Krista Kamer

Macroalgal bloom dynamics in a highly eutrophic southern California estuary

A 16-mo long monitoring study was carried out in Upper Newport Bay estuary (UNB), Orange County, California, to quantify the macroalgal community of a southern California estuary. Quarterly sampling began December 1996 at 8 stations along the main channel and tidal creeks ranging from the head to the lower end of UNB. At each station, two strata (one at high and one at low elevation) were surveyed. Macroalgal species abundance (% cover and biomass) and algal tissue nitrogen (N) and phosphorus (P) were measured. The algal community changed from sparse macroalgal cover during winter 1996 to larger patches dominated byEnteromorpha intestinalis in spring 1997. The community was characterized by a thick cover of macroalgae comprised ofE. intestinalis andUlva expansa in summer 1997 andU. expansa andCeramium spp. in fall 1997. UNB returned to sparse macroalgal cover by spring 1998. In summer and fall 1997, biomass ofE. intestinalis andCeramium reached over 1,000 g wet wt m−2 each, andU. expansa biomass exceeded 700 g wet wt m−2. Tissue N was high inE. intestinalis andU. expansa collected from UNB (≈3% dry wt) and higher inCeramium (≈3.5% dry wt). Tissue P in all three algae ranged from 0.24–0.28% dry wt. Tissue N∶P (molar) ratios inE. intestinalis andU. expansa ranged from 16.4 to 30.0 and inCeramium from 21.8 to 40.1. A field experiment was conducted in whichE. intestinalis was used as a bioassay of N and P availability. Algal tissue was cultured under known conditions and samples were deployed throughout the estuary and left for 24 h. Tissue N of algae from these bags showed a nominal increase in N with proximity to the primary nutrient input to the system, San Diego Creek (p=0.0251; r2=0.200). Our data indicate that UNB is already a highly eutrophic estuary, but macroalgal blooms in UNB may increase if more N is added to the system.

A fluctuating salinity regime mitigates the negative effects of reduced salinity on the estuarine macroalga, Enteromorpha intestinalis (L.) link

We tested the response of Enteromorpha intestinalis to fluctuating reduced salinity regimes which may occur in coastal estuaries due to both natural and anthropogenic influences. In a fully crossed two factor experiment, we subjected E. intestinalis to 0, 5, 15 and 25 psu water enriched with nutrients for 1-, 5-, 11- and 23-day periods. Each period was followed by 24 h of exposure to 25 psu (ambient) water that was not nutrient enriched. Following 24 h in ambient salinity water, algae were returned to reduced salinity conditions for the appropriate period and the cycle continued over the 24 days for which all treatments were maintained. Exposure to 0 psu for 5 days or longer resulted in loss of pigmentation, decreased wet and dry biomass, increased wet wt:dry wt ratios, decreased removal of nitrogen (N) and phosphorus (P) from the water column and an accumulation of NH(4) in the water column. More frequent exposure to ambient salinity in the 1-day treatment mitigated these effects. Across all salinity levels tested, biomass increased as frequency of exposure to ambient salinity increased. At all durations of exposure to low salinity tested, biomass increased as salinity level increased. We conclude that growth of E. intestinalis is decreased by reduced salinity. E. intestinalis is able to withstand exposure to 0 psu but there is a temporal limit to this tolerance that is somewhere between 1 and 5 days. Populations of E. intestinalis in coastal estuaries may suffer from freshwater inputs if salinity conditions are persistently reduced.

The relative importance of sediment and water column supplies of nutrients to the growth and tissue nutrient content of the green macroalga Enteromorpha intestinalis along an estuarine resource gradient

Large blooms of opportunistic green macroalgae such as Enteromorpha intestinalis are of ecological concern in estuaries worldwide. Macroalgae derive their nutrients from the water column but estuarine sediments may also be an important nutrient source. We hypothesized that the importance of these nutrient sources to E. intestinalis varies along a nutrient-resource gradient within an estuary. We tested this in experimental units constructed with water and sediments collected from 3 sites in Upper Newport Bay estuary, California, US, that varied greatly in water column nutrient concentrations. For each site there were three treatments: sediments + water; sediments + water + Enteromorpha intestinalis (algae); inert sand + water + algae. Water in units was exchanged weekly simulating low turnover characteristic of poorly flushed estuaries. The importance of the water column versus sediments as a source of nutrients to E. intestinalis varied with the magnitude of the different sources. When initial water column levels of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were low, estuarine sediments increased E. intestinalis growth and tissue nutrient content. In experimental units from sites where initial water column DIN was high, there was no effect of estuarine sediments on E. intestinalis growth or tissue N content. Salinity, however, was low in these units and may have inhibited growth. E. intestinalis growth and tissue P content were highest in units from the site with highest initial sediment nutrient content. Water column DIN was depleted each week of the experiment. Thus, the water column was a primary source of nutrients to the algae when water column nutrient supply was high, and the sediments supplemented nutrient supply to the algae when water column nutrient sources were low. Depletion of water column DIN in sediment + water units indicated that the sediments may have acted as a nutrient sink in the absence of macroalgae. Our data provide direct experimental evidence that macroalgae utilize and ecologically benefit from nutrients stored in estuarine sediments.

Spatial and temporal patterns in sediment and water column nutrients in a eutrophic Southern California estuary

Quarterly field sampling was conducted to characterize variations in water column and sediment nutrients in a eutrophic southern California estuary with a history of frequent macroalgal blooms. Water column and sediment nutrient measures demonstrated that Upper Newport Bay (UNB) is a highly enriched estuary. High nitrate (NO3−) loads from the river entered the estuary at all sampling times with a rainy season (winter) maximum estimated at 2,419 mol h−1. This resulted in water NO3− concentration in the estuary near the river mouth at least one order of magnitude above all other sampling locations during every seasons; maximum mean water NO3− concentration was 800 μM during springer 1997. Phosphorus (P)-loading was high year round (5.7–90.4 mol h−1) with no seasonal pattern. Sediment nitrogen (N)-content showed a seasonal pattern with a spring maximum declining through fall. sediment and water nutrients, as well as percent cover of three dominant macroalgae, varied between the main channel and tidal creeks. During all seasons, water column NO3− concentrations were higher in the main channel than in tidal creeks while tidal creeks had higher levels of sediment total Kjeldhal nitrogen (TKN) and P. During each of the four sampling periods, percent cover ofEntermorpha intestinalis andCeramium spp. was higher in tidal creeks than in the main channel, while percent cover ofUlva expansa was always higher in the main channel. Decreases in sediment N in both creek and channel habitats were concurrent with increases in macroalgal cover, possibly reflecting use of stored sediment TKN by macroalgae. Our data suggest a shift in primary nutrient sources for macroalgae in UNB from riverine input during winter and spring to recycling from sediments duirng summer and fall.

Rapid nitrate uptake rates and large short-term storage capacities may explain why opportunistic green macroalgae dominate shallow eutrophic estuaries.

We quantified the effects of initial macroalgal tissue nitrogen (N) status (depleted and enriched) and varying pulses of nitrate (NO3−) concentration on uptake and storage of nitrogen in Ulva intestinalis L. and Ulva expansa (Setch.) Setch. et N. L. Gardner using mesocosms modeling shallow coastal estuaries in Mediterranean climates. Uptake of NO3− (μmol · g dry weight [dwt]−1 · h−1) was measured as loss from the water after 1, 2, 4, 8, 12, and 24 h and storage as total tissue nitrogen (% dwt) and nitrate (ppm). Both species of algae exhibited a high affinity for NO3− across all N pulses and initial tissue contents. There was greater NO3− removal from the water for depleted than enriched algae across all time intervals. In the low‐N‐pulse treatment, U. intestinalis and U. expansa removed all measurable NO3− within 8 and 12 h, respectively, and in the medium and high treatments, removal was high and then decreased over time. Maximum mean uptake rates of nitrate were greater for U. expansa (∼300 μmol · g dwt−1 · h−1) than U. intestinalis (∼100 μmol · g dwt−1 · h−1); however, uptake rates were highly variable over time. Overall, U. expansa uptake rates were double those of U. intestinalis. Maximum tissue NO3− for U. expansa was >1,000 ppm, five times that of U. intestinalis, suggesting that U. expansa has a greater storage capacity in this cellular pool. These results showed that opportunistic green algae with differing tissue nutrient histories were able to efficiently remove nitrate from the water across a wide range of N pulses; thus, both are highly adapted to proliferate in estuarine environments with pulsed nutrient supplies.

Application of Color Infrared Aerial Photography to Assess Macroalgal Distribution in an Eutrophic Estuary, Upper Newport Bay, California

Newport Bay is a large estuary in southern California that is subject to anthropogenic nutrient loading, eutrophication, and hypoxia. Ground-based methods of assessing algal extent for monitoring and management are limited in that they cannot provide a synoptic view of algal distribution over comparatively large areas. The goal of this study was to explore the application of color infrared aerial photography as an alternative for analyzing the changes in the abundance of exposed macroalgae. Three surveys combining remote sensing (color infrared aerial photography) and ground-based sampling to quantify macroalgal mat coverage were carried out in Upper Newport Bay (UNB) between July and October 2005. Airborne photographs (scale 1:6000) collected during daytime low tides, clear skies, and appropriate sun angle were digitized to 25-cm resolution, orthorectified, georegistered, and combined into three mosaic composite digital images: one for each survey. During each aerial photography survey, macroalgal percent cover was measured on the ground by the pointintercept method in a 6.25-m2 area at ca. 30 locations distributed along the water’s edge throughout the intertidal mudflat area. There were three main types of cover:Ulva spp. (green algae),Ceranrium spp. (red algae), and bare surface (mud and mussel beds). To analyze similarities between spectral signatures in the images and cover types, the pixels corresponding to the ground samples from each survey were grouped into clusters based on similarity of their spectral signatures. To establish relationships between spectral signatures in the images and cover as determined from ground data, pixels in each composite image corresponding to ground samples from the same day that were characterized by > 90% of one cover type were attributed to that cover type. Ground samples comprised of a mixture of cover types were used for accuracy assessment. Before classification, each digital image was transformed by the Minimum Noise Fraction Rotation method to remove noise and enhance contrast between the classes. For classification of each composite image, the Spectral Angle Mapper scheme was used: all pixels in each image were attributed to the identified classes and the areal extent of each class was estimated. According to these assessments, the macroalgal coverage in UNB increased from 37% in July to 57% in September to 80% in October, and during this timeUlva spp. replacedCeramium spp. as the dominant alga. This analysis showed that color infrared aerial photography is an effective tool for assessing estuarine, intertidal macroalgal coverage.

Nutrient Limitation of the Macroalga Enteromorpha intestinalis Collected along a Resource Gradient in a Highly Eutrophic Estuary

We conducted a laboratory experiment to quantify nutrient (nitrogen and phosphorus) limitation of macroalgae collected along a gradient in water column nutrient availability in Upper Newport Bay estuary, a relatively nutrient-rich system in southern California, United States. We collectedEnteromorpha intestinalis and water for use in the experiment from five sites ranging from the lower end of the estuary to the head. Initial algal tissue N and P concentrations and molar N∶P ratios—as well as water column NO3 and total Kjeldahl nitrogen (TKN)—increased along a spatial gradient from the lower end toward the head. Water column soluble reactive phosphorus (SRP) varied among sites as well but did not follow a pattem of increasing from the seaward end toward the head. Algae from each site were assigned to one of four experimental treatments: control (C), nitrogen enrichment (+N), phosphorus enrichment (+P), and nitrogen and phosphorus enrichment (+N+P). Each week for 3 wk we replaced the water in each unit with the appropriate treatment water to mimic a poorly flushed estuary. After 3 wk, the degree of nutrient limitation ofE. intestinalis varied spatially with distance from the head of the estuary. Growth ofE. intestinalis collected from several sites increased with N enrichment alone and increased further when P was added in combination with N This indicated that N was limiting and that when N was sufficient, P became limiting. Sites from whichE. intestinalis exhibited nutrient limitation spanned the range of background water column NO3 (12.9±0.4 to 55.2±2.1 μM) and SRP (0.8±0.0 to 2.9±0.2 μM) concentrations. Algae that were N limited had initial tissue N levels ranging from 1.18±0.03 to 2.81±0.08% dry weight and molar N∶P ratios ranging from 16.75±0.39 to 26.40±1.98.