. (2012) observed that the temperate Mediterranean octocoral Cornularia cornucopiae (Pallas) (a soft coral) developed a characteristic perisacral envelope covering the stolon and the calyx of each polyp formed. This covering isolated the dormant living tissue from the exterior. They also found that during Figure 5. Coral–tunicate (n = 20) halo-width changes over the monitoring period in both the intertidal habitat Bass Rock (A) and subtidal habitat Fort Wetherill (B). Halo-widths (cm) represented by closed black circles (mean ± 1 SD) and average water temperature (°C) on monitoring dates (taken from continuous temperature recordings) represented by open circles (mean ± 1 SD). There was a significant site by date interaction (Table 3A) with increases in size for both habitats but it was significantly greater in the intertidal than the subtidal during January through September 2014 (Table 3B). Northeastern Naturalist B129 S. Grace 2017 Vol. 24, Special Issue 7 winter, the polyps degenerate and the dormant stolons remain in their envelopes. One interesting observation made on all subtidal colonies in the current study was the release of mesenterial filaments through the coral mouth; the reason for this behavior is unknown. Although quiescence in Northern Star-coral involves a similar pulling in of tissue and the formation of a protective sac as described by Betti et al. (2012) for C. cornucopiae, the release of mesenterial filaments observed in Northern Star-coral at the end of quiescence has not been documented for other corals. Quiescence is not only a cold-temperature phenomenon. A number of recent studies have demonstrated quiescence at warmer temperatures in Mediterranean corals (Caroselli et al. 2015, Coma and Ribes 2003, Teixidó et al. 2015). Coma and Ribes (2003) suggested that low food-availability (energetic constraint) underlies the summer-dormancy phenomenon observed in benthic suspension feeders. Also, Caroselli et al. (2015) found that Balanophyllia europaea (Risso) (Pig-tooth Coral) becomes dormant in the summer months due to lower nutrient levels and zooplankton densities typically found in stratified summer waters in the Mediterranean. Northern Star-corals and other temperate anthozoans, including Alcyonium siderium Verrill (a soft coral) and Metridium senile (L.) (Plumose Anemone) (Sebens and Table 3. (A) 2-way repeated-measures ANOVA. Coral–assemblage halo-width comparisons (n = 20) at 2 sites (BR = intertidal, FW = subtidal) and at monthly intervals (October 2013–September 2014). (B) Post hoc Holm-Sidak test demonstrating between-site comparisons per date (significance level = 0.025). Subject equals individual coral–tunicate assemblage. df = degrees of freedom, SS = sum of squares, and MS = mean square. (A) Source of variation df SS MS F P Subject 19 185.515 9.764 Site 1 268.329 268.329 34.629 less than 0.001 Site x subject 19 147.223 7.749 Date 11 279.853 25.441 64.206 less than 0.001 Date x subject 209 82.814 0.396 Site x date 11 172.131 15.648 50.405 less than 0.001 Residual 209 64.884 0.310 Total 479 1200.749 2.507 (B) Comparison Difference of Means t P P < 0.025 October 2013 0.322 1.057 0.297 No November 2013 0.455 1.492 0.144 No December 2013 0.145 0.477 0.636 No January 2014 1.353 4.437 less than 0.001 Yes February 2014 1.831 6.004 less than 0.001 Yes March 2014 2.554 8.372 less than 0.001 Yes April 2014 2.848 9.338 less than 0.001 Yes May 2014 2.586 8.480 less than 0.001 Yes June 2014 2.798 9.174 less than 0.001 Yes July 2014 2.407 7.891 less than 0.001 Yes August 2014 1.738 5.697 less than 0.001 Yes September 2014 0.752 2.465 0.018 Yes Northeastern Naturalist S. Grace 2017 B130 Vol. 24, Special Issue 7 Koehl 1984), rely heavily on substrate-associated Corophium spp. (amphipods) as prey (Grace 1996). These amphipods experience dormancy in winter months (Wilson and Parker 1996). Hence, because prey is scarce when temperatures decrease, it is likely that temperature is not the only environmental cue to initiate quiescence in these temperate corals. All corals sampled grew in both intertidal and subtidal habitats. Even intertidal corals, which are subject to emersion, wind exposure, freezing temperatures, and ice, survived throughout the period of this observational study and added polyps. Results on intertidal coral-growth rate coincide with those reported in Dimond and Carrington (2007), where growth increased through December and decreased thereafter till March with a recovery of growth in the warmer months (Fig. 3). In the present study, the decrease in growth was evident in intertidal but not subtidal colonies from December to March. Most intertidal corals in this study exhibited partial mortality along the colony’s peripheral thinnest polyps, which may be due to freezing winter temperatures. Similarly, Betti et al. (2012) found that during winter, the temperate Mediterranean octocoral Cornularia cornucopiae shrank, but commenced growth again in summer months. Unlike the intertidal colonies, the subtidal colonies in the present study did not lose nor add polyps during quiescence. The loss of peripheral polyps in intertidal coral may be due to other factors. Wave exposure, UV stress, or high irradiance and resultant desiccation (during low tide) could have affected peripheral polyps (Miller 1995, Miller and Hay 1996); I did not assess these factors in the current study. Although Dimond et al. (2012) suggested the possibility of overgrowth in dormant corals, I did not observe overgrowth, overtopping, or depredation by other invertebrates (tunicates, barnacles, mussels or sponges) during this year-long study. The macroalga Chondrus crispus Stackhouse (Irish-moss) settled directly on the skeleton (between polyps) of several intertidal encrusting colonies, but upon the cessation of quiescence the algae did not interfere with polyp behavior or activity, and all polyps responded when touched. Competition Coral–tunicate assemblages were more common than coral–sponge assemblages at both sites (Fig. 4), and coral–sponge assemblages were more common at the subtidal than intertidal site. The percent change in halo-width—a measure of the competitive interaction between corals and tunicates—increased with decreasing water temperature significantly more in the intertidal than subtidal (Fig. 5). Valentine et al. (2007) studied the effects of emersion on tunicates and found that these organisms undergo fission in the intertidal when exposed to colder temperatures, and are open to predation by Littorina littorea (L.) (Common Periwinkle). During this study, I noted the presence of L. littorea near coral–tunicate assemblages, but saw no direct predation. The temporal consistency of these coral–tunicate and coral–sponge assemblages suggests that this competition is continuous, but the ultimate outcomes of the interactions are unknown. This particular coral–tunicate interaction is relatively recent because Carpet SquirtTunicate is non-native, whereas Northern Star-coral and Red Northeastern Naturalist B131 S. Grace 2017 Vol. 24, Special Issue 7 Boring Sponge are native to Narragansett Bay. Thus, this study documents the first occurance of a coral–tunicate competition in local waters. The coral–tunicate competitive stand-off (halo effect) lasts only as long as there are warm temperatures. Some tunicates do “hibernate” (go dormant) or die off when temperatures decrease (Burighel et al. 1976, Valentine et al. 2007), though the opposite is also true, in that some become dormant in the summer (López-Legentil 2013). Both corals and tunicates experience quiescence; thus, it appears that both are released from this competition yearly. During the winter release, the organisms are open to predation, settlement, and overgrowth by other organisms. However, I observed no overgrowth of either corals, tunicates, or sponges during this study. The competitive release noted in the coral–tunicate assemblage was not obvious in the coral–sponge assemblage. The coral–sponge competition did not appear to change at all during the study because there was no change in halo-width. Although clionaid sponges are known to bio-erode corals on tropical reefs (Glynn and Manzello 2015), the rate of sponge bioerosion taking place under Northern Star-coral is difficult to determine and was not measured. Decreasing temperature is known to decrease the rate of sponge bioerosion (Duckworth and Peterson 2013, Fang et al. 2013); however, I did not assess this parameter in the current study. I observed that Red Boring Sponge affects corals by eroding under the coral skeleton, dislodging the colony yet holding the coral in place within a sponge matrix. By doing so, the sponge decreases coral structural integrity, opening it up to dislodgement forces via water flow in the subtidal, or both water flow and wave exposure in the intertidal. Reduced attachment strength caused by sponges has been documented in the tropics (Bell et al. 2013) but remains little studied on temperate reefs. The growth and bioerosion rates of sponges increase in warmer waters; thus, it is likely that with global climate change, more temperate and tropical corals will become unattached (Bell et al. 2013, Wisshak et al. 2012), which may lead to a possible alternative stable state in the tropics (Norström et al. 2009) and an increase in sponge abundance on temperate reefs. In conclusion, all corals entered and exited winter quiescence, though intertidal corals did both earlier than subtidal corals. All corals grew from September to December, but intertidal corals lost polyps from December to March, whereas subtidal corals maintained their polyp numbers during this time. After quiescence, both intertidal and subtidal colonies resumed growth. Halo-width, used as a measure of competition, increased in coral–tunicate assemblages under colder temperatures, suggesting a competitive release. In contrast, I observed little change in halo-width in coral–sponge interactions. I did not observe overgrowth in either the intertidal or subtidal habitat. Acknowledgments I thank J. Dimond for editing and providing comments on the manuscript. S. Smedley, T. Wickman, and 3 anonymous reviewers provided valuable insight which made the manuscript stronger. I am grateful for the taxonomic consultations of J. Reinhardt and L. Stefaniak. G. DiPreta, S. Koerner, and T. Massari provided diving and logistical support. The Northeastern Naturalist S. Grace 2017 B132 Vol. 24, Special Issue 7 work was completed with the aid of a research grant from the Connecticut State University and partly supported by the Werth Center for Coastal and Marine Studies at SCSU. Literature Cited Anthony, K.R.N., and A.P. Kerswell. 2007. Coral mortality following extreme low tides and high solar radiation. Marine Biology 151:1623–1631. Bell, J.J., S.K. Davy, T. Jones, M.W. Taylor, and N.S. Webster. 2013. Could some coral reefs become sponge reefs as our climate changes? Global Change Biology 19:2613–2624. Betti, F., M. Bo, C.G. Di Camillo, and G. Bavestrello. 2012. Life history of Cornularia cornucopiae (Anthozoa: Octocorallia) on the Conero Promontory (North Adriatic Sea). Marine Ecology 33:49–55. Brown, B., K. Clarke, and R. Warwick. 2002. Serial patterns of biodiversity change in corals across shallow-reef flats in Ko Phuket, Thailand, due to the effects of local (sedimentation) and regional (climatic) perturbations. Marine Biology 141:21–29. Brusca, R.C., and G.J. Brusca. 1990. Phylum Porifera: The sponges. Pp. 181–210, In A.D. Sinauer (Ed.), Invertebrates. Sinauer Press, Sunderland, MA. 922 pp. Bullard, S.G., G. Lambert, M.R. Carman, J. Byrnes, R.B. Whitlatch, G.Ruiz, R.J. Miller, L. Harris, P.C. Valentine, J.S. Collie, J. Pederson, D.C. McNaught, A.N. Cohen, R.G. Asch, J. Dijkstra, and K. Heinonen. 2007. The colonial ascidian Didemnum sp. A: Current distribution, basic biology, and potential threat to marine communities of the northeast and west coasts of North America. Journal of Experimental Marine Biology and Ecology 342:99–108. Burighel, P., R. Brunetti, and G. Zaniolo. 1976. Hibernation of the colonial ascidian Botrylloides leachi (Savigny): Histological observations. Italian Journal of Zoology 43:293–301. Cáceres, C.E. 1997. Dormancy in invertebrates. Invertebrate Biology 116: 371–383. Caroselli, E., G. Falini, S. Goffredo, Z. Dubinsky, and O. Levy. 2015. Negative response of photosynthesis to natural and projected high seawater-temperatures estimated by pulse amplitude-modulation fluorometry in a temperate coral. Frontiers in Physiology 6:317. Carrington, E. 2002. Seasonal variation in the attachment strength of Blue Mussels: Causes and consequences. Limnology and Oceanography 47:1723–1733. Coma, R., and M. Ribes. 2003. Seasonal energetic constraints in Mediterranean benthic suspension-feeders: Effects at different levels of ecological organization. Oikos 101:205–215. Comeau, L., E. Mayrand, and A. Mallet. 2012. Winter quiescence and spring awakening of the Eastern Oyster, Crassostrea virginica, at its northernmost distribution limit. Marine Biology 159:2269–2279. Cummings, C.E. 1983. The biology of Astrangia danae. Ph.D. Dissertation. University of Rhode Island, Kingston, RI. 147 pp. Dimond, J., and E. Carrington. 2007. Temporal variation in the symbiosis and growth of the temperate scleractinian coral Astrangia poculata. Marine Ecology Progress Series 341:161–172. Dimond, J.L., A.H. Kerwin, R. Rotjan, K. Sharp, F.J. Stewart, and D. Thornhill. 2012. A simple temperature-based model predicts the upper latitudinal limit of the temperate coral Astrangia poculata. Coral Reefs 32:401–409. Duckworth, A.R., and B.J. Peterson. 2013. Effects of seawater temperature and pH on the boring rates of the sponge Cliona celata in scallop shells. Marine Biology 160:27–35. Northeastern Naturalist B133 S. Grace 2017 Vol. 24, Special Issue 7 Fang, J. K. H., M.A. Mello-Athayde, C.H.L. Schönberg, D.I. Kline, O. Hoegh-Guldberg, and S. Dove. 2013. Sponge biomass and bioerosion rates increase under-ocean warming and acidification. Global Change Biology 19:3581–3591. Glynn, P.W., and D.P. Manzello. 2015. Bioerosion and coral reef growth: A dynamic balance. Pp. 67-97, In Charles Birkeland (Ed.). Coral Reefs in the Anthropocene. Springer, Dordrecht, The Netherlands. 271 pp. Grace, S.P. 1996. The effects of water flow on the in situ feeding and growth of the temperate scleractinian coral Astrangia poculata. M.Sc. Thesis. University of Rhode Island, Kingston, RI. 146 pp. Grace, S.P. 2004. Ecomorphology of the temperate scleractinian Astrangia poculata: Coral–macroalgal interactions in Narragansett Bay (Rhode Island). Ph.D. Dissertation. University of Rhode Island, Kingston, RI. 182 pp. Harlin, M.M., and H.M. Rines. 1993. Spatial cover of eight common macrophytes and three associated invertebrates in Narragansett Bay and contiguous waters, Rhode Island, US. Botanica Marina 36:35–45. Hellberg, M.E. 1994. Relationships between inferred levels of gene flow and geographic distance in a philopatric coral, Balanophyllia elegans. Evolution 48:1829–1854. Helmuth, B.S.T. 1998. Intertidal mussel micro-climates: Predicting the body temperature of a sessile invertebrate. Ecological Monographs 68:51–74. Hoeksema, B.W., and N.J. de Voogd. 2012. On the run: Free-living mushroom corals avoiding interactions with sponges. Coral Reefs 31:455–459. Jacques, T.G., N. Marshall, and M.E.Q. Pilson. 1983. Experimental ecology of the temperate scleractinian coral Astrangia danae. II. Effect of temperature, light intensity and symbiosis with zooxanthellae on metabolic rate and calcification. Marine Biology 76:135–148. Keppel, G., and T. D. Wickens. 2004 Design and Analysis: A Researcher’s Handbook. Prentice Hall, Upper Saddle River, NJ. 611 pp. Littler, M.M., and D.S. Littler. 1995. A colonial tunicate smothers corals and coralline algae on the Great Astrolabe Reef, Fiji. Coral Reefs 14:148–149. López-Legentil, S., P.M. Erwin, M. Velasco, and X. Turon. 2013. Growing or reproducing in a temperate sea: Optimization of resource allocation in a colonial ascidian. Invertebrate Biology 132:69–80. Menge, B.A., and G.M. Branch. 2001. Rocky intertidal communities. Pp. 221–251, In M.D. Bertness, S.D. Gaines, and M.E. Hay (Eds.). Marine Community Ecology. Sinauer Associates, Sunderland, MA. 566 pp. Miller, M.W. 1995. Growth of a temperate coral: Effects of temperature, light, depth, and heterotrophy. Marine Ecology Progress Series 122:217–225. Miller, M.W., and M.E. Hay. 1996. Coral–seaweed–grazer–nutrient interactions on temperate reefs. Ecological Monographs 66:323–344. Norström, A.V., M. Nyström, J. Lokrantz, and C. Folke. 2009. Alternative states on coral reefs: Beyond coral–macroalgal phase shifts. Marine Ecology Progress Series 376:295–306. Peters, E.C., S.D. Cairns, M.E.Q. Pilson, J.W. Wells, W.C. Japp, J.C. Lang, C.E. Vasleski, and L.S.P. Gollahon. 1988. Nomenclature and biology of Astrangia poculata (= A. danae, = A. astreiformis) (Cnidaria: Anthozoa). Proceedings of the Biological Society of Washington 101:234–250. Scott, P.J.B. 1984. The Corals of Hong Kong: Equality, Competition, and Honor in East Asian Nationalism (Vol. 1). Hong Kong University Press, Hong Kong. 111 pp. Northeastern Naturalist S. Grace 2017 B134 Vol. 24, Special Issue 7 Sebens, K.P., and M.A.R. Koehl. 1984. Predation on zooplankton by the benthic anthozoans Alcyonium siderium (Alcynacea) and Metridium senile (Actinaria) in the New England subtidal. Marine Biology 81:255–271. Sebens, K.P., and J.S. Miles. 1988. Sweeper tentacles in a gorgonian octocoral: Morphological modifications for interference competition. Biological B ulletin 175:378–387. Teixidó, N., N. Bensoussan, A. Gori, I. Fiorillo, and N. Viladrich. 2015. Sexual reproduction and early life-history traits of the Mediterranean soft coral Alcyonium acaule. Marine Ecology 37:134–144. Valentine, P.C., M.R. Carman, D.S. Blackwood, and E.J. Heffron. 2007. Ecological observations on the colonial ascidian Didemnum sp. in a New England tide-pool habitat. Journal of Experimental Marine Biology and Ecology 342:109–121. Velimirov, B.J., and C.L. Griffiths. 1979. Wave-induced kelp movement and its importance for community structure. Botanica Marina 22:169–172. Wilson, W.H, Jr., and K. Parker. 1996. The life history of the amphipod Corophium volutator: The effects of temperature and shorebird predation. Journal of Experimental Marine Biology and Ecology 196:239–250. Wisshak, M., C.H.L. Schönberg, A. Form, and A. Freiwald. 2012. Sponge bioerosion accelerated by ocean acidification across species and latitudes? Helgoland Marine Research 68:253–262. Witman, J.D., and K.R. Grange. 1998. Links between rain, salinity, and predation in the rocky subtidal community. Ecology 79:2429–2447. Witman, J.D., and K.P. Sebens. 1988. Benthic-community structure at a subtidal rock pinnacle in the central Gulf of Maine. Pp. 67–104, In I. Babb and M. De Luca (Eds.). Benthic Productivity and Marine Resources of the Gulf of Maine. National Undersea Research Program Research Report 83-3. National Oceanic and Atmospheric Administration, Northeast Fisheries Science Center, Woods Hole, MA.