Robert A. Kinzie

The temporal pattern and rate of release of zooxanthellae from the reef coral Pocillopora damicornis (Linnaeus) under nitrogen-enrichment and control conditions *

Abstract The rate of loss of zooxanthellae from intact Pocillopora damicornis (Linnaeus) was determined for colonies growing in laboratory tanks supplied with either ambient seawater or seawater enriched with dissolved inorganic N. Algal release peaked during midday in both treatments. Corals in N-enriched water released 40% more algae · U −1 surface area · day −1 than did control corals. However, algal densities in the N-enriched corals were three times higher than in controls, so specific release rate was lower for N-enriched corals. Lipid content of the N-enriched corals was also lower than in the controls. These results suggest that N enrichment results in: greater algal standing stock and a reduced rate of transfer of photosynthate to the host. N enrichment more than doubled algal densities in this coral indicating that zooxanthellae in situ may be nutrient limited and that algal densities are, to some extent, a function of nutrient levels in the external environment and not entirely regulated by the host.

Molecular phylogeny of symbiotic dinoflagellates inferred from partial chloroplast large subunit (23S)-rDNA sequences

Symbiotic associations between invertebrates and dinoflagellates of the genus Symbiodinium are a common occurrence in marine environments. However, despite our extensive knowledge concerning the physiological contributions of these algae to their symbiotic partners, our understanding of zooxanthella phylogenetics is still in its early stages. In the past 10 years, studies of Symbiodinium phylogenetics have relied solely on nuclear ribosomal (rDNA) genes. To date, organellar DNA sequences have not been employed to infer phylogenies for this genus of symbiotic dinoflagellates. We address this by presenting the first Symbiodinium phylogeny based on chloroplast (cp) large subunit (23S)-rDNA sequences. Cp23S-rDNA Domain V sequences were determined for 35 dinoflagellate cultures isolated from a range of invertebrate host species and geographical locations. Symbiodinium phylogenies inferred from cp23S-rDNA produced topologies that were not statistically different from those generated from nuclear rDNA, providing the first independent evidence supporting the published major clades of Symbiodinium. In addition, comparisons of sequence dissimilarity indicated that cp23S-rDNA Domain V evolves 9-30 times faster than the V1-V4 regions of nuclear small subunit (n18S)-rDNA, 1-7 times as fast as the D1-D3 regions of nuclear large subunit (n28S)-rDNA, and 0.27-2.25 times that of the internal transcribed spacer (ITS)-rDNA region. Our data suggested that cp23S-rDNA Domain V will prove to be a useful molecule for exploring Symbiodinium phylogenetics.

The Adaptive Bleaching Hypothesis: Experimental Tests of Critical Assumptions

Coral bleaching, the loss of color due to loss of symbiotic zooxanthellae or their pigment, appears to be increasing in intensity and geographic extent, perhaps related to increasing sea surface temperatures. The adaptive bleaching hypothesis (ABH) posits that when environmental circumstances change, the loss of one or more kinds of zooxanthellae is rapidly, sometimes unnoticeably, followed by formation of a new symbiotic consortium with different zooxanthellae that are more suited to the new conditions in the host’s habitat. Fundamental assumptions of the ABH include (1) different types of zooxanthellae respond differently to environmental conditions, specifically temperature, and (2) bleached adults can secondarily acquire zooxanthellae from the environment. We present simple tests of these assumptions and show that (1) genetically different strains of zooxanthellae exhibit different responses to elevated temperature, (2) bleached adult hosts can acquire algal symbionts with an apparently dose-dependent relationship between the concentration of zooxanthellae and the rate of establishment of the symbiosis, (3) and finally, bleached adult hosts can acquire symbionts from the water column.

Age at recruitment of Hawaiian freshwater gobies

SynopsisVery little is known about the dynamics of native Hawaiian stream fishes. Five species are restricted, as adults, to freshwater streams and estuaries on the major islands of the Hawaiian archipelago. This paucity of information is partly due to difficulties inherent in determination of age and subsequent determinations of life history characteristics. In the present study, we determined the age of newly recruited Hawaiian gobies,Stenogobius genivittatus andAwaous stamineus using otolith microtechniques. Internal otolith increments were enumerated using scanning electron microscopy (SEM). Increments of newly recruited juveniles were deposited on a daily basis as validated through a marking study. Results showed recruitment at an average age of 135 and 161 days for these two species, respectively, with more rapid growth following recruitment to freshwater. Chemical analyses of otolith carbonate of the Hawaiian gobies by electron microprobe for strontium and calcium concentrations provided valuable insights into a fishs past history. A combination of structural and chemical analyses makes it possible to link growth and recruitment to nutritional and environmental factors. Such information developed as a broad model would be applicable to the management of Hawaiian gobies and would greatly improve the quality of information available for these unique fish populations and other fish populations

Experimental infection of aposymbiotic gorgonian polyps with zooxanthellae

The planula larvae and young polyp stages of the West Indian gorgonian Pseudopterogorgia bipinnata (Verrill) do not have symbiotic zooxanthellae. Planulae were allowed to settle in water free of any algae and presented with a number of strains of dinoflagellates. Motile forms of these algae were attracted to the polyps and in some cases were seen to swim into the polyps open mouth. Successful infection was obtained only with Gymnocdinium (probably microadriaticum (Freudenthal)). Algae of the genus Amphidinium were apparently not able to infect polyps. The differences in transmission of zooxanthellae in symbiotic animals are discussed.

Molecular Characterization of Nuclear Small Subunit (18S)-rDNA Pseudogenes in a Symbiotic Dinoflagellate ( Symbiodinium, Dinophyta)

Abstract For the dinoflagellates, an important group of single-cell protists, some nuclear rDNA phylogenetic studies have reported the discovery of rDNA pseudogenes. However, it is unknown if these aberrant molecules are confined to free-living taxa or occur in other members of the group. We have cultured a strain of symbiotic dinoflagellate, belonging to the genus Symbiodinium, which produces three distinct amplicons following PCR for nuclear small subunit (18S) rDNA genes. These amplicons contribute to a unique restriction fragment length polymorphism pattern diagnostic for this particular strain. Sequence analyses revealed that the largest amplicon was the expected region of 18S-rDNA, while the two smaller amplicons are Symbiodinium nuclear 18S-rDNA genes that contain single long tracts of nucleotide deletions. Reverse transcription (RT)-PCR experiments did not detect RNA transcripts of these latter genes, suggesting that these molecules represent the first report of nuclear 18S-rDNA pseudogenes from the genome of Symbiodinium. As in the free-living dinoflagellates, nuclear rDNA pseudogenes are effective indicators of unique Symbiodinium strains. Furthermore, the evolutionary pattern of dinoflagellate nuclear rDNA pseudogenes appears to be unique among organisms studied to date, and future studies of these unusual molecules will provide insight on the cellular biology and genomic evolution of these protists.

Evidence of a Marine Larval Stage in Endemic Hawaiian Stream Gobies from Isolated High-Elevation Locations

Abstract Tropical streams on high oceanic islands are characterized by populations of amphidromous gobioid fishes. Adult fish live and breed in freshwater and many spawn at high (>300 m) elevations. Newly hatched fry are swept down to the sea where they develop for a period of time before recruiting to a stream. In analogous habitats in other geographic areas, amphidromous populations have further evolved into landlocked forms (i.e., populations that spend their entire life cycle in freshwater). We analyzed depositional patterns of trace elements in the otoliths of adult Lentipes concolor, an amphidromous goby endemic to Hawaii, to determine whether landlocked forms occurred. Otoliths were obtained from fish collected from the Hawaiian stream habitats most likely to harbor landlocked populations—upper elevations of interrupted streams and sections of streams above high waterfalls. A transition from a marine phase to freshwater existence was demonstrated as a decrease from high to low strontium : calcium r...

THE EFFECT OF DIFFERENT ZOOXANTHELLAE ON THE GROWTH OF EXPERIMENTALLY REINFECTED HOSTS

1. A method is given enabling the differential effects of different strains of zooxanthellae on host growth to be assessed. This technique uses the increase in the number of tentacles as the measure of growth. 2. Aposymbiotic polyps of the anemone Aiptasia pulchella reinfected with strains of Symbiodinium microadriaticum isolated from the anemone Aiptasia pulchella and the scyphozoan Cassiopea xamachana grow as well as normal Aiptasia polyps. 3. Aposymbiotic Aiptasia polyps reinfected with zooxanthellae from the gastropod Melibe pilosa and the clam Tridacna maxima grew no better than polyps lacking zooxanthellae. 4. These results lead to the conclusion that strains of zooxanthellae differ in their ability to enhance growth of Aiptasia polyps under the experimental conditions and that these differences may have important ecological consequences.

Early development of zooxanthella-containing eggs of the corals Pocillopora verrucosa and P. eydouxi with special reference to the distribution of zooxanthellae.

Some hermatypic corals spawn eggs that contain zooxanthellae. We followed development of zooxanthella-containing eggs of two such species, Pocillopora verrucosa and P. eydouxi. We also documented changes in the distribution pattern of zooxanthellae during development. Oocytes of both species took up zooxanthellae 3 to 4 days before spawning. At first, zooxanthellae were evenly distributed in oocytes, but they later moved to the hemisphere that contained the germinal vesicle. After fertilization, early cleavage events were holoblastic, progressing by furrow formation. The first cleavage furrow started at the hemisphere that contained zooxanthellae, dividing the zooxanthellate complement of the zygote about equally into the two blastomeres. The second division divided each blastomere into one zooxanthellae-rich cell and one with few zooxanthellae. With continued cell division, blastomeres containing zooxanthellae moved into the blastocoel. The blastocoel disappeared at about 5 h after the first cleavage, and the central region of the embryo was filled with cells containing either zooxanthellae or lipid droplets, forming a stereogastrula. Our results suggest that only blastomeres that had been determined to develop into gastrodermal cells receive zooxanthellae during cleavage. This determination appears to take place, at the latest, by the second cell division at the four-cell stage.

EFFECTS OF ULTRAVIOLET RADIATION ON PHOTOSYNTHESIS IN THE SUBTROPICAL MARINE DIATOM, CHAETOCEROS GRACILIS (BACILLARIOPHYCEAE)1

Acclimation to ambient ultraviolet radiation (UVR) was examined in a subtropical marine diatom, Chaetoceros gracilis Schutt. Short‐term exposure to UVR (<24 h) reduced the efficiency of photosynthetic energy conversion, carbon fixation, activity of 1,5‐bisphosphate carboxylase‐loxygenase (RUBISCO), and the rapid turnover of the putative Dl reaction center (32 kda) protein, whereas longer‐term exposure to ambient UVR (24–48 h) revealed a steady‐state acclimation, defined as recovery of carbon fixation and RUBISCO activity to rates equivalent to treatments without exposure to UVR. The turnover of D1 and chlorophyll a (Chl a) remained high during exposure to UVR. Efficiency of energy conversion by photosystem II, measured with double flash (pump and probe) fluorometry, increased by 24% in cells acclimated to UVR. Acclimation to UVR had no detectable effect on the functional absorption cross‐section or cellular concentrations of Chl a, Chl c, or total carotenoids. However, the maximum rate of carbon fixation was reduced by UVR on a Chl a basis but remained unaffected on a per‐cell basis. Response to UVR exposure in this subtropical diatom has two components: a short‐term inhibitory response and a longer‐term acclimation process that ameliorates the inhibition of carbon fixation.