Growth and Carbonate Production by Adeonellopsis (Bryozoa: Cheilostomata) in Doubtful Sound, New Zealand
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Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 201^210 www.elsevier.com/locate/palaeo Growth and carbonate production by Adeonellopsis (Bryozoa: Cheilostomata) in Doubtful Sound, New Zealand A.M. Smith a;*, B. Stewart a, M.M. Key Jr. b, C.M. Jamet b a Department of Marine Science, University of Otago, P.O. Box 56, Dunedin, New Zealand b Department of Geology, Dickinson College, Carlisle, PA 17013-2896, USA Received 16 March 2000; accepted 31 July 2001 Abstract The erect arborescent bryozoan Adeonellopsis sp. is an important component of the attached fauna on rock faces in Doubtful Sound, New Zealand. A program of marking and harvesting, radiocarbon dating, and morphometric study was undertaken to determine age, growth rate, and carbonate production rate of these colonies. Data from 40 branches on each of five colonies show a growth rate of 6.9 mm/yr in branch length. Colony growth rate varied, with 71% of growth (5 mm per branch) occurring from mid-summer and to mid-winter, and 29% (2 mm per branch) from mid- winter to late summer. Since proximal secondary thickening is common in adeoniform species, and occurs in Adeonellopsis, additional carbonate may be precipitated annually by this means. The largest colonies found in Doubtful Sound, some up to 30 cm in diameter, may be as much as 20 yr old, and precipitate calcium carbonate at a rate of 24 g CaCO3/yr. At Bauza Island, where our study was carried out, population densities of one large colony/m produced 2 2 carbonate at a rate of 24 g CaCO3/m /yr; maximum theoretical density could produce carbonate at 1042 g CaCO3/m / yr. Carbonate produced at these rates would accumulate in sediments at 4^174 cm/kyr, reasonable rates for temperate carbonates. Adeonellopsis provides substrate for epizoa and hiding places for motile organisms. They form a potentially important fiord microhabitat, and their longevity allows both more ephemeral organisms and young longer-lived colonies to grow under their protection. ß 2001 Elsevier Science B.V. All rights reserved. Keywords: Bryozoa; calci¢cation; growth rate; New Zealand 1. Introduction Adeonidae (Gymnolaemata: Cheilostomata: As- cophorina) were classi¢ed as Adeonellopsis yar- The erect, robust-branching bryozoan Adeonel- raensis (e.g. Gordon, 1984, 1986), but it is now lopsis is a large conspicuous subtidal species clear that at least ¢ve morphologically similar found throughout New Zealand (Nelson et al., Adeonellopsis species occur in New Zealand 1988). Initially all New Zealand members of the and Australian waters (Lidgard and Buckley, 1994). The Adeonellopsis species which occurs in Doubtful Sound, Fiordland in southwestern New Zealand is probably morphospecies B of * Corresponding author. Tel.: +64-3-479-8306; Fax: +64-3-479-8336. Lidgard and Buckley (1994). Colonial growth be- E-mail address: [email protected] (A.M. Smith). gins with a small encrusting spot which sprouts a 0031-0182 / 01 / $ ^ see front matter ß 2001 Elsevier Science B.V. All rights reserved. PII: S0031-0182(01)00372-8 PALAEO 2740 27-12-01 202 A.M. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 201^210 Fig. 1. Adeonellopsis sp. from Doubtful Sound, New Zealand: (A) living colony in situ on the wall of Bauza Island in 12 m water depth (scale = 5 cm); (B) bleached and dried colony (scale = 1 cm); (C) scanning electron micrograph showing zooid charac- teristics (scale = 1 mm). bilaminar sheet. Branches grow and fork, forming curs as (possibly secondary) calci¢cation to- a fairly dense bush-like colony some 20^30 cm ward the colony bases (Cheetham, 1986). Ex- high (Fig. 1A). The branches are £attened, about trazooidal thickening toward the colony bases 3^6 mm wide, and bluntly rounded at the tips results in the eventual occlusion of the entire (Fig. 1B). Individual zooids show the ornateness zooidal frontal surfaces (Lidgard and Buckley, typical of ascophorine cheilostomes; they are dia- 1994; Lidgard, 1996). This increasing secondary mond-shaped, about 0.5U0.25 mm in size, with calci¢cation results in stronger colonies able to various pores, avicularia and concavities on the resist breakage; young adeoniform colonies frontal wall (Fig. 1C). have been shown to withstand current as rapid Adeonellopsis species mainly precipitate ara- as 3 m/s (Cheetham et al., 1981; Cheetham, gonite with 0^11 (mean 3.1) wt% calcite (Smith 1986). et al., 1998). The calcite contains on average In Doubtful Sound, the purplish^black colonies about 6 wt% MgCO3, which is relatively high of Adeonellopsis can be found growing in reason- for New Zealand bryozoans (Smith et al., ably exposed areas on the steeply sloping rock 1998). Much of this carbonate deposition oc- walls near the entrance of the ¢ord. These rock PALAEO 2740 27-12-01 A.M. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 201^210 203 walls are home for a diverse range of encrusting organisms; Adeonellopsis is one of the more prominent (see Fig. 1A). Its arborescent bilami- nate growth form provides numerous interstices for attached epifauna. Doubtful Sound is a temperate ¢ord on the west coast of South Island, New Zealand. It ex- tends 33 km from Deep Cove to its mouth at the Tasman Sea and has a number of signi¢cant side branches (Fig. 2). As with other ¢ords in the re- gion, Doubtful Sound is steep sided and deep, reaching a maximum depth of 434 m, but with a shallow sill of 40^60 m protecting the entrance. The region receives very high rainfall, as much as 8000 mm/yr, as a result of the prevailing mois- ture-laden westerly winds blowing o¡ the Tasman Sea. The rainwater accumulates humic substances as it percolates through the catchment's forest and creates a darkly stained low salinity layer on the surface of the ¢ord. This layer, up to 10 m thick depending on rainfall, ¢lters out much of the light striking the surface of the ¢ord. Coupled with low current and minimal wave ac- tion, the low light conditions mimic deepwater conditions and enable usually deepwater and cryptozoic species to live at SCUBA-accessible Fig. 2. Location map of Doubtful Sound in western South depths. Adeonellopsis is not common within Island, New Zealand: New Zealand; Doubtful Sound, with Doubtful Sound, but in some localized areas, study site near Bauza Island marked. such as around Bauza Island (Fig. 2), colonies may be found at depths from 10 to 25 m at den- sities ranging from 0.01 to 1 colonies/m2. later may become sediment and eventually lime- As is the case with most bryozoans, age, stone. growth, and carbonate production rates of Adeo- The most direct ways to ascertain colony nellopsis are unknown. While non-colonial organ- growth rates are by laboratory culture and in isms often have an upper limit to their age, which situ observation. Both are problematic. Bryozoans may be determined fairly easily using population are generally di¤cult to culture, and large, long- dynamic theory, colonies, which add more and lived species have never been maintained in the more genetically identical individuals to a single laboratory for more than a few weeks. Large structure, may theoretically live forever (Palumbi complex erect zoarial growth forms are di¤cult and Jackson, 1983). This `clonal building block' to assess using photogrammetry or in situ mea- strategy means that individuals live and die but surement, and breakage during handling is com- the colony itself can grow and thrive. Size of a mon. We have, therefore, taken three indirect but colony is thus not a good indicator of age. A independent tactics for quantifying growth rate better estimate of age and growth rate is impor- and carbonate productivity: marking and recap- tant in understanding ¢ord benthic ecology, devel- ture, radiocarbon dating, and morphological anal- opment and succession; life history and evolution ysis. Taken together, they enable us to character- of the Bryozoa; and productivity both in the ize growth and carbonate production of benthic food web and of skeletal carbonate, which Adeonellopsis in Doubtful Sound. PALAEO 2740 27-12-01 204 A.M. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 201^210 Fig. 3. Staining with calcein: (A) in the ¢eld, a plastic bag is anchored over a single colony of Adeonellopsis (scale = 4 cm); (B) £uorescent bands (arrowed) in zooid carbonate of an Adeonellopsis colony collected 24 h after staining (scale = 0.5 mm). 2. Methods ony using cable ties. The saturated solution was loaded into 25-ml plastic syringes and 10 ml was 2.1. Marking and recapturing injected into each polythene bag. The bagged col- onies were then left for 24 h before the bags were Tetracycline hydrochloride and calcein (2,4-bis- removed (Fig. 3A). The site was revisited 6 [N,NP-di-(carbomethyl)-aminomethyl]£uorescein) months later on 28 July 1998 and three of the have both been used successfully to `tag' the cal- ¢ve marked colonies were removed, killed in ci¢ed elements of a variety of live organisms, in- 70% alcohol, and stored. Seven months later, on cluding ¢sh (Tsukamoto, 1988; Wilson et al., 24 February 1999, the study site was revisited and 1987), brachiopods (Rowley and McKinnon, the remaining two colonies were located and re- 1995) and echinoderms (Stump and Lucas, 1990; trieved. Dobson and Stancyk, 1994). Tetracycline and cal- In the laboratory, specimens were placed in in- cein incorporated at the site of calci¢cation £uo- dividual plastic containers and soaked in full resce when viewed under ultraviolet (UV) light strength household bleach solution (sodium hypo- (Suzuki and Mathews, 1966; Kobayashi and chlorite) for 6 h to remove the soft tissues. The Taki, 1969; Seeto, 1992). Calcein was selected as skeletal colony remains were washed in gently the preferred marker for this study as it is re- running tap water for 1 h to remove all traces ported less toxic than tetracycline (Wilson et al., of the sodium hypochlorite solution, then placed 1987; Rowley and McKinnon, 1995) and proved in a drying oven at 60³C until completely dry.