Background, This Week In The Lab

Niche Theory In Everyday Life

SYDNEY, AUS: In the day to day here, as I commute to work, take the bus around town, and observe, I’m frequently overwhelmed by daily demonstrations of niche theory and convergent evolution in the world around me. The terrestrial flora in Sydney is of an entirely different lineage, primarily of the Myrtoideaen tribe Eucalypteae, than what I know from the Pacific Northwest. Though Eucalypts have long been present on Earth, their radiation in Australia is apparently relatively recent. Eucalypts now make up ¾ of the vegetation on this island continent, and fill nearly every ecological function that I, as a North American, attribute to other trees. For instance, coastal swamplands similar to the cypress swamps of Louisiana and Texas are here inhabited by swamp gum trees, other Eucalyptus spp., and their Myrtoideaen cousins, the paperbark trees. Savanna and temperate grassland habitats that in the US would have scattered oaks, cottonwoods, or willows, are here are inhabited by bimble box and coolibah eucalyptus trees. The Sydney red gum is one of several Eucalypts that plays the role of North American fruit trees, providing food for fruigivores. On my commute home at night, I often get to watch enormous ‘flying foxes’, or Ku-ring-gai bats (Pteropus poliocephalus), indulging in the tree’s nectar.

This, of course, is entirely tangential from my work on man-made alterations to urban shorelines in Sydney Harbour. While I know I should be entirely focused on the project that brought me here, the natural history nerd within has a hard time ignoring what Darwin and many others since found astonishing upon first traveling to the opposite hemisphere: That a similar set of ecological professions (niches) exist everywhere, and who fills them (which species) is heavily influenced by chance.

Post about ancient Eucalyptus from Eliza’s Instagram

Eliza’s instagram


Do algal subsidies from riprap alter soft sediment community structure?

In my last post, I provided some background information about spatial subsidies and how I think they may be playing a role in urban marine ecosystems. Specifically, I considered whether the red algae that grows on riprap may have an effect when it gets incorporated into adjacent soft sediments.

To test this, I set up a field experiment at the beginning of the summer.

Photo of enrichment plot

Enrichment plot treated with shredded read algae

The experiment consisted of a series of half-meter, circular plots, each marked at the center with a construction flag. The plots were set up in a large square grid.  In the days leading up to the experiment, I collected large amounts of shell hash and red algae from nearby dive sites.  All of the shell hash was sieved through a 0.5mm sieve. The algae were all ground up using a cheese grater so that they resembled the tiny pieces of red algae that I often find in sediment samples. Each plot then received one of the following treatments: 100mL of algae, 100mL of shell hash, 100mL of algae and 100mL of shell hash combined, 500mL of algae, 500mL of shell hash, or no treatment (as a control).  There are obviously many specific details to this that I’m leaving out, but please don’t hesitate to contact me if you have questions.

Photo of enrichment plot

Enrichment plot treated with shell hash

I’ll be collecting core samples from the plots at 8 weeks and at 16 weeks. Each sample will then be sorted and all macrofauna (worms, clams, snails, etc) will be removed.  By comparing the inhabitants of each sample, I should be able to detect whether the community of species that lives in soft sediment is affected by the introduction of shell hash and red algae, which appear to originate from riprap.


Spatial subsidies from riprap… say what?

As promised, I wanted to provide some background information about spatial subsidies and explain one way in which I think they may occur in urban marine ecosystems…

Since the late 1990s, there has been growing recognition among ecologists that the structure of ecological communities may be heavily influenced by the movement of resources from neighboring habitats. This movement of nutrients or energy has been identified by the term spatial subsidies, and has been the subject of considerable discussion in recent ecological literature. Spatial subsidies have been shown to alter the abundance of recipient species in a variety of different ecosystems.  The effects of subsidies appear to be particularly apparent among consumers of lower trophic levels (things that eat plants, for instance).  They may also impact other trophic levels, either directly or through indirect interactions.

photograph of red macroalgae on riprap

A photoquadrat of red macroalgae growing on riprap.

The introduction of artificial rocky material, such as riprap, to urban marine environments may alter neighboring soft sediment communities by providing them with new spatial subsidies.  Riprap is most commonly introduced to soft sediment environments that are not already protected by naturally occurring rocky material.  The biological community on riprap is substantially different from that in neighboring soft sediments, and has the potential to introduce a considerable amount of biomass into adjacent habitats in the form of detritus or debris.

My initial findings suggest that several species of red macroalgae may provide a flux of detrital material into soft sediment habitats. In addition, the sediment close to riprap installations is coarser than that farther away and contains shell hash from barnacles and jingle shells, which are found in high density on riprap.

Several studies have considered how soft sediment communities are altered by the presence and proximity of rocky structures, but with mixed results (see Davis et al. 1982, Ambrose and Anderson 1990, Posey and Ambrose Jr. 1994, Barros et al. 2001, Fabi et al. 2002, Jaramillo et al. 2002, Martin et al. 2005, Bertasi et al. 2007).  While some studies have found differences in the soft sediment community at varying distances from rocky substrates, the mechanism proposed to explain these differences has primarily been physical in nature. Martin et al. (2005) and Bertasi et al. (2007) attributed differences in soft sediment species richness and composition near rocky material to hydrodynamic patterns that trap coarser materials that are transported there by waves.  Fabi et al (2002) considered both physical factors and increased predation as potential reasons for differences in infaunal community structure adjacent to artificial reefs. Barros et al. (2001) provided one of the only suggestions that addition of reef-originating material into soft sediments nearby could be altering infaunal assemblages.

In my next post, I’ll tell you more about the experiments I’ve set up to test whether soft sediment communities are impacted by spatial subsidies from riprap. Thanks for reading and please don’t hesitate to contact me if you have any questions!


Photo of Seattle from Don Armeni Boatramp
Background, Ecosystem Services, Historical Context

Urban Marine Environments as Coupled Human and Natural Systems

Over the last decade, a growing faction of scientists in the world of ecology and conservation biology has pushed the idea that most ecosystems on Earth are now comprised of coupled human and natural components.  They’ve come up with a variety of different names of these entities, but the one that I like most is “Coupled Human and Natural Systems,” or CHANS.  The idea is that although we’ve spent decades studying natural ecosystems, we have to take a step back and include humans before we can really understand how ecosystems function.

The literature describes several key qualities of coupled human and natural systems.  They are structured in a hierarchical manner and consist of complex networks of interactions.  These interactions are commonly reciprocal, with humans acting in ways that influence natural components, and natural components in turn influencing humans.  They also may involve positive or negative feedback loops that can accelerate or decelerate key processes.  Coupled human and natural systems exhibit emergent properties, which differ from the properties of individual system parts.  They exhibit nonlinearity in their dynamics, and may shift between multiple states or equilibria when certain thresholds are exceeded or system resilience is reduced.

If that sounds like Greek, don’t worry, I’m not here to drone on about models or theories.  I simply wanted to introduce the idea of CHANS.  By definition, CHANS are systems in which natural and human components interact. It’s undeniable then that urban marine ecosystems qualify.  Graphical model of human and natural interactions in urban marine ecosystemsThey are created out of long, intense interactions between humans and nature. Does the theory above then  give us insight into how urban marine ecosystems function? Do urban marine ecosystems evolve over time according to the theoretical framework for CHANS?

As I explore urban marine ecology in posts and research, I will do my best to highlight the coupled human and natural components of the system.  This may come in the form of historical information about interactions between humans and urban marine environments, explorations of the ecosystem services urban marine environments provide, and evaluations of these systems through the lens of resilience theory.  It may seem tangential at times, but the bottom line is that urban marine ecosystems are not just comprised of the marine organisms we encounter underwater.  Humans are very much a part of the ecological processes in urbanized marine habitats, and we may not be able to understand these processes or habitats until we have fully integrated ourselves into the ecological picture.

Map of population change in US coastal watersheds

Why Urban Marine Ecology?

Despite all my hype about urban marine ecology, it’s a field that really doesn’t exist yet. At least not in any standardized or formal way. It’s a discipline in the making, inspired by the explosion of research in terrestrial urban ecology and a void of comparable knowledge when it comes to the marine environment in cities.

You may have seen the statistics about coastal population growth. Overall, it’s estimated that we will reach a population of 8 billion in ten years. Currently about 50% of people live in coastal areas, but by 2025, it’s expected that that percentage will increase to 75%. That an estimated 6 million people living within 100km of a coastline!

The movement of people to coastal areas is not uniform. Check out this graphic from the National Oceanic and Atmospheric Administration (NOAA) of population change in coastal watersheds (link). From this, you can see that population in more rural coastal areas is actually decreasing. People aren’t just moving to the coasts. They’re moving to coastal cities.

What will be the effect of population growth on marine ecosystems?  We have no idea.  Not only are we limited in our understanding of what these will look like in the future – we know almost nothing about the characteristics of urban marine ecosystems today.  Much work is needed to characterize the biodiversity of these systems, understand their ecological processes and identify how they differ from their natural, more rural ecological counterparts.  In many respects, these are systems of our own making. Don’t you want to know what we’ve created?  I certainly do.  There’s much work ahead!