John A. Kilar’s research while affiliated with University of Connecticut and other places

Temporal variability in certain morphological and taxonomically important features was quantified for Sargassum polyceratium Mont. from a population in the Content Keys, Florida (U.S.A.). Patterns of blade development, senescence, and loss caused pronounced seasonal changes in blade length-width ratios. Blade length and width were maximal early in the growing season (August-November) and decreased as the annual stems matured. Early in the growing season, plants had broader blades with randomly distributed cryptostomata. Late in the growing season (February-April), plants had more linear blades with cryptostomata approximately arranged in two rows, one on each side of the midrib. The length-width ratio of blades increased acropetally along the stems and were directly correlated to the size of the cryptostomatal opening and inversely correlated with the number of cryptostomata. The branching pattern of the annual stems ranged from short spur branches to well-developed, lateral axillary branches. The frequency of bifurcated blades increased significantly late in the growing season. Vesicle shape and size and pedicel length were temporally stable. Alated pedicels and mucronate vesicles occurred in low frequencies. The variability of the morphological features used to delineate species within the genus Sargassum on the tropical eastern coasts of the Americas is poorly understood.

Sargassum mathiesonii sp. nov. is described from a population at the mouth of the Homosassa River, Homosassa, Florida. Patterns of morphological variation were quantified as well as the plant's phenology and ontogeny. Sargassum mathiesonii is dioecious (50/50 sex ratio), produces receptacles basipetally along laterals, and has vesicle pedicels that average 1–1.7 mm in length. As judged from coefficients of variation and measurements of between-plant variation, vesicle diameter was the most stable continuous trait, followed by vesicle length, blade length: width ratio, blade width, and blade length. Anatomical variation was attributed primarily to ontogeny. Plants were smallest in March and April and grew to their maximum size in June (ca. 2 m). Biomass was augmented by additional main axes and primary laterals in October and receptacles in December. At maturity, male receptacles were longer and more loosely branched than female receptacles. A few vesicles developed viable oogonia in their cryptostomata and gave rise to fertile branches, situations previously unknown for Sargassum. Sargassum mathiesonii is determined to be morphologically and developmentally distinct from the lectotype and other North American populations of S. filipendula C. Ag. A more utilitarian approach to Sargassum taxonomy is achievable if species descriptions incorporate an understanding of morphological variability, reproductive periodicity, and ontogenetic patterns.

Lectotype specimens are designated for the brown alga, Sargassum filipendula C. Agardh var. filipendula, and two of its varieties, S. filipendula var. laxum J. Agardh and S. filipendula var. contractum J. Agardh.

Local-scale population differentiation of Sargassum polyceratium Montagne from the Content Keys, Florida, was evaluated. Forty-seven phenotypes were recognized based on blade features. The most common phenotype had lanceolate, often undulate, blades with serrated margins. Plants with flat or curly ovate blades or flat linear blades were common. Other phenotypes were rare (< 2% of population). Blade shape occurred over a continuum, ranging from linear to lanceolate to ovate. Intraspecific differences in blade features were extensive; otherwise, morphological traits were usually similar. Unlike previous descriptions of intraspecific variation, divergent morphologies were intermixed, occurring at distances of a few centimeters. There was no evidence to indicate that short-term environmental effects or hybridization between species were responsible for the considerable morphological variation in this population. Furthermore, the failure to recognize the range of phenotypic variability in the genus Sargassum may result in taxonomic inconsistencies when few specimens are collected, when morphological features cross perceived intraspecific boundaries, when phenotypes display different developmental rates, or when species descriptions originate from a single specimen or population. Designating species or intraspecific taxa should be avoided without a complete appreciation of their morphological variability in nature. Local-scale population differentiation of Sargassum polyceratium Montagne from the Content Keys, Florida, was evaluated. Forty-seven phenotypes were recognized based on blade features. The most common phenotype had lanceolate, often undulate, blades with serrated margins. Plants with flat or curly ovate blades or flat linear blades were common. Other phenotypes were rare (< 2% of population). Blade shape occurred over a continuum, ranging from linear to lanceolate to ovate. Intraspecific differences in blade features were extensive; otherwise, morphological traits were usually similar. Unlike previous descriptions of intraspecific variation, divergent morphologies were intermixed, occurring at distances of a few centimeters. There was no evidence to indicate that short-term environmental effects or hybridization between species were responsible for the considerable morphological variation in this population. Furthermore, the failure to recognize the range of phenotypic variability in the genus Sargassum may result in taxonomic inconsistencies when few specimens are collected, when morphological features cross perceived intraspecific boundaries, when phenotypes display different developmental rates, or when species descriptions originate from a single specimen or population. Designating species or intraspecific taxa should be avoided without a complete appreciation of their morphological variability in nature.

Phenotypic and ontogenetic changes in apparent photosynthesis and dark respiration for Sargassum polyceratium Mont. were related to the differential allocation of resources into blades, stems, vesicles, and fertile branches as well as anatomical parameters of surface area, volume, and blade density from a population in the Content Keys, Florida. Three divergent phenotypes were evaluated during four phases of ontogeny: maximum growth (October), peak reproduction (December), senescence (April), and stasis (July). Photosynthetic and respiratory rates changed throughout the year, at different stages of morphogenesis, and among different phenotypes. Photosynthesis was highest during active growth, decreased during reproduction and senescence, and was lowest during stasis. In contrast, respiration was higher during peak reproduction and stasis. Temporal, phenotypic, and ontogenetic changes in apparent photosynthesis were best explained by interactions among anatomical features, growth stages, and source-sink relationships of metabolic reserves and pigments. Surface area: volume (SA:V) ratios played a secondary role. Photosynthetic performance of mature axes decreased with the allocation of resources away from blades to air bladders and fertile branches. Apparent productivity and development of fertile branches on phenotypes were not correlated. High respiratory rates, SA:V ratios, blade areas, and low blade densities occurred on developing axes and were consistent with adaptations to low light fields. Sargassum polyceratium, because of its morphological differentiation, is a relatively complex, physiologically variable alga.

For 15 months, the composition and abundance of drift vegetation were determined from a plantdominated fringing reef at Galeta Point, Caribbean Panama. Five nets located downstream of the reef platform continuously sampled 1.0–1.3 ha of reef flat which included 137–202 m of fore reef. Time series and multiple correlation analysis were done to evaluate the dependence of drift biomass on selected physical and biological factors. Export and import rates and turnover times were derived and compared between the dominant species. Floating leaves, branches, and seeds of higher plants were the major components of imported drift with 52% of the dry weight mass, followed by algae and seagrass each with 19%, the water hyacinth Eichhornia with 2%, and floating tar with 8%. Exported biomass from the reef platform was higher in the dry-season (late November–March) than in the wet-season (April-early November). Within the 1.0–1.3 ha sampling area, export estimates ranged from 37–294 kg mo-1 for the seagrass Thalassia, 3–171 kg mo-1 for the alga Laurencia, and 3–74 kg mo-1 for the alga Acanthophora. Multiple correlation models indicated that meteorological and hydrographic conditions explained between 31 to 65% of the variance in the drift biomass and that the best predictors of exported biomass were tidal elevation and wind speed (3 week lag). Export rates increased with high tides and strong winds and decreased with elevated water temperatures. Autocorrelations of drift biomass were generally highest at 2 week intervals, suggesting that the quantity of drift removed from the platform was, in part, related to spring and neap tide cycles. Export rates were also affected by the morphology of the vegetation, development of uprights, and location on the reef platform. Import rates of terrestrial-plant debris, the hyacinth Eichhornia, the seagrass Syringodium, and the brown alga Sargassum did not exhibit pronounced seasonal patterns in abundance and averaged 60.2, 1.9, 1.1, and 2.7 g d-1m-1, respectively. Wind speed was negatively correlated with Sargassum abundance, suggesting that strong winds depleted it from nearshore waters. Floating tar averaged about 10 g d-1m-1, the highest reported in the Caribbean. The plant-dominated fringing reef at Galeta Point is shown to be a major source, as well as a recipient, of drift vegetation.

The propagation of Acanthophora spicifera (Vahl) Børg. was studied on a fringing-reef platform at Galeta Point, Caribbean Panama. Manipulative experiments and detailed descriptive data indicated that fragmentation accounted for this alga's standing crop and distribution. Fragments were broken off by turbulence in the fore reef, transported by currents across a seagrass meadow, snagged, and attached or entangled in the back reef. Accumulations of ≈66 g (dry wt.)·m−2 occurred.A. spicifera was a major contributor to drift biomass, and, depending on prevailing current velocities, fragments entering the back reef had a 49 to 93% chance of recruiting. Higher current velocities (≈0.24m·s−1) decreased the ability of free-floating fragments to snag by decreasing the frequency of fragment-substratum contacts. 25% of the snagged fragments remained > 3 days, and fragments required < 2 days to attach to Laurencia papillosa (Forsk.) Grev. or to another frond of Acanthophora spicifera. Fragments were unable to recruit into plots of Thalassia testudinum Bank ex König and Sims.Tetrasporic plants were common, comprising as much as 96% of fore-reef and 80% of the back-reef populations. In October, 3% of the fore-reef population had cystocarps; otherwise, no other gametophytes were found. The percentage of spore-bearing tetrasporophytes was significantly greater in the Laurencia zone than in the fragment-derived Acanthophora zone. Vegetative fragmentation was demonstrated as an effective means of propagation, while the ecological significance of tetraspores was unclear.