Clinton J. Dawes

The effects of anthropogenic nutrient enrichment on turtle grass (Thalassia testudinum) in Sarasota Bay, Florida

Four meadows of turtle grass (Thalassia testudinum Banks ex Konig) in Sarasota Bay, Florida were sampled on a bimonthly basis from June 1992 to July 1993 to determine spatial and temporal variation in short shoot density, biomass, productivity, and epiphyte loads. Concurrent with the seagrass sampling, quarterly water-quality monitoring was undertaken at ≥3 sites in the vicinity of each studied seagrass meadow. Three months after termination of the seagrass sampling effort, a biweekly water-quality monitoring program was instituted at two of the seagrass sampling sites. In addition, a nitrogen loading model was calibrated for the various watersheds influencing the seagrass meadows. Substantial spatial and temporal differences in turtle grass parameters but smaller spatial variation in water quality parameters are indicated by data from both the concurrent quarterly monitoring program and the biweekly monitoring program instituted after termination of the seagrass study. Turtle grass biomass and productivity were negatively correlated with watershed nitrogen loads, while water quality parameters did not clearly reflect differences in watershed nutrient inputs. We suggest that traditional water-quality monitoring programs can fail to detect the onset or continuance of nutrient-induced declines in seagrass health. Consequently, seagrass meadows should be monitored directly as a part of any effort to determine status and/or trends in the health of estuarine environments. *** DIRECT SUPPORT *** A01BY074 00029

Regrowth of the seagrass Thalassia testudinum into propeller scars

Regrowth of turtle grass, Thalassia testudinum Banks ex Konig, into existing propeller scars and artificial cuts was studied in a mangal estuary located in Tampa Bay, Florida. Sediments from scars and cuts and adjacent grass beds were not significantly different in relation to particle size distribution and levels of calcium carbonate. Significantly lower concentrations of total organic matter and extractable ammonium but not phosphate were detected in scars. Increases in ammonium levels coincided with the expansion of T. testudinum into a propeller scar. Seagrass blade morphology and productivity did not significantly differ in short shoots growing along the edges of scars or cuts relative to those in adjacent seagrass beds. Rhizome architectural studies revealed that apical meristems were few in number (19 to 38% of rhizomes) and randomly orientated in undisturbed grass beds (31 to 53% oriented toward center). In contrast, a greater percentage of apical meristems (78 to 88%) along the edges and in scars or cuts were directed towards the center. Full regrowth required an average of 3.5 to 4.1 years in existing propeller scars and could take up to 7.6 years in artificial cuts. The lack of changes in shoot productivity and limited production of rhizome meristems in T. testudinum result in slow regrowth in propeller cuts. The management implication is that turtle grass meadows will show long-term damage from propeller scars if not protected.

Seasonal changes in the proximate constituents of the seagrasses Thalassia testudinum, Halodule wrightii. and Syringodium filiforme

Abstract Levels of soluble carbohydrate in the rhizome of Thalassia testudinum Banks ex Konig, Syringodium filiforme Kutzing, and Halodule wrightii (Aschers) Aschers. are highest in the fall and lowest in the spring. This suggests that soluble carbohydrate is a nutrient reserve used to sustain the plants during the period of decreased productivity in the winter. Ash and dry weight levels for three plant-parts (leaf blades, photosynthetically inactive parts of short shoots, and rhizomes) were generally highest in the fall. Protein levels were highest in the summer in all plant parts in T. testudinum and S. filiforme suggesting highest cellular activity. Calorific levels were similar for all three species, the rhizomes having the highest levels, although no seasonal pattern was evident. The organic biomass of an average-sized plant of T. testudinum is 8–12 times greater than that of the other two species in the fall and the short-shoot biomass may account for half of the entire plant. The rhizome of T. testudinum has the highest level of organic matter of the three, for most of the year. The blades of H. wrightii and S. filiforme account for the largest amount of organic material in the fall when compared with the photosynthetically inactive parts of short shoots and rhizomes of the same plant.

Branch, micropropagule and tissue culture of the red algae Eucheuma denticulatum and Kappaphycus alvarezii farmed in the Philippines.

Three forms of the iota-producing carrageenophyte,Eucheuma denticulatum, and four forms of the kappa-producing carrageenophyte,Kappaphycus alvarezii, obtained from seaweed farms in the Philippines have been grown in the laboratory under unialgal and axenic conditions. Comparison of media indicates that seed stocks of both species can be cultured using enriched seawater media ranging from ESS and SWMD-1 to inexpensive soil extract (Erdshreibers) or holding in sterile seawater for up to three weeks. Micropropagation has been successful with at least two forms of each species resulting in clonal propagation from axenic explants within 4 to 8 weeks. Callus development and branch regeneration has also been induced in two forms of each species. The results indicate that culture facilities in the farming areas of the Philippines could maintain high-yielding and rapidly growing seed stock for the seaweed farmers.

Laboratory and field growth studies of commercial strains ofEucheuma denticulatum andKappaphycus alvarezii in the Philippines

Daily growth rates of 0.1 to 8.4% d-1 for the brown form and 0.2 to 6.3% d-1 of the green form were measured for 3 to 5-cm long branches of the tropical red seaweedKappaphycus alvarezii cultured in the laboratory. Highest growth rates were found using inexpensive enrichments such as soil water and coconut water supplemented with 0.7 mM N and 13 µM P and with a liquid fertilizer, Algafer, produced from seaweeds in the Philippines. Laboratory grown branches of bothK. alvarezii andEucheuma denticulatum transplanted to rafts in the field showed daily growth rates of 4.4 to 8.9% d-1, as high or higher than other reported growth rates. The studies, carried out in the Philippines, demonstrate the viability and high yield of laboratory cultivars and methods to keep laboratory culture costs low.

Response of the tropical red seaweed Gracilaria cornea to temperature, salinity and irradiance

The agarophyte Gracilaria cornea, collected over 2.5 y in the Florida Keys, shows adaptations to oceanic salinities and subtropical to tropical water temperatures in its photosynthetic and respiratory responses as measured with a respirometer. No seasonal pattern in responses to irradiance, temperature, and salinity were evident between five collections over a 20-month period, indicating the tropical nature of the populations from Bahia Honda and Pigeon Keys. Concentrations of chlorophyll a (0.09 to 0.41 mg g d wt-1) and phycoerythrin (0.06 to 0.36 mg g d wt- 1) were low and reflect the low nutrient regime of the habitats, especially when compared to laboratory cultured plants. Compensation and saturation irradiances were also low (11–38 and 90–127 μmol photon m-2 s-1), indicating acclimation to lower irradiances in their shallow (1–2 m depth) habitats where turbidity can be high. In comparison with other subtropical and warm temperate species of Gracilaria, G. cornea had lower levels of pigment, but similarly high photosynthetic efficiency, demonstrating shade adaptation; it had only limited tolerance to salinities below 20‰ and temperatures below 15 °C. Thus, G. cornea from the Florida Keys in mariculture would require subtropical to tropical temperatures and stable oceanic salinities.

The influence of whole lake aeration on the limnology of a hypereutrophic lake in central Florida

To determine the influence of a multiple inversion aeration system upon the limnology of a small sinkhole lake, we monitored physical-chemical and biological parameters for 15 months prior to starting aeration and for 24 months thereafter. Aeration eliminated thermal stratification and dissolved oxygen concentrations of bottom waters increased significantly. Secchi disk transparency increased during aeration while turbidity, pH, alkalinity, total nitrogen, hydrogen sulfide and iron concentrations decreased significantly. Primary production and mean chlorophyll a did not change significantly during aeration but total phytoplankton cell volume decreased 2-fold. This decrease was caused by a marked reduction in blue-green algae which appears to be attributable to rapid mixing of the lake and to decreases in the pH. Cell volumes of green algae remained constant but numbers of taxa increased 70%. Densities of crustacean zooplankton were reduced markedly by aeration while densities of rotifers increased significantly during the first year but then returned to preaeration levels during the second year. Large-bodied cladocerans were replaced by small-bodied forms during aeration, and copepod populations became dominated by nauplii (97%). Densities of benthic macroinvertebrates declined 2-fold during aeration due to to a marked reduction (10-fold) in the Chaoborus population which correlated strongly with decreases in crustacean zooplankton abundance. The total number of taxa collected on individual sample dates increased throughout the two year aeration period (from 12 to 25) and chironomids became the predominant group (70%).The multiple inversion aeration system successfully eliminated many of the undesirable features of eutrophication (e.g., oxygen depletion, blue-green algal blooms, low benthic diversity), but it did not change the trophic state. Aeration of hypereutrophic lakes for multiple years may be necessary to maintain desired conditions.

Clonal propagation of Eucheuma denticulatum and Kappaphycus alvarezii for Philippine seaweed farms

Technique improvement and cost reduction of branch culture, micropropagation, and callus production of carrageenan-yielding seaweeds Kappaphycus alvarezii and Eucheuma denticulatum is presented. Low cost branch culture is possible by enriching seawater with 0.1% coconut water with 1 mg l−1 indole-3-butyric acid for 24 h wk−1 or continuous culture with 0.01% Algafer, a Philippine fertilizer. Micropropagation of 0.5 cm explants had almost 100% new branch production demonstrating the viability of callus regenerated plants. The use of carrageenan as a media for callus production was not effective when compared to agar. Propagules of both species, transferred from the University of the Philippine Marine Science Institute (UPMSI) culture facility to the field, showed daily percent growth rates of 5 to 5.5% d−1 over 84 days. Based on the costs of the UPMSI laboratory, a culture facility in the seaweed farming area is estimated to cost about U. S.

The photosynthetic and respiratory rates and tolerances of benthic algae from a mangrove and salt marsh estuary: A comparative study

22000 during the initial year and 58% less the second year.

Effects of blade removal on the proximate composition of the rhizome of the seagrass Thalassia testudinum banks ex könig

Abstract Net photosynthetic and respiratory rates were studied for four species of estuarine algae dominant in a mangrove and a salt marsh on the west coast of Florida with relation to light, temperature, salinity, and periods of desiccation. Bostrychia bindert (intertidal) and Gracilaria verrucosa (subtidal) were common to both sites: Cladophora repens (intertidal) and Acanthophora spicifera (subtidal) were included from the mangrove community while Catenella repens (intertidal) and Spyridia filamentosa (subtidal) were included from the salt marsh community. Quantitative analysis of chlorophyll a showed higher levels in the salt marsh algae as compared to algae from the mangrove community. Net photosynthetic and respiratory rates were similar for both intertidal species from each site. The intertidal species showed broad tolerances to salinity with positive photosynthetic responses even when held for 3 days in distilled water. All intertidal species had high rates of photosynthesis after periods of desiccation of 4, 8 or 16 h day −1 for 3 days and these rates were evident in specimens monitored in the air as well as submerged. Peak rates of photosynthesis for all 8 species occurred under 1·12 × 10 4 μW cm −2 white light, at 30–36 °C and in 20–30%. The subtidal algae from the mangrove community ( Acanthophora and Gracilaria ) had 5- to 10-fold increases in photosynthetic rates over the subtidal species from the salt marsh community ( Spyridia and Gracilaria ). The physiological tolerances of the algae to site and location in salt marsh and mangrove estuaries along the west coast of Florida are discussed.