Land and sea

ecological links both obvious and obscure

We often think of land and sea as totally separate entities, and this is commonly reflected in separate governmental jurisdictions. But the biological reality is that the two “entities” are very closely linked, and here in Southeast Alaska that connectedness is very evident.

Perhaps the most well-known ecological link between sea and land is told in the story of the ‘salmon forest’. Spawning salmon return to freshwater streams, bringing marine-derived nutrients (and pollutants) in their bodies. The spawners die or are eaten by predators such as bears, wolves, and eagles. Smaller consumers, including mink, otters, and some song birds, also nibble on the carcasses. The fish-eaters sometimes drag the carcasses into the forest and all the consumers deposit digested fish and the contained nutrients on the landscape, sometimes quite far from the streams. Flies and other insects lay eggs on the carcasses and aquatic insects have bountiful dinners; the flourishing abundances of insects are consumed by birds that contribute to the spread of nutrients over the landscape. These animals help fertilize the surrounding land.

Crows catching sand lance in the intertidal. Photo by Bob Armstrong

But there are also many other channels by which marine-derived nutrients reach land. Less spectacular, perhaps, than the salmon runs and the attendant consumers, these other links make their contribution to the connection between sea and land. Lots of critters forage at the edge of the sea and then move up into the forest and meadows, where they deposit their digested dinners. Bears dig clams in muddy intertidal zones and gnaw barnacles off rocks. Bears, geese, and probably our beach marmots graze in the sedge meadows. Deer graze on sedges and intertidal plants. Ravens dig up sand lance and clams from the sediments. Eagles harvest herring and sand lance, and sometimes capture marine birds. Crows and ravens prey on sea urchins and small crabs and, during a eulachon run, these birds are known to store captured fish in grass tussocks and in trees.

Black bear eating mussels and barnacles. Photo by Jos Bakker

It’s not all one-way, of course; it’s a two-way connectedness. The land has some major influences on the sea. Run-off from rain and snow-melt regularly carry the products of erosion, including sediment, fallen trees, and some dissolved nutrients, eventually to the sea. Glacier-fed streams send a rich supply of minerals and organic nutrients to the sea, feeding the plankton that feeds the herring and the whales and lots of other organisms.

Human activity can have some major effects too. A recent excursion to Hawk Inlet on Admiralty Island made this abundantly clear. This was a SEACC cruise, so the emphasis was on what the mining activities near the inlet are probably doing to things in the sea. Waste products from the mine are pumped out into the lower inlet, where some sink to the bottom and some are swirled about by the incoming and outgoing tides. Leachates from the tailings piles ooze downhill toward the beach. The situation there came to our attention when a harbor seal, harvested in that area and eaten by humans, was found to be heavily laden with toxic chemicals. Then the levels of various toxic metals (e.g., lead, selenium, and several others) in blue mussels, shrimp, crabs, clams, and cockles from the inlet were found to be several times higher than in other parts of Alaska. Perhaps not coincidentally, local herring spawning aggregations and littleneck clams have recently disappeared; so has a run of king salmon. The initial concern has been for humans that harvest wild food in this area.

However, if mussels, clams, shrimp, and cockles are picking up high levels of contaminants, it’s a sure thing that many other organisms are too, leading to ramifying consequences throughout the food chains. Contaminants, such as the toxic metals of direct concern here, get passed up the food chain, accumulating at higher and higher levels, until the top predators get really big doses. Even before the contaminant concentrations become lethal, sub-lethal levels (sometimes very small amounts) can change body chemistry in serious ways, including growth rates, behavior, and even the gender of some consumers. Such changes would be reflected in population sizes of the consumers and that, in turn, would affect the populations of their predators.

On this cruise, we saw some of the spectacular wildlife for which Southeast is famous. There were brown bears foraging on sedges in beach-side meadows. Dall’s porpoises dashed past the boat. Humpback whales cruised by and dove. A group of killer whales moseyed back and forth, sometimes making impressive vertical leaps out of the water. All of those species depend on resources that could be affected by contaminants. To take just one example: Killer whales are top predators that could accumulate high levels of contaminants from their prey. Resident killer whales eat fish, those that eat plankton directly and those that eat plankton-eaters, while transient killer whales eat marine mammals that eat fish that…

The other animals we observed could also be exposed to some level of potentially toxic mine effluent. Even though the effluent from the inlet presumably gets diluted in the larger channel, sometimes a little bit can have huge impacts. It is unlikely that anyone will look to see if that occurs, so it would be wiser to prevent it from happening in the first place.

Learned in Alaska

a midwestern naturalist becomes a Southeast Alaskan

When I moved to Juneau, almost twenty-five years ago, I knew no people, almost no plants, and about five birds in this area. So I had a lot of learning to do! I’ve been working on that. Of all the things I’ve been learning, two big patterns stand out.

First: I grew up in the Midwest and spent most of my professional career there. So I was accustomed to seeing much the same landscape from year to year. Yes, the Pleistocene glaciers had come and gone, ten or twelve thousand years ago, the Mississippi occasionally shifted its channel, and there was a massive earthquake back in the 1800s. But day to day, week to week, month to month, the look of the land was pretty similar. So it was easy to think of the ecological landscape as being quite stable.

Not so in Juneau! We have earthquakes, sometimes with many aftershocks. There are landslides and avalanches, jökulhlaups, and tsunamis (small ones…). The most recent glaciation was only two or three hundred years ago (my house would have been under the ice), and glaciers continue to recede (and occasionally advance). There is the continual rise of land that follows disappearance of the glaciers; this isostatic rebound amounts to almost an inch a year in some places, bringing meadows up out of the sea. This is a very dynamic landscape, and any sense of landscape stability gets blown right out the window!

Second: As an ecologist, I am accustomed to thinking about interactions among organisms: predator and prey, pollinator and flower, succulent fruits and seed dispersal by fruit-eaters, and so on. I can do that here too. But the striking thing is that here the scale of interactions is huge, occurring over many miles.

This initially came home to me when (twenty four years ago) I first watched salmon making their way upstream to spawn, after spending a year or more in the ocean, growing to adult size by eating oceanic foods. Then I began to appreciate the many connections to this influx from the ocean: We studied the predators on the incoming salmon, and these consumers spread marine-derived nutrients over the landscape, by hauling fish carcasses into the forest and by voiding waste products, sometimes miles away from the stream. These nutrients get into the vegetation, both in the water and on land, and help feed the many creatures that eat vegetation. Fish carcasses are a bonanza for many insects and other scavengers. A further spin-off is that more birds nest near salmon-spawning streams than along streams that don’t host spawners, perhaps because the vegetation is denser or because there is more insect prey. Most of our coastal streams are relatively small, but on bigger systems, such as the Taku River, many of the tributaries support salmon runs, spreading the inflow of nutrients over a wide watershed. The basic story of the ‘salmon forest’ is well-known to most of us here.

Upstream nutrient transfer in action. Photo by Bob Armstrong

Less well known is the story about what goes downstream. Of course we all know that fresh water flows downhill and much of it eventually reaches salt water. However, we often do not think about what that water carries to the sea. It bears a load of sediment that gets deposited in estuaries, often changing their configuration, and providing fine habitat for migrating shorebirds. It also carries lots of nutrients, from many different sources: nitrogen and carbon from forests and muskegs, iron and phosphorous from weathered rocks, a diversity of materials from the decomposition of salmon and from the rich bacterial community that inhabits glaciers. All these nutrients enter the nearshore zone, where they nourish algae and eelgrass and even the sedges and other plants that grow in the upper intertidal zone. Some of that rich input is eventually entrained by the coastal currents that sweep north and west in the Gulf of Alaska and carried along for great distances.


In addition, at the mouths of large rivers (such as the Copper River), broad deltas often form. At seasons of low water flow, huge dust storms sometimes develop over the dry deltas; these storms blow sediment and lots of nutrients far out to sea, providing iron and other necessary nutrients for marine organisms.


All the organisms that benefit directly from the influx of nutrients from land and fresh water to the sea have a multitude of effects on still more organisms. The eelgrass makes great habitat for lots of little fishes, the sedges and grasses feed geese and finches. Some algae, attached to rocks and shells, make habitat and food for many invertebrates. Other algae, particularly the tiny phytoplankton floating in the open water, feed small crustaceans (such as krill) that feed herring and other forage fishes; both krill and the forage fishes feed our locally famous humpback whales. So you could say that the glaciers, forests and muskegs, and streams feed the whales.


Here in Southeast, there are hundreds of small, coastal streams, along with a few large, transmontane rivers. These dump huge amount of fresh water into the sea every year. Coastal Alaskan streams have been estimated to be equivalent to one or two Mississippi rivers or perhaps four Yukon rivers, in terms of their output. A big difference is that the coastal streams enter the sea all along the coast, so the input is more spread out along the coast. Because most of these streams are short, much of the material goes directly into the sea, with less in-stream processing of material on the way than is the case for longer, bigger rivers. Another big difference is that a number of coastal streams have glaciers at their headwaters, and these provide unique combinations of nutrients to the coast, different from streams originating in muskegs or forest.


Many aspects of these far-reaching connections are still subjects of active research. A nice, and very productive, feature of this research is that, at last, biologists and geologists and hydrologists and biogeochemists and oceanographers are talking more to each other, and the land and sea, once treated as totally separate entities, are no longer viewed that way, but rather as parts of a connected whole.


The bottom line, in personal terms, is that this old Midwesterner had her eyes opened when she came to Juneau. New thoughts barged in, forever changing my perspectives. That has been great fun.