Phillip R. Taylor

EVOLUTIONARY STRATEGIES IN A TROPICAL BARRIER REEF SYSTEM: FUNCTIONAL-FORM GROUPS OF MARINE MACROALGAE1

Predictions of an evolutionary model were examined for 43 tropical macroalgae using a functional‐form group approach. The ranking from high to low primary producers (Sheet‐ and Filamentous‐Groups > Coarsely Branched‐ and Thick Leathery‐Groups > Jointed Calcareous‐ and Crustose‐Groups), and data from the literature, support the hypothesis that persistent forms which allocate resources for environmental resistance, interference competition or antiherbivory defenses do so at the cost of lower primary production rates. The results for percent thallus lost to fish grazing over a 24 h period support the hypothesis that members of the Thick Leathery‐, Jointed Calcareous‐ and Crustose‐Groups have evolved antipredator defenses, with a tendency for decreasing herbivore resistance toward the Sheet‐ and Filamentous‐Groups. The most heavily‐calcified species (e.g. crustose corallines) ranked among the most grazer resistant as did the thick rubbery or leathery species. The ranking of functional‐form group means for resistance to predation was as follows: Filamentous‐Group (62% lost‐24 h−1), Sheet‐Group (42%), Coarsely Branched‐Group (33%), Jointed Calcareous‐Group (10%), Thick Leathery‐Group (7%) and Crustose‐Group (0%), in accordance with the hypothesis. The algal groups generally showed an increase in mean penetration toughness from filaments (<200 g‐cm−2 to shear thallus) to sheets (216 g·cm2), coarsely branched forms (328 g·cm−2) and thick leathery species (1800 g·cm−2) in agreement with the predictions of the model. Contrary to earlier findings, there was no consistent gradation between the first four groups (i.e. fleshy algae) based on calorific values. However, in partial support of the functional‐form model, a seven‐fold difference was noted when the mean for these groups (1.7 kcal·g−1) was compared with that of the Jointed Calcareous‐ and Crustose‐Groups (0.2 kcal·g−1. The functional‐form group approach appears to have powerful capabilities in that it can indicate important morphological‐metabolic‐ecological interactions in a given community, where the macroalgae are known, without the need to examine each population in detail and without being constrained to a specific habitat or geographical region.

Algal resistance to herbivory on a caribbean barrier reef

Field and laboratory research at Carrie Bow Cay, Belize showed that macroalgae, grouped in functional-form units resisted fish and urchin herbivory in the following order (from high to low resistance): Crustose-Group, Jointed Calcareous-Group, Thick Leathery-Group, Coarsely Branched-Group, Filamentous-Group and Sheet-Group; thereby supporting the hypothesis that crustose, calcareous and thick algae have evolved antipredator defenses and should show the greatest resistance to herbivory with a gradation of increasing palatability towards filaments and sheets. Of the 21 species examined, several (e.g.,Dictyota cervicornis on grids,Laurencia obtusa andStypopodium zonale) had exceptionally low losses to fish grazing, probably due to chemical defences. The sea urchin,Diadema antillarum, was more inclined to feed on algae with known toxic secondary metabolites than were herbivorous fishes; hypothetically related to the differences in mobility and concomitant modes of feeding. Tough leathery forms such asSargassum polyceratium andTurbinaria turbinata resisted grazing by bottom feeding parrotfishes (Scaridae) and surgeonfishes (Acanthuridae) but were susceptible when suspended midway in the water column, possibly due to the presence of rudderfishes (Kyphosidae) which readily consume drift Sargassaceae. The overall tendencies support our predicted relationship between grazer-resistance and algal morphology. In conjunction with our previously reported findings concerning primary productivity, toughness and calorimetry for many of the same species, these results lend credence to generalizations relating form with function in marine macroalgae.

Competition between herbivourous fishes and urchins on Caribbean reefs

SummaryWhen the common sea urchin Diadema antillarum was removed from a 50 m strip of reef in St. Thomas, US Virgin Islands, cover of upright algae and the grazing rates and densities of herbivorous parrotfish and surgeonfish increased significantly within 11–16 weeks when compared to immediately adjacent control areas. Sixteen months after removal, Diadema had recovered to 70% of original density, abundance of upright algae no longer differed between removal and control areas, and the abundance and grazing activity of herbivorous fish in the removal was approaching equivalence with control areas. On a patch reef in St. Croix that had been cleared of Diadema 10–11 years earlier (Ogden et al. 1973b), urchins had recovered to only 50–60% of original density. This reef still showed significantly higher rates of grazing by fish and a significantly greater density of parrotfish and surgeonfish than a nearby control reef where Diadema densities had not been altered. These results indicate that high Diadema densities (7–12/m2 for this study) may suppress the densities of herbivorous fish on Caribbean reefs.

Selective Herbivore Increases Biomass of Its Prey: A Chiton‐Coralline Reef‐Building Association

The intimate association between a selective herbivore (the chiton Choneplax lata) and its primary prey (the crustose coralline alga Porolithon pachydermum) results in increased biomass and accretion of the alga. This process, over ecological and geological time scales, comprises a major component of Caribbean reef-building systems. Manipulative experiments showed that as the chiton grazes the alga it stimulates new meristematic activity and removes sporlings of the competitively superior frondose and filamentous algae, thereby increasing the survival rate of P. pachydermum on the intertidal reef crest. Furthermore, in the absence of C. lata, overgrowths of frondose and filamentous epiphytes provide an attractive food source for parrotfishes (Scaridae), which accelerates bioerosion of the coralline reef-crest structure due to the deep rasping action of feeding activity. Algal removal experiments suggest that the role of P. pachydermum is to provide a predictable food source and refuge substratum, which increases survivorship of the burrowing chiton by minimizing expenditure of energy during foraging and risk to predation. The chiton/coralline alga association is abundant throughout tropical western Atlantic islands and augments reef-building processes on the shallow algal crest portion of Caribbean reefs. Cover of the Choneplax/Porolithon association in the Belize Barrier Reef crest averages 13% (maximum to 70%) with a mean chiton density of 664 individuals/m 2 within the association. On average, the extensive networks of interconnected chiton burrows extend between 6 and 10 cm deep and contain one C. lata for every six openings, with the majority of animals (66%) ranging from 16 to 30 mm in length. Gut contents of the chiton consist predominantly of P. pachydermum (51%), followed by bacterial detritus (30%), Cyanophyta (13%), Bacillariophyta (3%), and fleshy microalgae (3%). The close SEM (scanning electron microscope) match between radular morphology of C. lata and grazing scars on the thallus surface of P. pachydermum shows how the chiton regularly feeds on the coralline alga without causing mortality. Virtually all P. pachydermum in the vicinity of C. lata burrows contain radular track scars of 10 μm in depth, whereas the photosynthetic, meristematic, and reproductive tissues of the coralline lie below 20 μm. P. pachydermum under intense chiton grazing is photosynthetically competent with 0.1 mg C fixed.g -1 organic dry mass.h -1 , which is not significantly different from ungrazed material and within the range of rates for other crustose coralline algae. The result is continuous net accretion at a mean rate of 2.3 mm/yr.

Complex interactions in the control of coral zonation on a Caribbean reef flat

SummaryThis study uses short-term assays and long-term transplant experiments to document the potential importance of fish predation and herbivory to the distribution and abundance of reef-building corals in a Caribbean back-reef system. Experimental manipulations of fish access reveal that the zonal patterns of the two reef-building corals Porites astreoides and P. porites f. furcata, dominant on shallow back-reef habitats, are strongly associated with the feeding intensity of parrotfishes. Differential palatability of the two corals to parrotfishes, the proximity of protective cover for large grazers and the availability of small refugia to harbor a cryptic grazer fauna are suggested as major features contributing to the observed patterns. A model predicting the interactions of various algivore/corallivore guilds on the relative dominance of Porites and algal populations is presented.

Functional similarity among isomorphic life-history phases of Polycavernosa debilis (Rhodophyta, Gracilariaceae)

Morphologically identical but different life‐history phases of the red alga Polycavernosa debilis (Forsskål) Fredericq and J. Norris showed no conspicuous differences in physiological or ecological performances. The costs and benefits of ploidy level, as measured by net photosynthesis, calorific content, structural makeup and resistance to predation, were not sufficient to result in statistically significant differences (P > 0.05 ANOA) for the various reproductive phases [haploid male or female (including cystocarps) and diploid tetrasporic]. The lack of measurable functional responses leads to two hypotheses: (1) that adaptive ecological‐physiological differences between life‐history phases are subtle, or (2) that predominantly genetic / reproductive factors are implicated in maintaining isomorphic life‐history phases.

The United States Coral Reef Initiative: an overview of the first steps

M.P. Crosby, S.F. Drake, C.M. Eakin, N.B. Fanning, A. Paterson, P. R. Taylor, J. Wilson Introduction The United States, along with many other nations, is con- cerned that the health of coral reefs and related ecosystems is deteriorating rapidly all over the world. Agenda 21, the final document of the 1992 Earth Summit, identifies corm reefs as ecosystems of great biodiversity and production to be accorded high priority for protection, and calls for an integrated management approach for their protection and sustainable use. The call by scientific, management and environmental advocacy communities for action towards a coordinated strategy for coral reef research and manage- ment has grown dramatically in recent years (i. e. Coral Reefs 13(4) editorial by R.W. Grigg). Some sources esti- mate that 10% of all reefs have been degraded beyond recovery, and another 20-30% are in peril over the next 10-20 years. As an initial effort to counter this trend, the United States is developing an interagency Coral Reef Ini- tiative (CRI) to create the base for a combined domestic and international effort aimed at the conservation and ef- fective management of coral reefs and related ecosystems (mangroves and sea grass beds). A U.S. CRI Coordination Team and Steering Committee have been created and staf- fed by personnel from a number of U.S. agencies to coordinate the development of the Initiative. Effective management of coral reef ecosystems addresses such glo- bal environmental concerns as biodiversity, land-based sources of marine pollution, sustainable development and climate change. Hence, the U.S., Japan, Australia, Jamai- ca, France, the United Kingdom, and the Philippines have also announced an International CRI to protect coral reefs in partnership with other coral reef nations around the world, non-governmental organizations, international or- ganizations, multilateral development banks, and private sector businesses. The State Department is currently pro- viding the overall Coordination Office for the international