Candidates for the most common sponge morphotypes that are likely being misidentified on iNaturalist
Background:
The #1 assumption used by sponge biologists when identifying a sponge is that you can't reliably identify it with just a photo and without context. The scientific gold-standard for identifying a sponge is notoriously difficult to perform and involves taxonomic protocols that needs caustic chemicals, microscopy, and fluency in taxonomy jargon. Tell me the last time you heard somebody use "oxyhexaster microsclere" in a sentence that didn't involve sponge taxonomy?
As a biodiversity scientist and a sponge ecologist in a past life, I've continually thought about bridging old-school methods with new-school technology (e.g. iNaturalist). In other words, can we find some general rules that everybody can use to narrow down the identification process for what is paradoxically the most common marine animal in Earth's history but also the most ignored by most marine biologists?
I've dug through much of the iNat sponge observations in the Pacific Northwest over the past few years to get a sense of what are the most photographed sponge morphotypes (i.e., whole-sponge shape/color/form that may or may not represent a single species) where the science jury is still out on the taxonomy to allow these observations to be useful 'biodiversity data'. I feel a little bit of scientific detective work could go a long way with resolving the confidence in the ID of these common encounters in the rocky intertidal.
Ground rules (basic assumptions when identifying sponges):
(I) Sponges are the poster child of what it means to be 'phenotypically plastic'.
Many species are expected to have a diverse range of whole sponge morphotypes. As in, the same species could be a flat featureless, encrusting blob in some areas, but also be an erect, branching form in others. Very often, this is in response to the environment such as gradients of wave action between sites (low to high).[1]
(II) Diagnostic analyses of the presence, absence, and morphometrics of microscopic skeletal features (i.e., spicules) are still the gold-standard for identifying a sponge to species with the highest level of confidence.[2]
(III) Official species names for sponges are frequently being revised. In other words, their scientific names are constantly changing.
Some commonly photographed sponge morphotypes in the Pacific Northwest.
(I) The purple-encrusting, intertidal demosponge
Phylum: Porifera (high certainty)
Class: Demospongiae (high certainty)
Order: Haplosclerida (likely)
What the iNaturalist AI algorithm has commonly identified this as: Haliclona cinerea
What popular field guides have synonymized this as: Haliclona permollis, Haliclona cinerea, Reniera cinera, Reniera rufescens, Haliclona sp., Undetermined sponge.[3][4][5]
Sponge thoughts: Neither of the two most commonly applied species-level IDs used to identify this sponge on iNaturalist, Haliclona cinerea and H. permollis, are actually scientifically valid names for sponges. H. permollis is no longer recognized. H. cinerea is split with a subspecies to H. (Reniera) cinerea which appears to originate as a species described from waters around Britian.[6] It's rare to have scientific evidence that validates a marine species with having a "globally cosmopolitan distribution". The more common scenario I've encountered is that this had been an unvalidated assumption and upon further inspection, the extrapolated species is a 'new species'.
Regardless, the bigger issue is this morphotype is more than likely not a single species but a complex that includes several genus and species. The last I checked, we likely have undescribed species hiding within this complex on this coast - see this observations' comments for scientific dialogue/context (). It would be interesting to combine proper sponge taxonomy with an understanding of the established marine biogeographic/oceanography history of the Pacific Northwest for this morphotype. The true identities of this super common, yet understudied sponge morphotype. My hand-wavey prediction is that there is at least n=8 cryptic species with this morphotype occurring in the Pacific Northwest. I'm also speculating that 'purple' is not a fixed trait and that what can be purple can also be yellow, green, and beige..
(II) The red-encrusting, intertidal demosponge.
Phylum: Porifera (high certainty)
Class: Demospongiae (high certainty)
Order: Poecilosclerida (likely)
Family: Microcionidae (likely)
What the iNaturalist AI algorithm has commonly identified this as: Clathria pennata
What popular field guides have synonymized this as: Ophlitaspongia pennata, Desmacella pennata, Biemna pennata, Tylodesma pennata, Clathria pennata, Clathria sp., Undetermined sponge.[3][4]
Sponge thoughts: The genus Clathria is also complex with a diverse number of associated species.[7] I would like to guess that there are a number of cryptic species sharing this morphotype in the Pacific Northwest but this one seems to have gotten less attention over the years compared to the encrusting purple morphotype. The latter's plasticity and taxonomic chaos is much more well known.
Marine invertebrate zoology courses with field trips in the Pacific Northwest (e.g. British Columbia, Washington, Oregon) often go looking for animals at low tide. Instructors would often find this common bright red sponge as an example of the phylum Porifera and call it "Ophlitaspongia" while also mentioning the natural history note of the associated red dorid nudibranch Rostanga pulcra which is often camouflaged and feeding on this sponge. While the natural history fact is still accurate (see the photo for the red nudibranchs!), the genus Ophlitaspongia is not scientifically valid anymore. I'd be curious to know if R. pulcra feeds on all species with this morphotype or if it was selective?
Trailing thoughts
There are a few more sponge morphotypes that jump to mind (e.g. 'boot' sponges, Class hexactinellida) but I'll leave this post at two for now. One of my past research projects involved developing models that could predict areas of sponge habitat throughout the Pacific Northwest [8]. A task that required sourcing reliable sources of georeferenced, sponge observations (e.g. museum records). I briefly considered iNaturalist at the start but stopped with 'needs further work on the species IDs' when I encountered how inaccurate some of the common sponges were being done. Since then, there has been some improvements made by others - have a look at some of the efforts @tomleeturner to implement sponge identifying protocols using spicule analysis (and even DNA analysis) with iNaturalist photographs for each georeferenced individual observation as a template to emulate [9].
References:
[1] Palumbi, S.R., 1986. How body plans limit acclimation: responses of a demosponge to wave force. Ecology, 67(1), pp.208-214.
[2] Hooper, J.N. and Van Soest, R.W., 2002. Systema Porifera. A guide to the classification of sponges. In Systema Porifera: A guide to the classification of sponges (pp. 1-7). Boston, MA: Springer Us.
[3] Lamb, A. and Hanby, B.P., 2005. Marine life of the Pacific Northwest: a photographic encyclopedia of invertebrates, seaweeds and selected fishes. Harbour Publishing.
[4] Harbo, R.M., 2022. Whelks to whales: coastal marine life of the Pacific Northwest. Harbour Publishing.
[5] Invertebrates of the Salish Sea
[6] WoRMS taxon details - Haliclona (Reniera) cinerea (Grant, 1826)
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