River restoration responses

The Lippe River in Germany has been subjected to many decades of channelization, deepening, floodplain drainage, straightening and consequent shortening, with one result being that the modern Lippe is 20% shorter than it was two centuries ago. Beginning in 1996, conservation managers began reversing this trend by widening the river, raising the level of the river bed, constructing small islands within the river and terminating floodplain drainage operations over a stretch of 3.3 km. As a result of these activities, a small portion of the river looks much like it did 200 years ago.

rivrestfig1

A section of the Lippe River before (left) and after (right) restoration.

Over a 21-year period, researchers from Arbeitsgemeinschaft Biologischer Umweltschutz have conducted systematic surveys of fish communities at the restored and unrestored sections of the river. Researchers sampled the fish community with electrofishing – inputting a direct electrical current into the river – which causes the fish to swim towards the boat where they are easily collected with nets, identified by species, and returned unharmed into the river. A data set over this length of time in association with a restoration project is very unusual; oftentimes (in part due to funding issues) only one survey is conducted to assess the fish community response to river restoration.

About eight years ago, while a postdoctoral researcher at Senckenberg Research Institute in Frankfurt, Germany, Stephan Stoll was asked to analyze some river restoration outcomes, and, as he describes, “became hooked to the topic.” To evaluate the response of the Lippe River fish community to restoration, a group of researchers headed by Stephanie Höckendorff, a Master’s student with Stoll, first asked a very simple question – how did fish abundance and species richness (the number of fish species) compare in the restored and unrestored regions of the river.

The graph below shows several striking trends. Abundance peaked about 2-3 years after restoration, declined sharply the next year, and recovered in subsequent years to about three times the abundance found in unrestored sections. Importantly, abundance varied extensively year-to-year. For example, if you had done only one survey in 2000, you would have erroneously concluded that restoration had no effect, which is why the researchers emphasize the importance of collecting data over a long stretch of time.

rivrest2a

Abundance of fish in restored (Rest-gray curve) and unrestored (Cont-black curve) sections of the Lippe River.  The gray vertical bar indicates the start of the restoration project in 1997.

Species richness increased sharply, but did not reach its peak until nine years after restoration. Again, there was extensive year-to-year variation in species richness.

rivrest2b

Fish species richness in restored (Rest-gray curve) and unrestored (Cont-black curve) sections of the Lippe River.  The gray vertical bar indicates the start of the restoration project in 1997.

Höckendorff and her colleagues were intrigued by this delay in species richness, and turned their attention to understanding what types of species benefited most from the restoration. Their analyses indicated that colonizing species, such as common minnows and three-spined sticklebacks, tended to have short life spans, early female maturity, several spawning events per year and a fusiform body shape – a body that is roughly cylindrical and tapers at both ends. Interestingly, some of the most successful colonizers took quite a long time to get well-established within the community.

Minnow

Common minnows, Phoxinus phoxinus. Credit: Carlo Morelli (Etrusko25)

Stickleback

The three-spined stickleback, Gasterosteus aculeatus. Credit: Ron Offermans

The restored habitat was highly dynamic, experiencing periodic flooding and the formation of temporary shallow bays and shifting sandbanks. These types of habitats tend to select for minnows, sticklebacks and other opportunistic species that are attracted to periodic disturbances. These opportunistic species were quick to move in, and continued to increase in abundance over time. Importantly, several rare and endangered species also colonized the restored habitat. However, large, deep-bodied, slow maturing and long-lived species did not benefit (at least over the 17 years of the survey), as these types of species are generally favored in less dynamic habitats, which are more stable and uniform.

Overall, these findings demonstrate the benefits of river restoration to the fish communities they harbor. But some species are more likely to benefit than others, and the time-scale over which recolonization occurs is highly variable. Surveys must be repeated over a long time-scale to tell conservation managers whether their restoration efforts are successful, and how they might change their future river restoration efforts.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Höckendorff, S., Tonkin, J. D., Haase, P., Bunzel-Drüke, M., Zimball, O., Scharf, M. and Stoll, S. (2017), Characterizing fish responses to a river restoration over 21 years based on species’ traits. Conservation Biology, 31: 1098–1108. doi:10.1111/cobi.12908. Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

Sushi in Disguise

As an ecology researcher, I’ve always been attracted to systems where you might be able or inclined to eat your organism after you completed your experiment or observations. Alas, I spent my research career studying spiders, dragonflies and zebrafish, all of which are high on nutrients but low on succulence. Thus I read with considerable gastronomic anticipation an article by Demian Willette and his colleagues that studied nine different species of fish served up at local sushi restaurants in Los Angeles, California.

Sushi

Mackerel, salmon and tuna (front to back) served at a Los Angeles sushi restaurant. Credit Demian Willette.

One of the co-authors, Sara Simmonds, had a great idea when she was a teaching assistant for the Introduction to Marine Science course at UCLA in 2012. Simmonds suggested that students in the class could investigate whether seafood served at sushi restaurants were always what they claimed to be, or might they sometimes travel under false identities. For example, is red snapper (which does not occur in California waters) really red snapper, or might merchants substitute one of 13 rockfish species in its stead? This project allowed students to investigate a real world marine-related topic, while also getting some experience using and applying molecular genetics tools.

Over the course of the four-year study, students ordered sushi from 26 different restaurants, confirmed the species identification with the wait-staff, and collected tissue samples from each order. They then subjected the samples to DNA barcoding, which amplifies and sequences an approximately 650 base pair segment of the mitochondrial COI gene. Once they determined the DNA sequence, students then compared it with known sequences using the Basic Local Assignment Search Tool database (National Center for Biotechnology Information).

Each year, between 40 and 52% of the fish were mislabeled. Though previous studies by other researchers had identified mislabeling, Willette and his colleagues were surprised that all 26 restaurants had at least one case of mislabeling, and that the mislabeling rate was so consistent from one year to the next.

SushiFig1

Percentage of sushi mislabelled (left y-axis – bar symbol) and number of restaurants sampled (right y-axis – diamond symbol) by year.  Number in bar is sample size for that year.

Overall substitution rates varied dramatically from one species to another. All fish species, except bluefin tuna, were mislabeled at least once, and two species – red snapper and halibut – were always mislabeled. Red snapper was often replaced with red seabream, while halibut was usually replaced with flounder.

SushiFig2

Percentage mislabeled (+ standard error) for each species in the study. Numbers above bars are number mislabeled (left) and total sample (right).  For example 6 out of 47 salmon were mislabeled.

Why should we care if we’re served the wrong species of fish, as long as it tastes good? As it turns out, there are several reasons. About 33% of halibut are substituted with olive flounder, which can harbor the parasite Kudoa septempunctata, which is known to cause severe food poisoning. In addition, some of the other halibut substitutes are actually overfished flounder species, so substituting these for halibut is depleting already at-risk fisheries. Similar problems, in which an at-risk species substitutes for the mislabeled species, were common in tuna and yellowtail as well.

The researchers recommend that seafood mislabeling must be attacked at all stages of the seafood supply chain. All seafood should be labeled to species, place of origin, and the type of fishing practice used. Inspectors must be trained to identify seafood – perhaps using portable, hand-held DNA sequencers. Retailers should be told when they sell mislabeled species, so they can insist that their suppliers deliver the correct goods. Finally social media can be used to inform the public of consistent mislabeling, so consumers can pressure retailers to make sure that a red snapper is what it claims to be.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Willette, D. A., Simmonds, S. E., Cheng, S. H., Esteves, S., Kane, T. L., Nuetzel, H., Pilaud, N., Rachmawati, R. and Barber, P. H. (2017), Using DNA barcoding to track seafood mislabeling in Los Angeles restaurants. Conservation Biology, 31: 1076–1085. doi:10.1111/cobi.12888. Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

Subsidized Shorelines: where pelagic meets benthic

Chris Harrod met his wife, Christina Dorador, while both were working at the Max Planck Institute for Limnology in Germany.   Subsequently Dorador began a postdoctoral position in her native Chile, and Harrod went for a visit over Christmas, 2007. He was impressed by the beautiful rocky inshore habitat that was dominated by kelp forests and many species of invertebrates and fish.

Macroalgal forest

Rocky shoreline near Tocopilla, Chile. Credit: Chris Harrod.

As a fisheries biologist, Harrod soon immersed himself in the inshore kelp forest-dominated ocean, and was stunned by the sheer volume of stuff floating around. The water was green rather than blue, and filled with decaying phytoplankton and zooplankton. Where did all this stuff come from? Harrod knew that off the Peruvian and north Chilean coasts, prevailing winds move surface waters away from the shoreline, inducing upwelling of deeper nutrient-rich waters to the surface. This nutrient flux is the basis of a huge anchoveta fishery, which feeds humans, fish, marine invertebrates and marine mammals. He wondered whether the mass of floating debris in the inshore habitat might originate from offshore waters brought in from upwelling, and if the debris actually fueled some of the larger fish and molluscs that dominate inshore kelp forests. The prevailing opinion was that the energy for these fish and molluscs originated from the inshore photosynthetic kelp, rather than from photosynthetic phytoplankton further offshore that get their nutrients from upwelling.

Bilagay

Two bilagay, Cheilodactylus variegatus, swim among green algae in a debris-laden inshore habitat off the coast of Chile. Credit: Chris Harrod.

While you can ask a fish or mollusc what they had for dinner, it is very difficult to get them to respond. Fortunately, ecologists can use stable isotope ratios – the ratio of a rare (and nonradioactive) isotope of an element to its standard common isotope – to help get the answers they need. Harrod collaborated with several researchers in this study, including his Master’s student, Felipe Docmac, who collected and analyzed much of the data and was the first author of the paper. Docmac and his colleagues used the ratio of heavy and light isotopes of carbon (C) and nitrogen (N) to calculate d13C (the ratio of 13C to 12C) and d15N (the ratio of 15N to 14N) to infer where inshore fish were getting their energy.

The basic question was whether the nutrients supporting the food web were primarily from pelagic or benthic sources. In this case, the pelagic source refers to phytoplankton from the offshore areas of upwelling, while the benthic source refers to kelp and green algae that grow on the bottom (benthos) of the inshore habitat. Docmac and his colleagues collected invertebrates and large fish from five different sites along the north Chilean Coast, and calculated 13C and 15N values from tissue samples. Invertebrates were divided into two groups: filter-feeders were represented by mussels, which fed on suspended materials (such as the prolific floating debris), while benthic grazers were gastropods (snails) that fed on benthic kelp and green algae.

Fig1A

Five collection sites along the northern coast of Chile.

I’m going to skip the precise details of how stable isotope analysis actually works; I’ll provide enough information so you can understand the findings. There are two important facts to keep in mind. First an animal’s stable isotope ratio is influenced by the stable isotope ratio of its food source. So an animal feeding on prey with high d13C and d15N will itself have higher stable isotope ratios than will an animal feeding on prey with lower d13C and d15N. Second, the stable isotope ratio increases as we go up the food chain in a predictable manner, because the lighter isotopes of carbon and nitrogen tend to be more readily excreted than are the heavier isotopes.

We are now ready to look at the data. First, notice that while there is some variation from location to location, the (Pelagic) mussels tend to have consistently lower d13C values than do the (Benthic) gastropods (X-axis of graph), but fairly equivalent d15N values (Y-axis of graph). The benthivorous fish have, as we would expect from animals higher up the food chain, much higher d15N values than either of the invertebrates. But here is the key. The benthivorous fish have a much lower d13C value than do the benthic invertebrates (gastropods). If gastropods (and presumably other grazers) were in the benthivorous fish food chain, then we would expect the fish to have a higher d13C value than do the benthic gastropods. The researchers thus conclude that these fish are deriving most of their energy from the pelagic debris that is washing in from ocean currents.

Fig1B

d13C (X-axis) and d15N (Y-axis) stable isotope values in benthivorous fish (black circles).  Bars emanating from each point indicate 95% confidence intervals (CI). Numbers inside symbols indicate the site of origin for each sample (see map above), Also shown are values for filter-feeding mussels (red up-pointing triangles) and grazing gastropods (blue down-pointing triangles). Gray lines indicated predicted values of diets that were based solely (100%) on pelagic or benthic sources.

The researchers were stunned by these findings. Going into the study, Harrod did not know what he would find, but would not have been surprised by a 15% contribution from pelagic sources, or maybe even 30%. But he was blown away that the data indicated estimates of greater than 90% pelagic contribution at most of the sites. Ecologists have long known that one ecosystem may subsidize a second ecosystem with resources. For example, salmon carcasses can provide nutrient subsidies to trees near riverways, or even deeper into the forest after being transported by bears. But the extent of the subsidy in this study is unprecedented. Docmac and his colleagues urge researchers to explore exactly how the pelagic materials get into the food web, and to see whether such subsidies are common near other upwelling zones worldwide so that coastal resources can be managed more effectively.

note: the paper that describes this research is from the journal Ecology. The reference is Docmac, Felipe, Miguel Araya, Ivan A. Hinojosa, Cristina Dorador, and Chris Harrod. 2017. Habitat coupling writ large: pelagic‐derived materials fuel benthivorous macroalgal reef fishes in an upwelling zone. Ecology doi:10.1002/ecy.1936. It was published online on Aug. 2, 2017, and should appear in print very soon. Thanks to the Ecological Society of America for allowing me to use figures from the paper. Copyright © 2017 by the Ecological Society of America. All rights reserved.