Abstract Coastal ecosystems in Alaska are undergoing rapid change due to warming and glacier recession. We used a natural gradient of glacierized to non-glacierized watersheds (0–60% glacier coverage) in two regions along the Gulf of Alaska—Kachemak Bay and Lynn Canal—to evaluate relationships between local environmental conditions and estuarine fish communities. Multivariate analyses of fish community data collected from five sites per region in 2019 showed that region accounted for the most variation in community composition, suggesting that local effects of watershed type were masked by regional-scale variables. Seasonal shifts in community composition were driven largely by the influx of juvenile Pacific salmon ( Oncorhynchus spp.) in late spring. Spatiotemporal differences among fish communities were partly explained by salinity and temperature, which accounted for 19.5% of the variation in community composition. We used a multi-year dataset from Lynn Canal (2014–2019) to examine patterns of mean length for two dominant species. Generalized additive mixed models indicated that Pacific staghorn sculpin ( Leptocottus armatus ) mean length varied along site-specific seasonal gradients, increasing gradually through the summer in the least glacially influenced sites and increasing rapidly to an asymptote of ~ 150 mm in the most glacially influenced sites. Starry flounder ( Platichthys stellatus ) mean length was more strongly related to environmental conditions, increasing with temperature and turbidity. Together, our findings suggest that community compositions of estuarine fishes show greater variation at the regional scale than the watershed scale, but species-specific variation in size distributions may indicate differences in habitat quality across watershed types within regions.
more »
« less
Seasonal and interannual variation in high-latitude estuarine fish community structure along a glacial to non-glacial watershed gradient in Southeast Alaska
Along the Gulf ofAlaska, rapid glacier retreat has driven changes in transport of freshwater, sediments, and nutrients to estuary habitats. Over the coming decades, deglaciation will lead to a temporary increase, followed by a long-term decline of glacial influence on estuaries. Therefore, quantifying the current variability in estuarine fish community structure in regions predicted to be most affected by glacier loss is necessary to anticipate future impacts. We analyzed fish community data collected monthly (April through September) over 7 years (2013–2019) from glacially influenced estuaries along the southeastern Gulf of Alaska. River delta sites within estuaries were sampled along a natural gradient of glacial to non-glacial watersheds to characterize variation in fish communities exposed to varying degrees of glacial influence. Differences in seasonal patterns of taxa richness and abundance between the most and least glacially influenced sites suggest that hydrological drivers influence the structure of delta fish communities. The most glacially influenced sites had lower richness but higher abundance overall compared to those with least glacial influence; however, differences among sites were small compared to differences across months. Two dominant species—Pacific staghorn sculpin and starry flounder—contributed most to spatial and temporal variation in community composition; however, given only small interannual differences in richness and abundance over the period of the study, we conclude that year-to-year variation at these sites is relatively low at present. Our study provides an important benchmark against which to compare shifts in fish communities as watersheds and downstream estuaries continue to transform in the coming decades.
more » « less- Award ID(s):
- 1757348
- NSF-PAR ID:
- 10365660
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Environmental Biology of Fishes
- Volume:
- 105
- Issue:
- 3
- ISSN:
- 0378-1909
- Page Range / eLocation ID:
- p. 431-452
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The Pacific blue mussel (Mytilus trossulus) is a foundation species in high-latitude intertidal and estuarine systems that creates complex habitats, provides sediment stability, is food for top predators, and links the water column and the benthos. M. trossulus also makes an ideal model species to assess biological responses to environmental variability; specifically, its size frequency distributions can be influenced by the environment in which it lives. Mussels that inhabit estuaries in high latitudes receive freshwater runoff from snow and glacial-fed rivers or can be under oceanic influence. These hydrographic conditions work together with local static environmental characteristics, such as substrate type, fetch, beach slope, distance to freshwater, and glacial discharge to influence mussel demographics. In 2019 and 2020, mussels were collected from two Gulf of Alaska ecoregions to determine whether mussel size frequencies change over spatial (local and ecoregional) and hydrographic scales and whether any static environmental characteristics correlate with this variability. This study demonstrated that mussel size frequencies were most comparable at sites with similar hydrographic conditions, according to the ecoregion and year they were collected. Hydrographic conditions explained approximately 43% of the variation in mussel size frequencies for both years, for the combined ecoregions. Mussel recruits (0–2 mm) were more abundant at sites with higher fetch, while large mussels (> 20 mm) were more abundant at more protected sites. Fetch and freshwater influence explained most of the variation in mussel size frequencies for both years and across both ecoregions, while substrate and slope were also important in 2019 and glacial influence in 2020. This study suggests that hydrographic and static environmental conditions may play an important role in structuring mussel sizes. Although differences in mussel size frequencies were found depending on environmental conditions, mussel sizes showed little difference across differing types of freshwater influence, and so they may be resilient to changes associated with melting glaciers.more » « less
-
more » « less
Abstract Aim Anthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change.
Location North Atlantic and Gulf of Mexico.
Taxa Fish.
Method We compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models.
Results Species richness, abundance and turnover have increased in North Atlantic and Gulf of Mexico estuaries in the last 30 years. These changes were mediated largely by sea‐surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced.
Main Conclusion The increasing trajectory of turnover in many estuaries suggests that fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability, and human resource use remain a pertinent task.
-
more » « less
Abstract A widely examined predictive model of invertebrate community dynamics in glacial‐melt streams describes longitudinal changes in community structure with changing water temperature and channel stability with increasing distance from glaciers. Previous studies conducted in Europe, Greenland, New Zealand, and South America have supported the predictions of the invertebrate model and contributed to its refinement. However, none has evaluated if the model fits invertebrate community dynamics over a full range of distances from the glacier and water temperature conditions within glacial‐melt streams in southeast Tibet.
We sampled invertebrates and measured water temperature, specific conductivity, turbidity, and associated glacier‐related variables within 14 sites in three subalpine glacial‐melt catchments in southeastern Tibet's Three Parallel Rivers region during 2010, 2011, 2013, and 2015. Our sites encompassed a temperature gradient from the upstream metakryal sites (maximum summer water temperature <2°C) to the furthest downstream site (maximum summer temperature >10°C) near the Mekong River.
We evaluated the relationships of invertebrate community structure with in situ water temperature and channel stability which are the focal habitat variables in the invertebrate model. The additional habitat variables of distance from the glacier, glacier size, conductivity, and turbidity were evaluated to see if these were more important determinants of community structure than in situ water temperature and channel stability.
Minimum and in situ water temperatures were positively correlated with distance from the glacier but Pfankuch Channel Stability Index bottom scores were not. Thus, the physical template within our study area differed from the expected template of the invertebrate model.
Similar to the invertebrate model, in situ water temperature by itself or combined with Pfankuch index best explained five invertebrate response variables. In contrast with the invertebrate model, conductivity and turbidity best explained invertebrate taxa richness, density, and the site scores of the first and second detrended correspondence analysis axes of relative abundance.
The invertebrate model predicts that only Diamesinae will occur in metakryal sites. However, in our metakryal sites we frequently captured 13 taxa (two Nemouridae morphotypes, Diamesinae, Orthocladiinae,
Rhyacophila ,Epeorus , Taeniopterygidae,Baetis ,Capnia , Simuliidae, Limnephilidae,Himalopsyche , and Collembola).Invertebrate‐habitat relationships and taxa occurrence trends in glacial‐melt catchments in southeast Tibet differed from the invertebrate model predictions. Our findings highlight the need to develop a regional version of the invertebrate model applicable to Asian glacial‐melt streams with unstable stream channels throughout their catchments and that do not freeze in the winter.
-
more » « less
Abstract Glaciers and ice sheets cover over 10 % of Earth's land surface area and store a globally significant amount of dissolved organic matter (DOM), which is highly bioavailable when exported to proglacial environments. Recent rapid glacier mass loss is hypothesized to have increased fluxes of DOM from these environments, yet the molecular composition of glacially derived DOM has only been studied for a handful of glaciers. We determine DOM composition using ultrahigh resolution mass spectrometry from a diverse suite of Arctic glacial environments, including time series sampling from an ice sheet catchment in Greenland (Russell Glacier) and outflow from valley glaciers in catchments with varying degrees of glacial cover in Svalbard. Samples from the Greenland outflow time series exhibited a higher degree of similarity than glacier outflow between glaciers in Svalbard; however, supraglacial meltwater samples from Greenland and Svalbard were more similar to each other than corresponding glacial outflow. Outflow from Russell Glacier was enriched in polyphenolic formulae, potentially reflecting upstream inputs from plants and soils, or inputs from paleosols overridden by the ice sheet, whereas Svalbard rivers exhibited a high level of molecular richness and dissimilarity between sites. When comparing DOM compositional analyses from other aquatic systems, aliphatic, and peptide‐like formulae appear particularly abundant in supraglacial meltwater, suggesting the DOM quickly metabolized in previous incubations of glacial water originates from energy‐rich supraglacial sources. Therefore, as glaciers lose mass across the region, higher‐quality fuel for microbial degradation will increase heterotrophy in coastal systems with ramifications for carbon cycling.
