The results reported in this paper demonstrate suboptimal experimental designs in some of the previously published manipulative methods and provide insights for the improvement of in-situ nutrient studies on coral reefs. Overgrown 0.5-liter porous clay-pot diffusers (“mini-reefs”—following a decade of recruitment, colonization and competition) were utilized to evaluate protocols for studies of controlled nutrient enrichment on coral reefs. A commonly used fertilizer, Tree Food Stakes resulted in detrimental 11-fold and 20-fold decreases of fleshy algae and calcareous coralline algae, respectively, relative to the Control treatments; while blue-green algae (Cyanobacteria) became significantly (6 times) more abundant. Osmocote-filled mini-reefs showed no such negative differences in mortality from the Controls for any functional group. By avoiding the pitfalls of inappropriate sources of enrichment, insufficient durations of colonization/competition studies, suboptimal study areas and inadequate nutrient detection limits in future research, the potential to provide new insights into the nutrient status of coral reefs is greatly increased.

1. Rapid assessment protocols for determining and monitoring the status of any given coral reef are provided and include measuring: (a) standing stocks of functional indicator groups, (b) herbivore populations, (c) water-column nutrient levels, (d) tissue C:N:P ratios, (e) algal physiological-response assays, and (f) herbivory assays. These measurements can reveal quantitative tipping-point levels beyond which resilience to undesirable phase shifts begins to become critically reduced. Universal tipping-point approximations are reviewed for inorganic nutrients, and posited for the first time for herbivory.2. The relative roles of top-down and bottom-up controls in determining benthic community structure and the health of coral reefs are especially important management concerns. This paper specifically addresses the top-down effects of herbivory and bottom-up effects of nutrient enrichment on critical indicator groups, i.e. reef-building corals, crustose coralline algae, dense turf algae and frondose macroalgae.3. A predominance of (a) massive corals and calcareous coralline algae relative to frondose macroalgae and algal turfs indicates a healthy spatially heterogeneous condition reflecting low nutrients and high herbivory. An abundance of (b) frondose macroalgae illustrates the least desirable condition of elevated nutrient levels and reduced herbivory, possibly reflecting pollution in concert with destructive herbivore fishing practices. High coverage of (c) coralline algae suggests healthy high herbivory levels, but problems with elevated nutrients that are inhibitory to some corals. Domination by (d) dense turf algae indicates desirably low nutrient levels, but an inadequate herbivory component.4. The fast growth and turnover rates of fleshy algae compared to other reef organisms highlight their value as early warning indicators of reef degradation.5. From a management perspective, levels of herbivory and nutrients rank among the most useful quantitative indicators of coral reef resilience; whereas, the degree of degradation and mortality are inferred from the above functional indicator groups of benthic primary producers. Published in 2006 by John Wiley & Sons, Ltd.

Since 1990, coral reefs off southeast Florida have experienced an unprecedented succession of macroalgal blooms and invasions. To determine if anthropogenic land-based nitrogen (N) sources support these HABs, we collected macroalgal tissue for stable nitrogen isotope (815 N) analysis at three spatially distinct depths ranging from the shallow subtidal to the shelf break (similar to 43 m) along seven transects from Jupiter to Deerfield Beach, Florida, USA. This sampling was initiated during a historically significant drought in the spring of 2001 when rainfall, stormwater runoff, and upwelling were at a minimum. The sampling was repeated in the summer wet season following significant stormwater runoff and during a strong upwelling event.Despite significant seasonal changes in N source availability, delta(15) N values did not vary between samplings. Collectively, delta(15) N values were significantly higher on inshore shallow reefs (+8.1 parts per thousand) compared to mid (+6.1 parts per thousand) and deep reefs (+6.7 parts per thousand). Values were also elevated in the southern portion of the study area (e.g., Boca Raton, +8.5 parts per thousand) where nearly 1.5 billion 1/day of secondarily treated wastewater is discharged into the ocean via coastal outfalls. Codium isthmocladum, a macroalga that assimilates its nutrients entirely from the water column, was the dominant bloom species in the southern study area, where tissue delta(15) N values matched source values of nearby sewage outfalls. The northern study area was dominated by species of the genus Caulerpa, particularly the invasive Pacific native C brachypus var. parvifolia, which are capable of accessing benthic nutrient sources (e.g., submarine groundwater discharge, SGD) by means of root-like rhizoids. The northern area does not have sewage outfalls but features a highly transmissive geologic zone where SGD may be enriched with septic tank leachate and effluent from municipal deep injection wells.Multiple lines of evidence supported the hypothesis that land-based sewage N was more important than upwelling as a N source to these HABs: (1)delta(15) N values were highest on shallow reefs and decreased with increasing depth, indicating land-based sources of enrichment; (2) elevated delta(15) N values occurred in these HABs during the dry season, prior to the onset of the summer upwelling; (3) elevated NH4+ concentrations occur on these reefs during both upwelling and non-upwelling periods and are kinetically preferred by macroalgae compared to upwelled NO3-. These findings provide a case study of a coupling between increasing anthropogenic activities and the development of macroalgal HABs, including invasive species that threaten economically important reef resources in southeast Florida. (c) 2005 Published by Elsevier B.V.

Since 1990, coral reefs off southeast Florida have experienced an unprecedented succession of macroalgal blooms and invasions. To determine if anthropogenic land-based nitrogen (N) sources support these HABs, we collected macroalgal tissue for stable nitrogen isotope (δ15N) analysis at three spatially distinct depths ranging from the shallow subtidal to the shelf break (∼43 m) along seven transects from Jupiter to Deerfield Beach, Florida, USA. This sampling was initiated during a historically significant drought in the spring of 2001 when rainfall, stormwater runoff, and upwelling were at a minimum. The sampling was repeated in the summer wet season following significant stormwater runoff and during a strong upwelling event. Despite significant seasonal changes in N source availability, δ15N values did not vary between samplings. Collectively, δ15N values were significantly higher on inshore shallow reefs (+8.1‰) compared to mid (+6.1‰) and deep reefs (+6.7‰). Values were also elevated in the southern portion of the study area (e.g., Boca Raton, +8.5‰) where nearly 1.5 billion l/day of secondarily treated wastewater is discharged into the ocean via coastal outfalls. Codium isthmocladum, a macroalga that assimilates its nutrients entirely from the water column, was the dominant bloom species in the southern study area, where tissue δ15N values matched source values of nearby sewage outfalls. The northern study area was dominated by species of the genus Caulerpa, particularly the invasive Pacific native C. brachypus var. parvifolia, which are capable of accessing benthic nutrient sources (e.g., submarine groundwater discharge, SGD) by means of root-like rhizoids. The northern area does not have sewage outfalls but features a highly transmissive geologic zone where SGD may be enriched with septic tank leachate and effluent from municipal deep injection wells. Multiple lines of evidence supported the hypothesis that land-based sewage N was more important than upwelling as a N source to these HABs: (1) δ15N values were highest on shallow reefs and decreased with increasing depth, indicating land-based sources of enrichment; (2) elevated δ15N values occurred in these HABs during the dry season, prior to the onset of the summer upwelling; (3) elevated NH4+ concentrations occur on these reefs during both upwelling and non-upwelling periods and are kinetically preferred by macroalgae compared to upwelled NO3−. These findings provide a case study of a coupling between increasing anthropogenic activities and the development of macroalgal HABs, including invasive species that threaten economically important reef resources in southeast Florida.

A new species of brown algae, Taonia abbottiana D.S. Littler et M.M. Littler, is described from the tropical western Atlantic. To date, this is the only member of the genus reported from the region. Taonia abbottiana differs from other species of the genus in having (1) sporangia raised above the surface layer on a stalk composed of two cells, and (2) in addition having a surface cortical layer of differentiated cells that are smaller than those of the medullary layers. Taonia abbottiana has often been confused with Stypopodium zonale, but the two differ anatomically in the development of cells directly behind the growing margin and, when living at similar depths, T abbottiana consistently has light colored concentric lines, while S. zonale has dark concentric lines.

The simultaneous effects of grazing and nutrient enrichment on macroalgal communities were experimentally investigated using plastic mesh enclosure/exclosure cages along a natural nutrient (DIN, SRP) gradient from the discharge of a tidal mangrove creek on the west side of Norman's Pond Cay, Exumas Cays, Bahamas. Nutrient enrichment was the only factor affecting total biomass of macroalgae whereas selective herbivory moderated species composition. Biomass ranged from >2 kg dry weight m−2 at the DIN-enriched Waterfall to <600 g dry weight m−2 in the DIN-limited Algal Halo. Grazing by the queen conch Strombus gigas and the sea hare Aplysia dactylomela significantly reduced biomass of the epiphyte Laurencia intricata, but not its host Digenea simplex at the DIN-enriched Waterfall. These two rhodophytes dominated the macroalgal community at the DIN-enriched Waterfall and inner Algal Halo, whereas the chlorophytes Microdictyon marinum and Cladophora catenata dominated the relatively DIN-depleted outer Algal Halo. Higher grazing rates by S. gigas, A. dactylomela, and juvenile parrotfish and surgeonfish at the DIN-enriched Waterfall compared to the more oligotrophic Algal Halo suggested selective grazing on higher quality (nitrogen) diets by these herbivores. A pronounced increase in the carbon/nitrogen (C:N) ratios of D. simplex and L. intricata from the Waterfall to the Algal Halo indicated increased DIN-limitation of growth in the more offshore, lower DIN macroalgal communities. In contrast, only modest increases in C:N ratios of M. marinum and C. catenata between the Waterfall and Algal Halo suggested that these species are better adapted to growth in reef environments with lower levels of DIN enrichment. Low coral cover (<2%) co-occurred with high macroalgal cover (>35%) at DIN-enriched reef sites around Norman's Pond Cay (Waterfall, Patch Reef, North Perry Reef) compared to relatively high coral cover (10–20%) and low macroalgal cover (<20%) at the lower DIN reef sites (Rainbow Reef, Lang's Reef). These results support ecological theory that bottom-up control via nutrient enrichment is a primary factor regulating overall biomass and taxonomic assemblages of macroalgae on coral reefs, whereas grazing is more important in controlling relative species composition via dietary preferences.

The strategy of blade abandonment and simultaneous rapid proliferation (via protoplasmic translocation) is unique to siphonaceous macroalgae owing to their lack of restrictive crosswalls. Siphonalean green algae often dominate the standing stocks and productivity of Caribbean mangrove island environs and are also abundant in virtually all calm-water reef habitats. The experimental organism Avrainvillea longicaulis is particularly abundant in the study sites west of Carrie Bow Cay and Curlew Gay, Belize. The recycling of protoplasm out of older epiphytically impaired blades of A. longicaulis, and simultaneous formation of apical siphon extensions elsewhere, leads to rapid proliferation of new blades-hypothetically, at relatively low energy cost to the plant. The rapidity of siphon extension occurs at least an order of magnitude faster than that possible by photosynthetic production alone, resulting in fully formed proliferations within 3 d. At the same time, the older epiphytized blades become empty, first at the tips, then progressively toward the holdfast, appearing translucent-brown and flaccid within 3 d, followed by senescence. We hypothesize that A. longicaulis rapidly responds to epiphyte colonization/impairment by reallocating protoplasm for new growth through protoplasmic streaming. The alternative hypothesis, that the herbivorous crab Thersandrus compressus might beneficially control epiphytes on A. longicaulis, was falsified by its strong negative effects (i.e., decreased growth and increased host mortality). The hypothesis that allelopathic secondary chemicals may play an antifouling role also was not supported by our experiments; i.e., the consistently vigorous growth rates of the five dominant epiphyte species attached to A. longicaulis were not significantly less than populations of the same species attached to carbonate rock. All of the manipulative results (i.e., experimental induction of blade abandonment followed by new proliferation), as well as the populational survey findings (i.e., greater proliferation by epiphytized plants) and physiological data (i.e., photosynthetic inhibition by epiphytes), support the blade abandonment/proliferation hypothesis, thereby documenting an effective epiphyte-control strategy.

A mechanism of competition between epiphytes and seagrasses potentially modulated by grazers was studied in a high-nutrient Thalassia testudinum meadow in the Indian River Lagoon (Florida, U.S.A.). The effects of fish grazing on epiphytes, and likely enhancing T. testudinum growth, was tested through an exclusion experiment. Twelve (2×2m) independent experimental plots were selected within a shallow monospecific bed to which three randomized treatments (exclusion fences, open fences and controls) with four replicates each were assigned. The epiphyte load was monitored on T. testudinum leaves inside the plots from January 1995 to March 1996. Treatment effects occurred during a chlorophyte bloom in March 1995, when the epiphyte biomass was significantly higher inside the exclusion cages than in either of the controls. The composition of the epiphytic community in March 1995 was dominated by sheet-like Enteromorpha and filamentous algae such as Cladophora , which are less resistant to herbivory than the coarsely-branched forms of red algae (e.g. Hypnea , Chondria and Acanthophora) that bloomed subsequently. These results suggest that herbivory change seasonally depending on the availability of different prey species to fish-grazers, which preferentially utilize the fleshy green algae typical of bloom conditions over the thicker coarsely-branched red algae. In the nutrient-rich lagoon the role of top-down interactions in enhancing T. testudinum growth is limited to the reduction of shading by green macroalgae.

A spectacular mound-like reef formation (126 m in circumference, 10 m high) dominated by highly arched and record-size colonies of the unattached mushroom coral Halomitra pileus, along with 17 other species of the family Fungiidae, occurs in 31 m of water on the sedimentary lagoon floor of the Great Astrolabe Reef, Fiji. Core samples show radiocarbon dates which indicate that the formation hypothetically began building ∼4500 y ago, with a calculated mean accretion rate of 2.2 mm ⋅ y-1. The majority of fossil and living material is contributed by H. pileus colonies between 40–70 cm mean diameter, with some individuals up to 1.5 m in diameter. The size, fungiid diversity, and geological history of the bioherm is unprecedented and represents the first example of a coral reef constructed almost entirely by Fungiidae.