Thomas A. Frankovich

Experimental nutrient enrichment causes complex changes in seagrass, microalgae, and macroalgae community structure in florida bay

We examined the spatial extent of nitrogen (N) and phosphorus (P) limitation of each of the major benthic primary producer groups in Florida Bay (seagrass, epiphytes, macroalgae, and benthic microalgae) and characterized the shifts in primary producer community composition following nutrient enrichment. We established 24 permanent 0.25-m2 study plots at each of six sites across. Florida Bay and added N and P to the sediments in a factorial design for 18 mo. Tissue nutrient content of the turtlegrassThalassia testudinum revealed a spatial pattern in P limitation, from severe limitation in the eastern bay (N:P>96:1), moderate limitation in two intermediate sites (approximately 63:1), and balanced with N availability in the western bay (approximately 31:1). P addition increasedT. testudinum cover by 50–75% and short-shoot productivity by up to 100%, but only at the severely P-limited sites. At sites with an ambient N:P ratio suggesting moderate P limitation, few seagrass responses to nutrients occurred. Where ambientT. testudinum tissue N:P ratios indicated N and P availability was balanced, seagrass was not affected by nutrient addition but was strongly influenced by disturbance (currents, erosion). Macroalgal and epiphytic and benthic microalgal biomass were variable between sites and treatments. In general, there was no algal overgrowth of the seagrass in enriched conditions, possibly due to the strength of seasonal influences on algal biomass or regulation by grazers., N addition had little effect on any benthic primary producers throughout the bay. The Florida Bay benthic primary producer community was P limited, but P-induced alterations of community structure were not uniform among primary producers or across Florida Bay and did not always agree with expected patterns of nutrient limitation based on stoichiometric predictions from field assays ofT. testudinum tissue, N:P ratios.

A rapid, precise and sensitive method for the determination of total nitrogen in natural waters

A rapid, automated method is described for the accurate determination of total combined nitrogen (TN) in natural waters. This methodology allows for TN analyses to be performed at three times the rate of previous techniques. The method is shown to be sensitive for a wide range of TN concentrations that may be found in various aquatic environments. The detection limits of this methodology are 2.0 μM (freshwater) and 2.3 μM (seawater). TN and TIN analysis of surface water samples from 300 sites inshore and offshore of south Florida, USA revealed predictable gradients in nitrogen concentrations. TN ranged from 7.56 μM offshore to 108.87 μM inshore. Organic forms of nitrogen constituted approximately 90% of the total nitrogen pool.

Nutrient effects on seagrass epiphyte community structure in Florida Bay.

A field experiment was employed in Florida Bay investigating the response of seagrass epiphyte communities to nitrogen (N) and phosphorus (P) additions. While most of the variability in epiphyte community structure was related to uncontrolled temporal and spatial environmental heterogeneity, P additions increased the relative abundance of the red algae–cyanobacterial complex and green algae, with a concomitant decrease in diatoms. When N was added along with P, the observed changes to the diatoms and the red algae–cyanobacterial complex were in the same direction as P‐only treatments, but the responses were decreased in magnitude. Within the diatom community, species relative abundances, species richness, and diversity responded weakly to nutrient addition. P additions produced changes in diatom community structure that were limited to summer and were stronger in eastern Florida Bay than in the western bay. These changes were consistent with well‐established temporal and spatial patterns of P limitation. Despite the significant change in community structure resulting from P addition, diatom communities from the same site and time, regardless of nutrient treatment, remained more similar to one another than to the diatom communities subject to identical nutrient treatments from different sites and times. Overall, epiphyte communities exhibited responses to P addition that were most evident at the division level.

Detection of Spirorchiid Trematodes in Gastropod Tissues by Polymerase Chain Reaction: Preliminary Identification of an Intermediate Host of Learedius learedi

Abstract Marine spirorchiid trematodes are associated with morbidity and mortality in sea turtles worldwide. The intermediate hosts remain unknown, and discovery efforts are hindered by the large number and great diversity of potential hosts within sea turtle habitats, as well the potential for low prevalence and overdispersion. A high-throughput DNA extraction and polymerase chain reaction–based method was developed to detect the internal transcribed spacer 2 (ITS2) region of the ribosomal gene of 2 spirorchiid genera, Learedius and Hapalotrema, within pooled samples of gastropod tissues. A model system consisting of freshwater snail (Pomacea bridgesii) tissues and DNA extracts spiked with adult Learedius learedi and known quantities of spirorchiid DNA was used to develop and test the technique. Threshold of detection was found to be equivalent to an early prepatent infection within 1.5 g of gastropod tissue. This technique was used to screen approximately 25 species of marine gastropods at a captive facility where green turtles (Chelonia mydas) become infected by L. learedi. The parasite was detected in a sample of knobby keyhole limpet (Fissurella nodosa), thus providing the first evidence of an intermediate host for a marine spirorchiid trematode. This technique has many potential applications in trematode life cycle discovery studies.

Differing temporal patterns of Chara hornemannii cover correlate to alternate regimes of phytoplankton and submerged aquatic-vegetation dominance

Cover of the alga Chara hornemannii Wallman and water-quality parameters were measured over a 3-year period in adjacent mangrove subestuaries in Florida Bay, so as to describe temporal variability and infer relationships betweenCharacoverandwaterqualitythatwillassistresourcemanagerstorestoreCharaabundancetohistoricallyhigher levels. A seasonal pattern of Chara cover was observed in the Alligator Creek subestuary that coincided with seasonal changes in water transparency in a relatively high-nutrient and phytoplankton environment. In contrast, higher Chara cover in the relatively low-nutrient and phytoplankton-abundance McCormick Creek subestuary did not exhibit a repeatable seasonal pattern, but was temporally negatively correlated with salinity and water depth. These observations suggest that water transparency may determine the importance of the salinity driver in these Chara communities. The present study demonstrates the differential importance of water quality and environmental drivers in estuaries distinguished by alternate regimes of phytoplankton and submerged aquatic-vegetation (SAV) dominance, and explains how differences in local estuarine geography may filter the response of SAV communities to environmental stressors.

Two new epizoic Achnanthes species (Bacillariophyta) living on marine turtles from Costa Rica

Abstract It has been known for a long time that marine mammals, such as whales and dolphins, host a very specific epizoic community on their skin. Whether or not a similar community exists on the carapaces of sea turtles is less studied. The present paper describes two new epizoic diatoms from the genus Achnanthes sensu stricto, Achnanthes elongata and Achnanthes squaliformis, found on the carapaces of nesting olive ridley sea turtles (Lepidochelys olivacea) in Ostional Beach on the Pacific coast of Costa Rica, based upon detailed scanning electron microscopy and comparison with the type material of Achnanthes groenlandica var. phinneyi and Achnanthes pseudogroenlandica. The two taxa appear to be closely related on the basis of their morphological features including long, slender valves, absence of terminal orbiculi, large cribrate areolae and absence of typical costae on the internal virgae of both valves. They can, however, be differentiated from each other by the number of areolae per stria, the position of the rapheless sternum and differences in their length/width ratio.