Hsing-Juh Lin

Responses of coastal lagoon plant communities to different forms of nutrient enrichment—a mesocosm experiment

We carried out an enrichment experiment to quantify the effects of different forms of nutrients on the plant communities characteristic of lagoons common along the north east coast of the USA. ‘Lagoon’ mesocosms were enriched with phosphate alone, nitrate alone, nitrate plus phosphate, or ammonium plus phosphate. Nitrogen and phosphorus were added at loadings of 8200 μmol m−2 day−1 and 685 μmol m−2 day−1, respectively. Two control mesocosms remained unenriched. In the controls, as in many unenriched field systems, phytoplankton biomass remained low, eelgrass (Zostera marina L.) beds were sustained, and drift macroalgae and epiphytes were abundant. In mesocosms enriched with phosphate alone, the plant communities were similar to the controls, except that below-ground eelgrass biomass was lowered. Enrichment with nitrate alone generated moderate phytoplankton blooms (dominated by Nannochloropsis spp.), declines of above- and below-ground eelgrass, and declines of drift macroalgae and epiphytes. With combined N + P enrichment the Nannochloropsis blooms were between 4 and 10 times more intense than with nitrate alone. The eelgrass declines also started earlier, proceeded more rapidly, and were ultimately more complete. For none of the plant components were we able to detect significant differences between the N + P mesocosms enriched with nitrate and the N + P mesocosms enriched with ammonium.

Responses of epiphytes on eelgrass, Zostera marina L., to separate and combined nitrogen and phosphorus enrichment

Abstract We examined the effects of separate and combined nitrogen (N) and phosphorus (P) enrichment on the development of epiphytes on eelgrass (Zostera marina L.). The experiment used ten mesocosms as living models of shallow coastal lagoons along the southern shore of Rhode Island, USA. The mesocosms comprised, in duplicate, controls with no anthropogenic nutrient additions and four nutrient treatments: daily water column enrichment with phosphate alone (PO4), nitrate alone (NO3), nitrate plus phosphate (NO3 + PO4), or ammonium plus phosphate (NH4 + PO4). In the mesocosms enriched with PO4 alone, the epiphyte biomass, organic content, chlorophyll a content and community composition were as in the controls, but the nutrient content of the epiphytes (N and P) increased. Enrichment with NO3 alone increased chlorophyll a content, nutrient content, and relative abundance of cyanobacteria during the summer. Enrichment with NO3 + PO4 and with NH4 + PO4 produced intense and long lasting phytoplankton blooms that lowered epiphyte biomass and chlorophyll a content, but increased the N and P content of the epiphytes and the relative abundance of diatoms. There were no significant differences between the mesocosms enriched with NO3 + PO4 and those enriched with NH4 + PO4. Epiphyte biomass appears not to be a good indicator of nutrient loading or eutrophication in shallow coastal lagoons.

A long-term survey on anthropogenic impacts to the water quality of coral reefs, southern Taiwan

Before 2001, the ecological protection area in the Kenting National Park (KTNP), southern Taiwan, was poorly described. In this study, a set of four-year data (2001-2004) of seawater qualities at 19 sampling sites around the Nanwan Bay in the KTNP was used to explore anthropogenic impacts to ecological environment, especially coral reefs. The parameters of water quality were analyzed immediately after collection. The results showed that higher values of nutrients and suspended solids were attributed to the higher run-off around Nanwan Bay. The fluxes of nutrients and suspended solids were consistently correlated to rainfall. Hence, equations were developed to calculate nutrient fluxes and suspended solids by using only rainfall data. Our results show that suspended solids and ammonia were the dominant factors leading to the drop in coral coverage. In summary, the water quality in the intertidal zone of Nanwan Bay has been degraded and required greater attention.

Fish Assemblages in the Mangrove Creeks of Northern and Southern Taiwan

A bimonthly study of the spatial variations in fish assemblages in the six mangrove creeks along the western coast of Taiwan was conducted from February 1996 to February 1997. Fyke nets were used to collect fishes in each of three creeks in the north (subtropical) and south (tropical) regions. A total of 79 fish species belonging to 33 families were collected and, of these, the Gobiidae, Mugilidae, Leiognathidae, and Cichlidae were the most diverse families. The fish assemblages in each creek were dominated by a small number of small fishes, most of which are the young of commercially important species. Their life cycles occurred to some extent in estuarine environments. Analyses by classification and ordination separated the assemblages into a northern group and a southern group and showed that the assemblages were far more temporally varied in the southern creeks than in the northern creeks. Fifty fish species were recorded in the northern creeks and 49 fish species in the southern creeks, with 20 species present in both regions. No significant difference in number of species per netting was detected between the regions. The number of individuals and biomass per netting were greater in the northern creeks than in the southern creeks. Rainfall and organic content of sediments may be responsible for the difference in fish abundance between the regions. In the northern creeks the assemblages were dominated by Liza macrolepis and Liza affinis in winter and spring, but the assemblages were more diverse in summer and fall. In the southern creeks, the assemblages were always characterized by several species and their dominance varied from month to month. The differences in the assemblage structure in northern and southern mangrove creeks are likely due to the oceanic current patterns around Taiwan.

A trophic model of fringing coral reefs in Nanwan Bay, southern Taiwan suggests overfishing

Several coral reefs of Nanwan Bay, Taiwan have recently undergone shifts to macroalgal or sea anemone dominance. Thus, a mass-balance trophic model was constructed to analyze the structure and functioning of the food web. The fringing reef model was comprised of 18 compartments, with the highest trophic level of 3.45 for piscivorous fish. Comparative analyses with other reef models demonstrated that Nanwan Bay was similar to reefs with high fishery catches. While coral biomass was not lower, fish biomass was lower than those of reefs with high catches. Consequently, the sums of consumption and respiratory flows and total system throughput were also decreased. The Nanwan Bay model potentially suggests an overfished status in which the mean trophic level of the catch, matter cycling, and trophic transfer efficiency are extremely reduced.

Recurrent disturbances and the degradation of hard coral communities in Taiwan.

Recurrent disturbances can have a critical effect on the structure and function of coral reef communities. In this study, long-term changes were examined in the hard coral community at Wanlitung, in southern Taiwan, between 1985 and 2010. In this 26 year interval, the reef has experienced repeated disturbances that include six typhoons and two coral-bleaching events. The frequency of disturbance has meant that species susceptible to disturbance, such as those in the genus Acropora and Montipora have almost disappeared from the reef. Indeed, almost all hard coral species have declined in abundance, with the result that total hard coral cover in 2010 (17.7%) was less than half what it was in 1985 (47.5%). In addition, macro-algal cover has increased from 11.3% in 2003 to 28.5% in 2010. The frequency of disturbance combined with possible chronic influence of a growing human population mean that a diverse reef assemblage is unlikely to persist on this reef into the future.

Biotic communities of freshwater marshes and mangroves in relation to saltwater incursions: implications for wetland regulation

An ecosystem-level study was conducted in the Guandu wetlands insubtropical coastal Taiwan to examine how salinity influences the abundance,diversity, and structure of biotic communities. We surveyed eight permanentstudy sites, spanning freshwater marshes, to the gate on the dyke, andmesohaline mangroves representing a gradient of the extent of saltwaterincursions. Analyses of abiotic variables showed that salinity was the primarydetermining factor for discriminating habitat types in the wetlands, butcommunities differed in their sensitivity to salinity. The composition of plantand insect communities was most affected by the salinity gradient, suggestingthe utility of these communities for ecological monitoring of saltwaterincursions. However, spatial changes in communities at higher trophic levels,including macrobenthos, mollusks, fish, and birds, could not be explained simplyby the salinity gradient. Instead, changes in these communities were morerelevant to the composition of other biotic communities. Our results show thatspecies richness and diversity of plant communities were higher in the marshesthan in the mangroves. Nevertheless, insect communities censused in themangroves had higher diversity, despite lower abundance and species richness.Macrobenthos surveyed in the mangroves showed higher biomass and number of taxa.Mollusks and fish were also more abundant at sites near the gate compared to themarsh sites. This suggests that maintaining a tidal flux by means of gateregulation is necessary for conserving the spatial heterogeneity andbiodiversity of coastal wetlands.

Effects of an oil spill on benthic community production and respiration on subtropical intertidal sandflats

This study determined effects of an oil spill on subtropical benthic community production and respiration by monitoring CO2 fluxes in benthic chambers on intertidal sandflats during emersion before and after an accidental spill. The oil spill decreased sediment chlorophyll a concentrations, altered benthic macrofaunal community, and affected ecological functioning by suppressing or even stopping microalgal production, increasing bacterial respiration, and causing a shift from an autotrophic system to a heterotrophic system. Effects of the oil spill on the macrofauna were more severe than on benthic microalgae, and affected sedentary infauna more than motile epifauna. Despite the oil spills impact on the benthic community and carbon metabolism, the affected area appeared to return to normal in about 23 days. Our results suggest that the prompt response of benthic metabolism to exposure to petroleum hydrocarbons can serve as a useful indicator of the impact of an oil spill.

Carbon budgets of multispecies seagrass beds at Dongsha Island in the South China Sea

Biomass, production, consumption, and detrital export and decomposition of four dominant seagrass species were determined in tropical multispecies beds as a means of constructing carbon budgets. These processes varied among seagrass species. The living biomass held a high carbon stock. The leaf production of multispecies beds was also higher than that of monospecific beds. However, the sediment organic carbon stock was much lower than the global median stock, which was likely due to decomposition of most of the detritus and export to nearshore waters. Reliable measurements of decomposition and export are particularly needed to estimate the organic carbon storage rate.

Seagrasses of Tongsha Island, with descriptions of four new records to Taiwan

The composition, abundance, and distribution of seagrasses on Tongsha island were studied from 21 to 29 April 2004. A total of seven seagrass species from six genera and two families were identified. Among them, four species were new to Taiwan, including Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., Cymodocea serrulata (R. Br.) Aschers. and Magnus, Syringodium isoetifolium (Aschers.) Dandy, and Thalassodendron ciliatum (Forsk.) den Hartog. The species number of seagrasses was 14% of the total global number. The total coverage area of the seagrass beds was estimated to be 8.2 km^2 distributed around Tongsha island and the lagoon. Mean percentage cover and shoot density were high, ranging from 20 to 95% and ＜1250 to ＞2500 shoots m^(-2), respectively. The large area of the seagrass bed, the high shoot density and coverage of seagrasses, and the diverse species of Tongsha island indicate that the seagrass resource on Tungsha island is very abundant. These seagrass beds must be conserved to ensure the sustainable management of Tongsha Island.