Abstract
Reports on the abundances and on metal concentrations in intertidal estuarine invertebrates from the Eastern Tropical Pacific are rare. Thus, the objectives of this report are to make accessible data on the abundances (1984-1987, 49 dates; 2013, 12 dates) of sipunculans, brachiopods and hemichordates from a sand-mud flat; and on trace metals (1996, 2000) and abundances (2015, 3 dates) of sipunculans and brachiopods at a sand flat in the Gulf of Nicoya estuary (10o N-85o W). Cores (17.7 cm2) were collected at the sand-mud flat, and quadrats (0.2 m2) at the sand flat. The flats contrasted in their sand (65 % vs 90 %) and silt+clay (31.5 % vs 5.6 %) contents. At the sand-mud flat (1984-87: 1.83 m2) the sipunculans were represented by 13 individuals, the brachiopods by 129 and the acorn worms by 185, with estimated maximum densities of: 5.7, 29, and 40 ind./m2, respectively. Trace metal (Fe, Mn, Ni, Cr, Cd, Zn, and Pb) analysis (Atomic Absorption Spectrometry) were conducted in specimens of Sipunculus nudus (Sipuncula) and Glottidia audebarti (Brachiopoda). Maximum mean concentrations in S. nudus were: For non-depurated worms, Fe (16.0 mg/g dw) > Mn (165 μg/g dw) > Zn (81 μg/g dw) > Cu (26 μg/g dw) > Cr (11 μg/g dw) > Ni (10.4 μg/g dw) > Pb (9.3 μg/g dw) > Cd (1.2 μg/g dw). For 72 hour depurated worms: Fe (5.0 mg/g dw) > Mn (61 μg/g dw) > Zn (39 μg/g dw) > Cu (24 μg/g dw) > Ni (8.4 μg/g dw) > Pb (2.7 μg/g dw) > Cd (0.62 μg/g dw). For G. audebarti: Fe (1.6 mg/g dw-soft parts) > Zn (123.5 μg/g dw-soft parts) > Cu (31.4 μg/g dw-pedicles) > Pb (21.0 μg/g dw-shells) > Cd (5.2 μg/g dw-soft parts) > Cr (4.7 μg/g dw-shells). For sediments; Fe (46 mg/g dw) > Mn (41.3 μg/g dw) > Zn (63 μg/g dw) > Cu (36.2 μg/g dw) > Cr (31.5 μg/g dw) > Pb (21.1 μg/g dw) > Ni (16.1 μg/g dw) > Cd (1.1 μg/g dw). These concentrations were expected for a nonindustrialized estuary. At the sand flat (Area sampled: 10.6 m2 ) 76 individuals of G. audebarti, 112 of G. albida, and 366 of S. nudus were collected in 2015, with estimated maximum densities of: 7.1, 10.5, and 31 ind./m2, respectively. Densities of G. audebarti and G. albida were relatively low, while those of S. nudus were relatively high when compared with other reports. The shell lenght of G. audebarti ranged from 9.0 mm to 38.0 mm and from 6.0 mm to 29.0 mm for G. albida. These ranges were within those found for these lingulides elsewhere. The mean length of S. nudus was 41 mm and the maximum weight was 1.6 g, which are small. No brachiopods were found at the sand-mud flat in 2013, nor enteropneusts at the sand flat in 2015. G. audebarti had a relatively stable presence, while G. albida almost vanished from the samples at the end of 2015. The spatial distributions of the three invertebrates were found aggregated at both intertidal flats. Strong ENSO warming events during 1983 and 2015, and red tides in 1985 may have influenced the abundances.
Highlights
From 1979 to 1983 benthic surveys were performed in the Gulf of Nicoya estuary, Pacific coast of Costa Rica, to evaluate its biodiversity and conservation status (Vargas 1995, 2016)
Recent reviews of the species of brachiopods and sipunculans reported from Costa Rica were conducted by Emig (2009) and Vargas and Dean (2009), respectively
The presence of imposex in Acanthais brevidentata snails from the Gulf was informed by Gravel, Johanning, McLachlan, Vargas, and Oberdörster (2006) and concentrations of PCBs in S. nudus and other sipunculans were reported by Spongberg (2006)
Summary
From 1979 to 1983 benthic surveys were performed in the Gulf of Nicoya estuary, Pacific coast of Costa Rica, to evaluate its biodiversity and conservation status (Vargas 1995, 2016). These surveys were followed by a three-year study (1984-1987) of the community of macro-invertebrates from the Punta Morales intertidal sand-mud flat in the upper estuary (Vargas, 1987, 1988, 1989, 1996). At the nearby Cocorocas sand flat, a preliminary evaluation of the presence of metals in S. nudus and G. audebarti was presented by Vargas and Abdullah (1997) and the final results are included . Vargas, Acuña-González, Gómez and Molina (2015) summarized data on trace metals from snails and clams collected at the four coastal sites, including the razor clam Tagelus affinis from the Cocorocas sand flat
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