Habitat Condition and Associated Macrofauna Reflect Differences Between Protected and Exposed Seagrass Landscapes

Seagrass landscape configurations associated with different physical settings can affect habitat-structure and plant-animal relationships. We compared shoal grass (Halodule wrightii) habitat and macrofaunal variables between two fragmented seagrass landscapes at barrier-island locations subject to different disturbance regimes. Five seagrass habitat variables including above ground biomass (AGB), shoot number, per shoot biomass, epiphyte biomass and below ground biomass (BGB), differed significantly between the island landscapes. Per shoot biomass and epiphyte biomass also varied significantly over the seagrass growing season; and epiphyte biomass showed a strong landscape-time interaction. Abundances of microgastropods normalized to AGB differed significantly between landscapes. An inverse relationship between the abundance of microgastropods and epiphyte loading suggests a possible functional link. However, additional temporal mismatch between epiphyte loading and microgastropod abundance indicates that controls on epiphyte loading were complex. Seagrass habitat was more fragmented within the Cat Island (CI) landscape. Wind direction and strength imply that the CI landscape experienced more physical disturbance than the Horn Island (HI) landscape. This study highlights some potential links involving landscape configuration, habitat structure, and macrofaunal associations which can be further addressed using hypothesis-driven research

Trophic Importance of Epiphytic Algae in Subtropical Seagrass Beds: Evidence from Multiple Stable Isotope Analyses

Multiple stable isotope analyses were employed to examine food web dynamics in a northern Gulf of Mexico seagrass system in which epiphytic algae were the single most important primary productivity component, being responsible for 46 and 60% of total system and benthic primary production, respectively. The seagrass Halodule wrightii Ascherson contributed only 13% to total system primary production on an annual basis. Stable isotope ratios of carbon (delta C-13), nitrogen (Omega N-15), and sulfur (delta S-34) Were measured for producer and consumer samples collected from May 1989 through November 1992. Epiphytes and leaves of H, wrightii had distinct delta C-13 values (-17.5 vs -12 parts per thousand, respectively) as well as distinct delta S-34 values parts per thousand (+18 vs +11 parts per thousand, respectively). delta C-13 values for the sand microflora, occasional macroalgae, and phytoplankton were -16, -17, and -22 parts per thousand, respectively; delta N-15 values were lowest for epiphytes and H. wrightii (+6 parts per thousand) and highest for phytoplankton (+100 parts per thousand). Virtually all consumers had delta C-13 values that fell within a narrow range of -20 to -15 parts per thousand, which included all delta C-13 values of epiphytes and the sand microflora but none of those for either H, wrightii or phytoplankton. Values for delta N-15 for consumers fell within a range of +8 to +16 parts per thousand, spanning herbivorous species with diets of microalgae to carnivorous species feeding at secondary to tertiary levels in the local food webs. Consumer values for delta S-34 ranged from +4 to +20 parts per thousand (mean = 14.2 parts per thousand), and indicate a stronger influence of seawater-derived sulfate than sediment-associated sulfides. The stable isotope data, in combination with measured high biomass and primary production rates of the epiphytic algae, strongly suggest that these algae are the primary source of organic matter for higher trophic levels in seagrass beds of Mississippi Sound. The contribution of H. wrightii to the food web appears to be minimal. The overall picture that has emerged based on the present and previous stable isotope studies is one of the major trophic importance of benthic microalgae (i.e, epiphytic and sediment-associated) in seagrass beds

Phylogenetic Relationship of \u3ci\u3eAlexandrium mondatum\u3c/i\u3e (Dinophyceae) to Other Alexandrium Species Based On 18S Ribosomal RNA Gene Sequences

The phylogenetic relationship of Alexatidrizan monilatum to other Alexandrium spp. was explored using 18S rDNA sequences. Maximum likelihood phylogenetic analysis of the combined rDNA sequences established that A. monilatum paired with Alexandrium taylori and that the pair was the first of the Alexandrium taxa to diverge, followed by Alexandrium margalefii. All three are members of the Alexandrium subgenus Gessnerium Halim nov. comb. (c) 2005 Elsevier B.V. All rights reserved

Effect of salinity on the distribution, growth, and toxicity of Karenia spp.

Abstract The first recorded bloom of Karenia spp., resulting in brevetoxin in oysters, in the low salinity waters of the Northern Gulf of Mexico (NGOMEX) occurred in November 1996. It raised questions about the salinity tolerance of Karenia spp., previously considered unlikely to occur at salinities \u3c24 psu, and the likelihood that the bloom would reoccur in the NGOMEX. Salinity was investigated as a factor controlling Karenia spp. abundance in the field, using data from the NGOMEX 1996 bloom and Florida coastal waters from 1954 to 2004, and growth and toxin production in cultures of Karenia brevis (Davis) G. Hansen and Moestrup. During the NGOMEX bloom, Karenia spp. occurred much more frequently at low salinities than in Florida coastal waters over the last 50 years. The data suggest that the NGOMEX bloom started on the NW Florida Shelf, an area with a higher frequency of Karenia spp. at low salinities than the rest of Florida, and was transported by an unusual westward surface current caused by Tropical Storm Josephine. The minimum salinity at which growth occurred in culture ranged between 17.5 and 20 psu, but the optimal salinity ranged between low values of 20 or 25 and high values of 37.5–45 psu, depending on the clone. The effect of salinity on toxin production in one clone ofK. brevis was complex, but at all salinities brevetoxin levels were highest during the stationary growth phase, suggesting that aging, high density blooms may pose the greatest public health threat. The results demonstrate that Karenia spp. can be a public health threat in low salinity areas, but the risk in the NGOMEX is relatively low. No bloom has occurred since the 1996 event, which was probably associated with a special set of conditions: a bloom along the Florida Panhandle and a tropical storm with a track that set up a westward current