Walter H. Adey

The effect of micrograzers on algal community structure in a coral reef microcosm

The effect of amphipod grazing on algal community structure was studied within a 75 l refuge tank connected to a 6500 l closed-system, coral reef microcosm. When amphipods (Ampithoe ramondi) were absent or present in low numbers, a high biomass of mostly filamentous algal species resulted, including Bryopsis hypnoides, Centroceras clavulatum, Ceramium flaccidum, Derbesia vaucheriaeformis, Enteromorpha prolifera, Giffordia rallsiae, and Polysiphonia havanensis. These microalgae disappeared when amphipod density increase beyond approximately 1 individual cm-2 of tank surface. The macroalga Hypnea spinella germinated in the system in association with amphipod tube sites. H. spinella plants remained rare until filamentous species were eliminated by amphipod grazing. Feeding trials confirmed that H. spinella was protected from grazing by its size rather than a chemical defense strategy. The H. spinella community we observed is similar to the flora described on algal ridges where physical conditions exclude fish grazing. We suggest that amphipods and similar micrograzers are responsible for the algal community structure of these ridges. Caging experiments may be subject to similar effects from increased amphipod grazing on the algae. Introduction of fish that are amphipod predators into the refuge tank caused an increase in algal species diversity but total H. spinella growth rates fell from 25 g dry wt month-1 to less than 8 g dry wt month-1. We describe amphipod behavior in relation to changes in population density and food supply, and we stress the potential for increasing the productivity of commercial seaweeds through maintenance of appropriate amphipod species in mariculture facilities.

Coral Reef Morphogenesis: A Multidimensional Model

Windward reef morphogenesis is a dynamic process directly controlled by the growth potential of dominant corals and coralline algae relative to wave energy and sea level rise. Moderate wave energy favors vertically rapid growth that is porous and uncemented; high wave energy favors slow but compact growth. Growth potentials of Caribbean and Indo-Pacific reefs are probably equivalent. Major differences are probably not due to biological or direct climatic factors but are in part related to differing patterns of sea level rise resulting from Holocene crustal adjustment. The nature and position of antecedent foundations developed by high interglacial and interstadial sea levels is especially critical and is largely controlled by regional tectonic factors, especially long-term subsidence.

Territorial behavior of threespot damselfish (Eupomacentrus planifrons) increases reef algal biomass and productivity

SynopsisAlgal growth and damselfish (Eupomacentrus planifrons) territories were studied in two reef habitats at Discovery Bay, Jamaica. Damselfish territories were contiguous in the reef flat (0 to 2.5 m), where the algal composition and biomass varied from territory to territory. In contrast, on the lower reef terrace (22 m), damselfish territories were often spatially segregated. While the algal composition of the territories was more uniform on the reef terrace, the total algal biomass was lower than in the territories on the reef flat. Damselfish are largely herbivorous, and they defend their territories against most intruding fish, including a number of herbivorous species. Areas of the reef terrace outside of damselfish territories were heavily grazed by herbivorous fishes and contained only small quantities of non-crustose algae.The reef terrace territories were characterized by a multispecific turf of algae (greens, blue-greens, and reds) covering the Acropora cervicornis framework and by the leafy, brown alga, Lobophora variegata. A rapid reduction in the biomass of brown algae and filamentous algae was noted when damselfish were permanently removed from their territories. Only calcified, encrusting algae — plants apparently somewhat undesirable as fish food sources — would be common on the terrace zone of this reef if damselfish territories were absent. Damselfish territoriality may significantly influence the dynamics of some reefs by increasing the biomass of the algal turf thereby increasing; reef productivity. Since blue-green algae, potential nitrogen fixers, occur in these algal turfs, the fish may also be indirectly affecting reef nutrition.

THERMOGEOGRAPHY OVER TIME CREATES BIOGEOGRAPHIC REGIONS: A TEMPERATURE/SPACE/TIME‐INTEGRATED MODEL AND AN ABUNDANCE‐WEIGHTED TEST FOR BENTHIC MARINE ALGAE

We developed a time‐integrated thermogeographic model to demonstrate conditions under which benthic marine algal assemblages evolve biogeographic patterns in their distribution and abundance. The graphical model applies to rocky marine sublittoral zones in which seasonal temperatures, coastline area, isolation, and evolutionary time are primary factors. Time is treated by using the temperature/area/distributions for the present (interglacial period) integrated with that of 18,000 years before present (glacial period). These two alternate states characterize the global marine realm since the late Pliocene to Pleistocene time during which many extant species have evolved. The resulting abiotic “thermogeographic” model defines 20 regions that correspond with the cores of 24 recognized biogeographic regions and/or provinces determined by published distributions of organisms. Modern biogeographic regions conform closely with thermogeographic regions where temperature, area, and time are integrated. We also propose that biogeographic patterns should be determined by the abundance of species assemblages rather than presence and absence or percent endemism as is commonly done. We test the efficacy of thermogeographic regions with abundance‐weighted patterns in the biogeography of crustose coralline red algae (Rhodophyta/Corallinales) in the colder part of the northern hemisphere. Based on abundance, rather than presence/absence, coralline red algal biogeographic regions correspond closely with the models thermogeographic regions.

Holocene bioherms (algal ridges and bank-barrier reefs) of the eastern Caribbean

Based on aerial and surface reconnaissance of shallow-water reefs and algal ridges throughout the Lesser Antilles and coring of reef-ridge structures on St. Croix, Martinique, Antigua, and Guadeloupe, major emergent and shallow-water Holocene bioherms are characterized by maps and sections. On St. Croix, an extensive bank-barrier reef about 13 to 18 m thick is developed on the inner part of the carbonate shelf. Stratigraphically, this reef has a lower Diploria - Montastrea -rubble-sand (or bank) facies, formed during middle to late Holocene time, overlain by a shallow-water Acropora palmata facies, formed during the past 1,000 yr. In exposed areas, at depths of less than 2 m, crustose coralline pavements are presently forming incipient algal ridges on the reef crest. Shoreward of the barrier reef, on preexisting benches at depths of 3 to 10 m, algal ridges had developed from 5000 to 2000 B.P. The developing barrier reef has since blocked wave action from the bench algal ridges, and many are now degenerating. This same pattern occurs on the windward sides of many Lesser Antillean islands with the following variations: (1) Where wave energy is generally greater than on St. Croix, an extensive coralline- Millepore crust in the form of mounds or spurs, incipient algal ridges, or even well-developed algal ridges cap bank-barrier systems. (2) Where bank barriers have not blocked inshore bench algal ridges (especially on limestone islands), they remain well-developed and active. (3) Under some conditions, apparently associated with high energy and turbidity, fleshy algal pavements cap some bank-barrier structures. In the Lesser Antilles where present shelf or bench depths are less than 10 to 12 m, the uppermost surfaces of Holocene bioherms have had sufficient time to build to maturity and now have reef flats and (or) algal ridges. Where shelf depths are between 10 and 20 m, modern Acropora palmata reef or algal ridge systems are forming on late Holocene deeper water bank bioherms. Where shelf depths are greater than 20 to 25 m, sufficient Holocene time has not elapsed to allow the extension of bioherms into shallow water. Shelf-edge reefs, especially without the possibility of a bank base, fall into this latter category and are generally immature and submerged.

A controlled stream mesocosm for tertiary treatment of sewage

Freshwater stream ecosystems are well known for their capabilities for “self-purification” of sewage and other wastewaters. Unfortunately, the efficiencies of treatment are low and concentrations and volumes now discharged cannot be treated by self-purification alone. This paper describes an experiment with a stream mesocosm, in central California, USA, using controlled ecosystem methodologies in the format of an algal turf scrubber (ATSTM). This system was used to drive primary production and export in the mesocosm to bring secondary sewage to tertiary levels. The mesocosm consisted of a natural, mixed assemblage of attached periphyton, microalgae and bacteria which colonized an inclined floway 152 m long and 6.7 m wide, over which wastewater flowed in a series of pulses. The capacity of the wastewater flow varied between 436 and 889 m3 per day and various operational parameters were tested. Biomass was mechanically harvested from the floway at 1- or 2-week intervals depending upon the season. This paper presents the results for nitrogen and phosphorus removal as well as that of other contaminants and productivity of the algal turf. Nitrogen and phosphorus removal from the secondary wastewater was measured twice a week during four, 8-week quarters corresponding to the solar seasons. Nitrogen and phosphorus content of the harvested solids was also measured during these periods. Based on the percentage of nutrients in the harvested solids (3.1 % N and 2.1 % P) and the operational productivity of 35 g dry solids m−2 day−1, the yearly mean removal of nitrogen and phosphorus was 1.11 ± 0.48 gN m−2 day−1 and 0.73 ± 0.28 gP m−2 day−1, respectively. Results indicate the strong potential of controlled stream mesocosms for the removal of nutrients and other contaminants from wastewater to achieve tertiary levels.

THE EFFECTS OF LIGHT AND TEMPERATURE ON GROWTH RATES IN BOREAL-SUBARCTIC CRUSTOSE CORALLINES1

A number of boreal‐subarctic crustose corallines were kept in natural seawater tanks at temperatures ranging from 0 to 19 C and, using fluorescent lamps at light intensities, ranging from 7 to 750 lux with periods of 8 and 14 hr/day. The resultant growth rates as a function of temperature and light are presented and discussed in relation to the ecology of the plants.

Algal Turf Scrubbing: Cleaning Surface Waters with Solar Energy while Producing a Biofuel

As human populations have expanded, Earths atmosphere and natural waters have become dumps for agricultural and industrial wastes. Remediation methods of the last half century have been largely unsuccessful. In many US watersheds, surface waters are eutrophic, and coastal water bodies, such as the Chesapeake Bay and the Gulf of Mexico, have become increasingly hypoxic. The algal turf scrubber (ATS) is an engineered system for flowing pulsed wastewaters over sloping surfaces with attached, naturally seeded filamentous algae. This treatment has been demonstrated for tertiary sewage, farm wastes, streams, and large aquaculture systems; rates as large as 40 million to 80 million liters per day (lpd) are routine. Whole-river-cleaning systems of 12 billion lpd are in development. The algal biomass, produced at rates 5 to 10 times those of other types of land-based agriculture, can be fermented, and significant research and development efforts to produce ethanol, butanol, and methane are under way. Unlike with algal photobioreactor systems, the cost of producing biofuels from the cleaning of wastewaters by ATS can be quite low.

The genus Clathromorphum (Corallinaceae) in the Gulf of Maine

SummaryThis paper is the second of a series covering the crustose corallines of the Gulf of Maine. Information on anatomy, cytology and the development of the reproductive structures is presented to show that Clathromorphum is a genus distinct from both Phymatolithon and the branching members of Lithothamnium. Also, for the two species of this genus present in the region, reproductive cycles and geographic and bathymetric distributions are presented and discussed.

The genera Lithothamnium, Leptophytum (nov. gen.) and Phymatolithon in the Gulf of Maine

SummaryThis paper is the fourth of a series covering the crustose corallines of the Gulf of Maine. Information on anatomy, cytology and the development of the reproductive structures is presented to show that Lithothamnium and Leptophytum (new genus) are distinct from Clathromorphum and Phymatolithon. An additional species, P. lenormandi, is placed in Phymatolithon. The reproductive patterns and geographic and bathymetric distributions of the five species involved are presented and discussed.