ABSTRACT
Mesozooplankton was sampled seasonally in a large microtidal estuary (Peel-Harvey) suffering from massive macroalgal growths and cyanobacterial blooms. Comparisons with other estuaries indicate that eutrophication led to copepod abundance declining and macroalgal-associated species increasing. Mesozooplankton species are almost exclusively autochthonous, i.e. spend entire life cycle within the estuary. Meroplanktonic species are virtually absent because main benthic macroinvertebrate species undergo direct benthic rather than planktotrophic development. There are also few abundant holoplanktonic species. Most species are tychoplanktonic, i.e. benthic and transported into plankton through physical disturbance of sediment. Species number, concentration and Simpson's Index are greater during night than day. Annual cyclical changes in species composition are related closely to changes in salinity. At the most degraded site, nematode concentrations were high and the species number and concentration changed markedly during extreme eutrophication, when oxygen concentrations were low, disrupting annual cyclical changes in species composition.
Subject(s)
Copepoda/physiology , Estuaries , Eutrophication , Zooplankton/physiology , Animals , Australia , Cyanobacteria/physiology , Environmental Monitoring , Population Density , Salinity , SeasonsABSTRACT
Abstract:Coral reef zooplankton represents a key community in coral ecosystems, as they are involved in trophic and biogeochemical dynamics, and recruitment processes. Zooplankton abundance, composition and biomass were surveyed at six stations within the coral reef at Cahuita National Park, Limon, Costa Rica, in order to compare with the only previous study conducted during 1984. Samples were collected monthly (September 2010-August 2011). Seston biomass (0.49-85.87 mg/m3) and total abundance (1 145-112 422 ind./ m3) fluctuated among the months and the stations. Higher values of these two variables were found in the rainiest months (November 2010 and May 2011). A total of 38 taxa were identified, of which calanoid copepods abundance dominated year round (66 %), followed by appendicularians (12 %). Zooplankton mean abundance in this survey resulted 20 times higher (13 184 ± 4 104 ind./m3) than in 1984 (645 ± 84 ind./m3). Copepods and appendicularians were the groups that differed the most, relative to the 1984 study, resulting in 63 and 170 times more abundant overall, respectively. An increase in terrestrial runoff and nutrient input during the past 30 years could explain these differences. High abundances of zooplankton may constitute an important food source for coral reef organisms in Cahuita ecosystem. In addition, zooplankton abundances here reported for Cahuita are among the worldwide highest coral reef zooplankton abundances, and further trophic models can help elucidate its role in coral reef resilience in the Caribbean Coast of Central America.
ResumenEl grupo de zooplancton representa una comunidad clave en los arrecifes de coral. Está involucrado en dinámicas tróficas y biogeoquímicas, y en procesos de reclutamiento. La abundancia, composición y biomasa del zooplancton fueron estudiadas en seis estaciones dentro del arrecife coralino del Parque Nacional Cahuita, para compararlas con el único estudio realizado durante 1984. Las muestras se recolectaron mensualmente (Septiembre 2010-Agosto 2011). La biomasa del seston (0.49-85.87 mg/m3) y la abundancia total (1 145-112 422 ind./m3) fluctuaron entre meses y estaciones. Los valores más altos se encontraron durante los meses más lluviosos (Noviembre 2010 y Mayo 2011). Treinta y ocho taxones fueron identificados, copépodos calanoidos (66 %) y apendicularias (12 %) dominaron la abundancia durante todo el año. La abundancia promedio en este estudio fue 20 veces más alta (13 184 ± 4 104 ind./m3) que en 1984 (645 ± 84 ind./m3). Copépodos y apendicularias fueron los grupos con mayor discrepancia con respecto al estudio de 1984. Un aumento en la descarga de nutrientes de origen terrestre, podría explicar estas grandes diferencias. Abundancias tan altas de zooplancton podrían constituir una importante fuente de alimento para los organismos del arrecife en Cahuita. Las abundancias aquí reportadas colocan al arrecife de Cahuita entre los arrecifes de coral con mayor abundancia de zooplancton en el mundo y estudios futuros en redes tróficas podrían elucidar el papel de esta comunidad en procesos de resiliencia en los arrecifes del Caribe centroamericano.
Subject(s)
Animals , Zooplankton/physiology , Biomass , Coral Reefs , Larva/physiology , Seasons , Weather , Population Dynamics , Analysis of Variance , Population Density , Caribbean Region , Statistics, Nonparametric , Costa Rica , Crustacea/physiology , Mollusca/physiologyABSTRACT
Zooplanktonic taxa have a greater number of distinct populations and species than might be predicted based on their large population sizes and open-ocean habitat, which lacks obvious physical barriers to dispersal and gene flow. To gain insight into the evolutionary mechanisms driving genetic diversification in zooplankton, we developed eight microsatellite markers to examine the population structure of an abundant, globally distributed mesopelagic copepod, Haloptilus longicornis, at 18 sample sites across the Atlantic and Pacific Oceans (n = 761). When comparing our microsatellite results with those of a prior study that used a mtDNA marker (mtCOII, n = 1059, 43 sample sites), we unexpectedly found evidence for the presence of a cryptic species pair. These species were globally distributed and apparently sympatric, and were separated by relatively weak genetic divergence (reciprocally monophyletic mtCOII lineages 1.6% divergent; microsatellite FST ranging from 0.28 to 0.88 across loci, P < 0.00001). Using both mtDNA and microsatellite data for the most common of the two species (n = 669 for microsatellites, n = 572 for mtDNA), we also found evidence for allopatric barriers to gene flow within species, with distinct populations separated by continental landmasses and equatorial waters in both the Atlantic and Pacific Ocean basins. Our study shows that oceanic barriers to gene flow can act as a mechanism promoting allopatric diversification in holoplanktonic taxa, despite the high potential dispersal abilities and pelagic habitat for these species.
