The Central Province of the Belize Barrier Reef showing the study sites on Twin Cays and Curlew Cay.

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... (to 12 cm long, 13 mm diam.). The blades, stipes and holdfasts are composed of dichotomously branched interconnected siphons entirely lacking cross walls. The thalli of A. f. longicaulis, A. asarifolia f. asarifolia and A. nigricans f. nigricans (Figs. 8, 9, 10) are typically anchored by a massive, perennating, bulbous, rhizoidal holdfast ( Fig. 11) in open sandy or seagrass areas of shallow (to 30 m) pristine ...

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... emphasized above, the discovery of incredible mound-building colonial morphs of Avrainvillea [A. longicaulis f. laxa (Fig. 8), A. asarifolia f. olivacea ( Fig. 9) and A. nigricans f. spongiosa (Fig. 10)] catalyzed this study. These three colossal mound-formers are restricted to shallow (<3 m), placid, peat-bottom, high-nutrient waters in the protected interiors of mangrove ...

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... reiterate, Avrainvillea longicaulis f. longicaulis and A. asarifolia f. asarifolia (Figs. 8, 9) are solitary in open lagoonal sandy environments with consistent wave action but can form extraordinary decades-old colonial (possibly clonal?) mounds (Fig. 12). The taxa, described (Littler and Littler, 1992) as A. longicaulis f. laxa ( Fig. 8) and A. asarifolia f. olivacea ( Fig. 9), are persistent in peaty, highly eutrophic, placid, interior mangrove habitats. The f. laxa and f. olivacea morphs hypothetically (i.e., . The massive perrenating, bulbous, rhizoidal holdfast of Avrainvillea ...

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... hypothesis") are uniquely adapted to utilizing flabellar stipes as shallow subterranean rhizomes that spread laterally to produce enormous (several meters-thick, to 30 m diameter, Fig. 12) mound-like colonies that overgrow rich organic peat bottoms. Massive columnar rhizoidal holdfasts, such as those found in the f. longicaulis (Fig. 11) and f. asarifolia ( Fig. 9) morphs, hypothetically would be superfluous under placid enriched water- column nutrient conditions as well as incapable of surviving the deeper anoxic ...

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... hypothesis") are uniquely adapted to utilizing flabellar stipes as shallow subterranean rhizomes that spread laterally to produce enormous (several meters-thick, to 30 m diameter, Fig. 12) mound-like colonies that overgrow rich organic peat bottoms. Massive columnar rhizoidal holdfasts, such as those found in the f. longicaulis (Fig. 11) and f. asarifolia ( Fig. 9) morphs, hypothetically would be superfluous under placid enriched water- column nutrient conditions as well as incapable of surviving the deeper anoxic conditions of the composting peat deposits. Conversely, open-water wave surge and current drag on the huge colonial morphs (lacking a strong anchoring ...

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... stipes or columnar holdfasts. We postulated (i.e., "perennation hypothesis") that the stipes and blades of Avrainvillea longicaulis f. longicaulis and A. asarifolia f. asarifolia serve as expendable photosynthetic assimilators with a major function of building a massive perennial storage organ, the columnar rhizoidal holdfast. This structure ( Fig. 11) can comprise up to 90% of the total thallus (Olsen-Stojkovich, 1985;Littler and Littler, 1999). In other words, physical disturbances (such as storms and herbivory) as well Figure 13. Conducting primary productivity experiments on Avrainvillea longicaulis f. laxa at Twin Cays using oxygen electrode methods (Littler and Littler, 1987). ...

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... structure ( Fig. 11) can comprise up to 90% of the total thallus (Olsen-Stojkovich, 1985;Littler and Littler, 1999). In other words, physical disturbances (such as storms and herbivory) as well Figure 13. Conducting primary productivity experiments on Avrainvillea longicaulis f. laxa at Twin Cays using oxygen electrode methods (Littler and Littler, 1987). ...

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... experiments on Avrainvillea longicaulis f. laxa at Twin Cays using oxygen electrode methods (Littler and Littler, 1987). as physiological stresses (such as epiphyte loading) should result in disproportionate losses of the relatively delicate above-ground assimilators, which can be replaced by perennation from the massive subterranean holdfasts (Fig. 11) during more favorable ...

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... We attempted to experimentally induce colony formation in the f. longicaulis and f. asarifolia morphs by burial of the flabellar stipes as well as by conducting reciprocal transplant experiments with appropriate control (C= tagged only) and transplant controls for both morphs. In each habitat (i.e., Curlew Cay and Twin Cays, Grouper Gardens, Figs. 1, 2), the transplant controls (TC) were completely removed by careful digging and gently replanted in holes wedged opened by titanium crowbars in the nearby general area. The experimental transplants (T) were carefully removed, floated into a 100-liter cooler of seawater and transferred to the reciprocal field sites where they were ...

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... productivity measurements were made for the dominant Avrainvillea longicaulis f. laxa using traditional light-dark bottle oxygen electrode techniques (Fig. 13). This, and the transect data, were used to ascertain an average mound's contribution to primary production at Twin Cays. We measured photosynthetic rates of the assimilators during early summer under ambient environmental conditions (30-31º C, 36 ppt salinity, 1500-2100 µmol photons per m 2 per sec) using the same methods detailed in ...

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... assimilators during early summer under ambient environmental conditions (30-31º C, 36 ppt salinity, 1500-2100 µmol photons per m 2 per sec) using the same methods detailed in Littler and Littler (1990). We incubated healthy assimilators containing natural levels of epiphytes and replicate blades with the epiphytes carefully removed by pinching (Fig. 13), as well as incubating the epiphytes separately (N =6 for all treatments), to ascertain the primary productivity contributions of the epiphytes. We chose photosynthesis as an indicator of physiological production since growth is relatively intractable due to the continual translocation processes and the inaccessibility of the stipe/ ...

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... species (Littler and Littler, 1992), presented unresolved taxonomic questions. The common-garden reciprocal-transplant approach provided definitive resolution of these issues. Following one year of transplantation, all experimental transplants had acquired the morphological features consistent with the taxa characteristic of the new habitats (Fig. 14, 15, 16, 17), thereby falsifying the hypothesis that the mound formers were distinct ...

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... morphs (i.e., f. laxa and f. olivacea) were not resistant to even the moderate current levels (3.6±0.5 cm per sec) encountered in the back-reef lagoon habitats of the deeply anchored morphs (i.e., f. longicaulis and f. asarifolia). When buried to normal depths, the massive natural colonial morphs would pull free and begin to drift downstream (Figs. 18, 21). However, the majority of the 2-to 3-blade clumps (Fig. 15), with their stipes deeply buried in the sandy sediments, were able to survive and ...

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... even the moderate current levels (3.6±0.5 cm per sec) encountered in the back-reef lagoon habitats of the deeply anchored morphs (i.e., f. longicaulis and f. asarifolia). When buried to normal depths, the massive natural colonial morphs would pull free and begin to drift downstream (Figs. 18, 21). However, the majority of the 2-to 3-blade clumps (Fig. 15), with their stipes deeply buried in the sandy sediments, were able to survive and ...

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... one year, the surviving 2-to 3-blade clumps transplanted from Twin Cays to Curlew Cay had developed rudimentary stages of the massive holdfast with the adherent sand grains (Fig. 15) characteristic of f. longicaulis and f. asarifolia. Conversely, all of the surviving morphs with normally massive holdfasts that were transplanted to the mangrove pools at Grouper Gardens showed degeneration of the columnar holdfasts (Fig. 17), with only remnant rhizoids containing clumped sand grains present at the end of one year. ...

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... to Curlew Cay had developed rudimentary stages of the massive holdfast with the adherent sand grains (Fig. 15) characteristic of f. longicaulis and f. asarifolia. Conversely, all of the surviving morphs with normally massive holdfasts that were transplanted to the mangrove pools at Grouper Gardens showed degeneration of the columnar holdfasts (Fig. 17), with only remnant rhizoids containing clumped sand grains present at the end of one year. Concurrently, they had developed new assimilators/stipes characteristic of the colonial morphs (f. laxa and f. olivacea). Both sets of surviving controls and transplant controls were 100% uniform in retaining morphs consistent with their original ...

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... also discovered unexpected evidence in further support of the coloniality hypothesis in the case of Avrainvillea longicaulis f. laxa. We found that the colonial morphology is uniquely reinforced by the intermingling of blade and stipe siphons at areas of contact (Figs. 19, 25). Contact frequently occurs for prolonged periods in such calm habitats, leading to abundant anastomosing points of fusion/adhesion. Figure 19. Typical inter-thallus fusions characteristic of the colonial mound-forming ...

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... frequently occurs for prolonged periods in such calm habitats, leading to abundant anastomosing points of fusion/adhesion. Figure 19. Typical inter-thallus fusions characteristic of the colonial mound-forming species. ...

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... of the smaller Avrainvillea longicaulis f. laxa colonies measuring 0.6 X 1.1 m in diam. (Fig. 21) and hand-cleaned of debris and epiphytes (mostly unusual forms of Laurencia intricata, Cladophoropsis membranacea and Polysiphonia flaccidissima, Fig. 22) weighed 19 kg. Similar weights were recorded for comparable colonies of A. asarifolia f. olivacea (Fig. 18). Given that transect studies documented that both A. longicaulis f. laxa ...

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... the smaller Avrainvillea longicaulis f. laxa colonies measuring 0.6 X 1.1 m in diam. (Fig. 21) and hand-cleaned of debris and epiphytes (mostly unusual forms of Laurencia intricata, Cladophoropsis membranacea and Polysiphonia flaccidissima, Fig. 22) weighed 19 kg. Similar weights were recorded for comparable colonies of A. asarifolia f. olivacea (Fig. 18). Given that transect studies documented that both A. longicaulis f. laxa and A. asarifolia f. olivacea form colonies in excess of 30 m diam. (Fig. 12), their contribution to biomass in Twin Cays ponds is ...

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... forms of Laurencia intricata, Cladophoropsis membranacea and Polysiphonia flaccidissima, Fig. 22) weighed 19 kg. Similar weights were recorded for comparable colonies of A. asarifolia f. olivacea (Fig. 18). Given that transect studies documented that both A. longicaulis f. laxa and A. asarifolia f. olivacea form colonies in excess of 30 m diam. (Fig. 12), their contribution to biomass in Twin Cays ponds is ...

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... result, and the internal anatomical data (Littler and Littler, 1992), supports the hypothesis that the mound forms are not distinct from the solitary forms (f. longicaulis and f. asarifolia) and, therefore, falsifies the hypothesis that mound-forming colonial taxa are separate species. Avrainvillea transplanted from Curlew Cay to Twin Cays Ponds (Fig. ...

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... is interesting to note that the mound formers, while capable of overtopping other psammophytic (sediment dwelling) organisms, tend to bear prodigious quantities of epiphytes such as Laurencia intricata, Cladophoropsis membranacea and Polysiphonia flaccidissima (Figs. 12, 22), which, given sufficient light, would add about 30% to overall colony productivity in this shallow light-and nutrient-rich environment (Fig. 23). An earlier study at Twin Cays ( Littler and Littler, 1985) recorded 17.2 and 13.4 grams of carbon fixed per square meter per day at outer fringe, dense seagrass/algal, bay-and channel-sites, ...

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... also showed that the stipes and blades of the open-water morphs (Avrainvillea longicaulis f. longicaulis and A. asarifolia f. asarifolia) indeed serve as expendable assimilators, with a major function of building a massive perennating/storage organ, the columnar holdfast (Fig. 11), which comprises the bulk of the thallus biomass (Olsen-Stojkovich, 1985). Among all the other Bryopsidales, Avrainvillea is uniquely long-lived (see Littler and Littler, 1992) and does not undergo holocarpic reproduction (Clifton, 1997) leading to death. Physical disturbances (such as storms and herbivory), as well as physiological ...